Source file src/cmd/api/goapi.go

Documentation: cmd/api

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Binary api computes the exported API of a set of Go packages.
     6  package main
     7  
     8  import (
     9  	"bufio"
    10  	"bytes"
    11  	"encoding/json"
    12  	"flag"
    13  	"fmt"
    14  	"go/ast"
    15  	"go/build"
    16  	"go/parser"
    17  	"go/token"
    18  	"go/types"
    19  	exec "internal/execabs"
    20  	"io"
    21  	"log"
    22  	"os"
    23  	"path/filepath"
    24  	"regexp"
    25  	"runtime"
    26  	"sort"
    27  	"strings"
    28  	"sync"
    29  )
    30  
    31  func goCmd() string {
    32  	var exeSuffix string
    33  	if runtime.GOOS == "windows" {
    34  		exeSuffix = ".exe"
    35  	}
    36  	path := filepath.Join(runtime.GOROOT(), "bin", "go"+exeSuffix)
    37  	if _, err := os.Stat(path); err == nil {
    38  		return path
    39  	}
    40  	return "go"
    41  }
    42  
    43  // Flags
    44  var (
    45  	checkFile  = flag.String("c", "", "optional comma-separated filename(s) to check API against")
    46  	allowNew   = flag.Bool("allow_new", true, "allow API additions")
    47  	exceptFile = flag.String("except", "", "optional filename of packages that are allowed to change without triggering a failure in the tool")
    48  	nextFile   = flag.String("next", "", "optional filename of tentative upcoming API features for the next release. This file can be lazily maintained. It only affects the delta warnings from the -c file printed on success.")
    49  	verbose    = flag.Bool("v", false, "verbose debugging")
    50  	forceCtx   = flag.String("contexts", "", "optional comma-separated list of <goos>-<goarch>[-cgo] to override default contexts.")
    51  )
    52  
    53  // contexts are the default contexts which are scanned, unless
    54  // overridden by the -contexts flag.
    55  var contexts = []*build.Context{
    56  	{GOOS: "linux", GOARCH: "386", CgoEnabled: true},
    57  	{GOOS: "linux", GOARCH: "386"},
    58  	{GOOS: "linux", GOARCH: "amd64", CgoEnabled: true},
    59  	{GOOS: "linux", GOARCH: "amd64"},
    60  	{GOOS: "linux", GOARCH: "arm", CgoEnabled: true},
    61  	{GOOS: "linux", GOARCH: "arm"},
    62  	{GOOS: "darwin", GOARCH: "amd64", CgoEnabled: true},
    63  	{GOOS: "darwin", GOARCH: "amd64"},
    64  	{GOOS: "windows", GOARCH: "amd64"},
    65  	{GOOS: "windows", GOARCH: "386"},
    66  	{GOOS: "freebsd", GOARCH: "386", CgoEnabled: true},
    67  	{GOOS: "freebsd", GOARCH: "386"},
    68  	{GOOS: "freebsd", GOARCH: "amd64", CgoEnabled: true},
    69  	{GOOS: "freebsd", GOARCH: "amd64"},
    70  	{GOOS: "freebsd", GOARCH: "arm", CgoEnabled: true},
    71  	{GOOS: "freebsd", GOARCH: "arm"},
    72  	{GOOS: "netbsd", GOARCH: "386", CgoEnabled: true},
    73  	{GOOS: "netbsd", GOARCH: "386"},
    74  	{GOOS: "netbsd", GOARCH: "amd64", CgoEnabled: true},
    75  	{GOOS: "netbsd", GOARCH: "amd64"},
    76  	{GOOS: "netbsd", GOARCH: "arm", CgoEnabled: true},
    77  	{GOOS: "netbsd", GOARCH: "arm"},
    78  	{GOOS: "netbsd", GOARCH: "arm64", CgoEnabled: true},
    79  	{GOOS: "netbsd", GOARCH: "arm64"},
    80  	{GOOS: "openbsd", GOARCH: "386", CgoEnabled: true},
    81  	{GOOS: "openbsd", GOARCH: "386"},
    82  	{GOOS: "openbsd", GOARCH: "amd64", CgoEnabled: true},
    83  	{GOOS: "openbsd", GOARCH: "amd64"},
    84  }
    85  
    86  func contextName(c *build.Context) string {
    87  	s := c.GOOS + "-" + c.GOARCH
    88  	if c.CgoEnabled {
    89  		s += "-cgo"
    90  	}
    91  	if c.Dir != "" {
    92  		s += fmt.Sprintf(" [%s]", c.Dir)
    93  	}
    94  	return s
    95  }
    96  
    97  func parseContext(c string) *build.Context {
    98  	parts := strings.Split(c, "-")
    99  	if len(parts) < 2 {
   100  		log.Fatalf("bad context: %q", c)
   101  	}
   102  	bc := &build.Context{
   103  		GOOS:   parts[0],
   104  		GOARCH: parts[1],
   105  	}
   106  	if len(parts) == 3 {
   107  		if parts[2] == "cgo" {
   108  			bc.CgoEnabled = true
   109  		} else {
   110  			log.Fatalf("bad context: %q", c)
   111  		}
   112  	}
   113  	return bc
   114  }
   115  
   116  func setContexts() {
