cmd/godoc: use go/build to determine package and example files

Also:
- faster code for example extraction
- simplify handling of command documentation:
  all "main" packages are treated as commands
- various minor cleanups along the way

For commands written in Go, any doc.go file containing
documentation must now be part of package main (rather
then package documentation), otherwise the documentation
won't show up in godoc (it will still build, though).

For commands written in C, documentation may still be
in doc.go files defining package documentation, but the
recommended way is to explicitly ignore those files with
a +build ignore constraint to define package main.

Fixes #4806.

R=adg, rsc, dave, bradfitz
CC=golang-dev
https://golang.org/cl/7333046

lib/godoc/package.html

@@ -10,7 +10,7 @@
 	correspond to Go identifiers).
 -->
 {{with .PDoc}}
-	{{if $.IsPkg}}
+	{{if not $.IsMain}}
 		<div id="short-nav">
 			<dl>
 			<dd><code>import "{{html .ImportPath}}"</code></dd>

lib/godoc/package.txt

@@ -2,7 +2,7 @@
 
 ---------------------------------------
 
-*/}}{{with .PDoc}}{{if $.IsPkg}}PACKAGE
+*/}}{{with .PDoc}}{{if not $.IsMain}}PACKAGE
 
 package {{.Name}}
     import "{{.ImportPath}}"

misc/dashboard/builder/doc.go

@@ -55,4 +55,4 @@ If the Google Code credentials are not provided the archival step
 will be skipped.
 
 */
-package documentation
+package main

misc/goplay/doc.go

@@ -20,4 +20,4 @@
 // security mechanisms. Do not deploy it in untrusted environments.
 // By default, goplay listens only on localhost. This can be overridden with
 // the -http parameter. Do so at your own risk.
-package documentation
+package main

src/cmd/5a/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 5a is a version of the Plan 9 assembler.  The original is documented at
@@ -11,4 +13,4 @@
 Its target architecture is the ARM, referred to by these tools as arm.
 
 */
-package documentation
+package main

src/cmd/5c/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 5c is a version of the Plan 9 C compiler.  The original is documented at
@@ -11,4 +13,4 @@
 Its target architecture is the ARM, referred to by these tools as arm.
 
 */
-package documentation
+package main

src/cmd/5g/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 5g is the version of the gc compiler for the ARM.
@@ -10,4 +12,4 @@ The $GOARCH for these tools is arm.
 It reads .go files and outputs .5 files. The flags are documented in ../gc/doc.go.
 
 */
-package documentation
+package main

src/cmd/5l/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 5l is the linker for the ARM.
@@ -10,4 +12,4 @@ The $GOARCH for these tools is arm.
 The flags are documented in ../ld/doc.go.
 
 */
-package documentation
+package main

src/cmd/6a/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 6a is a version of the Plan 9 assembler.  The original is documented at
@@ -11,4 +13,4 @@
 Its target architecture is the x86-64, referred to by these tools as amd64.
 
 */
-package documentation
+package main

src/cmd/6c/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 6c is a version of the Plan 9 C compiler.  The original is documented at
@@ -11,4 +13,4 @@
 Its target architecture is the x86-64, referred to by these tools as amd64.
 
 */
-package documentation
+package main

src/cmd/6g/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 6g is the version of the gc compiler for the x86-64.
@@ -10,4 +12,4 @@ The $GOARCH for these tools is amd64.
 It reads .go files and outputs .6 files. The flags are documented in ../gc/doc.go.
 
 */
-package documentation
+package main

src/cmd/6l/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 6l is the linker for the x86-64.
@@ -10,4 +12,4 @@ The $GOARCH for these tools is amd64.
 The flags are documented in ../ld/doc.go.
 
 */
-package documentation
+package main

src/cmd/8a/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 8a is a version of the Plan 9 assembler.  The original is documented at
@@ -11,4 +13,4 @@
 Its target architecture is the x86, referred to by these tools for historical reasons as 386.
 
 */
-package documentation
+package main

src/cmd/8c/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 8c is a version of the Plan 9 C compiler.  The original is documented at
@@ -11,4 +13,4 @@
 Its target architecture is the x86, referred to by these tools for historical reasons as 386.
 
 */
-package documentation
+package main

src/cmd/8g/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 8g is the version of the gc compiler for the x86.
@@ -10,4 +12,4 @@ The $GOARCH for these tools is 386.
 It reads .go files and outputs .8 files. The flags are documented in ../gc/doc.go.
 
 */
-package documentation
+package main

src/cmd/8l/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 8l is the linker for the 32-bit x86.
@@ -10,4 +12,4 @@ The $GOARCH for these tools is 386.
 The flags are documented in ../ld/doc.go.
 
