Upgrade clap_derive to 4.2.0 am: 324bd852e0 am: 5e5c42af66 am: 424e13ee69 am: 1c7a38475e am: fcfe0b80e5 am: ec93ee1024

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/clap_derive/+/2520756

Change-Id: Ief2b676421352aaebb87819cbe7630853cc04cbc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

18 files changed, 741 insertions, 628 deletions

diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
index 447f5f0..89e449a 100644
--- a/.cargo_vcs_info.json
+++ b/.cargo_vcs_info.json
@@ -1,6 +1,6 @@
 {
   "git": {
-    "sha1": "f931de694a5478d7e4bd424613e6699f7d4f4e9f"
+    "sha1": "8fc65e28b66878f6d1ee45c725fbfb31b35321e3"
   },
   "path_in_vcs": "clap_derive"
 }
\ No newline at end of file
diff --git a/Android.bp b/Android.bp
index b504f5e..16c0dc4 100644
--- a/Android.bp
+++ b/Android.bp
@@ -41,14 +41,13 @@ rust_proc_macro {
     name: "libclap_derive",
     crate_name: "clap_derive",
     cargo_env_compat: true,
-    cargo_pkg_version: "4.1.8",
+    cargo_pkg_version: "4.2.0",
     srcs: ["src/lib.rs"],
     edition: "2021",
     features: ["default"],
     rustlibs: [
         "libheck",
         "libproc_macro2",
-        "libproc_macro_error",
         "libquote",
         "libsyn",
     ],
diff --git a/Cargo.toml b/Cargo.toml
index be05b33..48793fb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,7 +13,7 @@
 edition = "2021"
 rust-version = "1.64.0"
 name = "clap_derive"
-version = "4.1.8"
+version = "4.2.0"
 include = [
     "build.rs",
     "src/**/*",
@@ -54,9 +54,6 @@ proc-macro = true
 [dependencies.heck]
 version = "0.4.0"
 
-[dependencies.proc-macro-error]
-version = "1"
-
 [dependencies.proc-macro2]
 version = "1.0.42"
 
@@ -64,7 +61,7 @@ version = "1.0.42"
 version = "1.0.9"
 
 [dependencies.syn]
-version = "1.0.74"
+version = "2.0.8"
 features = ["full"]
 
 [features]
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
index a32d823..bd5b5ef 100644
--- a/Cargo.toml.orig
+++ b/Cargo.toml.orig
@@ -1,6 +1,6 @@
 [package]
 name = "clap_derive"
-version = "4.1.8"
+version = "4.2.0"
 description = "Parse command line argument by defining a struct, derive crate."
 repository = "https://github.com/clap-rs/clap/tree/master/clap_derive"
 categories = ["command-line-interface", "development-tools::procedural-macro-helpers"]
@@ -29,11 +29,10 @@ proc-macro = true
 bench = false
 
 [dependencies]
-syn = { version = "1.0.74", features = ["full"] }
+syn = { version = "2.0.8", features = ["full"] }
 quote = "1.0.9"
 proc-macro2 = "1.0.42"
 heck = "0.4.0"
-proc-macro-error = "1"
 
 [features]
 default = []
diff --git a/METADATA b/METADATA
index d2ca19f..684ef04 100644
--- a/METADATA
+++ b/METADATA
@@ -11,13 +11,13 @@ third_party {
   }
   url {
     type: ARCHIVE
-    value: "https://static.crates.io/crates/clap_derive/clap_derive-4.1.8.crate"
+    value: "https://static.crates.io/crates/clap_derive/clap_derive-4.2.0.crate"
   }
-  version: "4.1.8"
+  version: "4.2.0"
   license_type: NOTICE
   last_upgrade_date {
     year: 2023
     month: 3
-    day: 2
+    day: 31
   }
 }
diff --git a/src/attr.rs b/src/attr.rs
index e282a8f..3bc9ac0 100644
--- a/src/attr.rs
+++ b/src/attr.rs
@@ -1,8 +1,6 @@
 use std::iter::FromIterator;
 
 use proc_macro2::TokenStream;
-use proc_macro_error::abort;
-use proc_macro_error::ResultExt;
 use quote::quote;
 use quote::ToTokens;
 use syn::spanned::Spanned;
@@ -24,49 +22,44 @@ pub struct ClapAttr {
 }
 
 impl ClapAttr {
-    pub fn parse_all(all_attrs: &[Attribute]) -> Vec<Self> {
-        all_attrs
-            .iter()
-            .filter_map(|attr| {
-                let kind = if attr.path.is_ident("clap") {
-                    Some(Sp::new(AttrKind::Clap, attr.path.span()))
-                } else if attr.path.is_ident("structopt") {
-                    Some(Sp::new(AttrKind::StructOpt, attr.path.span()))
-                } else if attr.path.is_ident("command") {
-                    Some(Sp::new(AttrKind::Command, attr.path.span()))
-                } else if attr.path.is_ident("group") {
-                    Some(Sp::new(AttrKind::Group, attr.path.span()))
-                } else if attr.path.is_ident("arg") {
-                    Some(Sp::new(AttrKind::Arg, attr.path.span()))
-                } else if attr.path.is_ident("value") {
-                    Some(Sp::new(AttrKind::Value, attr.path.span()))
-                } else {
-                    None
-                };
-                kind.map(|k| (k, attr))
-            })
-            .flat_map(|(k, attr)| {
-                attr.parse_args_with(Punctuated::<ClapAttr, Token![,]>::parse_terminated)
-                    .unwrap_or_abort()
-                    .into_iter()
-                    .map(move |mut a| {
-                        a.kind = k;
-                        a
-                    })
-            })
-            .collect()
+    pub fn parse_all(all_attrs: &[Attribute]) -> Result<Vec<Self>, syn::Error> {
+        let mut parsed = Vec::new();
+        for attr in all_attrs {
+            let kind = if attr.path().is_ident("clap") {
+                Sp::new(AttrKind::Clap, attr.path().span())
+            } else if attr.path().is_ident("structopt") {
+                Sp::new(AttrKind::StructOpt, attr.path().span())
+            } else if attr.path().is_ident("command") {
+                Sp::new(AttrKind::Command, attr.path().span())
+            } else if attr.path().is_ident("group") {
+                Sp::new(AttrKind::Group, attr.path().span())
+            } else if attr.path().is_ident("arg") {
+                Sp::new(AttrKind::Arg, attr.path().span())
+            } else if attr.path().is_ident("value") {
+                Sp::new(AttrKind::Value, attr.path().span())
+            } else {
+                continue;
+            };
+            for mut attr in
+                attr.parse_args_with(Punctuated::<ClapAttr, Token![,]>::parse_terminated)?
+            {
+                attr.kind = kind;
+                parsed.push(attr);
+            }
+        }
+        Ok(parsed)
     }
 
-    pub fn value_or_abort(&self) -> &AttrValue {
+    pub fn value_or_abort(&self) -> Result<&AttrValue, syn::Error> {
         self.value
             .as_ref()
-            .unwrap_or_else(|| abort!(self.name, "attribute `{}` requires a value", self.name))
+            .ok_or_else(|| format_err!(self.name, "attribute `{}` requires a value", self.name))
     }
 
-    pub fn lit_str_or_abort(&self) -> &LitStr {
-        let value = self.value_or_abort();
+    pub fn lit_str_or_abort(&self) -> Result<&LitStr, syn::Error> {
+        let value = self.value_or_abort()?;
         match value {
-            AttrValue::LitStr(tokens) => tokens,
+            AttrValue::LitStr(tokens) => Ok(tokens),
             AttrValue::Expr(_) | AttrValue::Call(_) => {
                 abort!(
                     self.name,
@@ -133,7 +126,7 @@ impl Parse for ClapAttr {
             let nested;
             parenthesized!(nested in input);
 
-            let method_args: Punctuated<_, Token![,]> = nested.parse_terminated(Expr::parse)?;
+            let method_args: Punctuated<_, _> = nested.parse_terminated(Expr::parse, Token![,])?;
             Some(AttrValue::Call(Vec::from_iter(method_args)))
         } else {
             None
diff --git a/src/derives/args.rs b/src/derives/args.rs
index d3b3692..e8611b6 100644
--- a/src/derives/args.rs
+++ b/src/derives/args.rs
@@ -13,38 +13,33 @@
 // MIT/Apache 2.0 license.
 
 use proc_macro2::{Ident, Span, TokenStream};
-use proc_macro_error::{abort, abort_call_site};
 use quote::{format_ident, quote, quote_spanned};
-use syn::ext::IdentExt;
 use syn::{
     punctuated::Punctuated, spanned::Spanned, token::Comma, Data, DataStruct, DeriveInput, Field,
     Fields, Generics,
 };
 
-use crate::dummies;
 use crate::item::{Item, Kind, Name};
 use crate::utils::{inner_type, sub_type, Sp, Ty};
 
-pub fn derive_args(input: &DeriveInput) -> TokenStream {
+pub fn derive_args(input: &DeriveInput) -> Result<TokenStream, syn::Error> {
     let ident = &input.ident;
 
-    dummies::args(ident);
-
     match input.data {
         Data::Struct(DataStruct {
             fields: Fields::Named(ref fields),
             ..
         }) => {
             let name = Name::Derived(ident.clone());
-            let item = Item::from_args_struct(input, name);
+            let item = Item::from_args_struct(input, name)?;
             let fields = fields
                 .named
                 .iter()
                 .map(|field| {
-                    let item = Item::from_args_field(field, item.casing(), item.env_casing());
-                    (field, item)
+                    let item = Item::from_args_field(field, item.casing(), item.env_casing())?;
+                    Ok((field, item))
                 })
-                .collect::<Vec<_>>();
+                .collect::<Result<Vec<_>, syn::Error>>()?;
             gen_for_struct(&item, ident, &input.generics, &fields)
         }
         Data::Struct(DataStruct {
@@ -52,15 +47,15 @@ pub fn derive_args(input: &DeriveInput) -> TokenStream {
             ..
         }) => {
             let name = Name::Derived(ident.clone());
-            let item = Item::from_args_struct(input, name);
+            let item = Item::from_args_struct(input, name)?;
             let fields = Punctuated::<Field, Comma>::new();
             let fields = fields
                 .iter()
                 .map(|field| {
-                    let item = Item::from_args_field(field, item.casing(), item.env_casing());
-                    (field, item)
+                    let item = Item::from_args_field(field, item.casing(), item.env_casing())?;
+                    Ok((field, item))
                 })
-                .collect::<Vec<_>>();
+                .collect::<Result<Vec<_>, syn::Error>>()?;
             gen_for_struct(&item, ident, &input.generics, &fields)
         }
         _ => abort_call_site!("`#[derive(Args)]` only supports non-tuple structs"),
@@ -72,7 +67,7 @@ pub fn gen_for_struct(
     item_name: &Ident,
     generics: &Generics,
     fields: &[(&Field, Item)],
-) -> TokenStream {
+) -> Result<TokenStream, syn::Error> {
     if !matches!(&*item.kind(), Kind::Command(_)) {
         abort! { item.kind().span(),
             "`{}` cannot be used with `command`",
@@ -82,22 +77,22 @@ pub fn gen_for_struct(
 
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
-    let constructor = gen_constructor(fields);
-    let updater = gen_updater(fields, true);
+    let constructor = gen_constructor(fields)?;
+    let updater = gen_updater(fields, true)?;
     let raw_deprecated = raw_deprecated();
 
     let app_var = Ident::new("__clap_app", Span::call_site());
-    let augmentation = gen_augment(fields, &app_var, item, false);
-    let augmentation_update = gen_augment(fields, &app_var, item, true);
+    let augmentation = gen_augment(fields, &app_var, item, false)?;
+    let augmentation_update = gen_augment(fields, &app_var, item, true)?;
 
     let group_id = if item.skip_group() {
         quote!(None)
     } else {
-        let group_id = item.ident().unraw().to_string();
+        let group_id = item.group_id();
         quote!(Some(clap::Id::from(#group_id)))
     };
 
-    quote! {
+    Ok(quote! {
         #[allow(dead_code, unreachable_code, unused_variables, unused_braces)]
         #[allow(
             clippy::style,
@@ -157,7 +152,7 @@ pub fn gen_for_struct(
                 #augmentation_update
             }
         }
-    }
+    })
 }
 