   117  	contexts = []*build.Context{}
   118  	for _, c := range strings.Split(*forceCtx, ",") {
   119  		contexts = append(contexts, parseContext(c))
   120  	}
   121  }
   122  
   123  var internalPkg = regexp.MustCompile(`(^|/)internal($|/)`)
   124  
   125  func main() {
   126  	flag.Parse()
   127  
   128  	if !strings.Contains(runtime.Version(), "weekly") && !strings.Contains(runtime.Version(), "devel") {
   129  		if *nextFile != "" {
   130  			fmt.Printf("Go version is %q, ignoring -next %s\n", runtime.Version(), *nextFile)
   131  			*nextFile = ""
   132  		}
   133  	}
   134  
   135  	if *forceCtx != "" {
   136  		setContexts()
   137  	}
   138  	for _, c := range contexts {
   139  		c.Compiler = build.Default.Compiler
   140  	}
   141  
   142  	walkers := make([]*Walker, len(contexts))
   143  	var wg sync.WaitGroup
   144  	for i, context := range contexts {
   145  		i, context := i, context
   146  		wg.Add(1)
   147  		go func() {
   148  			defer wg.Done()
   149  			walkers[i] = NewWalker(context, filepath.Join(build.Default.GOROOT, "src"))
   150  		}()
   151  	}
   152  	wg.Wait()
   153  
   154  	var featureCtx = make(map[string]map[string]bool) // feature -> context name -> true
   155  	for _, w := range walkers {
   156  		pkgNames := w.stdPackages
   157  		if flag.NArg() > 0 {
   158  			pkgNames = flag.Args()
   159  		}
   160  
   161  		for _, name := range pkgNames {
   162  			pkg, err := w.Import(name)
   163  			if _, nogo := err.(*build.NoGoError); nogo {
   164  				continue
   165  			}
   166  			if err != nil {
   167  				log.Fatalf("Import(%q): %v", name, err)
   168  			}
   169  			w.export(pkg)
   170  		}
   171  
   172  		ctxName := contextName(w.context)
   173  		for _, f := range w.Features() {
   174  			if featureCtx[f] == nil {
   175  				featureCtx[f] = make(map[string]bool)
   176  			}
   177  			featureCtx[f][ctxName] = true
   178  		}
   179  	}
   180  
   181  	var features []string
   182  	for f, cmap := range featureCtx {
   183  		if len(cmap) == len(contexts) {
   184  			features = append(features, f)
   185  			continue
   186  		}
   187  		comma := strings.Index(f, ",")
   188  		for cname := range cmap {
   189  			f2 := fmt.Sprintf("%s (%s)%s", f[:comma], cname, f[comma:])
   190  			features = append(features, f2)
   191  		}
   192  	}
   193  
   194  	fail := false
   195  	defer func() {
   196  		if fail {
   197  			os.Exit(1)
   198  		}
   199  	}()
   200  
   201  	bw := bufio.NewWriter(os.Stdout)
   202  	defer bw.Flush()
   203  
   204  	if *checkFile == "" {
   205  		sort.Strings(features)
   206  		for _, f := range features {
   207  			fmt.Fprintln(bw, f)
   208  		}
   209  		return
   210  	}
   211  
   212  	var required []string
   213  	for _, file := range strings.Split(*checkFile, ",") {
   214  		required = append(required, fileFeatures(file)...)
   215  	}
   216  	optional := fileFeatures(*nextFile)
   217  	exception := fileFeatures(*exceptFile)
   218  	fail = !compareAPI(bw, features, required, optional, exception, *allowNew)
   219  }
   220  
   221  // export emits the exported package features.
   222  func (w *Walker) export(pkg *types.Package) {
   223  	if *verbose {
   224  		log.Println(pkg)
   225  	}
   226  	pop := w.pushScope("pkg " + pkg.Path())
   227  	w.current = pkg
   228  	scope := pkg.Scope()
   229  	for _, name := range scope.Names() {
   230  		if token.IsExported(name) {
   231  			w.emitObj(scope.Lookup(name))
   232  		}
   233  	}
   234  	pop()
   235  }
   236  
   237  func set(items []string) map[string]bool {
   238  	s := make(map[string]bool)
   239  	for _, v := range items {
   240  		s[v] = true
   241  	}
   242  	return s
   243  }
   244  
   245  var spaceParensRx = regexp.MustCompile(` \(\S+?\)`)
   246  
   247  func featureWithoutContext(f string) string {
   248  	if !strings.Contains(f, "(") {
   249  		return f
   250  	}
   251  	return spaceParensRx.ReplaceAllString(f, "")
   252  }
   253  
   254  // portRemoved reports whether the given port-specific API feature is
   255  // okay to no longer exist because its port was removed.
