Merge pull request #1944 from dtolnay/metaarrow

Support parsing Meta followed by fat arrow

Author: dtolnay

src/attr.rs

@@ -721,7 +721,7 @@ pub(crate) mod parsing {
     pub(crate) fn parse_meta_after_path(path: Path, input: ParseStream) -> Result<Meta> {
         if input.peek(token::Paren) || input.peek(token::Bracket) || input.peek(token::Brace) {
             parse_meta_list_after_path(path, input).map(Meta::List)
-        } else if input.peek(Token![=]) {
+        } else if input.peek(Token![=]) && !input.peek(Token![==]) && !input.peek(Token![=>]) {
             parse_meta_name_value_after_path(path, input).map(Meta::NameValue)
         } else {
             Ok(Meta::Path(path))

tests/test_meta.rs

@@ -11,7 +11,9 @@ mod snapshot;
 
 mod debug;
 
-use syn::{Meta, MetaList, MetaNameValue};
+use quote::quote;
+use syn::parse::{ParseStream, Parser as _, Result};
+use syn::{Meta, MetaList, MetaNameValue, Token};
 
 #[test]
 fn test_parse_meta_item_word() {
@@ -156,3 +158,23 @@ fn test_parse_path() {
     }
     "#);
 }
+
+#[test]
+fn test_fat_arrow_after_meta() {
+    fn parse(input: ParseStream) -> Result<()> {
+        while !input.is_empty() {
+            let _: Meta = input.parse()?;
+            let _: Token![=>] = input.parse()?;
+            let brace;
+            syn::braced!(brace in input);
+        }
+        Ok(())
+    }
+
+    let input = quote! {
+        target_os = "linux" => {}
+        windows => {}
+    };
+
+    parse.parse2(input).unwrap();
+}