 /// Generate a block of code to add arguments/subcommands corresponding to
@@ -167,11 +162,12 @@ pub fn gen_augment(
     app_var: &Ident,
     parent_item: &Item,
     override_required: bool,
-) -> TokenStream {
+) -> Result<TokenStream, syn::Error> {
     let mut subcommand_specified = false;
-    let args = fields.iter().filter_map(|(field, item)| {
+    let mut args = Vec::new();
+    for (field, item) in fields {
         let kind = item.kind();
-        match &*kind {
+        let genned = match &*kind {
             Kind::Command(_)
             | Kind::Value
             | Kind::Skip(_, _)
@@ -179,7 +175,10 @@ pub fn gen_augment(
             | Kind::ExternalSubcommand => None,
             Kind::Subcommand(ty) => {
                 if subcommand_specified {
-                    abort!(field.span(), "`#[command(subcommand)]` can only be used once per container");
+                    abort!(
+                        field.span(),
+                        "`#[command(subcommand)]` can only be used once per container"
+                    );
                 }
                 subcommand_specified = true;
 
@@ -354,8 +353,9 @@ pub fn gen_augment(
                     });
                 })
             }
-        }
-    });
+        };
+        args.push(genned);
+    }
 
     let deprecations = if !override_required {
         parent_item.deprecations()
@@ -367,7 +367,7 @@ pub fn gen_augment(
     let group_app_methods = if parent_item.skip_group() {
         quote!()
     } else {
-        let group_id = parent_item.ident().unraw().to_string();
+        let group_id = parent_item.group_id();
         let literal_group_members = fields
             .iter()
             .filter_map(|(_field, item)| {
@@ -400,15 +400,18 @@ pub fn gen_augment(
             }};
         }
 
+        let group_methods = parent_item.group_methods();
+
         quote!(
             .group(
                 clap::ArgGroup::new(#group_id)
                     .multiple(true)
+                    #group_methods
                     .args(#literal_group_members)
             )
         )
     };
-    quote! {{
+    Ok(quote! {{
         #deprecations
         let #app_var = #app_var
             #initial_app_methods
@@ -416,15 +419,15 @@ pub fn gen_augment(
             ;
         #( #args )*
         #app_var #final_app_methods
-    }}
+    }})
 }
 
-pub fn gen_constructor(fields: &[(&Field, Item)]) -> TokenStream {
+pub fn gen_constructor(fields: &[(&Field, Item)]) -> Result<TokenStream, syn::Error> {
     let fields = fields.iter().map(|(field, item)| {
         let field_name = field.ident.as_ref().unwrap();
         let kind = item.kind();
         let arg_matches = format_ident!("__clap_arg_matches");
-        match &*kind {
+        let genned = match &*kind {
             Kind::Command(_)
             | Kind::Value
             | Kind::ExternalSubcommand => {
@@ -519,18 +522,20 @@ pub fn gen_constructor(fields: &[(&Field, Item)]) -> TokenStream {
             },
 
             Kind::Arg(ty) | Kind::FromGlobal(ty) => {
-                gen_parsers(item, ty, field_name, field, None)
+                gen_parsers(item, ty, field_name, field, None)?
             }
-        }
-    });
+        };
+        Ok(genned)
+    }).collect::<Result<Vec<_>, syn::Error>>()?;
 
-    quote! {{
+    Ok(quote! {{
         #( #fields ),*
-    }}
+    }})
 }
 
-pub fn gen_updater(fields: &[(&Field, Item)], use_self: bool) -> TokenStream {
-    let fields = fields.iter().map(|(field, item)| {
+pub fn gen_updater(fields: &[(&Field, Item)], use_self: bool) -> Result<TokenStream, syn::Error> {
+    let mut genned_fields = Vec::new();
+    for (field, item) in fields {
         let field_name = field.ident.as_ref().unwrap();
         let kind = item.kind();
 
@@ -544,10 +549,8 @@ pub fn gen_updater(fields: &[(&Field, Item)], use_self: bool) -> TokenStream {
         };
         let arg_matches = format_ident!("__clap_arg_matches");
 
-        match &*kind {
-            Kind::Command(_)
-            | Kind::Value
-            | Kind::ExternalSubcommand => {
+        let genned = match &*kind {
+            Kind::Command(_) | Kind::Value | Kind::ExternalSubcommand => {
                 abort! { kind.span(),
                     "`{}` cannot be used with `arg`",
                     kind.name(),
@@ -617,17 +620,20 @@ pub fn gen_updater(fields: &[(&Field, Item)], use_self: bool) -> TokenStream {
                         #updater
                     }
                 }
-            },
+            }
 
             Kind::Skip(_, _) => quote!(),
 
-            Kind::Arg(ty) | Kind::FromGlobal(ty) => gen_parsers(item, ty, field_name, field, Some(&access)),
-        }
-    });
-
-    quote! {
-        #( #fields )*
+            Kind::Arg(ty) | Kind::FromGlobal(ty) => {
+                gen_parsers(item, ty, field_name, field, Some(&access))?
+            }
+        };
+        genned_fields.push(genned);
     }
+
+    Ok(quote! {
+        #( #genned_fields )*
+    })
 }
 
 fn gen_parsers(
@@ -636,7 +642,7 @@ fn gen_parsers(
     field_name: &Ident,
     field: &Field,
     update: Option<&TokenStream>,
-) -> TokenStream {
+) -> Result<TokenStream, syn::Error> {
     let span = ty.span();
     let convert_type = inner_type(&field.ty);
     let id = item.id();
@@ -709,7 +715,7 @@ fn gen_parsers(
         }
     };
 
-    if let Some(access) = update {
+    let genned = if let Some(access) = update {
         quote_spanned! { field.span()=>
             if #arg_matches.contains_id(#id) {
                 #access
@@ -718,7 +724,8 @@ fn gen_parsers(
         }
     } else {
         quote_spanned!(field.span()=> #field_name: #field_value )
-    }
+    };
+    Ok(genned)
 }
 
 #[cfg(feature = "raw-deprecated")]
diff --git a/src/derives/into_app.rs b/src/derives/into_app.rs
index dfb676a..72f081f 100644
--- a/src/derives/into_app.rs
+++ b/src/derives/into_app.rs
@@ -18,7 +18,11 @@ use syn::{Generics, Ident};
 
 use crate::item::Item;
 
-pub fn gen_for_struct(item: &Item, item_name: &Ident, generics: &Generics) -> TokenStream {
+pub fn gen_for_struct(
+    item: &Item,
+    item_name: &Ident,
+    generics: &Generics,
+) -> Result<TokenStream, syn::Error> {
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
     let name = item.cased_name();
@@ -51,16 +55,20 @@ pub fn gen_for_struct(item: &Item, item_name: &Ident, generics: &Generics) -> To
         }
     };
 
-    tokens
+    Ok(tokens)
 }
 
-pub fn gen_for_enum(item: &Item, item_name: &Ident, generics: &Generics) -> TokenStream {
+pub fn gen_for_enum(
+    item: &Item,
+    item_name: &Ident,
+    generics: &Generics,
+) -> Result<TokenStream, syn::Error> {
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
     let name = item.cased_name();
     let app_var = Ident::new("__clap_app", Span::call_site());
 
-    quote! {
+    Ok(quote! {
         #[allow(dead_code, unreachable_code, unused_variables, unused_braces)]
         #[allow(
             clippy::style,
@@ -89,5 +97,5 @@ pub fn gen_for_enum(item: &Item, item_name: &Ident, generics: &Generics) -> Toke
                     .arg_required_else_help(false)
             }
         }
-    }
+    })
 }
diff --git a/src/derives/parser.rs b/src/derives/parser.rs
index 617857c..39b0b8a 100644
--- a/src/derives/parser.rs
+++ b/src/derives/parser.rs
@@ -13,7 +13,6 @@
 // MIT/Apache 2.0 license.
 
 use proc_macro2::TokenStream;
-use proc_macro_error::abort_call_site;
 use quote::quote;
 use syn::Ident;
 use syn::Variant;
@@ -23,11 +22,10 @@ use syn::{
 };
 
 use crate::derives::{args, into_app, subcommand};
-use crate::dummies;
 use crate::item::Item;
 use crate::item::Name;
 
-pub fn derive_parser(input: &DeriveInput) -> TokenStream {
+pub fn derive_parser(input: &DeriveInput) -> Result<TokenStream, syn::Error> {
     let ident = &input.ident;
     let pkg_name = std::env::var("CARGO_PKG_NAME").ok().unwrap_or_default();
 
@@ -36,52 +34,46 @@ pub fn derive_parser(input: &DeriveInput) -> TokenStream {
             fields: Fields::Named(ref fields),
             ..
         }) => {
-            dummies::parser_struct(ident);
-
             let name = Name::Assigned(quote!(#pkg_name));
-            let item = Item::from_args_struct(input, name);
+            let item = Item::from_args_struct(input, name)?;
             let fields = fields
                 .named
                 .iter()
                 .map(|field| {
-                    let item = Item::from_args_field(field, item.casing(), item.env_casing());
-                    (field, item)
+                    let item = Item::from_args_field(field, item.casing(), item.env_casing())?;
+                    Ok((field, item))
                 })
-                .collect::<Vec<_>>();
+                .collect::<Result<Vec<_>, syn::Error>>()?;
             gen_for_struct(&item, ident, &input.generics, &fields)
         }
         Data::Struct(DataStruct {
             fields: Fields::Unit,
             ..
         }) => {
-            dummies::parser_struct(ident);
-
             let name = Name::Assigned(quote!(#pkg_name));
-            let item = Item::from_args_struct(input, name);
+            let item = Item::from_args_struct(input, name)?;
             let fields = Punctuated::<Field, Comma>::new();
             let fields = fields
                 .iter()
                 .map(|field| {
-                    let item = Item::from_args_field(field, item.casing(), item.env_casing());
-                    (field, item)
+                    let item = Item::from_args_field(field, item.casing(), item.env_casing())?;
+                    Ok((field, item))
                 })
-                .collect::<Vec<_>>();
+                .collect::<Result<Vec<_>, syn::Error>>()?;
             gen_for_struct(&item, ident, &input.generics, &fields)
         }
         Data::Enum(ref e) => {
-            dummies::parser_enum(ident);
-
             let name = Name::Assigned(quote!(#pkg_name));
-            let item = Item::from_subcommand_enum(input, name);
+            let item = Item::from_subcommand_enum(input, name)?;
             let variants = e
                 .variants
                 .iter()
                 .map(|variant| {
                     let item =
-                        Item::from_subcommand_variant(variant, item.casing(), item.env_casing());
-                    (variant, item)
+                        Item::from_subcommand_variant(variant, item.casing(), item.env_casing())?;
+                    Ok((variant, item))
                 })
-                .collect::<Vec<_>>();
+                .collect::<Result<Vec<_>, syn::Error>>()?;
             gen_for_enum(&item, ident, &input.generics, &variants)
         }
         _ => abort_call_site!("`#[derive(Parser)]` only supports non-tuple structs and enums"),
@@ -93,18 +85,18 @@ fn gen_for_struct(
     item_name: &Ident,
     generics: &Generics,
     fields: &[(&Field, Item)],
-) -> TokenStream {
+) -> Result<TokenStream, syn::Error> {
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
-    let into_app = into_app::gen_for_struct(item, item_name, generics);
-    let args = args::gen_for_struct(item, item_name, generics, fields);
+    let into_app = into_app::gen_for_struct(item, item_name, generics)?;
+    let args = args::gen_for_struct(item, item_name, generics, fields)?;
 
-    quote! {
+    Ok(quote! {
         impl #impl_generics clap::Parser for #item_name #ty_generics #where_clause {}
 
         #into_app
         #args
-    }
+    })
 }
 
 fn gen_for_enum(
@@ -112,16 +104,16 @@ fn gen_for_enum(
     item_name: &Ident,
     generics: &Generics,
     variants: &[(&Variant, Item)],
-) -> TokenStream {
+) -> Result<TokenStream, syn::Error> {
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
-    let into_app = into_app::gen_for_enum(item, item_name, generics);
-    let subcommand = subcommand::gen_for_enum(item, item_name, generics, variants);
+    let into_app = into_app::gen_for_enum(item, item_name, generics)?;
+    let subcommand = subcommand::gen_for_enum(item, item_name, generics, variants)?;
 
-    quote! {
+    Ok(quote! {
         impl #impl_generics clap::Parser for #item_name #ty_generics #where_clause {}
 
         #into_app
         #subcommand
-    }
+    })
 }
diff --git a/src/derives/subcommand.rs b/src/derives/subcommand.rs
index ffe22ec..403fe45 100644
--- a/src/derives/subcommand.rs
+++ b/src/derives/subcommand.rs
@@ -13,33 +13,29 @@
 // MIT/Apache 2.0 license.
 
 use proc_macro2::{Ident, Span, TokenStream};
-use proc_macro_error::{abort, abort_call_site};
 use quote::{format_ident, quote, quote_spanned};
 use syn::{spanned::Spanned, Data, DeriveInput, FieldsUnnamed, Generics, Variant};
 
 use crate::derives::args;
-use crate::dummies;
 use crate::item::{Item, Kind, Name};
 use crate::utils::{is_simple_ty, subty_if_name};
 