   256  func portRemoved(feature string) bool {
   257  	return strings.Contains(feature, "(darwin-386)") ||
   258  		strings.Contains(feature, "(darwin-386-cgo)")
   259  }
   260  
   261  func compareAPI(w io.Writer, features, required, optional, exception []string, allowAdd bool) (ok bool) {
   262  	ok = true
   263  
   264  	optionalSet := set(optional)
   265  	exceptionSet := set(exception)
   266  	featureSet := set(features)
   267  
   268  	sort.Strings(features)
   269  	sort.Strings(required)
   270  
   271  	take := func(sl *[]string) string {
   272  		s := (*sl)[0]
   273  		*sl = (*sl)[1:]
   274  		return s
   275  	}
   276  
   277  	for len(required) > 0 || len(features) > 0 {
   278  		switch {
   279  		case len(features) == 0 || (len(required) > 0 && required[0] < features[0]):
   280  			feature := take(&required)
   281  			if exceptionSet[feature] {
   282  				// An "unfortunate" case: the feature was once
   283  				// included in the API (e.g. go1.txt), but was
   284  				// subsequently removed. These are already
   285  				// acknowledged by being in the file
   286  				// "api/except.txt". No need to print them out
   287  				// here.
   288  			} else if portRemoved(feature) {
   289  				// okay.
   290  			} else if featureSet[featureWithoutContext(feature)] {
   291  				// okay.
   292  			} else {
   293  				fmt.Fprintf(w, "-%s\n", feature)
   294  				ok = false // broke compatibility
   295  			}
   296  		case len(required) == 0 || (len(features) > 0 && required[0] > features[0]):
   297  			newFeature := take(&features)
   298  			if optionalSet[newFeature] {
   299  				// Known added feature to the upcoming release.
   300  				// Delete it from the map so we can detect any upcoming features
   301  				// which were never seen.  (so we can clean up the nextFile)
   302  				delete(optionalSet, newFeature)
   303  			} else {
   304  				fmt.Fprintf(w, "+%s\n", newFeature)
   305  				if !allowAdd {
   306  					ok = false // we're in lock-down mode for next release
   307  				}
   308  			}
   309  		default:
   310  			take(&required)
   311  			take(&features)
   312  		}
   313  	}
   314  
   315  	// In next file, but not in API.
   316  	var missing []string
   317  	for feature := range optionalSet {
   318  		missing = append(missing, feature)
   319  	}
   320  	sort.Strings(missing)
   321  	for _, feature := range missing {
   322  		fmt.Fprintf(w, "±%s\n", feature)
   323  	}
   324  	return
   325  }
   326  
   327  // aliasReplacer applies type aliases to earlier API files,
   328  // to avoid misleading negative results.
   329  // This makes all the references to os.FileInfo in go1.txt
   330  // be read as if they said fs.FileInfo, since os.FileInfo is now an alias.
   331  // If there are many of these, we could do a more general solution,
   332  // but for now the replacer is fine.
   333  var aliasReplacer = strings.NewReplacer(
   334  	"os.FileInfo", "fs.FileInfo",
   335  	"os.FileMode", "fs.FileMode",
   336  	"os.PathError", "fs.PathError",
   337  )
   338  
   339  func fileFeatures(filename string) []string {
   340  	if filename == "" {
   341  		return nil
   342  	}
   343  	bs, err := os.ReadFile(filename)
   344  	if err != nil {
   345  		log.Fatalf("Error reading file %s: %v", filename, err)
   346  	}
   347  	s := string(bs)
   348  	s = aliasReplacer.Replace(s)
   349  	lines := strings.Split(s, "\n")
   350  	var nonblank []string
   351  	for _, line := range lines {
   352  		line = strings.TrimSpace(line)
   353  		if line != "" && !strings.HasPrefix(line, "#") {
   354  			nonblank = append(nonblank, line)
   355  		}
   356  	}
   357  	return nonblank
   358  }
   359  
   360  var fset = token.NewFileSet()
   361  
   362  type Walker struct {
   363  	context     *build.Context
   364  	root        string
   365  	scope       []string
   366  	current     *types.Package
   367  	features    map[string]bool              // set
   368  	imported    map[string]*types.Package    // packages already imported
   369  	stdPackages []string                     // names, omitting "unsafe", internal, and vendored packages
   370  	importMap   map[string]map[string]string // importer dir -> import path -> canonical path
   371  	importDir   map[string]string            // canonical import path -> dir
   372  
   373  }
   374  
   375  func NewWalker(context *build.Context, root string) *Walker {
   376  	w := &Walker{
   377  		context:  context,
   378  		root:     root,
   379  		features: map[string]bool{},
   380  		imported: map[string]*types.Package{"unsafe": types.Unsafe},
   381  	}
   382  	w.loadImports()
   383  	return w
   384  }
   385  
   386  func (w *Walker) Features() (fs []string) {
   387  	for f := range w.features {
   388  		fs = append(fs, f)
   389  	}
   390  	sort.Strings(fs)
   391  	return
   392  }
   393  
   394  var parsedFileCache = make(map[string]*ast.File)
   395  
   396  func (w *Walker) parseFile(dir, file string) (*ast.File, error) {
   397  	filename := filepath.Join(dir, file)
   398  	if f := parsedFileCache[filename]; f != nil {
   399  		return f, nil
   400  	}
   401  
   402  	f, err := parser.ParseFile(fset, filename, nil, 0)
   403  	if err != nil {
   404  		return nil, err
   405  	}
   406  	parsedFileCache[filename] = f
   407  
   408  	return f, nil
   409  }
   410  
   411  // Disable before debugging non-obvious errors from the type-checker.
