syntax: Fix regression in diagnostics for patterns in trait method parameters

Author: petrochenkov

src/libsyntax/parse/parser.rs

@@ -1866,7 +1866,8 @@ impl<'a> Parser<'a> {
             let parser_snapshot_before_ty = self.clone();
             self.eat_incorrect_doc_comment("a method argument's type");
             let mut ty = self.parse_ty();
-            if ty.is_ok() && self.token == token::Colon {
+            if ty.is_ok() && self.token != token::Comma &&
+               self.token != token::CloseDelim(token::Paren) {
                 // This wasn't actually a type, but a pattern looking like a type,
                 // so we are going to rollback and re-parse for recovery.
                 ty = self.unexpected();

src/test/ui/E0642.rs

@@ -6,6 +6,8 @@ trait T {
 
     fn bar((x, y): (i32, i32)) {} //~ ERROR patterns aren't allowed in methods without bodies
 
+    fn method(S { .. }: S) {} //~ ERROR patterns aren't allowed in methods without bodies
+
     fn f(&ident: &S) {} // ok
     fn g(&&ident: &&S) {} // ok
     fn h(mut ident: S) {} // ok

src/test/ui/E0642.stderr

@@ -18,6 +18,16 @@ help: give this argument a name or use an underscore to ignore it
 LL |     fn bar(_: (i32, i32)) {} //~ ERROR patterns aren't allowed in methods without bodies
    |            ^
 
-error: aborting due to 2 previous errors
+error[E0642]: patterns aren't allowed in methods without bodies
+  --> $DIR/E0642.rs:9:15
+   |
+LL |     fn method(S { .. }: S) {} //~ ERROR patterns aren't allowed in methods without bodies
+   |               ^^^^^^^^
+help: give this argument a name or use an underscore to ignore it
+   |
+LL |     fn method(_: S) {} //~ ERROR patterns aren't allowed in methods without bodies
+   |               ^
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0642`.