cmd/compile/internal/syntax: better recovery after missing closing parentheses

Fine-tune skipping of tokens after missing closing parentheses in lists.

Fixes #22164.

Change-Id: I575d86e21048cd40340a2c08399e8b0deec337cf
Reviewed-on: https://go-review.googlesource.com/71250
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/syntax/parser.go

@@ -377,8 +377,10 @@ func (p *parser) list(open, sep, close token, f func() bool) src.Pos {
 			//            to the expected close token only
 		default:
 			p.syntax_error(fmt.Sprintf("expecting %s or %s", tokstring(sep), tokstring(close)))
-			p.advance(close)
-			done = true
+			p.advance(_Rparen, _Rbrack, _Rbrace)
+			if p.tok != close {
+				return p.pos()
+			}
 		}
 	}
 

test/fixedbugs/issue22164.go

@@ -0,0 +1,26 @@
+// errorcheck
+
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test error recovery after missing closing parentheses in lists.
+
+package p
+
+func f() {
+	x := f(g() // ERROR "unexpected newline"
+	y := 1
+}
+
+func g() {
+}
+
+func h() {
+	x := f(g() // ERROR "unexpected newline"
+}
+
+func i() {
+	x := []int{1, 2, 3 // ERROR "unexpected newline"
+	y := 0
+}