 */
-package documentation
+package main

src/cmd/cc/doc.go

@@ -2,10 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 This directory contains the portable section of the Plan 9 C compilers.
 See ../6c, ../8c, and ../5c for more information.
 
 */
-package documentation
+package main

src/cmd/cgo/doc.go

@@ -133,4 +133,4 @@ Cgo does not yet work with gccgo.
 See "C? Go? Cgo!" for an introduction to using cgo:
 http://golang.org/doc/articles/c_go_cgo.html
 */
-package documentation
+package main

src/cmd/cov/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 Cov is a rudimentary code coverage tool.
@@ -31,4 +33,4 @@ The options are:
 The program is the same for all architectures: 386, amd64, and arm.
 
 */
-package documentation
+package main

src/cmd/fix/doc.go

@@ -33,4 +33,4 @@ Fix does not make backup copies of the files that it edits.
 Instead, use a version control system's ``diff'' functionality to inspect
 the changes that fix makes before committing them.
 */
-package documentation
+package main

src/cmd/gc/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 Gc is the generic label for the family of Go compilers
@@ -86,4 +88,4 @@ in Go) does not allow any of the pointers passed as arguments to escape into the
 heap or into the values returned from the function. This information can be used as
 during the compiler's escape analysis of Go code calling the function.
 */
-package documentation
+package main

src/cmd/go/doc.go

@@ -812,6 +812,6 @@ See the documentation of the testing package for more information.
 
 
 */
-package documentation
+package main
 
 // NOTE: cmdDoc is in fmt.go.

src/cmd/go/main.go

@@ -200,7 +200,7 @@ var documentationTemplate = `// Copyright 2011 The Go Authors.  All rights reser
 
 
 {{end}}*/
-package documentation
+package main
 
 // NOTE: cmdDoc is in fmt.go.
 `

src/cmd/godoc/dirtrees.go

@@ -74,7 +74,7 @@ func (b *treeBuilder) newDirTree(fset *token.FileSet, path, name string, depth i
 	// determine number of subdirectories and if there are package files
 	ndirs := 0
 	hasPkgFiles := false
-	var synopses [4]string // prioritized package documentation (0 == highest priority)
+	var synopses [3]string // prioritized package documentation (0 == highest priority)
 	for _, d := range list {
 		switch {
 		case isPkgDir(d):
@@ -95,12 +95,10 @@ func (b *treeBuilder) newDirTree(fset *token.FileSet, path, name string, depth i
 						switch file.Name.Name {
 						case name:
 							i = 0 // normal case: directory name matches package name
-						case fakePkgName:
-							i = 1 // synopses for commands
 						case "main":
-							i = 2 // directory contains a main package
+							i = 1 // directory contains a main package
 						default:
-							i = 3 // none of the above
+							i = 2 // none of the above
 						}
 						if 0 <= i && i < len(synopses) && synopses[i] == "" {
 							synopses[i] = doc.Synopsis(file.Doc.Text())

src/cmd/godoc/doc.go

@@ -127,4 +127,4 @@ See "Godoc: documenting Go code" for how to write good comments for godoc:
 http://golang.org/doc/articles/godoc_documenting_go_code.html
 
 */
-package documentation
+package main

src/cmd/godoc/godoc.go

@@ -86,8 +86,8 @@ var (
 
 func initHandlers() {
 	fileServer = http.FileServer(&httpFS{fs})
-	cmdHandler = docServer{"/cmd/", "/src/cmd", false}
-	pkgHandler = docServer{"/pkg/", "/src/pkg", true}
+	cmdHandler = docServer{"/cmd/", "/src/cmd"}
+	pkgHandler = docServer{"/pkg/", "/src/pkg"}
 }
 
 func registerPublicHandlers(mux *http.ServeMux) {
@@ -794,10 +794,6 @@ func serveSearchDesc(w http.ResponseWriter, r *http.Request) {
 // ----------------------------------------------------------------------------
 // Packages
 
