[release-branch.go1.23] revert "go/types, types2: only use fileVersio…

…n if 1.21 or greater"

This reverts commit CL 604935.

Reason for revert: The team has decided that this change will be added to a point release.

Change-Id: I1c1032b881c3a98312a4753b9767cb7c8eed9e09
Reviewed-on: https://go-review.googlesource.com/c/go/+/605096
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

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

@@ -2903,21 +2903,17 @@ func TestFileVersions(t *testing.T) {
 		{"", "go1.20", ""},             // file upgrade ignored
 		{"go1.19", "go1.20", "go1.20"}, // file upgrade permitted
 		{"go1.20", "go1.19", "go1.20"}, // file downgrade not permitted
-		{"go1.21", "go1.20", "go1.21"}, // file downgrade not permitted
-		{"go1.22", "go1.21", "go1.21"}, // file downgrade permitted (file and module version are >= go1.21)
+		{"go1.21", "go1.19", "go1.19"}, // file downgrade permitted (module version is >= go1.21)
 
 		// versions containing release numbers
 		// (file versions containing release numbers are considered invalid)
 		{"go1.19.0", "", "go1.19.0"},         // no file version specified
 		{"go1.20", "go1.20.1", "go1.20"},     // file upgrade ignored
 		{"go1.20.1", "go1.20", "go1.20.1"},   // file upgrade ignored
-		{"go1.21.0", "go1.21.1", "go1.21.0"}, // file upgrade ignored
-		{"go1.21", "go1.21.1", "go1.21"},     // file upgrade ignored
 		{"go1.20.1", "go1.21", "go1.21"},     // file upgrade permitted
-		{"go1.21.1", "go1.21", "go1.21.1"},   // file downgrade ignored
 		{"go1.20.1", "go1.19", "go1.20.1"},   // file downgrade not permitted
 		{"go1.21.1", "go1.19.1", "go1.21.1"}, // file downgrade not permitted (invalid file version)
-		{"go1.22.1", "go1.21", "go1.21"},     // file downgrade permitted (file and module version is >= go1.21)
+		{"go1.21.1", "go1.19", "go1.19"},     // file downgrade permitted (module version is >= go1.21)
 	} {
 		var src string
 		if test.fileVersion != "" {

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

@@ -354,25 +354,12 @@ func (check *Checker) initFiles(files []*syntax.File) {
 				// To work around this, downgrades are only allowed when the
 				// module's Go version is Go 1.21 or later.
 				//
-				// Downgrades are also only allowed to Go versions Go 1.21 or later.
-				// In GOPATH mode, there's no way to set a module version and the
-				// -lang is set to the local toolchain version to allow the use of
-				// new features in GOPATH mode. But //go:build lines added before go1.21
-				// weren't intended to downgrade, so code with //go:build lines for
-				// go versions earlier than 1.21 may use language features added
-				// in later versions and compile.
-				//
-				// We should probably change the downgradeOk condition to capture this
-				// instead of adding an extra condition, but to make the change simpler,
-				// we've tried to limit it to one line.
-				// TODO(gri): simplify this code after 1.23 has shipped
-				//
 				// If there is no valid check.version, then we don't really know what
 				// Go version to apply.
 				// Legacy tools may do this, and they historically have accepted everything.
 				// Preserve that behavior by ignoring //go:build constraints entirely in that
 				// case (!pkgVersionOk).
-				if cmp > 0 || cmp < 0 && downgradeOk && fileVersion.cmp(go1_21) >= 0 {
+				if cmp > 0 || cmp < 0 && downgradeOk {
 					v = file.GoVersion
 				}
 			}

src/go/types/api_test.go

@@ -2909,21 +2909,17 @@ func TestFileVersions(t *testing.T) {
 		{"", "go1.20", ""},             // file upgrade ignored
 		{"go1.19", "go1.20", "go1.20"}, // file upgrade permitted
 		{"go1.20", "go1.19", "go1.20"}, // file downgrade not permitted
-		{"go1.21", "go1.20", "go1.21"}, // file downgrade not permitted
-		{"go1.22", "go1.21", "go1.21"}, // file downgrade permitted (file and module version are >= go1.21)
+		{"go1.21", "go1.19", "go1.19"}, // file downgrade permitted (module version is >= go1.21)
 