-pub fn derive_subcommand(input: &DeriveInput) -> TokenStream {
+pub fn derive_subcommand(input: &DeriveInput) -> Result<TokenStream, syn::Error> {
     let ident = &input.ident;
 
-    dummies::subcommand(ident);
-
     match input.data {
         Data::Enum(ref e) => {
             let name = Name::Derived(ident.clone());
-            let item = Item::from_subcommand_enum(input, name);
+            let item = Item::from_subcommand_enum(input, name)?;
             let variants = e
                 .variants
                 .iter()
                 .map(|variant| {
                     let item =
-                        Item::from_subcommand_variant(variant, item.casing(), item.env_casing());
-                    (variant, item)
+                        Item::from_subcommand_variant(variant, item.casing(), item.env_casing())?;
+                    Ok((variant, item))
                 })
-                .collect::<Vec<_>>();
+                .collect::<Result<Vec<_>, syn::Error>>()?;
             gen_for_enum(&item, ident, &input.generics, &variants)
         }
         _ => abort_call_site!("`#[derive(Subcommand)]` only supports enums"),
@@ -51,7 +47,7 @@ pub fn gen_for_enum(
     item_name: &Ident,
     generics: &Generics,
     variants: &[(&Variant, Item)],
-) -> TokenStream {
+) -> Result<TokenStream, syn::Error> {
     if !matches!(&*item.kind(), Kind::Command(_)) {
         abort! { item.kind().span(),
             "`{}` cannot be used with `command`",
@@ -61,14 +57,14 @@ pub fn gen_for_enum(
 
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
-    let from_arg_matches = gen_from_arg_matches(variants);
-    let update_from_arg_matches = gen_update_from_arg_matches(variants);
+    let from_arg_matches = gen_from_arg_matches(variants)?;
+    let update_from_arg_matches = gen_update_from_arg_matches(variants)?;
 
-    let augmentation = gen_augment(variants, item, false);
-    let augmentation_update = gen_augment(variants, item, true);
-    let has_subcommand = gen_has_subcommand(variants);
+    let augmentation = gen_augment(variants, item, false)?;
+    let augmentation_update = gen_augment(variants, item, true)?;
+    let has_subcommand = gen_has_subcommand(variants)?;
 
-    quote! {
+    Ok(quote! {
         #[allow(dead_code, unreachable_code, unused_variables, unused_braces)]
         #[allow(
             clippy::style,
@@ -119,225 +115,222 @@ pub fn gen_for_enum(
                 #has_subcommand
             }
         }
-    }
+    })
 }
 
 fn gen_augment(
     variants: &[(&Variant, Item)],
     parent_item: &Item,
     override_required: bool,
-) -> TokenStream {
+) -> Result<TokenStream, syn::Error> {
     use syn::Fields::*;
 
     let app_var = Ident::new("__clap_app", Span::call_site());
 
-    let subcommands: Vec<_> = variants
-        .iter()
-        .filter_map(|(variant, item)| {
-            let kind = item.kind();
+    let mut subcommands = Vec::new();
+    for (variant, item) in variants {
+        let kind = item.kind();
 
-            match &*kind {
-                Kind::Skip(_, _) |
-                Kind::Arg(_) |
-                Kind::FromGlobal(_) |
-                Kind::Value => None,
+        let genned = match &*kind {
+            Kind::Skip(_, _) | Kind::Arg(_) | Kind::FromGlobal(_) | Kind::Value => None,
 
-                Kind::ExternalSubcommand => {
-                    let ty = match variant.fields {
-                        Unnamed(ref fields) if fields.unnamed.len() == 1 => &fields.unnamed[0].ty,
+            Kind::ExternalSubcommand => {
+                let ty = match variant.fields {
+                    Unnamed(ref fields) if fields.unnamed.len() == 1 => &fields.unnamed[0].ty,
 
-                        _ => abort!(
-                            variant,
-                            "The enum variant marked with `external_subcommand` must be \
+                    _ => abort!(
+                        variant,
+                        "The enum variant marked with `external_subcommand` must be \
                              a single-typed tuple, and the type must be either `Vec<String>` \
                              or `Vec<OsString>`."
-                        ),
-                    };
+                    ),
+                };
+                let deprecations = if !override_required {
+                    item.deprecations()
+                } else {
+                    quote!()
+                };
+                let subty = subty_if_name(ty, "Vec").ok_or_else(|| {
+                    format_err!(
+                        ty.span(),
+                        "The type must be `Vec<_>` \
+                             to be used with `external_subcommand`."
+                    )
+                })?;
+                let subcommand = quote_spanned! { kind.span()=>
+                    #deprecations
+                    let #app_var = #app_var
+                        .external_subcommand_value_parser(clap::value_parser!(#subty));
+                };
+                Some(subcommand)
+            }
+
+            Kind::Flatten(_) => match variant.fields {
+                Unnamed(FieldsUnnamed { ref unnamed, .. }) if unnamed.len() == 1 => {
+                    let ty = &unnamed[0];
                     let deprecations = if !override_required {
                         item.deprecations()
                     } else {
                         quote!()
                     };
-                    let subty = subty_if_name(ty, "Vec").unwrap_or_else(|| {
-                        abort!(
-                            ty.span(),
-                            "The type must be `Vec<_>` \
-                             to be used with `external_subcommand`."
-                        )
-                    });
-                    let subcommand = quote_spanned! { kind.span()=>
-                        #deprecations
-                        let #app_var = #app_var
-                            .external_subcommand_value_parser(clap::value_parser!(#subty));
+                    let next_help_heading = item.next_help_heading();
+                    let next_display_order = item.next_display_order();
+                    let subcommand = if override_required {
+                        quote! {
+                            #deprecations
+                            let #app_var = #app_var
+                                #next_help_heading
+                                #next_display_order;
+                            let #app_var = <#ty as clap::Subcommand>::augment_subcommands_for_update(#app_var);
+                        }
+                    } else {
+                        quote! {
+                            #deprecations
+                            let #app_var = #app_var
+                                #next_help_heading
+                                #next_display_order;
+                            let #app_var = <#ty as clap::Subcommand>::augment_subcommands(#app_var);
+                        }
                     };
                     Some(subcommand)
                 }
+                _ => abort!(
+                    variant,
+                    "`flatten` is usable only with single-typed tuple variants"
+                ),
+            },
 
-                Kind::Flatten(_) => match variant.fields {
+            Kind::Subcommand(_) => {
+                let subcommand_var = Ident::new("__clap_subcommand", Span::call_site());
+                let arg_block = match variant.fields {
+                    Named(_) => {
+                        abort!(variant, "non single-typed tuple enums are not supported")
+                    }
+                    Unit => quote!( #subcommand_var ),
                     Unnamed(FieldsUnnamed { ref unnamed, .. }) if unnamed.len() == 1 => {
                         let ty = &unnamed[0];
-                        let deprecations = if !override_required {
-                            item.deprecations()
-                        } else {
-                            quote!()
-                        };
-                        let next_help_heading = item.next_help_heading();
-                        let next_display_order = item.next_display_order();
-                        let subcommand = if override_required {
-                            quote! {
-                                #deprecations
-                                let #app_var = #app_var
-                                    #next_help_heading
-                                    #next_display_order;
-                                let #app_var = <#ty as clap::Subcommand>::augment_subcommands_for_update(#app_var);
+                        if override_required {
+                            quote_spanned! { ty.span()=>
+                                {
+                                    <#ty as clap::Subcommand>::augment_subcommands_for_update(#subcommand_var)
+                                }
                             }
                         } else {
-                            quote! {
-                                #deprecations
-                                let #app_var = #app_var
-                                    #next_help_heading
-                                    #next_display_order;
-                                let #app_var = <#ty as clap::Subcommand>::augment_subcommands(#app_var);
-                            }
-                        };
-                        Some(subcommand)
-                    }
-                    _ => abort!(
-                        variant,
-                        "`flatten` is usable only with single-typed tuple variants"
-                    ),
-                },
-
-                Kind::Subcommand(_) => {
-                    let subcommand_var = Ident::new("__clap_subcommand", Span::call_site());
-                    let arg_block = match variant.fields {
-                        Named(_) => {
-                            abort!(variant, "non single-typed tuple enums are not supported")
-                        }
-                        Unit => quote!( #subcommand_var ),
-                        Unnamed(FieldsUnnamed { ref unnamed, .. }) if unnamed.len() == 1 => {
-                            let ty = &unnamed[0];
-                            if override_required {
-                                quote_spanned! { ty.span()=>
-                                    {
-                                        <#ty as clap::Subcommand>::augment_subcommands_for_update(#subcommand_var)
-                                    }
-                                }
-                            } else {
-                                quote_spanned! { ty.span()=>
-                                    {
-                                        <#ty as clap::Subcommand>::augment_subcommands(#subcommand_var)
-                                    }
+                            quote_spanned! { ty.span()=>
+                                {
+                                    <#ty as clap::Subcommand>::augment_subcommands(#subcommand_var)
                                 }
                             }
                         }
-                        Unnamed(..) => {
-                            abort!(variant, "non single-typed tuple enums are not supported")
-                        }
-                    };
+                    }
+                    Unnamed(..) => {
+                        abort!(variant, "non single-typed tuple enums are not supported")
+                    }
+                };
 
-                    let name = item.cased_name();
-                    let deprecations = if !override_required {
-                        item.deprecations()
-                    } else {
-                        quote!()
-                    };
-                    let initial_app_methods = item.initial_top_level_methods();
-                    let final_from_attrs = item.final_top_level_methods();
-                    let override_methods = if override_required {
-                        quote_spanned! { kind.span()=>
-                            .subcommand_required(false)
-                            .arg_required_else_help(false)
-                        }
-                    } else {
-                        quote!()
-                    };
-                    let subcommand = quote! {
-                        let #app_var = #app_var.subcommand({
-                            #deprecations;
-                            let #subcommand_var = clap::Command::new(#name);
-                            let #subcommand_var = #subcommand_var
-                                .subcommand_required(true)
-                                .arg_required_else_help(true);
+                let name = item.cased_name();
+                let deprecations = if !override_required {
+                    item.deprecations()
+                } else {
+                    quote!()
+                };
+                let initial_app_methods = item.initial_top_level_methods();
+                let final_from_attrs = item.final_top_level_methods();
+                let override_methods = if override_required {
+                    quote_spanned! { kind.span()=>
+                        .subcommand_required(false)
+                        .arg_required_else_help(false)
+                    }
+                } else {
+                    quote!()
+                };
+                let subcommand = quote! {
+                    let #app_var = #app_var.subcommand({
+                        #deprecations;
+                        let #subcommand_var = clap::Command::new(#name);
+                        let #subcommand_var = #subcommand_var
+                            .subcommand_required(true)
+                            .arg_required_else_help(true);
+                        let #subcommand_var = #subcommand_var #initial_app_methods;
+                        let #subcommand_var = #arg_block;
+                        #subcommand_var #final_from_attrs #override_methods
+                    });
+                };
+                Some(subcommand)
+            }
+
+            Kind::Command(_) => {
+                let subcommand_var = Ident::new("__clap_subcommand", Span::call_site());
+                let sub_augment = match variant.fields {
+                    Named(ref fields) => {
+                        // Defer to `gen_augment` for adding cmd methods
+                        let fields = fields
+                            .named
+                            .iter()
+                            .map(|field| {
+                                let item =
+                                    Item::from_args_field(field, item.casing(), item.env_casing())?;
+                                Ok((field, item))
+                            })
+                            .collect::<Result<Vec<_>, syn::Error>>()?;
+                        args::gen_augment(&fields, &subcommand_var, item, override_required)?
+                    }
+                    Unit => {
+                        let arg_block = quote!( #subcommand_var );
+                        let initial_app_methods = item.initial_top_level_methods();
+                        let final_from_attrs = item.final_top_level_methods();
+                        quote! {
                             let #subcommand_var = #subcommand_var #initial_app_methods;
                             let #subcommand_var = #arg_block;
-                            #subcommand_var #final_from_attrs #override_methods
-                        });
-                    };
-                    Some(subcommand)
-                }
-
-                Kind::Command(_) => {
-                    let subcommand_var = Ident::new("__clap_subcommand", Span::call_site());
-                    let sub_augment = match variant.fields {
-                        Named(ref fields) => {
-                            // Defer to `gen_augment` for adding cmd methods
-                            let fields = fields
-                                .named
-                                .iter()
-                                .map(|field| {
-                                    let item = Item::from_args_field(field, item.casing(), item.env_casing());
-                                    (field, item)
-                                })
-                                .collect::<Vec<_>>();
-                            args::gen_augment(&fields, &subcommand_var, item, override_required)
+                            #subcommand_var #final_from_attrs
                         }
-                        Unit => {
-                            let arg_block = quote!( #subcommand_var );
-                            let initial_app_methods = item.initial_top_level_methods();
-                            let final_from_attrs = item.final_top_level_methods();
-                            quote! {
-                                let #subcommand_var = #subcommand_var #initial_app_methods;
-                                let #subcommand_var = #arg_block;
-                                #subcommand_var #final_from_attrs
-                            }
-                        },
-                        Unnamed(FieldsUnnamed { ref unnamed, .. }) if unnamed.len() == 1 => {
-                            let ty = &unnamed[0];
-                            let arg_block = if override_required {
-                                quote_spanned! { ty.span()=>
-                                    {
-                                        <#ty as clap::Args>::augment_args_for_update(#subcommand_var)
-                                    }
+                    }
+                    Unnamed(FieldsUnnamed { ref unnamed, .. }) if unnamed.len() == 1 => {
+                        let ty = &unnamed[0];
+                        let arg_block = if override_required {
+                            quote_spanned! { ty.span()=>
+                                {
+                                    <#ty as clap::Args>::augment_args_for_update(#subcommand_var)
                                 }
-                            } else {
-                                quote_spanned! { ty.span()=>
-                                    {
-                                        <#ty as clap::Args>::augment_args(#subcommand_var)
-                                    }
+                            }
+                        } else {
+                            quote_spanned! { ty.span()=>
+                                {
+                                    <#ty as clap::Args>::augment_args(#subcommand_var)
                                 }
-                            };
-                            let initial_app_methods = item.initial_top_level_methods();
-                            let final_from_attrs = item.final_top_level_methods();
-                            quote! {
-                                let #subcommand_var = #subcommand_var #initial_app_methods;
-                                let #subcommand_var = #arg_block;
-                                #subcommand_var #final_from_attrs
                             }
+                        };
+                        let initial_app_methods = item.initial_top_level_methods();
+                        let final_from_attrs = item.final_top_level_methods();
+                        quote! {
+                            let #subcommand_var = #subcommand_var #initial_app_methods;
+                            let #subcommand_var = #arg_block;
+                            #subcommand_var #final_from_attrs
                         }
-                        Unnamed(..) => {
-                            abort!(variant, "non single-typed tuple enums are not supported")
-                        }
-                    };
+                    }
+                    Unnamed(..) => {
+                        abort!(variant, "non single-typed tuple enums are not supported")
+                    }
+                };
 
