Rollup merge of #39179 - petrochenkov:objparen, r=eddyb

Fix regression in parsing of trait object types

Fixes https://github.com/rust-lang/rust/issues/39169

Accepting parens in this position is a regression itself, introduced in Rust 1.6 by https://github.com/rust-lang/rust/pull/29870, so I hope to revert this in my next bounds refactoring patch (possibly with a warning,  crater run, etc).

r? @eddyb

1 files changed, 9 insertions, 2 deletions

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index fd6abc58b63..5dd772041e2 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -1236,10 +1236,17 @@ impl<'a> Parser<'a> {
                           "at least one type parameter bound \
                           must be specified");
         }
-        if let TyKind::Path(None, ref path) = lhs.node {
+
+        let mut lhs = lhs.unwrap();
+        if let TyKind::Paren(ty) = lhs.node {
+            // We have to accept the first bound in parens for backward compatibility.
+            // Example: `(Bound) + Bound + Bound`
+            lhs = ty.unwrap();
+        }
+        if let TyKind::Path(None, path) = lhs.node {
             let poly_trait_ref = PolyTraitRef {
                 bound_lifetimes: Vec::new(),
-                trait_ref: TraitRef { path: path.clone(), ref_id: lhs.id },
+                trait_ref: TraitRef { path: path, ref_id: lhs.id },
                 span: lhs.span,
             };
             let poly_trait_ref = TraitTyParamBound(poly_trait_ref, TraitBoundModifier::None);