Rollup merge of #32682 - petrochenkov:field3, r=Manishearth

 The AST part of https://github.com/rust-lang/rust/pull/31937

Unlike HIR, AST still uses `Option` for field names because parser can't know field indexes reliably due to constructions like
```
struct S(#[cfg(false)] u8, u8); // The index of the second field changes from 1 during parsing to 0 after expansion.
```
and I wouldn't like to put the burden of renaming fields on expansion passes and syntax extensions.

plugin-[breaking-change] cc https://github.com/rust-lang/rust/issues/31645
r? @Manishearth

1 files changed, 5 insertions, 3 deletions

diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 0eb42f17f68..a4e5b68277d 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -1007,12 +1007,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
 
     fn variant(&self, span: Span, name: Ident, tys: Vec<P<ast::Ty>> ) -> ast::Variant {
         let fields: Vec<_> = tys.into_iter().map(|ty| {
-            Spanned { span: ty.span, node: ast::StructField_ {
+            ast::StructField {
+                span: ty.span,
                 ty: ty,
-                kind: ast::UnnamedField(ast::Visibility::Inherited),
+                ident: None,
+                vis: ast::Visibility::Inherited,
                 attrs: Vec::new(),
                 id: ast::DUMMY_NODE_ID,
-            }}
+            }
         }).collect();
 
         let vdata = if fields.is_empty() {