-                    let deprecations = if !override_required {
-                        item.deprecations()
-                    } else {
-                        quote!()
-                    };
-                    let name = item.cased_name();
-                    let subcommand = quote! {
-                        let #app_var = #app_var.subcommand({
-                            #deprecations
-                            let #subcommand_var = clap::Command::new(#name);
-                            #sub_augment
-                        });
-                    };
-                    Some(subcommand)
-                }
+                let deprecations = if !override_required {
+                    item.deprecations()
+                } else {
+                    quote!()
+                };
+                let name = item.cased_name();
+                let subcommand = quote! {
+                    let #app_var = #app_var.subcommand({
+                        #deprecations
+                        let #subcommand_var = clap::Command::new(#name);
+                        #sub_augment
+                    });
+                };
+                Some(subcommand)
             }
-        })
-        .collect();
+        };
+        subcommands.push(genned);
+    }
 
     let deprecations = if !override_required {
         parent_item.deprecations()
@@ -346,15 +339,15 @@ fn gen_augment(
     };
     let initial_app_methods = parent_item.initial_top_level_methods();
     let final_app_methods = parent_item.final_top_level_methods();
-    quote! {
+    Ok(quote! {
         #deprecations;
         let #app_var = #app_var #initial_app_methods;
         #( #subcommands )*;
         #app_var #final_app_methods
-    }
+    })
 }
 
-fn gen_has_subcommand(variants: &[(&Variant, Item)]) -> TokenStream {
+fn gen_has_subcommand(variants: &[(&Variant, Item)]) -> Result<TokenStream, syn::Error> {
     use syn::Fields::*;
 
     let mut ext_subcmd = false;
@@ -391,19 +384,20 @@ fn gen_has_subcommand(variants: &[(&Variant, Item)]) -> TokenStream {
         .map(|(variant, _attrs)| match variant.fields {
             Unnamed(ref fields) if fields.unnamed.len() == 1 => {
                 let ty = &fields.unnamed[0];
-                quote! {
+                Ok(quote! {
                     if <#ty as clap::Subcommand>::has_subcommand(__clap_name) {
                         return true;
                     }
-                }
+                })
             }
             _ => abort!(
                 variant,
                 "`flatten` is usable only with single-typed tuple variants"
             ),
-        });
+        })
+        .collect::<Result<Vec<_>, syn::Error>>()?;
 
-    if ext_subcmd {
+    let genned = if ext_subcmd {
         quote! { true }
     } else {
         quote! {
@@ -413,77 +407,79 @@ fn gen_has_subcommand(variants: &[(&Variant, Item)]) -> TokenStream {
 
             false
         }
-    }
+    };
+    Ok(genned)
 }
 
-fn gen_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
+fn gen_from_arg_matches(variants: &[(&Variant, Item)]) -> Result<TokenStream, syn::Error> {
     use syn::Fields::*;
 
-    let mut ext_subcmd = None;
-
     let subcommand_name_var = format_ident!("__clap_name");
     let sub_arg_matches_var = format_ident!("__clap_arg_matches");
-    let (flatten_variants, variants): (Vec<_>, Vec<_>) = variants
-        .iter()
-        .filter_map(|(variant, item)| {
-            let kind = item.kind();
-            match &*kind {
-                Kind::Skip(_, _) | Kind::Arg(_) | Kind::FromGlobal(_) | Kind::Value => None,
 
-                Kind::ExternalSubcommand => {
-                    if ext_subcmd.is_some() {
-                        abort!(
-                            item.kind().span(),
-                            "Only one variant can be marked with `external_subcommand`, \
+    let mut ext_subcmd = None;
+    let mut flatten_variants = Vec::new();
+    let mut unflatten_variants = Vec::new();
+    for (variant, item) in variants {
+        let kind = item.kind();
+        match &*kind {
+            Kind::Skip(_, _) | Kind::Arg(_) | Kind::FromGlobal(_) | Kind::Value => {}
+
+            Kind::ExternalSubcommand => {
+                if ext_subcmd.is_some() {
+                    abort!(
+                        item.kind().span(),
+                        "Only one variant can be marked with `external_subcommand`, \
                          this is the second"
-                        );
-                    }
+                    );
+                }
 
-                    let ty = match variant.fields {
-                        Unnamed(ref fields) if fields.unnamed.len() == 1 => &fields.unnamed[0].ty,
+                let ty = match variant.fields {
+                    Unnamed(ref fields) if fields.unnamed.len() == 1 => &fields.unnamed[0].ty,
 
-                        _ => abort!(
-                            variant,
-                            "The enum variant marked with `external_subcommand` must be \
+                    _ => abort!(
+                        variant,
+                        "The enum variant marked with `external_subcommand` must be \
                          a single-typed tuple, and the type must be either `Vec<String>` \
                          or `Vec<OsString>`."
-                        ),
-                    };
-
-                    let (span, str_ty) = match subty_if_name(ty, "Vec") {
-                        Some(subty) => {
-                            if is_simple_ty(subty, "String") {
-                                (subty.span(), quote!(::std::string::String))
-                            } else if is_simple_ty(subty, "OsString") {
-                                (subty.span(), quote!(::std::ffi::OsString))
-                            } else {
-                                abort!(
-                                    ty.span(),
-                                    "The type must be either `Vec<String>` or `Vec<OsString>` \
+                    ),
+                };
+
+                let (span, str_ty) = match subty_if_name(ty, "Vec") {
+                    Some(subty) => {
+                        if is_simple_ty(subty, "String") {
+                            (subty.span(), quote!(::std::string::String))
+                        } else if is_simple_ty(subty, "OsString") {
+                            (subty.span(), quote!(::std::ffi::OsString))
+                        } else {
+                            abort!(
+                                ty.span(),
+                                "The type must be either `Vec<String>` or `Vec<OsString>` \
                                  to be used with `external_subcommand`."
-                                );
-                            }
+                            );
                         }
+                    }
 
-                        None => abort!(
-                            ty.span(),
-                            "The type must be either `Vec<String>` or `Vec<OsString>` \
+                    None => abort!(
+                        ty.span(),
+                        "The type must be either `Vec<String>` or `Vec<OsString>` \
                          to be used with `external_subcommand`."
-                        ),
-                    };
+                    ),
+                };
 
-                    ext_subcmd = Some((span, &variant.ident, str_ty));
-                    None
+                ext_subcmd = Some((span, &variant.ident, str_ty));
+            }
+            Kind::Flatten(_) | Kind::Subcommand(_) | Kind::Command(_) => {
+                if matches!(&*item.kind(), Kind::Flatten(_)) {
+                    flatten_variants.push((variant, item));
+                } else {
+                    unflatten_variants.push((variant, item));
                 }
-                Kind::Flatten(_) | Kind::Subcommand(_) | Kind::Command(_) => Some((variant, item)),
             }
-        })
-        .partition(|(_, item)| {
-            let kind = item.kind();
-            matches!(&*kind, Kind::Flatten(_))
-        });
+        }
+    }
 
-    let subcommands = variants.iter().map(|(variant, item)| {
+    let subcommands = unflatten_variants.iter().map(|(variant, item)| {
         let sub_name = item.cased_name();
         let variant_name = &variant.ident;
         let constructor_block = match variant.fields {
@@ -492,11 +488,11 @@ fn gen_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
                     .named
                     .iter()
                     .map(|field| {
-                        let item = Item::from_args_field(field, item.casing(), item.env_casing());
-                        (field, item)
+                        let item = Item::from_args_field(field, item.casing(), item.env_casing())?;
+                        Ok((field, item))
                     })
-                    .collect::<Vec<_>>();
-                args::gen_constructor(&fields)
+                    .collect::<Result<Vec<_>, syn::Error>>()?;
+                args::gen_constructor(&fields)?
             },
             Unit => quote!(),
             Unnamed(ref fields) if fields.unnamed.len() == 1 => {
@@ -506,18 +502,18 @@ fn gen_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
             Unnamed(..) => abort_call_site!("{}: tuple enums are not supported", variant.ident),
         };
 
-        quote! {
+        Ok(quote! {
             if #subcommand_name_var == #sub_name && !#sub_arg_matches_var.contains_id("") {
                 return ::std::result::Result::Ok(Self :: #variant_name #constructor_block)
             }
-        }
-    });
+        })
+    }).collect::<Result<Vec<_>, syn::Error>>()?;
     let child_subcommands = flatten_variants.iter().map(|(variant, _attrs)| {
         let variant_name = &variant.ident;
         match variant.fields {
             Unnamed(ref fields) if fields.unnamed.len() == 1 => {
                 let ty = &fields.unnamed[0];
-                quote! {
+                Ok(quote! {
                     if __clap_arg_matches
                         .subcommand_name()
                         .map(|__clap_name| <#ty as clap::Subcommand>::has_subcommand(__clap_name))
@@ -526,14 +522,14 @@ fn gen_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
                         let __clap_res = <#ty as clap::FromArgMatches>::from_arg_matches_mut(__clap_arg_matches)?;
                         return ::std::result::Result::Ok(Self :: #variant_name (__clap_res));
                     }
-                }
+                })
             }
             _ => abort!(
                 variant,
                 "`flatten` is usable only with single-typed tuple variants"
             ),
         }
-    });
+    }).collect::<Result<Vec<_>, syn::Error>>()?;
 
     let wildcard = match ext_subcmd {
         Some((span, var_name, str_ty)) => quote_spanned! { span=>
@@ -555,7 +551,7 @@ fn gen_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
     };
 
     let raw_deprecated = args::raw_deprecated();
-    quote! {
+    Ok(quote! {
         fn from_arg_matches_mut(__clap_arg_matches: &mut clap::ArgMatches) -> ::std::result::Result<Self, clap::Error> {
             #raw_deprecated
 
@@ -570,10 +566,10 @@ fn gen_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
                 ::std::result::Result::Err(clap::Error::raw(clap::error::ErrorKind::MissingSubcommand, "A subcommand is required but one was not provided."))
             }
         }
-    }
+    })
 }
 
