1 files changed, 47 insertions, 0 deletions
diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 0000000..7c5badb
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,47 @@
+use proc_macro::{Delimiter, Group, Ident, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
+use std::iter::FromIterator;
+
+pub type Result<T> = std::result::Result<T, Error>;
+
+pub struct Error {
+    begin: Span,
+    end: Span,
+    msg: String,
+}
+
+impl Error {
+    pub fn new(span: Span, msg: &str) -> Self {
+        Self::new2(span, span, msg)
+    }
+
+    pub fn new2(begin: Span, end: Span, msg: &str) -> Self {
+        Error {
+            begin,
+            end,
+            msg: msg.to_owned(),
+        }
+    }
+
+    pub fn to_compile_error(&self) -> TokenStream {
+        // compile_error! { $msg }
+        TokenStream::from_iter(vec![
+            TokenTree::Ident(Ident::new("compile_error", self.begin)),
+            TokenTree::Punct({
+                let mut punct = Punct::new('!', Spacing::Alone);
+                punct.set_span(self.begin);
+                punct
+            }),
+            TokenTree::Group({
+                let mut group = Group::new(Delimiter::Brace, {
+                    TokenStream::from_iter(vec![TokenTree::Literal({
+                        let mut string = Literal::string(&self.msg);
+                        string.set_span(self.end);
+                        string
+                    })])
+                });
+                group.set_span(self.end);
+                group
+            }),
+        ])
+    }
+}