cmd/api: rewrite as package test

No one ever runs 'go tool api', because the invocation
has gotten unwieldy enough that it's not practical.
And we don't support it as a standalone tool for other
packages - it's not even in the distribution.

Making it an ordinary package test lets us invoke it
more easily from cmd/dist (as go test cmd/api -check)
and avoids the increasingly baroque code in run.go to
build a command line.

Left in cmd/api even though it's no longer a command
because (1) it uses a package from cmd/vendor and
(2) it uses internal/testenv. Otherwise it could be misc/api.

Fixes #56845.

Change-Id: I00a13d9c19b1e259fa0e6bb93d1a4dca25f0e8c1
Reviewed-on: https://go-review.googlesource.com/c/go/+/453258
Auto-Submit: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>

Author: rsc

src/cmd/api/goapi.go renamed to src/cmd/api/api.go

@@ -2,8 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Api computes the exported API of a set of Go packages.
-package main
+// Package api computes the exported API of a set of Go packages.
+// It is only a test, not a command, nor a usefully importable package.
+package api
 
 import (
 	"bufio"
@@ -16,6 +17,7 @@ import (
 	"go/parser"
 	"go/token"
 	"go/types"
+	"internal/testenv"
 	"io"
 	"log"
 	"os"
@@ -27,33 +29,23 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"testing"
 )
 
+const verbose = false
+
 func goCmd() string {
 	var exeSuffix string
 	if runtime.GOOS == "windows" {
 		exeSuffix = ".exe"
 	}
-	if goroot := build.Default.GOROOT; goroot != "" {
-		path := filepath.Join(goroot, "bin", "go"+exeSuffix)
-		if _, err := os.Stat(path); err == nil {
-			return path
-		}
+	path := filepath.Join(testenv.GOROOT(nil), "bin", "go"+exeSuffix)
+	if _, err := os.Stat(path); err == nil {
+		return path
 	}
 	return "go"
 }
 
-// Flags
-var (
-	checkFiles      = flag.String("c", "", "optional comma-separated filename(s) to check API against")
-	requireApproval = flag.String("approval", "", "require approvals in comma-separated list of `files`")
-	allowNew        = flag.Bool("allow_new", true, "allow API additions")
-	exceptFile      = flag.String("except", "", "optional filename of packages that are allowed to change without triggering a failure in the tool")
-	nextFiles       = flag.String("next", "", "comma-separated list of `files` for upcoming API features for the next release. These files can be lazily maintained. They only affects the delta warnings from the -c file printed on success.")
-	verbose         = flag.Bool("v", false, "verbose debugging")
-	forceCtx        = flag.String("contexts", "", "optional comma-separated list of <goos>-<goarch>[-cgo] to override default contexts.")
-)
-
 // contexts are the default contexts which are scanned, unless
 // overridden by the -contexts flag.
 var contexts = []*build.Context{
@@ -117,36 +109,25 @@ func parseContext(c string) *build.Context {
 	return bc
 }
 
-func setContexts() {
-	contexts = []*build.Context{}
-	for _, c := range strings.Split(*forceCtx, ",") {
-		contexts = append(contexts, parseContext(c))
-	}
-}
-
 var internalPkg = regexp.MustCompile(`(^|/)internal($|/)`)
 
 var exitCode = 0
 
-func main() {
-	log.SetPrefix("api: ")
-	log.SetFlags(0)
-	flag.Parse()
-
-	if build.Default.GOROOT == "" {
-		log.Fatalf("GOROOT not found. (If binary was built with -trimpath, $GOROOT must be set.)")
+func Check(t *testing.T) {
+	checkFiles, err := filepath.Glob(filepath.Join(testenv.GOROOT(t), "api/go1*.txt"))
+	if err != nil {
+		t.Fatal(err)
 	}
 
-	if !strings.Contains(runtime.Version(), "weekly") && !strings.Contains(runtime.Version(), "devel") {
-		if *nextFiles != "" {
-			fmt.Printf("Go version is %q, ignoring -next %s\n", runtime.Version(), *nextFiles)
-			*nextFiles = ""
+	var nextFiles []string
+	if strings.Contains(runtime.Version(), "devel") {
+		next, err := filepath.Glob(filepath.Join(testenv.GOROOT(t), "api/next/*.txt"))
+		if err != nil {
+			t.Fatal(err)
 		}
+		nextFiles = next
 	}
 
-	if *forceCtx != "" {
-		setContexts()
-	}
 	for _, c := range contexts {
 		c.Compiler = build.Default.Compiler
 	}
@@ -158,7 +139,7 @@ func main() {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-			walkers[i] = NewWalker(context, filepath.Join(build.Default.GOROOT, "src"))
+			walkers[i] = NewWalker(context, filepath.Join(testenv.GOROOT(t), "src"))
 		}()
 	}
 	wg.Wait()
@@ -204,40 +185,29 @@ func main() {
 	}
 
 	bw := bufio.NewWriter(os.Stdout)
-	defer func() {
-		bw.Flush()
-		if exitCode != 0 {
-			os.Exit(exitCode)
-		}
-	}()
-
-	if *checkFiles == "" {
-		sort.Strings(features)
-		for _, f := range features {
-			fmt.Fprintln(bw, f)
-		}
-		return
-	}
+	defer bw.Flush()
 
 	var required []string
-	for _, file := range strings.Split(*checkFiles, ",") {
-		required = append(required, fileFeatures(file)...)
+	for _, file := range checkFiles {
+		required = append(required, fileFeatures(file, needApproval(file))...)
 	}
 	var optional []string
-	if *nextFiles != "" {
-		for _, file := range strings.Split(*nextFiles, ",") {
-			optional = append(optional, fileFeatures(file)...)
-		}
+	for _, file := range nextFiles {
+		optional = append(optional, fileFeatures(file, true)...)
 	}
-	exception := fileFeatures(*exceptFile)
-	if !compareAPI(bw, features, required, optional, exception, *allowNew) {
-		exitCode = 1
+	exception := fileFeatures(filepath.Join(testenv.GOROOT(t), "api/except.txt"), false)
+
+	if exitCode == 1 {
+		t.Errorf("API database problems found")
+	}
+	if !compareAPI(bw, features, required, optional, exception, false) {
+		t.Errorf("API differences found")
 	}
 }
 
