cmd/compile: remove interfacecycles debug flag

Per the discussion on the issue, since no problems related to this
appeared since Go 1.20, remove the ability to disable the check for
anonymous interface cycles permanently.

Adjust various tests accordingly.

For #56103.

Change-Id: Ica2b28752dca08934bbbc163a9b062ae1eb2a834
Reviewed-on: https://go-review.googlesource.com/c/go/+/550896
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/base/debug.go

@@ -36,7 +36,6 @@ type DebugFlags struct {
 	Gossahash             string `help:"hash value for use in debugging the compiler"`
 	InlFuncsWithClosures  int    `help:"allow functions with closures to be inlined" concurrent:"ok"`
 	InlStaticInit         int    `help:"allow static initialization of inlined calls" concurrent:"ok"`
-	InterfaceCycles       int    `help:"allow anonymous interface cycles"`
 	Libfuzzer             int    `help:"enable coverage instrumentation for libfuzzer"`
 	LoopVar               int    `help:"shared (0, default), 1 (private loop variables), 2, private + log"`
 	LoopVarHash           string `help:"for debugging changes in loop behavior. Overrides experiment and loopvar flag."`

src/cmd/compile/internal/noder/irgen.go

@@ -92,23 +92,22 @@ func checkFiles(m posMap, noders []*noder) (*types2.Package, *types2.Info) {
 	}
 
 	// Check for anonymous interface cycles (#56103).
-	if base.Debug.InterfaceCycles == 0 {
-		var f cycleFinder
-		for _, file := range files {
-			syntax.Inspect(file, func(n syntax.Node) bool {
-				if n, ok := n.(*syntax.InterfaceType); ok {
-					if f.hasCycle(n.GetTypeInfo().Type.(*types2.Interface)) {
-						base.ErrorfAt(m.makeXPos(n.Pos()), errors.InvalidTypeCycle, "invalid recursive type: anonymous interface refers to itself (see https://go.dev/issue/56103)")
+	// TODO(gri) move this code into the type checkers (types2 and go/types)
+	var f cycleFinder
+	for _, file := range files {
+		syntax.Inspect(file, func(n syntax.Node) bool {
+			if n, ok := n.(*syntax.InterfaceType); ok {
+				if f.hasCycle(n.GetTypeInfo().Type.(*types2.Interface)) {
+					base.ErrorfAt(m.makeXPos(n.Pos()), errors.InvalidTypeCycle, "invalid recursive type: anonymous interface refers to itself (see https://go.dev/issue/56103)")
 
-						for typ := range f.cyclic {
-							f.cyclic[typ] = false // suppress duplicate errors
-						}
+					for typ := range f.cyclic {
+						f.cyclic[typ] = false // suppress duplicate errors
 					}
-					return false
 				}
-				return true
-			})
-		}
+				return false
+			}
+			return true
+		})
 	}
 	base.ExitIfErrors()
 

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

@@ -311,6 +311,7 @@ func TestStdFixed(t *testing.T) {
 
 	testTestDir(t, filepath.Join(testenv.GOROOT(t), "test", "fixedbugs"),
 		"bug248.go", "bug302.go", "bug369.go", // complex test instructions - ignore
+		"bug398.go",      // types2 doesn't check for anonymous interface cycles (go.dev/issue/56103)
 		"issue6889.go",   // gc-specific test
 		"issue11362.go",  // canonical import path check
 		"issue16369.go",  // types2 handles this correctly - not an issue

src/go/types/stdlib_test.go

@@ -312,6 +312,7 @@ func TestStdFixed(t *testing.T) {
 
 	testTestDir(t, filepath.Join(testenv.GOROOT(t), "test", "fixedbugs"),
 		"bug248.go", "bug302.go", "bug369.go", // complex test instructions - ignore
+		"bug398.go",      // go/types doesn't check for anonymous interface cycles (go.dev/issue/56103)
 		"issue6889.go",   // gc-specific test
 		"issue11362.go",  // canonical import path check
 		"issue16369.go",  // go/types handles this correctly - not an issue

test/fixedbugs/bug398.go

@@ -1,4 +1,4 @@
-// compile -d=interfacecycles
+// errorcheck
 
 // Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -11,11 +11,11 @@ package p
 
 // exported interfaces
 
-type I1 interface {
+type I1 interface { // ERROR "invalid recursive type: anonymous interface refers to itself"
       F() interface{I1}
 }
 
-type I2 interface {
+type I2 interface { // ERROR "invalid recursive type: anonymous interface refers to itself"
       F() interface{I2}
 }
 
@@ -28,11 +28,11 @@ func F() bool {
 
 // non-exported interfaces
 
-type i1 interface {
+type i1 interface { // ERROR "invalid recursive type: anonymous interface refers to itself"
       F() interface{i1}
 }
 
-type i2 interface {
+type i2 interface { // ERROR "invalid recursive type: anonymous interface refers to itself"
       F() interface{i2}
 }
 

test/fixedbugs/issue16369.go

@@ -1,4 +1,4 @@
-// compile -d=interfacecycles
+// errorcheck
 
 // Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -6,7 +6,7 @@
 
 package p
 
-type T interface {
+type T interface { // ERROR "invalid recursive type: anonymous interface refers to itself"
 	M(interface {
 		T
 	})