go/types, types2: collect per-file Go version in Info.FileVersions

The go/types changes are matching but the API changes are hidden
for now, pending acceptance of a respective proposal.

Change-Id: I2e38ff215ddbdcf93f182d3e70c03802d3ca4338
Reviewed-on: https://go-review.googlesource.com/c/go/+/515135
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>

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

@@ -288,6 +288,11 @@ type Info struct {
 	// in source order. Variables without an initialization expression do not
 	// appear in this list.
 	InitOrder []*Initializer
+
+	// FileVersions maps a file's position base to the file's Go version.
+	// If the file doesn't specify a version and Config.GoVersion is not
+	// given, the reported version is the zero version (Major, Minor = 0, 0).
+	FileVersions map[*syntax.PosBase]Version
 }
 
 func (info *Info) recordTypes() bool {
@@ -421,6 +426,12 @@ func (init *Initializer) String() string {
 	return buf.String()
 }
 
+// A Version represents a released Go version.
+type Version struct {
+	Major int
+	Minor int
+}
+
 // Check type-checks a package and returns the resulting package object and
 // the first error if any. Additionally, if info != nil, Check populates each
 // of the non-nil maps in the Info struct.

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

@@ -2764,3 +2764,42 @@ var _ = f(1, 2)
 		t.Errorf("src1: unexpected error: got %v", err)
 	}
 }
+
+func TestFileVersions(t *testing.T) {
+	for _, test := range []struct {
+		moduleVersion string
+		fileVersion   string
+		want          Version
+	}{
+		{"", "", Version{0, 0}},              // no versions specified
+		{"go1.19", "", Version{1, 19}},       // module version specified
+		{"", "go1.20", Version{0, 0}},        // file upgrade ignored
+		{"go1.19", "go1.20", Version{1, 20}}, // file upgrade permitted
+		{"go1.20", "go1.19", Version{1, 20}}, // file downgrade not permitted
+		{"go1.21", "go1.19", Version{1, 19}}, // file downgrade permitted (module version is >= go1.21)
+	} {
+		var src string
+		if test.fileVersion != "" {
+			src = "//go:build " + test.fileVersion + "\n"
+		}
+		src += "package p"
+
+		conf := Config{GoVersion: test.moduleVersion}
+		versions := make(map[*syntax.PosBase]Version)
+		var info Info
+		info.FileVersions = versions
+		mustTypecheck(src, &conf, &info)
+
+		n := 0
+		for _, v := range info.FileVersions {
+			want := test.want
+			if v.Major != want.Major || v.Minor != want.Minor {
+				t.Errorf("%q: unexpected file version: got %v, want %v", src, v, want)
+			}
+			n++
+		}
+		if n != 1 {
+			t.Errorf("%q: incorrect number of map entries: got %d", src, n)
+		}
+	}
+}

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

@@ -285,6 +285,8 @@ func (check *Checker) initFiles(files []*syntax.File) {
 	}
 
 	for _, file := range check.files {
+		fbase := base(file.Pos())                     // fbase may be nil for tests
+		check.recordFileVersion(fbase, check.version) // record package version (possibly zero version)
 		v, _ := parseGoVersion(file.GoVersion)
 		if v.major > 0 {
 			if v.equal(check.version) {
@@ -309,7 +311,8 @@ func (check *Checker) initFiles(files []*syntax.File) {
 			if check.posVers == nil {
 				check.posVers = make(map[*syntax.PosBase]version)
 			}
-			check.posVers[base(file.Pos())] = v
+			check.posVers[fbase] = v
+			check.recordFileVersion(fbase, v) // overwrite package version
 		}
 	}
 }
@@ -673,3 +676,9 @@ func (check *Checker) recordScope(node syntax.Node, scope *Scope) {
 		m[node] = scope
 	}
 }
+
+func (check *Checker) recordFileVersion(fbase *syntax.PosBase, v version) {
+	if m := check.FileVersions; m != nil {
+		m[fbase] = Version{v.major, v.minor}
+	}
+}

src/go/types/api.go

@@ -285,6 +285,11 @@ type Info struct {
 	// in source order. Variables without an initialization expression do not
 	// appear in this list.
 	InitOrder []*Initializer
+
+	// _FileVersions maps a file to the file's Go version.
+	// If the file doesn't specify a version and Config.GoVersion is not
+	// given, the reported version is the zero version (Major, Minor = 0, 0).
+	_FileVersions map[*token.File]_Version
 }
 
 func (info *Info) recordTypes() bool {
@@ -409,6 +414,12 @@ func (init *Initializer) String() string {
 	return buf.String()
 }
 