 // export emits the exported package features.
 func (w *Walker) export(pkg *types.Package) {
-	if *verbose {
+	if verbose {
 		log.Println(pkg)
 	}
 	pop := w.pushScope("pkg " + pkg.Path())
@@ -353,17 +323,7 @@ var aliasReplacer = strings.NewReplacer(
 	"os.PathError", "fs.PathError",
 )
 
-func fileFeatures(filename string) []string {
-	if filename == "" {
-		return nil
-	}
-	needApproval := false
-	for _, name := range strings.Split(*requireApproval, ",") {
-		if filename == name {
-			needApproval = true
-			break
-		}
-	}
+func fileFeatures(filename string, needApproval bool) []string {
 	bs, err := os.ReadFile(filename)
 	if err != nil {
 		log.Fatal(err)
@@ -406,6 +366,11 @@ func fileFeatures(filename string) []string {
 				exitCode = 1
 			}
 			line = strings.TrimSpace(feature)
+		} else {
+			if strings.Contains(line, " #") {
+				log.Printf("%s:%d: unexpected approval\n", filename, i+1)
+				exitCode = 1
+			}
 		}
 		nonblank = append(nonblank, line)
 	}
@@ -1140,7 +1105,20 @@ func (w *Walker) emitf(format string, args ...any) {
 	}
 	w.features[f] = true
 
-	if *verbose {
+	if verbose {
 		log.Printf("feature: %s", f)
 	}
 }
+
+func needApproval(filename string) bool {
+	name := filepath.Base(filename)
+	if name == "go1.txt" {
+		return false
+	}
+	minor := strings.TrimSuffix(strings.TrimPrefix(name, "go1."), ".txt")
+	n, err := strconv.Atoi(minor)
+	if err != nil {
+		log.Fatalf("unexpected api file: %v", name)
+	}
+	return n >= 19 // started tracking approvals in Go 1.19
+}

src/cmd/api/goapi_test.go renamed to src/cmd/api/api_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package main
+package api
 
 import (
 	"flag"
@@ -17,6 +17,8 @@ import (
 	"testing"
 )
 
+var flagCheck = flag.Bool("check", false, "run API checks")
+
 func TestMain(m *testing.M) {
 	if !testenv.HasExec() {
 		os.Stdout.WriteString("skipping test: platform cannot exec")
@@ -40,7 +42,7 @@ func TestMain(m *testing.M) {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-			_ = NewWalker(context, filepath.Join(build.Default.GOROOT, "src"))
+			_ = NewWalker(context, filepath.Join(testenv.GOROOT(nil), "src"))
 		}()
 	}
 	wg.Wait()
@@ -53,6 +55,10 @@ var (
 )
 
 func TestGolden(t *testing.T) {
+	if *flagCheck {
+		// slow, not worth repeating in -check
+		t.Skip("skipping with -check set")
+	}
 	td, err := os.Open("testdata/src/pkg")
 	if err != nil {
 		t.Fatal(err)
@@ -194,7 +200,7 @@ func TestSkipInternal(t *testing.T) {
 func BenchmarkAll(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		for _, context := range contexts {
-			w := NewWalker(context, filepath.Join(build.Default.GOROOT, "src"))
+			w := NewWalker(context, filepath.Join(testenv.GOROOT(b), "src"))
 			for _, name := range w.stdPackages {
 				pkg, _ := w.Import(name)
 				w.export(pkg)
@@ -205,6 +211,10 @@ func BenchmarkAll(b *testing.B) {
 }
 
 func TestIssue21181(t *testing.T) {
+	if *flagCheck {
+		// slow, not worth repeating in -check
+		t.Skip("skipping with -check set")
+	}
 	for _, context := range contexts {
 		w := NewWalker(context, "testdata/src/issue21181")
 		pkg, err := w.Import("p")
@@ -217,6 +227,10 @@ func TestIssue21181(t *testing.T) {
 }
 
 func TestIssue29837(t *testing.T) {
+	if *flagCheck {
+		// slow, not worth repeating in -check
+		t.Skip("skipping with -check set")
+	}
 	for _, context := range contexts {
 		w := NewWalker(context, "testdata/src/issue29837")
 		_, err := w.Import("p")
@@ -227,9 +241,13 @@ func TestIssue29837(t *testing.T) {
 }
 
 func TestIssue41358(t *testing.T) {
+	if *flagCheck {
+		// slow, not worth repeating in -check
+		t.Skip("skipping with -check set")
+	}
 	context := new(build.Context)
 	*context = build.Default
-	context.Dir = filepath.Join(context.GOROOT, "src")
+	context.Dir = filepath.Join(testenv.GOROOT(t), "src")
 
 	w := NewWalker(context, context.Dir)
 	for _, pkg := range w.stdPackages {
@@ -238,3 +256,10 @@ func TestIssue41358(t *testing.T) {
 		}
 	}
 }
+
+func TestCheck(t *testing.T) {
+	if !*flagCheck {
+		t.Skip("-check not specified")
+	}
+	Check(t)
+}

src/cmd/api/goapi_boring_test.go renamed to src/cmd/api/boring_test.go

@@ -4,7 +4,7 @@
 
 //go:build boringcrypto
 
-package main
+package api
 
 import (
 	"fmt"