 		// versions containing release numbers
 		// (file versions containing release numbers are considered invalid)
 		{"go1.19.0", "", "go1.19.0"},         // no file version specified
 		{"go1.20", "go1.20.1", "go1.20"},     // file upgrade ignored
 		{"go1.20.1", "go1.20", "go1.20.1"},   // file upgrade ignored
-		{"go1.21.0", "go1.21.1", "go1.21.0"}, // file upgrade ignored
-		{"go1.21", "go1.21.1", "go1.21"},     // file upgrade ignored
 		{"go1.20.1", "go1.21", "go1.21"},     // file upgrade permitted
-		{"go1.21.1", "go1.21", "go1.21.1"},   // file downgrade ignored
 		{"go1.20.1", "go1.19", "go1.20.1"},   // file downgrade not permitted
 		{"go1.21.1", "go1.19.1", "go1.21.1"}, // file downgrade not permitted (invalid file version)
-		{"go1.22.1", "go1.21", "go1.21"},     // file downgrade permitted (file and module version is >= go1.21)
+		{"go1.21.1", "go1.19", "go1.19"},     // file downgrade permitted (module version is >= go1.21)
 	} {
 		var src string
 		if test.fileVersion != "" {

src/go/types/check.go

@@ -376,25 +376,12 @@ func (check *Checker) initFiles(files []*ast.File) {
 				// To work around this, downgrades are only allowed when the
 				// module's Go version is Go 1.21 or later.
 				//
-				// Downgrades are also only allowed to Go versions Go 1.21 or later.
-				// In GOPATH mode, there's no way to set a module version and the
-				// -lang is set to the local toolchain version to allow the use of
-				// new features in GOPATH mode. But //go:build lines added before go1.21
-				// weren't intended to downgrade, so code with //go:build lines for
-				// go versions earlier than 1.21 may use language features added
-				// in later versions and compile.
-				//
-				// We should probably change the downgradeOk condition to capture this
-				// instead of adding an extra condition, but to make the change simpler,
-				// we've tried to limit it to one line.
-				// TODO(gri): simplify this code after 1.23 has shipped
-				//
 				// If there is no valid check.version, then we don't really know what
 				// Go version to apply.
 				// Legacy tools may do this, and they historically have accepted everything.
 				// Preserve that behavior by ignoring //go:build constraints entirely in that
 				// case (!pkgVersionOk).
-				if cmp > 0 || cmp < 0 && downgradeOk && fileVersion.cmp(go1_21) >= 0 {
+				if cmp > 0 || cmp < 0 && downgradeOk {
 					v = file.GoVersion
 				}
 			}

src/internal/types/testdata/check/go1_20_19.go

@@ -14,4 +14,4 @@ type Slice []byte
 type Array [8]byte
 
 var s Slice
-var p = (Array)(s /* ok because downgrades below 1.21 are ignored */)
+var p = (Array)(s /* ok because Go 1.20 ignored the //go:build go1.19 */)

src/internal/types/testdata/check/go1_21_19.go

@@ -14,4 +14,4 @@ type Slice []byte
 type Array [8]byte
 
 var s Slice
-var p = (Array)(s /* ok because downgrades below 1.21 are ignored */)
+var p = (Array)(s /* ERROR "requires go1.20 or later" */)

src/internal/types/testdata/fixedbugs/issue66285.go

@@ -1,9 +1,14 @@
-// -lang=go1.13
+// -lang=go1.21
 
 // Copyright 2024 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.
 
+// Note: Downgrading to go1.13 requires at least go1.21,
+//       hence the need for -lang=go1.21 at the top.
+
+//go:build go1.13
+
 package p
 
 import "io"

test/fixedbugs/issue63489a.go

@@ -1,20 +1,16 @@
-// errorcheck -lang=go1.22
+// errorcheck -lang=go1.21
 
 // 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 file has been changed from its original version as
-// //go:build language downgrades below go1.21 are no longer
-// supported. The original tested a downgrade from go1.21 to
-// go1.4 while this new version tests a downgrade from go1.22
-// to go1.21
-
-//go:build go1.21
+//go:build go1.4
 
 package p
 
-func f() {
-	for _ = range 10 { // ERROR "file declares //go:build go1.21"
-	}
-}
+const c = 0o123 // ERROR "file declares //go:build go1.4"
+
+// ERROR "file declares //go:build go1.4"
+
+//line issue63489a.go:13:1
+const d = 0o124