-fn gen_update_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
+fn gen_update_from_arg_matches(variants: &[(&Variant, Item)]) -> Result<TokenStream, syn::Error> {
     use syn::Fields::*;
 
     let (flatten, variants): (Vec<_>, Vec<_>) = variants
@@ -607,11 +603,11 @@ fn gen_update_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
                     .named
                     .iter()
                     .map(|field| {
-                        let item = Item::from_args_field(field, item.casing(), item.env_casing());
-                        (field, item)
+                        let item = Item::from_args_field(field, item.casing(), item.env_casing())?;
+                        Ok((field, item))
                     })
-                    .collect::<Vec<_>>();
-                let update = args::gen_updater(&fields, false);
+                    .collect::<Result<Vec<_>, syn::Error>>()?;
+                let update = args::gen_updater(&fields, false)?;
                 (quote!( { #( #field_names, )* }), quote!( { #update } ))
             }
             Unit => (quote!(), quote!({})),
@@ -630,38 +626,38 @@ fn gen_update_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
             }
         };
 
-        quote! {
+        Ok(quote! {
             Self :: #variant_name #pattern if #sub_name == __clap_name => {
                 let (_, mut __clap_arg_sub_matches) = __clap_arg_matches.remove_subcommand().unwrap();
                 let __clap_arg_matches = &mut __clap_arg_sub_matches;
                 #updater
             }
-        }
-    });
+        })
+    }).collect::<Result<Vec<_>, _>>()?;
 
     let child_subcommands = flatten.iter().map(|(variant, _attrs)| {
         let variant_name = &variant.ident;
         match variant.fields {
             Unnamed(ref fields) if fields.unnamed.len() == 1 => {
                 let ty = &fields.unnamed[0];
-                quote! {
+                Ok(quote! {
                     if <#ty as clap::Subcommand>::has_subcommand(__clap_name) {
                         if let Self :: #variant_name (child) = s {
                             <#ty as clap::FromArgMatches>::update_from_arg_matches_mut(child, __clap_arg_matches)?;
                             return ::std::result::Result::Ok(());
                         }
                     }
-                }
+                })
             }
             _ => abort!(
                 variant,
                 "`flatten` is usable only with single-typed tuple variants"
             ),
         }
-    });
+    }).collect::<Result<Vec<_>, _>>()?;
 
     let raw_deprecated = args::raw_deprecated();
-    quote! {
+    Ok(quote! {
         fn update_from_arg_matches_mut<'b>(
             &mut self,
             __clap_arg_matches: &mut clap::ArgMatches,
@@ -679,5 +675,5 @@ fn gen_update_from_arg_matches(variants: &[(&Variant, Item)]) -> TokenStream {
             }
             ::std::result::Result::Ok(())
         }
-    }
+    })
 }
diff --git a/src/derives/value_enum.rs b/src/derives/value_enum.rs
index 7a9d870..6f107c0 100644
--- a/src/derives/value_enum.rs
+++ b/src/derives/value_enum.rs
@@ -9,39 +9,36 @@
 // except according to those terms.
 
 use proc_macro2::TokenStream;
-use proc_macro_error::{abort, abort_call_site};
 use quote::quote;
 use quote::quote_spanned;
 use syn::{spanned::Spanned, Data, DeriveInput, Fields, Ident, Variant};
 
-use crate::dummies;
 use crate::item::{Item, Kind, Name};
 
-pub fn derive_value_enum(input: &DeriveInput) -> TokenStream {
+pub fn derive_value_enum(input: &DeriveInput) -> Result<TokenStream, syn::Error> {
     let ident = &input.ident;
 
-    dummies::value_enum(ident);
-
     match input.data {
         Data::Enum(ref e) => {
             let name = Name::Derived(ident.clone());
-            let item = Item::from_value_enum(input, name);
-            let variants = e
-                .variants
-                .iter()
-                .map(|variant| {
-                    let item =
-                        Item::from_value_enum_variant(variant, item.casing(), item.env_casing());
-                    (variant, item)
-                })
-                .collect::<Vec<_>>();
+            let item = Item::from_value_enum(input, name)?;
+            let mut variants = Vec::new();
+            for variant in &e.variants {
+                let item =
+                    Item::from_value_enum_variant(variant, item.casing(), item.env_casing())?;
+                variants.push((variant, item));
+            }
             gen_for_enum(&item, ident, &variants)
         }
         _ => abort_call_site!("`#[derive(ValueEnum)]` only supports enums"),
     }
 }
 
-pub fn gen_for_enum(item: &Item, item_name: &Ident, variants: &[(&Variant, Item)]) -> TokenStream {
+pub fn gen_for_enum(
+    item: &Item,
+    item_name: &Ident,
+    variants: &[(&Variant, Item)],
+) -> Result<TokenStream, syn::Error> {
     if !matches!(&*item.kind(), Kind::Value) {
         abort! { item.kind().span(),
             "`{}` cannot be used with `value`",
@@ -49,11 +46,11 @@ pub fn gen_for_enum(item: &Item, item_name: &Ident, variants: &[(&Variant, Item)
         }
     }
 
-    let lits = lits(variants);
+    let lits = lits(variants)?;
     let value_variants = gen_value_variants(&lits);
     let to_possible_value = gen_to_possible_value(item, &lits);
 
-    quote! {
+    Ok(quote! {
         #[allow(dead_code, unreachable_code, unused_variables, unused_braces)]
         #[allow(
             clippy::style,
@@ -71,33 +68,31 @@ pub fn gen_for_enum(item: &Item, item_name: &Ident, variants: &[(&Variant, Item)
             #value_variants
             #to_possible_value
         }
-    }
+    })
 }
 
-fn lits(variants: &[(&Variant, Item)]) -> Vec<(TokenStream, Ident)> {
-    variants
-        .iter()
-        .filter_map(|(variant, item)| {
-            if let Kind::Skip(_, _) = &*item.kind() {
-                None
-            } else {
-                if !matches!(variant.fields, Fields::Unit) {
-                    abort!(variant.span(), "`#[derive(ValueEnum)]` only supports unit variants. Non-unit variants must be skipped");
-                }
-                let fields = item.field_methods();
-                let deprecations = item.deprecations();
-                let name = item.cased_name();
-                Some((
-                    quote_spanned! { variant.span()=> {
-                        #deprecations
-                        clap::builder::PossibleValue::new(#name)
-                        #fields
-                    }},
-                    variant.ident.clone(),
-                ))
-            }
-        })
-        .collect::<Vec<_>>()
+fn lits(variants: &[(&Variant, Item)]) -> Result<Vec<(TokenStream, Ident)>, syn::Error> {
+    let mut genned = Vec::new();
+    for (variant, item) in variants {
+        if let Kind::Skip(_, _) = &*item.kind() {
+            continue;
+        }
+        if !matches!(variant.fields, Fields::Unit) {
+            abort!(variant.span(), "`#[derive(ValueEnum)]` only supports unit variants. Non-unit variants must be skipped");
+        }
+        let fields = item.field_methods();
+        let deprecations = item.deprecations();
+        let name = item.cased_name();
+        genned.push((
+            quote_spanned! { variant.span()=> {
+                #deprecations
+                clap::builder::PossibleValue::new(#name)
+                #fields
+            }},
+            variant.ident.clone(),
+        ));
+    }
+    Ok(genned)
 }
 
 fn gen_value_variants(lits: &[(TokenStream, Ident)]) -> TokenStream {
diff --git a/src/dummies.rs b/src/dummies.rs
index 1f54e1d..b10bedc 100644
--- a/src/dummies.rs
+++ b/src/dummies.rs
@@ -1,23 +1,20 @@
 //! Dummy implementations that we emit along with an error.
 
 use proc_macro2::Ident;
-use proc_macro_error::append_dummy;
 use quote::quote;
 
-pub fn parser_struct(name: &Ident) {
-    into_app(name);
-    args(name);
-    append_dummy(quote!( impl clap::Parser for #name {} ));
+#[must_use]
+pub fn parser(name: &Ident) -> proc_macro2::TokenStream {
+    let into_app = into_app(name);
+    quote!(
+        impl clap::Parser for #name {}
+        #into_app
+    )
 }
 
-pub fn parser_enum(name: &Ident) {
-    into_app(name);
-    subcommand(name);
-    append_dummy(quote!( impl clap::Parser for #name {} ));
-}
-
-pub fn into_app(name: &Ident) {
-    append_dummy(quote! {
+#[must_use]
+pub fn into_app(name: &Ident) -> proc_macro2::TokenStream {
+    quote! {
         impl clap::CommandFactory for #name {
             fn command<'b>() -> clap::Command {
                 unimplemented!()
@@ -26,11 +23,12 @@ pub fn into_app(name: &Ident) {
                 unimplemented!()
             }
         }
-    });
+    }
 }
 
-pub fn from_arg_matches(name: &Ident) {
-    append_dummy(quote! {
+#[must_use]
+pub fn from_arg_matches(name: &Ident) -> proc_macro2::TokenStream {
+    quote! {
         impl clap::FromArgMatches for #name {
             fn from_arg_matches(_m: &clap::ArgMatches) -> ::std::result::Result<Self, clap::Error> {
                 unimplemented!()
@@ -39,12 +37,13 @@ pub fn from_arg_matches(name: &Ident) {
                 unimplemented!()
             }
         }
-    });
+    }
 }
 
-pub fn subcommand(name: &Ident) {
-    from_arg_matches(name);
-    append_dummy(quote! {
+#[must_use]
+pub fn subcommand(name: &Ident) -> proc_macro2::TokenStream {
+    let from_arg_matches = from_arg_matches(name);
+    quote! {
         impl clap::Subcommand for #name {
             fn augment_subcommands(_cmd: clap::Command) -> clap::Command {
                 unimplemented!()
@@ -56,12 +55,14 @@ pub fn subcommand(name: &Ident) {
                 unimplemented!()
             }
         }
-    });
+        #from_arg_matches
+    }
 }
 
-pub fn args(name: &Ident) {
-    from_arg_matches(name);
-    append_dummy(quote! {
+#[must_use]
+pub fn args(name: &Ident) -> proc_macro2::TokenStream {
+    let from_arg_matches = from_arg_matches(name);
+    quote! {
         impl clap::Args for #name {
             fn augment_args(_cmd: clap::Command) -> clap::Command {
                 unimplemented!()
@@ -70,11 +71,13 @@ pub fn args(name: &Ident) {
                 unimplemented!()
             }
         }
-    });
+        #from_arg_matches
+    }
 }
 
-pub fn value_enum(name: &Ident) {
-    append_dummy(quote! {
+#[must_use]
+pub fn value_enum(name: &Ident) -> proc_macro2::TokenStream {
+    quote! {
         impl clap::ValueEnum for #name {
             fn value_variants<'a>() -> &'a [Self]{
                 unimplemented!()
@@ -86,5 +89,5 @@ pub fn value_enum(name: &Ident) {
                 unimplemented!()
             }
         }
-    })
+    }
 }
diff --git a/src/item.rs b/src/item.rs
index 5e8272a..9b29ff9 100644
--- a/src/item.rs
+++ b/src/item.rs
@@ -16,7 +16,6 @@ use std::env;
 
 use heck::{ToKebabCase, ToLowerCamelCase, ToShoutySnakeCase, ToSnakeCase, ToUpperCamelCase};
 use proc_macro2::{self, Span, TokenStream};
-use proc_macro_error::abort;
 use quote::{format_ident, quote, quote_spanned, ToTokens};
 use syn::DeriveInput;
 use syn::{self, ext::IdentExt, spanned::Spanned, Attribute, Field, Ident, LitStr, Type, Variant};
@@ -33,7 +32,6 @@ pub const DEFAULT_ENV_CASING: CasingStyle = CasingStyle::ScreamingSnake;
 #[derive(Clone)]
 pub struct Item {
     name: Name,
-    ident: Ident,
     casing: Sp<CasingStyle>,
     env_casing: Sp<CasingStyle>,
     ty: Option<Type>,
@@ -49,11 +47,13 @@ pub struct Item {
     is_enum: bool,
     is_positional: bool,
     skip_group: bool,
+    group_id: Name,
+    group_methods: Vec<Method>,
     kind: Sp<Kind>,
 }
 
 impl Item {
-    pub fn from_args_struct(input: &DeriveInput, name: Name) -> Self {
+    pub fn from_args_struct(input: &DeriveInput, name: Name) -> Result<Self, syn::Error> {
         let ident = input.ident.clone();
         let span = input.ident.span();
         let attrs = &input.attrs;
@@ -62,15 +62,15 @@ impl Item {
         let kind = Sp::new(Kind::Command(Sp::new(Ty::Other, span)), span);
 
         let mut res = Self::new(name, ident, None, argument_casing, env_casing, kind);
-        let parsed_attrs = ClapAttr::parse_all(attrs);
-        res.infer_kind(&parsed_attrs);
-        res.push_attrs(&parsed_attrs);
+        let parsed_attrs = ClapAttr::parse_all(attrs)?;
+        res.infer_kind(&parsed_attrs)?;
+        res.push_attrs(&parsed_attrs)?;
         res.push_doc_comment(attrs, "about", Some("long_about"));
 