   412  const usePkgCache = true
   413  
   414  var (
   415  	pkgCache = map[string]*types.Package{} // map tagKey to package
   416  	pkgTags  = map[string][]string{}       // map import dir to list of relevant tags
   417  )
   418  
   419  // tagKey returns the tag-based key to use in the pkgCache.
   420  // It is a comma-separated string; the first part is dir, the rest tags.
   421  // The satisfied tags are derived from context but only those that
   422  // matter (the ones listed in the tags argument plus GOOS and GOARCH) are used.
   423  // The tags list, which came from go/build's Package.AllTags,
   424  // is known to be sorted.
   425  func tagKey(dir string, context *build.Context, tags []string) string {
   426  	ctags := map[string]bool{
   427  		context.GOOS:   true,
   428  		context.GOARCH: true,
   429  	}
   430  	if context.CgoEnabled {
   431  		ctags["cgo"] = true
   432  	}
   433  	for _, tag := range context.BuildTags {
   434  		ctags[tag] = true
   435  	}
   436  	// TODO: ReleaseTags (need to load default)
   437  	key := dir
   438  
   439  	// explicit on GOOS and GOARCH as global cache will use "all" cached packages for
   440  	// an indirect imported package. See https://github.com/golang/go/issues/21181
   441  	// for more detail.
   442  	tags = append(tags, context.GOOS, context.GOARCH)
   443  	sort.Strings(tags)
   444  
   445  	for _, tag := range tags {
   446  		if ctags[tag] {
   447  			key += "," + tag
   448  			ctags[tag] = false
   449  		}
   450  	}
   451  	return key
   452  }
   453  
   454  type listImports struct {
   455  	stdPackages []string                     // names, omitting "unsafe", internal, and vendored packages
   456  	importDir   map[string]string            // canonical import path → directory
   457  	importMap   map[string]map[string]string // import path → canonical import path
   458  }
   459  
   460  var listCache sync.Map // map[string]listImports, keyed by contextName
   461  
   462  // listSem is a semaphore restricting concurrent invocations of 'go list'.
   463  var listSem = make(chan semToken, runtime.GOMAXPROCS(0))
   464  
   465  type semToken struct{}
   466  
   467  // loadImports populates w with information about the packages in the standard
   468  // library and the packages they themselves import in w's build context.
   469  //
   470  // The source import path and expanded import path are identical except for vendored packages.
   471  // For example, on return:
   472  //
   473  //	w.importMap["math"] = "math"
   474  //	w.importDir["math"] = "<goroot>/src/math"
   475  //
   476  //	w.importMap["golang.org/x/net/route"] = "vendor/golang.org/x/net/route"
   477  //	w.importDir["vendor/golang.org/x/net/route"] = "<goroot>/src/vendor/golang.org/x/net/route"
   478  //
   479  // Since the set of packages that exist depends on context, the result of
   480  // loadImports also depends on context. However, to improve test running time
   481  // the configuration for each environment is cached across runs.
