cmd/vet: add stdversion analyzer

+ release note, test

Fixes #46136

Change-Id: Ib157c5343dde379f8d6f67bdfa64b3f6a6432bab
Reviewed-on: https://go-review.googlesource.com/c/go/+/582556
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

doc/next/3-tools.md

@@ -8,5 +8,19 @@ Distributions that install the `go` command to a location other than
 `$GOROOT/bin/go` should install a symlink instead of relocating
 or copying the `go` binary.
 
+### Vet {#vet}
+
+The `go vet` subcommand now includes the
+[stdversion](https://beta.pkg.go.dev/golang.org/x/tools/go/analysis/passes/stdversion)
+analyzer, which flags references to symbols that are too new for the version
+of Go in effect in the referring file. (The effective version is determined
+by the `go` directive in the file's enclosing `go.mod` file, and
+by any [`//go:build` constraints](https://pkg.go.dev/cmd/go#hdr-Build_constraints)
+in the file.)
+
+For example, it will report a diagnostic for a reference to the
+`reflect.TypeFor` function (introduced in go1.22) from a file in a
+module whose go.mod file specifies `go 1.21`.
+
 ### Cgo {#cgo}
 

src/cmd/go/internal/test/flagdefs.go

@@ -67,6 +67,7 @@ var passAnalyzersToVet = map[string]bool{
 	"sigchanyzer":      true,
 	"slog":             true,
 	"stdmethods":       true,
+	"stdversion":       true,
 	"stringintconv":    true,
 	"structtag":        true,
 	"testinggoroutine": true,

src/cmd/vet/main.go

@@ -32,6 +32,7 @@ import (
 	"golang.org/x/tools/go/analysis/passes/sigchanyzer"
 	"golang.org/x/tools/go/analysis/passes/slog"
 	"golang.org/x/tools/go/analysis/passes/stdmethods"
+	"golang.org/x/tools/go/analysis/passes/stdversion"
 	"golang.org/x/tools/go/analysis/passes/stringintconv"
 	"golang.org/x/tools/go/analysis/passes/structtag"
 	"golang.org/x/tools/go/analysis/passes/testinggoroutine"
@@ -70,6 +71,7 @@ func main() {
 		sigchanyzer.Analyzer,
 		slog.Analyzer,
 		stdmethods.Analyzer,
+		stdversion.Analyzer,
 		stringintconv.Analyzer,
 		structtag.Analyzer,
 		tests.Analyzer,

src/cmd/vet/testdata/stdversion/go.mod

@@ -0,0 +1,3 @@
+module stdversion
+
+go 1.21

src/cmd/vet/testdata/stdversion/stdversion.go

@@ -0,0 +1,5 @@
+package stdversion
+
+import "reflect"
+
+var _ = reflect.TypeFor[int]() // ERROR "reflect.TypeFor requires go1.22 or later \(module is go1.21\)"

src/cmd/vet/vet_test.go

@@ -152,6 +152,37 @@ func TestVet(t *testing.T) {
 			t.Log("vet stderr:\n", cmd.Stderr)
 		}
 	})
+
+	// The stdversion analyzer requires a lower-than-tip go
+	// version in its go.mod file for it to report anything.
+	// So again we use a testdata go.mod file to "downgrade".
+	t.Run("stdversion", func(t *testing.T) {
+		cmd := testenv.Command(t, testenv.GoToolPath(t), "vet", "-vettool="+vetPath(t), ".")
+		cmd.Env = append(os.Environ(), "GOWORK=off")
+		cmd.Dir = "testdata/stdversion"
+		cmd.Stderr = new(strings.Builder) // all vet output goes to stderr
+		cmd.Run()
+		stderr := cmd.Stderr.(fmt.Stringer).String()
+
+		filename := filepath.FromSlash("testdata/stdversion/stdversion.go")
+
+		// Unlike the tests above, which runs vet in cmd/vet/, this one
+		// runs it in subdirectory, so the "full names" in the output
+		// are in fact short "./rangeloop.go".
+		// But we can't just pass "./rangeloop.go" as the "full name"
+		// argument to errorCheck as it does double duty as both a
+		// string that appears in the output, and as file name
+		// openable relative to the test directory, containing text
+		// expectations.
+		//
+		// So, we munge the file.
+		stderr = strings.ReplaceAll(stderr, filepath.FromSlash("./stdversion.go"), filename)
+
+		if err := errorCheck(stderr, false, filename, filepath.Base(filename)); err != nil {
+			t.Errorf("error check failed: %s", err)
+			t.Log("vet stderr:\n", cmd.Stderr)
+		}
+	})
 }
 
 func cgoEnabled(t *testing.T) bool {