-        res
+        Ok(res)
     }
 
-    pub fn from_subcommand_enum(input: &DeriveInput, name: Name) -> Self {
+    pub fn from_subcommand_enum(input: &DeriveInput, name: Name) -> Result<Self, syn::Error> {
         let ident = input.ident.clone();
         let span = input.ident.span();
         let attrs = &input.attrs;
@@ -79,15 +79,15 @@ impl Item {
         let kind = Sp::new(Kind::Command(Sp::new(Ty::Other, span)), span);
 
         let mut res = Self::new(name, ident, None, argument_casing, env_casing, kind);
-        let parsed_attrs = ClapAttr::parse_all(attrs);
-        res.infer_kind(&parsed_attrs);
-        res.push_attrs(&parsed_attrs);
+        let parsed_attrs = ClapAttr::parse_all(attrs)?;
+        res.infer_kind(&parsed_attrs)?;
+        res.push_attrs(&parsed_attrs)?;
         res.push_doc_comment(attrs, "about", Some("long_about"));
 
-        res
+        Ok(res)
     }
 
-    pub fn from_value_enum(input: &DeriveInput, name: Name) -> Self {
+    pub fn from_value_enum(input: &DeriveInput, name: Name) -> Result<Self, syn::Error> {
         let ident = input.ident.clone();
         let span = input.ident.span();
         let attrs = &input.attrs;
@@ -96,9 +96,9 @@ impl Item {
         let kind = Sp::new(Kind::Value, span);
 
         let mut res = Self::new(name, ident, None, argument_casing, env_casing, kind);
-        let parsed_attrs = ClapAttr::parse_all(attrs);
-        res.infer_kind(&parsed_attrs);
-        res.push_attrs(&parsed_attrs);
+        let parsed_attrs = ClapAttr::parse_all(attrs)?;
+        res.infer_kind(&parsed_attrs)?;
+        res.push_attrs(&parsed_attrs)?;
         // Ignoring `push_doc_comment` as there is no top-level clap builder to add documentation
         // to
 
@@ -110,14 +110,14 @@ impl Item {
             );
         }
 
-        res
+        Ok(res)
     }
 
     pub fn from_subcommand_variant(
         variant: &Variant,
         struct_casing: Sp<CasingStyle>,
         env_casing: Sp<CasingStyle>,
-    ) -> Self {
+    ) -> Result<Self, syn::Error> {
         let name = variant.ident.clone();
         let ident = variant.ident.clone();
         let span = variant.span();
@@ -138,9 +138,9 @@ impl Item {
             env_casing,
             kind,
         );
-        let parsed_attrs = ClapAttr::parse_all(&variant.attrs);
-        res.infer_kind(&parsed_attrs);
-        res.push_attrs(&parsed_attrs);
+        let parsed_attrs = ClapAttr::parse_all(&variant.attrs)?;
+        res.infer_kind(&parsed_attrs)?;
+        res.push_attrs(&parsed_attrs)?;
         if matches!(&*res.kind, Kind::Command(_) | Kind::Subcommand(_)) {
             res.push_doc_comment(&variant.attrs, "about", Some("long_about"));
         }
@@ -164,14 +164,14 @@ impl Item {
             | Kind::Arg(_) => (),
         }
 
-        res
+        Ok(res)
     }
 
     pub fn from_value_enum_variant(
         variant: &Variant,
         argument_casing: Sp<CasingStyle>,
         env_casing: Sp<CasingStyle>,
-    ) -> Self {
+    ) -> Result<Self, syn::Error> {
         let ident = variant.ident.clone();
         let span = variant.span();
         let kind = Sp::new(Kind::Value, span);
@@ -183,21 +183,21 @@ impl Item {
             env_casing,
             kind,
         );
-        let parsed_attrs = ClapAttr::parse_all(&variant.attrs);
-        res.infer_kind(&parsed_attrs);
-        res.push_attrs(&parsed_attrs);
+        let parsed_attrs = ClapAttr::parse_all(&variant.attrs)?;
+        res.infer_kind(&parsed_attrs)?;
+        res.push_attrs(&parsed_attrs)?;
         if matches!(&*res.kind, Kind::Value) {
             res.push_doc_comment(&variant.attrs, "help", None);
         }
 
-        res
+        Ok(res)
     }
 
     pub fn from_args_field(
         field: &Field,
         struct_casing: Sp<CasingStyle>,
         env_casing: Sp<CasingStyle>,
-    ) -> Self {
+    ) -> Result<Self, syn::Error> {
         let name = field.ident.clone().unwrap();
         let ident = field.ident.clone().unwrap();
         let span = field.span();
@@ -211,9 +211,9 @@ impl Item {
             env_casing,
             kind,
         );
-        let parsed_attrs = ClapAttr::parse_all(&field.attrs);
-        res.infer_kind(&parsed_attrs);
-        res.push_attrs(&parsed_attrs);
+        let parsed_attrs = ClapAttr::parse_all(&field.attrs)?;
+        res.infer_kind(&parsed_attrs)?;
+        res.push_attrs(&parsed_attrs)?;
         if matches!(&*res.kind, Kind::Arg(_)) {
             res.push_doc_comment(&field.attrs, "help", Some("long_help"));
         }
@@ -244,7 +244,7 @@ impl Item {
             | Kind::ExternalSubcommand => {}
         }
 
-        res
+        Ok(res)
     }
 
     fn new(
@@ -255,9 +255,9 @@ impl Item {
         env_casing: Sp<CasingStyle>,
         kind: Sp<Kind>,
     ) -> Self {
+        let group_id = Name::Derived(ident);
         Self {
             name,
-            ident,
             ty,
             casing,
             env_casing,
@@ -273,11 +273,17 @@ impl Item {
             is_enum: false,
             is_positional: true,
             skip_group: false,
+            group_id,
+            group_methods: vec![],
             kind,
         }
     }
 
     fn push_method(&mut self, kind: AttrKind, name: Ident, arg: impl ToTokens) {
+        self.push_method_(kind, name, arg.to_token_stream());
+    }
+
+    fn push_method_(&mut self, kind: AttrKind, name: Ident, arg: TokenStream) {
         if name == "id" {
             match kind {
                 AttrKind::Command | AttrKind::Value => {
@@ -291,10 +297,15 @@ impl Item {
                             kind.as_str()
                         ),
                     });
+                    self.name = Name::Assigned(arg);
+                }
+                AttrKind::Group => {
+                    self.group_id = Name::Assigned(arg);
+                }
+                AttrKind::Arg | AttrKind::Clap | AttrKind::StructOpt => {
+                    self.name = Name::Assigned(arg);
                 }
-                AttrKind::Group | AttrKind::Arg | AttrKind::Clap | AttrKind::StructOpt => {}
             }
-            self.name = Name::Assigned(quote!(#arg));
         } else if name == "name" {
             match kind {
                 AttrKind::Arg => {
@@ -309,27 +320,29 @@ impl Item {
                             kind.as_str()
                         ),
                     });
+                    self.name = Name::Assigned(arg);
+                }
+                AttrKind::Group => self.group_methods.push(Method::new(name, arg)),
+                AttrKind::Command | AttrKind::Value | AttrKind::Clap | AttrKind::StructOpt => {
+                    self.name = Name::Assigned(arg);
                 }
-                AttrKind::Group
-                | AttrKind::Command
-                | AttrKind::Value
-                | AttrKind::Clap
-                | AttrKind::StructOpt => {}
             }
-            self.name = Name::Assigned(quote!(#arg));
         } else if name == "value_parser" {
-            self.value_parser = Some(ValueParser::Explicit(Method::new(name, quote!(#arg))));
+            self.value_parser = Some(ValueParser::Explicit(Method::new(name, arg)));
         } else if name == "action" {
-            self.action = Some(Action::Explicit(Method::new(name, quote!(#arg))));
+            self.action = Some(Action::Explicit(Method::new(name, arg)));
         } else {
             if name == "short" || name == "long" {
                 self.is_positional = false;
             }
-            self.methods.push(Method::new(name, quote!(#arg)));
+            match kind {
+                AttrKind::Group => self.group_methods.push(Method::new(name, arg)),
+                _ => self.methods.push(Method::new(name, arg)),
+            };
         }
     }
 
-    fn infer_kind(&mut self, attrs: &[ClapAttr]) {
+    fn infer_kind(&mut self, attrs: &[ClapAttr]) -> Result<(), syn::Error> {
         for attr in attrs {
             if let Some(AttrValue::Call(_)) = &attr.value {
                 continue;
@@ -339,7 +352,7 @@ impl Item {
             let kind = match &attr.magic {
                 Some(MagicAttrName::FromGlobal) => {
                     if attr.value.is_some() {
-                        let expr = attr.value_or_abort();
+                        let expr = attr.value_or_abort()?;
                         abort!(expr, "attribute `{}` does not accept a value", attr.name);
                     }
                     let ty = self
@@ -352,7 +365,7 @@ impl Item {
                 }
                 Some(MagicAttrName::Subcommand) if attr.value.is_none() => {
                     if attr.value.is_some() {
-                        let expr = attr.value_or_abort();
+                        let expr = attr.value_or_abort()?;
                         abort!(expr, "attribute `{}` does not accept a value", attr.name);
                     }
                     let ty = self
@@ -365,7 +378,7 @@ impl Item {
                 }
                 Some(MagicAttrName::ExternalSubcommand) if attr.value.is_none() => {
                     if attr.value.is_some() {
-                        let expr = attr.value_or_abort();
+                        let expr = attr.value_or_abort()?;
                         abort!(expr, "attribute `{}` does not accept a value", attr.name);
                     }
                     let kind = Sp::new(Kind::ExternalSubcommand, attr.name.clone().span());
@@ -373,7 +386,7 @@ impl Item {
                 }
                 Some(MagicAttrName::Flatten) if attr.value.is_none() => {
                     if attr.value.is_some() {
-                        let expr = attr.value_or_abort();
+                        let expr = attr.value_or_abort()?;
                         abort!(expr, "attribute `{}` does not accept a value", attr.name);
                     }
                     let ty = self
@@ -396,12 +409,14 @@ impl Item {
             };
 
             if let Some(kind) = kind {
-                self.set_kind(kind);
+                self.set_kind(kind)?;
             }
         }
+
+        Ok(())
     }
 
-    fn push_attrs(&mut self, attrs: &[ClapAttr]) {
+    fn push_attrs(&mut self, attrs: &[ClapAttr]) -> Result<(), syn::Error> {
         for attr in attrs {
             let actual_attr_kind = *attr.kind.get();
             let expected_attr_kind = self.kind.attr_kind();
@@ -437,7 +452,7 @@ impl Item {
 
             match &attr.magic {
                 Some(MagicAttrName::Short) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     self.push_method(
                         *attr.kind.get(),
@@ -447,13 +462,13 @@ impl Item {
                 }
 
                 Some(MagicAttrName::Long) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     self.push_method(*attr.kind.get(), attr.name.clone(), self.name.clone().translate(*self.casing));
                 }
 
                 Some(MagicAttrName::ValueParser) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     self.deprecations.push(Deprecation {
                         span: attr.name.span(),
@@ -465,7 +480,7 @@ impl Item {
                 }
 
                 Some(MagicAttrName::Action) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     self.deprecations.push(Deprecation {
                         span: attr.name.span(),
@@ -477,7 +492,7 @@ impl Item {
                 }
 
                 Some(MagicAttrName::Env) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     self.push_method(
                         *attr.kind.get(),
@@ -487,7 +502,7 @@ impl Item {
                 }
 
                 Some(MagicAttrName::ValueEnum) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     self.is_enum = true
                 }
@@ -497,45 +512,45 @@ impl Item {
                 }
 
                 Some(MagicAttrName::About) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Command]);
+                    assert_attr_kind(attr, &[AttrKind::Command])?;
 
                     if let Some(method) =
-                        Method::from_env(attr.name.clone(), "CARGO_PKG_DESCRIPTION")
+                        Method::from_env(attr.name.clone(), "CARGO_PKG_DESCRIPTION")?
                     {
                         self.methods.push(method);
                     }
                 }
 
                 Some(MagicAttrName::LongAbout) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Command]);
+                    assert_attr_kind(attr, &[AttrKind::Command])?;
 
                     self.force_long_help = true;
                 }
 
                 Some(MagicAttrName::LongHelp) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     self.force_long_help = true;
                 }
 
