Merge pull request #836 from dtolnay/vis

Parse empty None-delimited group as inherited visibility

src/data.rs

@@ -316,6 +316,17 @@ pub mod parsing {
 
     impl Parse for Visibility {
         fn parse(input: ParseStream) -> Result<Self> {
+            // Recognize an empty None-delimited group, as produced by a $:vis
+            // matcher that matched no tokens.
+            if input.peek(token::Group) {
+                let ahead = input.fork();
+                let group = crate::group::parse_group(&ahead)?;
+                if group.content.is_empty() {
+                    input.advance_to(&ahead);
+                    return Ok(Visibility::Inherited);
+                }
+            }
+
             if input.peek(Token![pub]) {
                 Self::parse_pub(input)
             } else if input.peek(Token![crate]) {

tests/test_visibility.rs

@@ -1,6 +1,10 @@
-use proc_macro2::TokenStream;
+#[macro_use]
+mod macros;
+
+use proc_macro2::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree};
+use std::iter::FromIterator;
 use syn::parse::{Parse, ParseStream};
-use syn::{Result, Visibility};
+use syn::{DeriveInput, Result, Visibility};
 
 #[derive(Debug)]
 struct VisRest {
@@ -95,3 +99,47 @@ fn test_crate_path() {
 fn test_junk_after_in() {
     assert_vis_parse!("pub(in some::path @@garbage)", Err);
 }
+
+#[test]
+fn test_empty_group_vis() {
+    // mimics `struct S { $vis $field: () }` where $vis is empty
+    let tokens = TokenStream::from_iter(vec![
+        TokenTree::Ident(Ident::new("struct", Span::call_site())),
+        TokenTree::Ident(Ident::new("S", Span::call_site())),
+        TokenTree::Group(Group::new(
+            Delimiter::Brace,
+            TokenStream::from_iter(vec![
+                TokenTree::Group(Group::new(Delimiter::None, TokenStream::new())),
+                TokenTree::Group(Group::new(
+                    Delimiter::None,
+                    TokenStream::from_iter(vec![TokenTree::Ident(Ident::new(
+                        "f",
+                        Span::call_site(),
+                    ))]),
+                )),
+                TokenTree::Punct(Punct::new(':', Spacing::Alone)),
+                TokenTree::Group(Group::new(Delimiter::Parenthesis, TokenStream::new())),
+            ]),
+        )),
+    ]);
+
+    snapshot!(tokens as DeriveInput, @r###"
+    DeriveInput {
+        vis: Inherited,
+        ident: "S",
+        generics: Generics,
+        data: Data::Struct {
+            fields: Fields::Named {
+                named: [
+                    Field {
+                        vis: Inherited,
+                        ident: Some("f"),
+                        colon_token: Some,
+                        ty: Type::Tuple,
+                    },
+                ],
+            },
+        },
+    }
+    "###);
+}