[dev.typeparams] cmd/compile/internal/types2: overlapping embedded interfaces requires go1.14

Add respective check to type checker.
Enables another excluded test in test/run.go.

This CL completes the currently required checks for
language compatibility in types2.

Updates #31793.

Change-Id: Icececff9e6023d38f600c93bcb54cdcafcf501b9
Reviewed-on: https://go-review.googlesource.com/c/go/+/290911
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/stdlib_test.go

@@ -192,7 +192,6 @@ func TestStdFixed(t *testing.T) {
 		"issue22200b.go", // go/types does not have constraints on stack size
 		"issue25507.go",  // go/types does not have constraints on stack size
 		"issue20780.go",  // go/types does not have constraints on stack size
-		"issue34329.go",  // go/types does not have constraints on language level (-lang=go1.13) (see #31793)
 		"issue42058a.go", // go/types does not have constraints on channel element size
 		"issue42058b.go", // go/types does not have constraints on channel element size
 		"bug251.go",      // issue #34333 which was exposed with fix for #34151

src/cmd/compile/internal/types2/testdata/go1_13.src

@@ -0,0 +1,21 @@
+// Copyright 2021 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.
+
+// Check Go language version-specific errors.
+
+package go1_13 // go1.13
+
+// interface embedding
+
+type I interface { m() }
+
+type _ interface {
+	m()
+	I // ERROR "duplicate method m"
+}
+
+type _ interface {
+	I
+	I // ERROR "duplicate method m"
+}

src/cmd/compile/internal/types2/typexpr.go

@@ -943,9 +943,13 @@ func (check *Checker) completeInterface(pos syntax.Pos, ityp *Interface) {
 			check.errorf(pos, "duplicate method %s", m.name)
 			check.errorf(mpos[other.(*Func)], "\tother declaration of %s", m.name) // secondary error, \t indented
 		default:
-			// check method signatures after all types are computed (issue #33656)
+			// We have a duplicate method name in an embedded (not explicitly declared) method.
+			// Check method signatures after all types are computed (issue #33656).
+			// If we're pre-go1.14 (overlapping embeddings are not permitted), report that
+			// error here as well (even though we could do it eagerly) because it's the same
+			// error message.
 			check.atEnd(func() {
-				if !check.identical(m.typ, other.Type()) {
+				if !check.allowVersion(m.pkg, 1, 14) || !check.identical(m.typ, other.Type()) {
 					check.errorf(pos, "duplicate method %s", m.name)
 					check.errorf(mpos[other.(*Func)], "\tother declaration of %s", m.name) // secondary error, \t indented
 				}

test/run.go

@@ -1964,7 +1964,6 @@ var excluded = map[string]bool{
 	"fixedbugs/issue28079b.go": true, // types2 reports follow-on errors
 	"fixedbugs/issue28268.go":  true, // types2 reports follow-on errors
 	"fixedbugs/issue33460.go":  true, // types2 reports alternative positions in separate error
-	"fixedbugs/issue34329.go":  true, // types2 is missing support for -lang flag
 	"fixedbugs/issue41575.go":  true, // types2 reports alternative positions in separate error
 	"fixedbugs/issue42058a.go": true, // types2 doesn't report "channel element type too large"
 	"fixedbugs/issue42058b.go": true, // types2 doesn't report "channel element type too large"