                 Some(MagicAttrName::Author) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Command]);
+                    assert_attr_kind(attr, &[AttrKind::Command])?;
 
-                    if let Some(method) = Method::from_env(attr.name.clone(), "CARGO_PKG_AUTHORS") {
+                    if let Some(method) = Method::from_env(attr.name.clone(), "CARGO_PKG_AUTHORS")? {
                         self.methods.push(method);
                     }
                 }
 
                 Some(MagicAttrName::Version) if attr.value.is_none() => {
-                    assert_attr_kind(attr, &[AttrKind::Command]);
+                    assert_attr_kind(attr, &[AttrKind::Command])?;
 
-                    if let Some(method) = Method::from_env(attr.name.clone(), "CARGO_PKG_VERSION") {
+                    if let Some(method) = Method::from_env(attr.name.clone(), "CARGO_PKG_VERSION")? {
                         self.methods.push(method);
                     }
                 }
 
                 Some(MagicAttrName::DefaultValueT) => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     let ty = if let Some(ty) = self.ty.as_ref() {
                         ty
@@ -543,7 +558,7 @@ impl Item {
                         abort!(
                             attr.name.clone(),
                             "#[arg(default_value_t)] (without an argument) can be used \
-                            only on field level";
+                            only on field level\n\n= note: {note}\n\n",
 
                             note = "see \
                                 https://github.com/clap-rs/clap/blob/master/examples/derive_ref/README.md#magic-attributes")
@@ -560,7 +575,7 @@ impl Item {
                         .any(|a| a.magic == Some(MagicAttrName::ValueEnum))
                     {
                         quote_spanned!(attr.name.clone().span()=> {
-                            static DEFAULT_VALUE: clap::__macro_refs::once_cell::sync::Lazy<String> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                            static DEFAULT_VALUE: clap::__derive_refs::once_cell::sync::Lazy<String> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                 let val: #ty = #val;
                                 clap::ValueEnum::to_possible_value(&val).unwrap().get_name().to_owned()
                             });
@@ -569,7 +584,7 @@ impl Item {
                         })
                     } else {
                         quote_spanned!(attr.name.clone().span()=> {
-                            static DEFAULT_VALUE: clap::__macro_refs::once_cell::sync::Lazy<String> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                            static DEFAULT_VALUE: clap::__derive_refs::once_cell::sync::Lazy<String> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                 let val: #ty = #val;
                                 ::std::string::ToString::to_string(&val)
                             });
@@ -583,7 +598,7 @@ impl Item {
                 }
 
                 Some(MagicAttrName::DefaultValuesT) => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     let ty = if let Some(ty) = self.ty.as_ref() {
                         ty
@@ -591,18 +606,18 @@ impl Item {
                         abort!(
                             attr.name.clone(),
                             "#[arg(default_values_t)] (without an argument) can be used \
-                            only on field level";
+                            only on field level\n\n= note: {note}\n\n",
 
                             note = "see \
                                 https://github.com/clap-rs/clap/blob/master/examples/derive_ref/README.md#magic-attributes")
                     };
-                    let expr = attr.value_or_abort();
+                    let expr = attr.value_or_abort()?;
 
                     let container_type = Ty::from_syn_ty(ty);
                     if *container_type != Ty::Vec {
                         abort!(
                             attr.name.clone(),
-                            "#[arg(default_values_t)] can be used only on Vec types";
+                            "#[arg(default_values_t)] can be used only on Vec types\n\n= note: {note}\n\n",
 
                             note = "see \
                                 https://github.com/clap-rs/clap/blob/master/examples/derive_ref/README.md#magic-attributes")
@@ -628,11 +643,11 @@ impl Item {
                                         })
                                 }
 
-                                static DEFAULT_STRINGS: clap::__macro_refs::once_cell::sync::Lazy<Vec<::std::string::String>> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                                static DEFAULT_STRINGS: clap::__derive_refs::once_cell::sync::Lazy<Vec<::std::string::String>> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                     iter_to_vals(#expr).collect()
                                 });
 
-                                static DEFAULT_VALUES: clap::__macro_refs::once_cell::sync::Lazy<Vec<&str>> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                                static DEFAULT_VALUES: clap::__derive_refs::once_cell::sync::Lazy<Vec<&str>> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                     DEFAULT_STRINGS.iter().map(::std::string::String::as_str).collect()
                                 });
                                 DEFAULT_VALUES.iter().copied()
@@ -648,11 +663,11 @@ impl Item {
                                     iterable.into_iter().map(|val| val.borrow().to_string())
                                 }
 
-                                static DEFAULT_STRINGS: clap::__macro_refs::once_cell::sync::Lazy<Vec<::std::string::String>> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                                static DEFAULT_STRINGS: clap::__derive_refs::once_cell::sync::Lazy<Vec<::std::string::String>> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                     iter_to_vals(#expr).collect()
                                 });
 
-                                static DEFAULT_VALUES: clap::__macro_refs::once_cell::sync::Lazy<Vec<&str>> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                                static DEFAULT_VALUES: clap::__derive_refs::once_cell::sync::Lazy<Vec<&str>> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                     DEFAULT_STRINGS.iter().map(::std::string::String::as_str).collect()
                                 });
                                 DEFAULT_VALUES.iter().copied()
@@ -667,7 +682,7 @@ impl Item {
                 }
 
                 Some(MagicAttrName::DefaultValueOsT) => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     let ty = if let Some(ty) = self.ty.as_ref() {
                         ty
@@ -675,7 +690,7 @@ impl Item {
                         abort!(
                             attr.name.clone(),
                             "#[arg(default_value_os_t)] (without an argument) can be used \
-                            only on field level";
+                            only on field level\n\n= note: {note}\n\n",
 
                             note = "see \
                                 https://github.com/clap-rs/clap/blob/master/examples/derive_ref/README.md#magic-attributes")
@@ -692,7 +707,7 @@ impl Item {
                         .any(|a| a.magic == Some(MagicAttrName::ValueEnum))
                     {
                         quote_spanned!(attr.name.clone().span()=> {
-                            static DEFAULT_VALUE: clap::__macro_refs::once_cell::sync::Lazy<::std::ffi::OsString> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                            static DEFAULT_VALUE: clap::__derive_refs::once_cell::sync::Lazy<::std::ffi::OsString> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                 let val: #ty = #val;
                                 clap::ValueEnum::to_possible_value(&val).unwrap().get_name().to_owned()
                             });
@@ -701,7 +716,7 @@ impl Item {
                         })
                     } else {
                         quote_spanned!(attr.name.clone().span()=> {
-                            static DEFAULT_VALUE: clap::__macro_refs::once_cell::sync::Lazy<::std::ffi::OsString> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                            static DEFAULT_VALUE: clap::__derive_refs::once_cell::sync::Lazy<::std::ffi::OsString> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                 let val: #ty = #val;
                                 ::std::ffi::OsString::from(val)
                             });
@@ -715,7 +730,7 @@ impl Item {
                 }
 
                 Some(MagicAttrName::DefaultValuesOsT) => {
-                    assert_attr_kind(attr, &[AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Arg])?;
 
                     let ty = if let Some(ty) = self.ty.as_ref() {
                         ty
@@ -723,18 +738,18 @@ impl Item {
                         abort!(
                             attr.name.clone(),
                             "#[arg(default_values_os_t)] (without an argument) can be used \
-                            only on field level";
+                            only on field level\n\n= note: {note}\n\n",
 
                             note = "see \
                                 https://github.com/clap-rs/clap/blob/master/examples/derive_ref/README.md#magic-attributes")
                     };
-                    let expr = attr.value_or_abort();
+                    let expr = attr.value_or_abort()?;
 
                     let container_type = Ty::from_syn_ty(ty);
                     if *container_type != Ty::Vec {
                         abort!(
                             attr.name.clone(),
-                            "#[arg(default_values_os_t)] can be used only on Vec types";
+                            "#[arg(default_values_os_t)] can be used only on Vec types\n\n= note: {note}\n\n",
 
                             note = "see \
                                 https://github.com/clap-rs/clap/blob/master/examples/derive_ref/README.md#magic-attributes")
@@ -760,11 +775,11 @@ impl Item {
                                         })
                                 }
 
-                                static DEFAULT_OS_STRINGS: clap::__macro_refs::once_cell::sync::Lazy<Vec<::std::ffi::OsString>> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                                static DEFAULT_OS_STRINGS: clap::__derive_refs::once_cell::sync::Lazy<Vec<::std::ffi::OsString>> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                     iter_to_vals(#expr).collect()
                                 });
 
-                                static DEFAULT_VALUES: clap::__macro_refs::once_cell::sync::Lazy<Vec<&::std::ffi::OsStr>> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                                static DEFAULT_VALUES: clap::__derive_refs::once_cell::sync::Lazy<Vec<&::std::ffi::OsStr>> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                     DEFAULT_OS_STRINGS.iter().map(::std::ffi::OsString::as_os_str).collect()
                                 });
                                 DEFAULT_VALUES.iter().copied()
@@ -780,11 +795,11 @@ impl Item {
                                     iterable.into_iter().map(|val| val.borrow().into())
                                 }
 
-                                static DEFAULT_OS_STRINGS: clap::__macro_refs::once_cell::sync::Lazy<Vec<::std::ffi::OsString>> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                                static DEFAULT_OS_STRINGS: clap::__derive_refs::once_cell::sync::Lazy<Vec<::std::ffi::OsString>> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                     iter_to_vals(#expr).collect()
                                 });
 
-                                static DEFAULT_VALUES: clap::__macro_refs::once_cell::sync::Lazy<Vec<&::std::ffi::OsStr>> = clap::__macro_refs::once_cell::sync::Lazy::new(|| {
+                                static DEFAULT_VALUES: clap::__derive_refs::once_cell::sync::Lazy<Vec<&::std::ffi::OsStr>> = clap::__derive_refs::once_cell::sync::Lazy::new(|| {
                                     DEFAULT_OS_STRINGS.iter().map(::std::ffi::OsString::as_os_str).collect()
                                 });
                                 DEFAULT_VALUES.iter().copied()
@@ -799,29 +814,29 @@ impl Item {
                 }
 
                 Some(MagicAttrName::NextDisplayOrder) => {
-                    assert_attr_kind(attr, &[AttrKind::Command]);
+                    assert_attr_kind(attr, &[AttrKind::Command])?;
 
-                    let expr = attr.value_or_abort();
+                    let expr = attr.value_or_abort()?;
                     self.next_display_order = Some(Method::new(attr.name.clone(), quote!(#expr)));
                 }
 
                 Some(MagicAttrName::NextHelpHeading) => {
-                    assert_attr_kind(attr, &[AttrKind::Command]);
+                    assert_attr_kind(attr, &[AttrKind::Command])?;
 
-                    let expr = attr.value_or_abort();
+                    let expr = attr.value_or_abort()?;
                     self.next_help_heading = Some(Method::new(attr.name.clone(), quote!(#expr)));
                 }
 
                 Some(MagicAttrName::RenameAll) => {
-                    let lit = attr.lit_str_or_abort();
-                    self.casing = CasingStyle::from_lit(lit);
+                    let lit = attr.lit_str_or_abort()?;
+                    self.casing = CasingStyle::from_lit(lit)?;
                 }
 
                 Some(MagicAttrName::RenameAllEnv) => {
-                    assert_attr_kind(attr, &[AttrKind::Command, AttrKind::Arg]);
+                    assert_attr_kind(attr, &[AttrKind::Command, AttrKind::Arg])?;
 
-                    let lit = attr.lit_str_or_abort();
-                    self.env_casing = CasingStyle::from_lit(lit);
+                    let lit = attr.lit_str_or_abort()?;
+                    self.env_casing = CasingStyle::from_lit(lit)?;
                 }
 
                 Some(MagicAttrName::Skip) if actual_attr_kind == AttrKind::Group => {
@@ -839,20 +854,20 @@ impl Item {
                 | Some(MagicAttrName::Author)
                 | Some(MagicAttrName::Version)
                  => {
-                    let expr = attr.value_or_abort();
+                    let expr = attr.value_or_abort()?;
                     self.push_method(*attr.kind.get(), attr.name.clone(), expr);
                 }
 
                 // Magic only for the default, otherwise just forward to the builder
                 Some(MagicAttrName::ValueParser) | Some(MagicAttrName::Action) => {
-                    let expr = attr.value_or_abort();
+                    let expr = attr.value_or_abort()?;
                     self.push_method(*attr.kind.get(), attr.name.clone(), expr);
                 }
 
                 // Directives that never receive a value
                 Some(MagicAttrName::ValueEnum)
                 | Some(MagicAttrName::VerbatimDocComment) => {
-                    let expr = attr.value_or_abort();
+                    let expr = attr.value_or_abort()?;
                     abort!(expr, "attribute `{}` does not accept a value", attr.name);
                 }
 
