1 files changed, 47 insertions, 41 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 3727bf6..11f5b49 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -11,9 +11,9 @@
 extern crate proc_macro;
 
 use proc_macro2::TokenStream;
-use proc_macro_error::{abort, abort_call_site, dummy::set_dummy, proc_macro_error, ResultExt};
 use quote::{quote, quote_spanned};
-use syn::Token;
+use std::convert::TryFrom;
+use syn::{Error, Result, Token};
 
 struct Field {
     name: syn::Member,
@@ -33,48 +33,51 @@ enum FieldAttr {
 }
 
 #[proc_macro_derive(Merge, attributes(merge))]
-#[proc_macro_error]
 pub fn merge_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let ast = syn::parse(input).unwrap();
-    impl_merge(&ast).into()
+    impl_merge(&ast)
+        .unwrap_or_else(Error::into_compile_error)
+        .into()
 }
 
-fn impl_merge(ast: &syn::DeriveInput) -> TokenStream {
+fn impl_merge(ast: &syn::DeriveInput) -> Result<TokenStream> {
     let name = &ast.ident;
 
-    set_dummy(quote! {
-        impl ::merge::Merge for #name {
-            fn merge(&mut self, other: Self) {
-                unimplemented!()
-            }
-        }
-    });
-
     if let syn::Data::Struct(syn::DataStruct { ref fields, .. }) = ast.data {
         impl_merge_for_struct(name, fields)
     } else {
-        abort_call_site!("merge::Merge can only be derived for structs")
+        Err(Error::new_spanned(
+            ast,
+            "merge::Merge can only be derived for structs",
+        ))
     }
 }
 
-fn impl_merge_for_struct(name: &syn::Ident, fields: &syn::Fields) -> TokenStream {
-    let assignments = gen_assignments(fields);
+fn impl_merge_for_struct(name: &syn::Ident, fields: &syn::Fields) -> Result<TokenStream> {
+    let assignments = gen_assignments(fields)?;
 
-    quote! {
+    Ok(quote! {
         impl ::merge::Merge for #name {
             fn merge(&mut self, other: Self) {
                 #assignments
             }
         }
-    }
+    })
 }
 
-fn gen_assignments(fields: &syn::Fields) -> TokenStream {
-    let fields = fields.iter().enumerate().map(Field::from);
-    let assignments = fields.filter(|f| !f.attrs.skip).map(|f| gen_assignment(&f));
-    quote! {
+fn gen_assignments(fields: &syn::Fields) -> Result<TokenStream> {
+    let fields = fields
+        .iter()
+        .enumerate()
+        .map(Field::try_from)
+        .collect::<Result<Vec<_>>>()?;
+    let assignments = fields
+        .iter()
+        .filter(|f| !f.attrs.skip)
+        .map(|f| gen_assignment(&f));
+    Ok(quote! {
         #( #assignments )*
-    }
+    })
 }
 
 fn gen_assignment(field: &Field) -> TokenStream {
@@ -88,34 +91,27 @@ fn gen_assignment(field: &Field) -> TokenStream {
     }
 }
 
-impl From<(usize, &syn::Field)> for Field {
-    fn from(data: (usize, &syn::Field)) -> Self {
+impl TryFrom<(usize, &syn::Field)> for Field {
+    type Error = syn::Error;
+
+    fn try_from(data: (usize, &syn::Field)) -> std::result::Result<Self, Self::Error> {
         use syn::spanned::Spanned;
 
         let (index, field) = data;
-        Field {
+        Ok(Field {
             name: if let Some(ident) = &field.ident {
                 syn::Member::Named(ident.clone())
             } else {
                 syn::Member::Unnamed(index.into())
             },
             span: field.span(),
-            attrs: field.attrs.iter().into(),
-        }
+            attrs: FieldAttrs::new(field.attrs.iter())?,
+        })
     }
 }
 
 impl FieldAttrs {
-    fn apply(&mut self, attr: FieldAttr) {
-        match attr {
-            FieldAttr::Skip => self.skip = true,
-            FieldAttr::Strategy(path) => self.strategy = Some(path),
-        }
-    }
-}
-
-impl<'a, I: Iterator<Item = &'a syn::Attribute>> From<I> for FieldAttrs {
-    fn from(iter: I) -> Self {
+    fn new<'a, I: Iterator<Item = &'a syn::Attribute>>(iter: I) -> Result<Self> {
         let mut field_attrs = Self::default();
 
         for attr in iter {
@@ -124,12 +120,19 @@ impl<'a, I: Iterator<Item = &'a syn::Attribute>> From<I> for FieldAttrs {
             }
 
             let parser = syn::punctuated::Punctuated::<FieldAttr, Token![,]>::parse_terminated;
-            for attr in attr.parse_args_with(parser).unwrap_or_abort() {
+            for attr in attr.parse_args_with(parser)? {
                 field_attrs.apply(attr);
             }
         }
 
-        field_attrs
+        Ok(field_attrs)
+    }
+
+    fn apply(&mut self, attr: FieldAttr) {
+        match attr {
+            FieldAttr::Skip => self.skip = true,
+            FieldAttr::Strategy(path) => self.strategy = Some(path),
+        }
     }
 }
 
@@ -144,7 +147,10 @@ impl syn::parse::Parse for FieldAttr {
             let path: syn::Path = input.parse()?;
             Ok(FieldAttr::Strategy(path))
         } else {
-            abort!(name, "Unexpected attribute: {}", name)
+            Err(Error::new_spanned(
+                &name,
+                format!("Unexpected attribute: {}", name),
+            ))
         }
     }
 }