   482  func (w *Walker) loadImports() {
   483  	if w.context == nil {
   484  		return // test-only Walker; does not use the import map
   485  	}
   486  
   487  	name := contextName(w.context)
   488  
   489  	imports, ok := listCache.Load(name)
   490  	if !ok {
   491  		listSem <- semToken{}
   492  		defer func() { <-listSem }()
   493  
   494  		cmd := exec.Command(goCmd(), "list", "-e", "-deps", "-json", "std")
   495  		cmd.Env = listEnv(w.context)
   496  		if w.context.Dir != "" {
   497  			cmd.Dir = w.context.Dir
   498  		}
   499  		out, err := cmd.CombinedOutput()
   500  		if err != nil {
   501  			log.Fatalf("loading imports: %v\n%s", err, out)
   502  		}
   503  
   504  		var stdPackages []string
   505  		importMap := make(map[string]map[string]string)
   506  		importDir := make(map[string]string)
   507  		dec := json.NewDecoder(bytes.NewReader(out))
   508  		for {
   509  			var pkg struct {
   510  				ImportPath, Dir string
   511  				ImportMap       map[string]string
   512  				Standard        bool
   513  			}
   514  			err := dec.Decode(&pkg)
   515  			if err == io.EOF {
   516  				break
   517  			}
   518  			if err != nil {
   519  				log.Fatalf("go list: invalid output: %v", err)
   520  			}
   521  
   522  			// - Package "unsafe" contains special signatures requiring
   523  			//   extra care when printing them - ignore since it is not
   524  			//   going to change w/o a language change.
   525  			// - Internal and vendored packages do not contribute to our
   526  			//   API surface. (If we are running within the "std" module,
   527  			//   vendored dependencies appear as themselves instead of
   528  			//   their "vendor/" standard-library copies.)
   529  			// - 'go list std' does not include commands, which cannot be
   530  			//   imported anyway.
   531  			if ip := pkg.ImportPath; pkg.Standard && ip != "unsafe" && !strings.HasPrefix(ip, "vendor/") && !internalPkg.MatchString(ip) {
   532  				stdPackages = append(stdPackages, ip)
   533  			}
   534  			importDir[pkg.ImportPath] = pkg.Dir
   535  			if len(pkg.ImportMap) > 0 {
   536  				importMap[pkg.Dir] = make(map[string]string, len(pkg.ImportMap))
   537  			}
   538  			for k, v := range pkg.ImportMap {
   539  				importMap[pkg.Dir][k] = v
   540  			}
   541  		}
   542  
   543  		sort.Strings(stdPackages)
   544  		imports = listImports{
   545  			stdPackages: stdPackages,
   546  			importMap:   importMap,
   547  			importDir:   importDir,
   548  		}
   549  		imports, _ = listCache.LoadOrStore(name, imports)
   550  	}
   551  
   552  	li := imports.(listImports)
   553  	w.stdPackages = li.stdPackages
   554  	w.importDir = li.importDir
   555  	w.importMap = li.importMap
   556  }
   557  
   558  // listEnv returns the process environment to use when invoking 'go list' for
   559  // the given context.
   560  func listEnv(c *build.Context) []string {
   561  	if c == nil {
   562  		return os.Environ()
   563  	}
   564  
   565  	environ := append(os.Environ(),
   566  		"GOOS="+c.GOOS,
   567  		"GOARCH="+c.GOARCH)
   568  	if c.CgoEnabled {
   569  		environ = append(environ, "CGO_ENABLED=1")
   570  	} else {
   571  		environ = append(environ, "CGO_ENABLED=0")
   572  	}
   573  	return environ
   574  }
   575  
   576  // Importing is a sentinel taking the place in Walker.imported
   577  // for a package that is in the process of being imported.
   578  var importing types.Package
   579  
   580  func (w *Walker) Import(name string) (*types.Package, error) {
   581  	return w.ImportFrom(name, "", 0)
   582  }
   583  
   584  func (w *Walker) ImportFrom(fromPath, fromDir string, mode types.ImportMode) (*types.Package, error) {
   585  	name := fromPath
   586  	if canonical, ok := w.importMap[fromDir][fromPath]; ok {
   587  		name = canonical
   588  	}
   589  
   590  	pkg := w.imported[name]
   591  	if pkg != nil {
   592  		if pkg == &importing {
   593  			log.Fatalf("cycle importing package %q", name)
   594  		}
   595  		return pkg, nil
   596  	}
   597  	w.imported[name] = &importing
   598  
   599  	// Determine package files.
   600  	dir := w.importDir[name]
   601  	if dir == "" {
   602  		dir = filepath.Join(w.root, filepath.FromSlash(name))
   603  	}
   604  	if fi, err := os.Stat(dir); err != nil || !fi.IsDir() {
   605  		log.Panicf("no source in tree for import %q (from import %s in %s): %v", name, fromPath, fromDir, err)
   606  	}
   607  
   608  	context := w.context
   609  	if context == nil {
   610  		context = &build.Default
   611  	}
   612  
   613  	// Look in cache.
   614  	// If we've already done an import with the same set
   615  	// of relevant tags, reuse the result.