@@ -883,6 +898,8 @@ impl Item {
                 );
             }
         }
+
+        Ok(())
     }
 
     fn push_doc_comment(&mut self, attrs: &[Attribute], short_name: &str, long_name: Option<&str>) {
@@ -912,7 +929,7 @@ impl Item {
         }
     }
 
-    fn set_kind(&mut self, kind: Sp<Kind>) {
+    fn set_kind(&mut self, kind: Sp<Kind>) -> Result<(), syn::Error> {
         match (self.kind.get(), kind.get()) {
             (Kind::Arg(_), Kind::FromGlobal(_))
             | (Kind::Arg(_), Kind::Subcommand(_))
@@ -932,6 +949,7 @@ impl Item {
                 abort!(kind.span(), "`{}` cannot be used with `{}`", new, old);
             }
         }
+        Ok(())
     }
 
     pub fn find_default_method(&self) -> Option<&Method> {
@@ -964,6 +982,15 @@ impl Item {
         quote!( #(#doc_comment)* #(#methods)* )
     }
 
+    pub fn group_id(&self) -> TokenStream {
+        self.group_id.clone().raw()
+    }
+
+    pub fn group_methods(&self) -> TokenStream {
+        let group_methods = &self.group_methods;
+        quote!( #(#group_methods)* )
+    }
+
     pub fn deprecations(&self) -> proc_macro2::TokenStream {
         let deprecations = &self.deprecations;
         quote!( #(#deprecations)* )
@@ -979,10 +1006,6 @@ impl Item {
         quote!( #(#next_help_heading)* )
     }
 
-    pub fn ident(&self) -> &Ident {
-        &self.ident
-    }
-
     pub fn id(&self) -> TokenStream {
         self.name.clone().raw()
     }
@@ -1211,19 +1234,21 @@ impl Method {
         Method { name, args }
     }
 
-    fn from_env(ident: Ident, env_var: &str) -> Option<Self> {
+    fn from_env(ident: Ident, env_var: &str) -> Result<Option<Self>, syn::Error> {
         let mut lit = match env::var(env_var) {
             Ok(val) => {
                 if val.is_empty() {
-                    return None;
+                    return Ok(None);
                 }
                 LitStr::new(&val, ident.span())
             }
             Err(_) => {
-                abort!(ident,
-                    "cannot derive `{}` from Cargo.toml", ident;
-                    note = "`{}` environment variable is not set", env_var;
-                    help = "use `{} = \"...\"` to set {} manually", ident, ident;
+                abort!(
+                    ident,
+                    "cannot derive `{}` from Cargo.toml\n\n= note: {note}\n\n= help: {help}\n\n",
+                    ident,
+                    note = format_args!("`{}` environment variable is not set", env_var),
+                    help = format_args!("use `{} = \"...\"` to set {} manually", ident, ident)
                 );
             }
         };
@@ -1233,7 +1258,7 @@ impl Method {
             lit = LitStr::new(&edited, lit.span());
         }
 
-        Some(Method::new(ident, quote!(#lit)))
+        Ok(Some(Method::new(ident, quote!(#lit))))
     }
 
     pub(crate) fn args(&self) -> &TokenStream {
@@ -1299,7 +1324,7 @@ impl ToTokens for Deprecation {
     }
 }
 
-fn assert_attr_kind(attr: &ClapAttr, possible_kind: &[AttrKind]) {
+fn assert_attr_kind(attr: &ClapAttr, possible_kind: &[AttrKind]) -> Result<(), syn::Error> {
     if *attr.kind.get() == AttrKind::Clap || *attr.kind.get() == AttrKind::StructOpt {
         // deprecated
     } else if !possible_kind.contains(attr.kind.get()) {
@@ -1315,6 +1340,7 @@ fn assert_attr_kind(attr: &ClapAttr, possible_kind: &[AttrKind]) {
             options.join(", ")
         );
     }
+    Ok(())
 }
 
 /// replace all `:` with `, ` when not inside the `<>`
@@ -1364,13 +1390,13 @@ pub enum CasingStyle {
 }
 
 impl CasingStyle {
-    fn from_lit(name: &LitStr) -> Sp<Self> {
+    fn from_lit(name: &LitStr) -> Result<Sp<Self>, syn::Error> {
         use self::CasingStyle::*;
 
         let normalized = name.value().to_upper_camel_case().to_lowercase();
         let cs = |kind| Sp::new(kind, name.span());
 
-        match normalized.as_ref() {
+        let s = match normalized.as_ref() {
             "camel" | "camelcase" => cs(Camel),
             "kebab" | "kebabcase" => cs(Kebab),
             "pascal" | "pascalcase" => cs(Pascal),
@@ -1380,7 +1406,8 @@ impl CasingStyle {
             "upper" | "uppercase" => cs(Upper),
             "verbatim" | "verbatimcase" => cs(Verbatim),
             s => abort!(name, "unsupported casing: `{}`", s),
-        }
+        };
+        Ok(s)
     }
 }
 
diff --git a/src/lib.rs b/src/lib.rs
index 84f2f0d..d3cae9b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -19,8 +19,11 @@
 extern crate proc_macro;
 
 use proc_macro::TokenStream;
-use proc_macro_error::proc_macro_error;
 use syn::{parse_macro_input, DeriveInput};
+use syn::{Data, DataStruct, Fields};
+
+#[macro_use]
+mod macros;
 
 mod attr;
 mod derives;
@@ -30,10 +33,14 @@ mod utils;
 
 /// Generates the `ValueEnum` impl.
 #[proc_macro_derive(ValueEnum, attributes(clap, value))]
-#[proc_macro_error]
 pub fn value_enum(input: TokenStream) -> TokenStream {
     let input: DeriveInput = parse_macro_input!(input);
-    derives::derive_value_enum(&input).into()
+    derives::derive_value_enum(&input)
+        .unwrap_or_else(|err| {
+            let dummy = dummies::value_enum(&input.ident);
+            to_compile_error(err, dummy)
+        })
+        .into()
 }
 
 /// Generates the `Parser` implementation.
@@ -43,24 +50,67 @@ pub fn value_enum(input: TokenStream) -> TokenStream {
 /// implementing a conversion code to instantiate an instance of the user
 /// context struct.
 #[proc_macro_derive(Parser, attributes(clap, structopt, command, arg, group))]
-#[proc_macro_error]
 pub fn parser(input: TokenStream) -> TokenStream {
     let input: DeriveInput = parse_macro_input!(input);
-    derives::derive_parser(&input).into()
+    derives::derive_parser(&input)
+        .unwrap_or_else(|err| {
+            let specific_dummy = match input.data {
+                Data::Struct(DataStruct {
+                    fields: Fields::Named(ref _fields),
+                    ..
+                }) => Some(dummies::args(&input.ident)),
+                Data::Struct(DataStruct {
+                    fields: Fields::Unit,
+                    ..
+                }) => Some(dummies::args(&input.ident)),
+                Data::Enum(_) => Some(dummies::subcommand(&input.ident)),
+                _ => None,
+            };
+            let dummy = specific_dummy
+                .map(|specific_dummy| {
+                    let parser_dummy = dummies::parser(&input.ident);
+                    quote::quote! {
+                        #parser_dummy
+                        #specific_dummy
+                    }
+                })
+                .unwrap_or_else(|| quote::quote!());
+            to_compile_error(err, dummy)
+        })
+        .into()
 }
 
 /// Generates the `Subcommand` impl.
 #[proc_macro_derive(Subcommand, attributes(clap, command, arg, group))]
-#[proc_macro_error]
 pub fn subcommand(input: TokenStream) -> TokenStream {
     let input: DeriveInput = parse_macro_input!(input);
-    derives::derive_subcommand(&input).into()
+    derives::derive_subcommand(&input)
+        .unwrap_or_else(|err| {
+            let dummy = dummies::subcommand(&input.ident);
+            to_compile_error(err, dummy)
+        })
+        .into()
 }
 
 /// Generates the `Args` impl.
 #[proc_macro_derive(Args, attributes(clap, command, arg, group))]
-#[proc_macro_error]
 pub fn args(input: TokenStream) -> TokenStream {
     let input: DeriveInput = parse_macro_input!(input);
-    derives::derive_args(&input).into()
+    derives::derive_args(&input)
+        .unwrap_or_else(|err| {
+            let dummy = dummies::args(&input.ident);
+            to_compile_error(err, dummy)
+        })
+        .into()
+}
+
+fn to_compile_error(
+    error: syn::Error,
+    dummy: proc_macro2::TokenStream,
+) -> proc_macro2::TokenStream {
+    let compile_errors = error.to_compile_error();
+    quote::quote!(
+        #dummy
+        #compile_errors
+    )
 }
diff --git a/src/macros.rs b/src/macros.rs
new file mode 100644
index 0000000..282048b
--- /dev/null
+++ b/src/macros.rs
@@ -0,0 +1,21 @@
+macro_rules! format_err {
+    ($obj:expr, $($format:tt)+) => {{
+        #[allow(unused_imports)]
+        use $crate::utils::error::*;
+        let msg = format!($($format)+);
+        $obj.EXPECTED_Span_OR_ToTokens(msg)
+    }};
+}
+
+macro_rules! abort {
+    ($obj:expr, $($format:tt)+) => {{
+        return Err(format_err!($obj, $($format)+));
+    }};
+}
+
+macro_rules! abort_call_site {
+    ($($format:tt)+) => {{
+        let span = proc_macro2::Span::call_site();
+        abort!(span, $($format)+)
+    }};
+}
diff --git a/src/utils/doc_comments.rs b/src/utils/doc_comments.rs
index 5183b6b..63c6ad1 100644
--- a/src/utils/doc_comments.rs
+++ b/src/utils/doc_comments.rs
@@ -6,24 +6,26 @@
 use std::iter;
 
 pub fn extract_doc_comment(attrs: &[syn::Attribute]) -> Vec<String> {
-    use syn::Lit::*;
-    use syn::Meta::*;
-    use syn::MetaNameValue;
-
     // multiline comments (`/** ... */`) may have LFs (`\n`) in them,
     // we need to split so we could handle the lines correctly
     //
     // we also need to remove leading and trailing blank lines
     let mut lines: Vec<_> = attrs
         .iter()
-        .filter(|attr| attr.path.is_ident("doc"))
+        .filter(|attr| attr.path().is_ident("doc"))
         .filter_map(|attr| {
-            if let Ok(NameValue(MetaNameValue { lit: Str(s), .. })) = attr.parse_meta() {
-                Some(s.value())
-            } else {
-                // non #[doc = "..."] attributes are not our concern
-                // we leave them for rustc to handle
-                None
+            // non #[doc = "..."] attributes are not our concern
+            // we leave them for rustc to handle
+            match &attr.meta {
+                syn::Meta::NameValue(syn::MetaNameValue {
+                    value:
+                        syn::Expr::Lit(syn::ExprLit {
+                            lit: syn::Lit::Str(s),
+                            ..
+                        }),
+                    ..
+                }) => Some(s.value()),
+                _ => None,
             }
         })
         .skip_while(|s| is_blank(s))
diff --git a/src/utils/error.rs b/src/utils/error.rs
new file mode 100644
index 0000000..276e349
--- /dev/null
+++ b/src/utils/error.rs
@@ -0,0 +1,22 @@
+pub trait SpanError {
+    #[allow(non_snake_case)]
+    fn EXPECTED_Span_OR_ToTokens<D: std::fmt::Display>(&self, msg: D) -> syn::Error;
+}
+
+pub trait ToTokensError {
+    #[allow(non_snake_case)]
+    fn EXPECTED_Span_OR_ToTokens<D: std::fmt::Display>(&self, msg: D) -> syn::Error;
+}
+
+impl<T: quote::ToTokens> ToTokensError for T {
+    fn EXPECTED_Span_OR_ToTokens<D: std::fmt::Display>(&self, msg: D) -> syn::Error {
+        // Curb monomorphization from generating too many identical `new_spanned`.
+        syn::Error::new_spanned(self.to_token_stream(), msg)
+    }
+}
+
+impl SpanError for proc_macro2::Span {
+    fn EXPECTED_Span_OR_ToTokens<D: std::fmt::Display>(&self, msg: D) -> syn::Error {
+        syn::Error::new(*self, msg)
+    }
+}
diff --git a/src/utils/mod.rs b/src/utils/mod.rs
index 9f8b6f3..13e6e71 100644
--- a/src/utils/mod.rs
+++ b/src/utils/mod.rs
@@ -1,3 +1,5 @@
+pub mod error;
+
 mod doc_comments;
 mod spanned;
 mod ty;