Auto merge of #11994 - eddyb:struct-literal-field-shorthand, r=nrc

Implement field shorthands in struct literal expressions.

Implements #37340 in a straight-forward way: `Foo { x, y: f() }` parses as `Foo { x: x, y: f() }`.
Because of the added `is_shorthand` to `ast::Field`, this is `[syntax-breaking]` (cc @Manishearth).

* [x] Mark the fields as being a shorthand (the exact same way we do it in patterns), for pretty-printing.
* [x] Gate the shorthand syntax with `#![feature(field_init_shorthand)]`.
* [x] Don't parse numeric field as identifiers.
* [x] Arbitrary field order tests.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index bdbc45471bb..0ef47bd6daa 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -713,7 +713,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         self.expr(b.span, ast::ExprKind::Block(b))
     }
     fn field_imm(&self, span: Span, name: Ident, e: P<ast::Expr>) -> ast::Field {
-        ast::Field { ident: respan(span, name), expr: e, span: span }
+        ast::Field { ident: respan(span, name), expr: e, span: span, is_shorthand: false }
     }
     fn expr_struct(&self, span: Span, path: ast::Path, fields: Vec<ast::Field>) -> P<ast::Expr> {
         self.expr(span, ast::ExprKind::Struct(path, fields, None))