   616  	var key string
   617  	if usePkgCache {
   618  		if tags, ok := pkgTags[dir]; ok {
   619  			key = tagKey(dir, context, tags)
   620  			if pkg := pkgCache[key]; pkg != nil {
   621  				w.imported[name] = pkg
   622  				return pkg, nil
   623  			}
   624  		}
   625  	}
   626  
   627  	info, err := context.ImportDir(dir, 0)
   628  	if err != nil {
   629  		if _, nogo := err.(*build.NoGoError); nogo {
   630  			return nil, err
   631  		}
   632  		log.Fatalf("pkg %q, dir %q: ScanDir: %v", name, dir, err)
   633  	}
   634  
   635  	// Save tags list first time we see a directory.
   636  	if usePkgCache {
   637  		if _, ok := pkgTags[dir]; !ok {
   638  			pkgTags[dir] = info.AllTags
   639  			key = tagKey(dir, context, info.AllTags)
   640  		}
   641  	}
   642  
   643  	filenames := append(append([]string{}, info.GoFiles...), info.CgoFiles...)
   644  
   645  	// Parse package files.
   646  	var files []*ast.File
   647  	for _, file := range filenames {
   648  		f, err := w.parseFile(dir, file)
   649  		if err != nil {
   650  			log.Fatalf("error parsing package %s: %s", name, err)
   651  		}
   652  		files = append(files, f)
   653  	}
   654  
   655  	// Type-check package files.
   656  	conf := types.Config{
   657  		IgnoreFuncBodies: true,
   658  		FakeImportC:      true,
   659  		Importer:         w,
   660  	}
   661  	pkg, err = conf.Check(name, fset, files, nil)
   662  	if err != nil {
   663  		ctxt := "<no context>"
   664  		if w.context != nil {
   665  			ctxt = fmt.Sprintf("%s-%s", w.context.GOOS, w.context.GOARCH)
   666  		}
   667  		log.Fatalf("error typechecking package %s: %s (%s)", name, err, ctxt)
   668  	}
   669  
   670  	if usePkgCache {
   671  		pkgCache[key] = pkg
   672  	}
   673  
   674  	w.imported[name] = pkg
   675  	return pkg, nil
   676  }
   677  
   678  // pushScope enters a new scope (walking a package, type, node, etc)
   679  // and returns a function that will leave the scope (with sanity checking
   680  // for mismatched pushes & pops)
   681  func (w *Walker) pushScope(name string) (popFunc func()) {
   682  	w.scope = append(w.scope, name)
   683  	return func() {
   684  		if len(w.scope) == 0 {
   685  			log.Fatalf("attempt to leave scope %q with empty scope list", name)
   686  		}
   687  		if w.scope[len(w.scope)-1] != name {
   688  			log.Fatalf("attempt to leave scope %q, but scope is currently %#v", name, w.scope)
   689  		}
   690  		w.scope = w.scope[:len(w.scope)-1]
   691  	}
   692  }
   693  
   694  func sortedMethodNames(typ *types.Interface) []string {
   695  	n := typ.NumMethods()
   696  	list := make([]string, n)
   697  	for i := range list {
   698  		list[i] = typ.Method(i).Name()
   699  	}
   700  	sort.Strings(list)
   701  	return list
   702  }
   703  
   704  func (w *Walker) writeType(buf *bytes.Buffer, typ types.Type) {
   705  	switch typ := typ.(type) {
   706  	case *types.Basic:
   707  		s := typ.Name()
   708  		switch typ.Kind() {
   709  		case types.UnsafePointer:
   710  			s = "unsafe.Pointer"
   711  		case types.UntypedBool:
   712  			s = "ideal-bool"
   713  		case types.UntypedInt:
   714  			s = "ideal-int"
   715  		case types.UntypedRune:
   716  			// "ideal-char" for compatibility with old tool
   717  			// TODO(gri) change to "ideal-rune"
   718  			s = "ideal-char"
   719  		case types.UntypedFloat:
   720  			s = "ideal-float"
   721  		case types.UntypedComplex:
   722  			s = "ideal-complex"
   723  		case types.UntypedString:
   724  			s = "ideal-string"
   725  		case types.UntypedNil:
   726  			panic("should never see untyped nil type")
   727  		default:
   728  			switch s {
   729  			case "byte":
   730  				s = "uint8"
   731  			case "rune":
   732  				s = "int32"
   733  			}
   734  		}
   735  		buf.WriteString(s)
   736  
   737  	case *types.Array:
   738  		fmt.Fprintf(buf, "[%d]", typ.Len())
   739  		w.writeType(buf, typ.Elem())
   740  
   741  	case *types.Slice:
   742  		buf.WriteString("[]")
   743  		w.writeType(buf, typ.Elem())
   744  
   745  	case *types.Struct:
   746  		buf.WriteString("struct")
   747  
   748  	case *types.Pointer:
   749  		buf.WriteByte('*')
   750  		w.writeType(buf, typ.Elem())
   751  
   752  	case *types.Tuple:
   753  		panic("should never see a tuple type")
   754  
   755  	case *types.Signature:
   756  		buf.WriteString("func")
   757  		w.writeSignature(buf, typ)
   758  
   759  	case *types.Interface:
   760  		buf.WriteString("interface{")
   761  		if typ.NumMethods() > 0 {
   762  			buf.WriteByte(' ')
   763  			buf.WriteString(strings.Join(sortedMethodNames(typ), ", "))
   764  			buf.WriteByte(' ')
   765  		}
   766  		buf.WriteString("}")
   767  
   768  	case *types.Map:
   769  		buf.WriteString("map[")
   770  		w.writeType(buf, typ.Key())
   771  		buf.WriteByte(']')
   772  		w.writeType(buf, typ.Elem())
   773  
   774  	case *types.Chan:
   775  		var s string
   776  		switch typ.Dir() {
   777  		case types.SendOnly:
   778  			s = "chan<- "
   779  		case types.RecvOnly:
   780  			s = "<-chan "
   781  		case types.SendRecv:
   782  			s = "chan "
   783  		default:
   784  			panic("unreachable")
   785  		}
   786  		buf.WriteString(s)
   787  		w.writeType(buf, typ.Elem())
   788  
   789  	case *types.Named:
   790  		obj := typ.Obj()
   791  		pkg := obj.Pkg()
   792  		if pkg != nil && pkg != w.current {
   793  			buf.WriteString(pkg.Name())
   794  			buf.WriteByte('.')
