go/types, types2: enable range over int w/o need for goexperiment

For #61405.

Change-Id: I047ec31bc36b1707799ffef25506070613477d1f
Reviewed-on: https://go-review.googlesource.com/c/go/+/538718
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>

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

@@ -994,7 +994,7 @@ func rangeKeyVal(typ Type) (key, val Type, cause string, isFunc, ok bool) {
 		if isString(typ) {
 			return Typ[Int], universeRune, "", false, true // use 'rune' name
 		}
-		if buildcfg.Experiment.Range && isInteger(typ) {
+		if isInteger(typ) {
 			return orig, nil, "", false, true
 		}
 	case *Array:

src/go/types/stmt.go

@@ -979,7 +979,7 @@ func rangeKeyVal(typ Type) (key, val Type, cause string, isFunc, ok bool) {
 		if isString(typ) {
 			return Typ[Int], universeRune, "", false, true // use 'rune' name
 		}
-		if buildcfg.Experiment.Range && isInteger(typ) {
+		if isInteger(typ) {
 			return orig, nil, "", false, true
 		}
 	case *Array:

src/internal/types/testdata/spec/range_int.go

@@ -0,0 +1,65 @@
+// Copyright 2023 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.
+
+// This is a subset of the tests in range.go for range over integers,
+// with extra tests, and without the need for -goexperiment=range.
+
+package p
+
+type MyInt int32
+
+func _() {
+	for range -1 {
+	}
+	for range 0 {
+	}
+	for range 1 {
+	}
+	for range uint8(1) {
+	}
+	for range int64(1) {
+	}
+	for range MyInt(1) {
+	}
+	for range 'x' {
+	}
+	for range 1.0 /* ERROR "cannot range over 1.0 (untyped float constant 1)" */ {
+	}
+
+	var i int
+	var mi MyInt
+	for i := range 10 {
+		_ = i
+	}
+	for i = range 10 {
+		_ = i
+	}
+	for i, j /* ERROR "range over 10 (untyped int constant) permits only one iteration variable" */ := range 10 {
+		_, _ = i, j
+	}
+	for i /* ERROR "cannot use i (value of type MyInt) as int value in assignment" */ = range MyInt(10) {
+		_ = i
+	}
+	for mi := range MyInt(10) {
+		_ = mi
+	}
+	for mi = range MyInt(10) {
+		_ = mi
+	}
+}
+
+func _[T int | string](x T) {
+	for range x /* ERROR "cannot range over x (variable of type T constrained by int | string): no core type" */ {
+	}
+}
+
+func _[T int | int64](x T) {
+	for range x /* ERROR "cannot range over x (variable of type T constrained by int | int64): no core type" */ {
+	}
+}
+
+func _[T ~int](x T) {
+	for range x { // ok
+	}
+}