+// A _Version represents a released Go version.
+type _Version struct {
+	_Major int
+	_Minor int
+}
+
 // Check type-checks a package and returns the resulting package object and
 // the first error if any. Additionally, if info != nil, Check populates each
 // of the non-nil maps in the Info struct.

src/go/types/api_test.go

@@ -2773,3 +2773,55 @@ var _ = f(1, 2)
 		t.Errorf("src1: unexpected error: got %v", err)
 	}
 }
+
+func TestFileVersions(t *testing.T) {
+	for _, test := range []struct {
+		moduleVersion string
+		fileVersion   string
+		want          Version
+	}{
+		{"", "", Version{0, 0}},              // no versions specified
+		{"go1.19", "", Version{1, 19}},       // module version specified
+		{"", "go1.20", Version{0, 0}},        // file upgrade ignored
+		{"go1.19", "go1.20", Version{1, 20}}, // file upgrade permitted
+		{"go1.20", "go1.19", Version{1, 20}}, // file downgrade not permitted
+		{"go1.21", "go1.19", Version{1, 19}}, // file downgrade permitted (module version is >= go1.21)
+	} {
+		var src string
+		if test.fileVersion != "" {
+			src = "//go:build " + test.fileVersion + "\n"
+		}
+		src += "package p"
+
+		conf := Config{GoVersion: test.moduleVersion}
+		versions := make(map[*token.File]Version)
+		var info Info
+		*_FileVersionsAddr(&info) = versions
+		mustTypecheck(src, &conf, &info)
+
+		n := 0
+		for _, v := range versions {
+			want := test.want
+			if v.Major != want.Major || v.Minor != want.Minor {
+				t.Errorf("%q: unexpected file version: got %v, want %v", src, v, want)
+			}
+			n++
+		}
+		if n != 1 {
+			t.Errorf("%q: incorrect number of map entries: got %d", src, n)
+		}
+	}
+}
+
+// Version must match types._Version exactly.
+// TODO(gri) remove this declaration once types.Version is exported.
+type Version struct {
+	Major int
+	Minor int
+}
+
+// _FileVersionsAddr(conf) returns the address of the field info._FileVersions.
+func _FileVersionsAddr(info *Info) *map[*token.File]Version {
+	v := reflect.Indirect(reflect.ValueOf(info))
+	return (*map[*token.File]Version)(v.FieldByName("_FileVersions").Addr().UnsafePointer())
+}

src/go/types/check.go

@@ -288,6 +288,8 @@ func (check *Checker) initFiles(files []*ast.File) {
 	}
 
 	for _, file := range check.files {
+		tfile := check.fset.File(file.FileStart)
+		check.recordFileVersion(tfile, check.version) // record package version (possibly zero version)
 		v, _ := parseGoVersion(file.GoVersion)
 		if v.major > 0 {
 			if v.equal(check.version) {
@@ -312,7 +314,8 @@ func (check *Checker) initFiles(files []*ast.File) {
 			if check.posVers == nil {
 				check.posVers = make(map[*token.File]version)
 			}
-			check.posVers[check.fset.File(file.FileStart)] = v
+			check.posVers[tfile] = v
+			check.recordFileVersion(tfile, v) // overwrite package version
 		}
 	}
 }
@@ -636,3 +639,9 @@ func (check *Checker) recordScope(node ast.Node, scope *Scope) {
 		m[node] = scope
 	}
 }
+
+func (check *Checker) recordFileVersion(tfile *token.File, v version) {
+	if m := check._FileVersions; m != nil {
+		m[tfile] = _Version{v.major, v.minor}
+	}
+}