   795  		}
   796  		buf.WriteString(typ.Obj().Name())
   797  
   798  	default:
   799  		panic(fmt.Sprintf("unknown type %T", typ))
   800  	}
   801  }
   802  
   803  func (w *Walker) writeSignature(buf *bytes.Buffer, sig *types.Signature) {
   804  	w.writeParams(buf, sig.Params(), sig.Variadic())
   805  	switch res := sig.Results(); res.Len() {
   806  	case 0:
   807  		// nothing to do
   808  	case 1:
   809  		buf.WriteByte(' ')
   810  		w.writeType(buf, res.At(0).Type())
   811  	default:
   812  		buf.WriteByte(' ')
   813  		w.writeParams(buf, res, false)
   814  	}
   815  }
   816  
   817  func (w *Walker) writeParams(buf *bytes.Buffer, t *types.Tuple, variadic bool) {
   818  	buf.WriteByte('(')
   819  	for i, n := 0, t.Len(); i < n; i++ {
   820  		if i > 0 {
   821  			buf.WriteString(", ")
   822  		}
   823  		typ := t.At(i).Type()
   824  		if variadic && i+1 == n {
   825  			buf.WriteString("...")
   826  			typ = typ.(*types.Slice).Elem()
   827  		}
   828  		w.writeType(buf, typ)
   829  	}
   830  	buf.WriteByte(')')
   831  }
   832  
   833  func (w *Walker) typeString(typ types.Type) string {
   834  	var buf bytes.Buffer
   835  	w.writeType(&buf, typ)
   836  	return buf.String()
   837  }
   838  
   839  func (w *Walker) signatureString(sig *types.Signature) string {
   840  	var buf bytes.Buffer
   841  	w.writeSignature(&buf, sig)
   842  	return buf.String()
   843  }
   844  
   845  func (w *Walker) emitObj(obj types.Object) {
   846  	switch obj := obj.(type) {
   847  	case *types.Const:
   848  		w.emitf("const %s %s", obj.Name(), w.typeString(obj.Type()))
   849  		x := obj.Val()
   850  		short := x.String()
   851  		exact := x.ExactString()
   852  		if short == exact {
   853  			w.emitf("const %s = %s", obj.Name(), short)
   854  		} else {
   855  			w.emitf("const %s = %s  // %s", obj.Name(), short, exact)
   856  		}
   857  	case *types.Var:
   858  		w.emitf("var %s %s", obj.Name(), w.typeString(obj.Type()))
   859  	case *types.TypeName:
   860  		w.emitType(obj)
   861  	case *types.Func:
   862  		w.emitFunc(obj)
   863  	default:
   864  		panic("unknown object: " + obj.String())
   865  	}
   866  }
   867  
   868  func (w *Walker) emitType(obj *types.TypeName) {
   869  	name := obj.Name()
   870  	typ := obj.Type()
   871  	if obj.IsAlias() {
   872  		w.emitf("type %s = %s", name, w.typeString(typ))
   873  		return
   874  	}
   875  	switch typ := typ.Underlying().(type) {
   876  	case *types.Struct:
   877  		w.emitStructType(name, typ)
   878  	case *types.Interface:
   879  		w.emitIfaceType(name, typ)
   880  		return // methods are handled by emitIfaceType
   881  	default:
   882  		w.emitf("type %s %s", name, w.typeString(typ.Underlying()))
   883  	}
   884  
   885  	// emit methods with value receiver
   886  	var methodNames map[string]bool
   887  	vset := types.NewMethodSet(typ)
   888  	for i, n := 0, vset.Len(); i < n; i++ {
   889  		m := vset.At(i)
   890  		if m.Obj().Exported() {
   891  			w.emitMethod(m)
   892  			if methodNames == nil {
   893  				methodNames = make(map[string]bool)
   894  			}
   895  			methodNames[m.Obj().Name()] = true
   896  		}
   897  	}
   898  
   899  	// emit methods with pointer receiver; exclude
   900  	// methods that we have emitted already
   901  	// (the method set of *T includes the methods of T)
   902  	pset := types.NewMethodSet(types.NewPointer(typ))
   903  	for i, n := 0, pset.Len(); i < n; i++ {
   904  		m := pset.At(i)
   905  		if m.Obj().Exported() && !methodNames[m.Obj().Name()] {
   906  			w.emitMethod(m)
   907  		}
   908  	}
   909  }
   910  
   911  func (w *Walker) emitStructType(name string, typ *types.Struct) {
   912  	typeStruct := fmt.Sprintf("type %s struct", name)
   913  	w.emitf(typeStruct)
   914  	defer w.pushScope(typeStruct)()
   915  
   916  	for i := 0; i < typ.NumFields(); i++ {
   917  		f := typ.Field(i)
   918  		if !f.Exported() {
   919  			continue
   920  		}
   921  		typ := f.Type()
   922  		if f.Anonymous() {
   923  			w.emitf("embedded %s", w.typeString(typ))
   924  			continue
   925  		}
   926  		w.emitf("%s %s", f.Name(), w.typeString(typ))
   927  	}
   928  }
   929  
   930  func (w *Walker) emitIfaceType(name string, typ *types.Interface) {
   931  	pop := w.pushScope("type " + name + " interface")
   932  
   933  	var methodNames []string
   934  	complete := true
   935  	mset := types.NewMethodSet(typ)
   936  	for i, n := 0, mset.Len(); i < n; i++ {
   937  		m := mset.At(i).Obj().(*types.Func)
   938  		if !m.Exported() {
   939  			complete = false
   940  			continue
   941  		}
   942  		methodNames = append(methodNames, m.Name())
   943  		w.emitf("%s%s", m.Name(), w.signatureString(m.Type().(*types.Signature)))
   944  	}
   945  
   946  	if !complete {
   947  		// The method set has unexported methods, so all the
   948  		// implementations are provided by the same package,
   949  		// so the method set can be extended. Instead of recording
   950  		// the full set of names (below), record only that there were
   951  		// unexported methods. (If the interface shrinks, we will notice
   952  		// because a method signature emitted during the last loop
   953  		// will disappear.)
   954  		w.emitf("unexported methods")
   955  	}
   956  
   957  	pop()
   958  
   959  	if !complete {
   960  		return
   961  	}
   962  
   963  	if len(methodNames) == 0 {
   964  		w.emitf("type %s interface {}", name)
   965  		return
   966  	}
   967  
   968  	sort.Strings(methodNames)
   969  	w.emitf("type %s interface { %s }", name, strings.Join(methodNames, ", "))
   970  }
   971  
   972  func (w *Walker) emitFunc(f *types.Func) {
   973  	sig := f.Type().(*types.Signature)
   974  	if sig.Recv() != nil {
   975  		panic("method considered a regular function: " + f.String())
   976  	}
   977  	w.emitf("func %s%s", f.Name(), w.signatureString(sig))
   978  }
   979  
   980  func (w *Walker) emitMethod(m *types.Selection) {
   981  	sig := m.Type().(*types.Signature)
   982  	recv := sig.Recv().Type()
   983  	// report exported methods with unexported receiver base type
   984  	if true {
   985  		base := recv
   986  		if p, _ := recv.(*types.Pointer); p != nil {
   987  			base = p.Elem()
   988  		}
   989  		if obj := base.(*types.Named).Obj(); !obj.Exported() {
   990  			log.Fatalf("exported method with unexported receiver base type: %s", m)
   991  		}
   992  	}
   993  	w.emitf("method (%s) %s%s", w.typeString(recv), m.Obj().Name(), w.signatureString(sig))
   994  }
   995  
   996  func (w *Walker) emitf(format string, args ...interface{}) {
   997  	f := strings.Join(w.scope, ", ") + ", " + fmt.Sprintf(format, args...)
   998  	if strings.Contains(f, "\n") {
   999  		panic("feature contains newlines: " + f)
  1000  	}
  1001  
  1002  	if _, dup := w.features[f]; dup {
  1003  		panic("duplicate feature inserted: " + f)
  1004  	}
  1005  	w.features[f] = true
  1006  
  1007  	if *verbose {
  1008  		log.Printf("feature: %s", f)
  1009  	}
  1010  }
  1011  

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