-// Fake package file and name for commands. Contains the command documentation.
-const fakePkgFile = "doc.go"
-const fakePkgName = "documentation"
-
 // Fake relative package path for built-ins. Documentation for all globals
 // (not just exported ones) will be shown for packages in this directory.
 const builtinPkgPath = "builtin"
@@ -854,16 +850,20 @@ func remoteSearchURL(query string, html bool) string {
 }
 
 type PageInfo struct {
-	Dirname  string         // directory containing the package
-	FSet     *token.FileSet // corresponding file set
-	PAst     *ast.File      // nil if no single AST with package exports
-	PDoc     *doc.Package   // nil if no single package documentation
+	Dirname string // directory containing the package
+	Err     error  // error or nil
+
+	// package info
+	FSet     *token.FileSet // nil if no package documentation
+	PDoc     *doc.Package   // nil if no package documentation
 	Examples []*doc.Example // nil if no example code
-	Dirs     *DirList       // nil if no directory information
-	DirTime  time.Time      // directory time stamp
-	DirFlat  bool           // if set, show directory in a flat (non-indented) manner
-	IsPkg    bool           // false if this is not documenting a real package
-	Err      error          // I/O error or nil
+	PAst     *ast.File      // nil if no AST with package exports
+	IsMain   bool           // true for package main
+
+	// directory info
+	Dirs    *DirList  // nil if no directory information
+	DirTime time.Time // directory time stamp
+	DirFlat bool      // if set, show directory in a flat (non-indented) manner
 }
 
 func (info *PageInfo) IsEmpty() bool {
@@ -873,7 +873,6 @@ func (info *PageInfo) IsEmpty() bool {
 type docServer struct {
 	pattern string // url pattern; e.g. "/pkg/"
 	fsRoot  string // file system root to which the pattern is mapped
-	isPkg   bool   // true if this handler serves real package documentation (as opposed to command documentation)
 }
 
 // fsReadDir implements ReadDir for the go/build package.
@@ -890,15 +889,6 @@ func fsOpenFile(name string) (r io.ReadCloser, err error) {
 	return ioutil.NopCloser(bytes.NewReader(data)), nil
 }
 
-func inList(name string, list []string) bool {
-	for _, l := range list {
-		if name == l {
-			return true
-		}
-	}
-	return false
-}
-
 // packageExports is a local implementation of ast.PackageExports
 // which correctly updates each package file's comment list.
 // (The ast.PackageExports signature is frozen, hence the local
@@ -912,9 +902,9 @@ func packageExports(fset *token.FileSet, pkg *ast.Package) {
 	}
 }
 
-// declNames returns the names declared by decl.
-// Method names are returned in the form Receiver_Method.
-func declNames(decl ast.Decl) (names []string) {
+// addNames adds the names declared by decl to the names set.
+// Method names are added in the form ReceiverTypeName_Method.
+func addNames(names map[string]bool, decl ast.Decl) {
 	switch d := decl.(type) {
 	case *ast.FuncDecl:
 		name := d.Name.Name
@@ -928,64 +918,52 @@ func declNames(decl ast.Decl) (names []string) {
 			}
 			name = typeName + "_" + name
 		}
-		names = []string{name}
+		names[name] = true
 	case *ast.GenDecl:
 		for _, spec := range d.Specs {
 			switch s := spec.(type) {
 			case *ast.TypeSpec:
-				names = append(names, s.Name.Name)
+				names[s.Name.Name] = true
 			case *ast.ValueSpec:
 				for _, id := range s.Names {
-					names = append(names, id.Name)
+					names[id.Name] = true
 				}
 			}
 		}
 	}
-	return
 }
 
-// globalNames finds all top-level declarations in pkgs and returns a map
-// with the identifier names as keys.
-func globalNames(pkgs map[string]*ast.Package) map[string]bool {
+// globalNames returns a set of the names declared by all package-level
+// declarations. Method names are returned in the form Receiver_Method.
+func globalNames(pkg *ast.Package) map[string]bool {
 	names := make(map[string]bool)
-	for _, pkg := range pkgs {
-		for _, file := range pkg.Files {
-			for _, decl := range file.Decls {
-				for _, name := range declNames(decl) {
-					names[name] = true
-				}
-			}
+	for _, file := range pkg.Files {
+		for _, decl := range file.Decls {
+			addNames(names, decl)
 		}
 	}
 	return names
 }
 
-// parseExamples gets examples for packages in pkgs from *_test.go files in dir.
-func parseExamples(fset *token.FileSet, pkgs map[string]*ast.Package, dir string) ([]*doc.Example, error) {
+// collectExamples collects examples for pkg from testfiles.
+func collectExamples(pkg *ast.Package, testfiles map[string]*ast.File) []*doc.Example {
+	var files []*ast.File
+	for _, f := range testfiles {
+		files = append(files, f)
+	}
+
 	var examples []*doc.Example
-	filter := func(d os.FileInfo) bool {
-		return isGoFile(d) && strings.HasSuffix(d.Name(), "_test.go")
-	}
-	testpkgs, err := parseDir(fset, dir, filter)
-	if err != nil {
-		return nil, err
-	}
-	globals := globalNames(pkgs)
-	for _, testpkg := range testpkgs {
-		var files []*ast.File
-		for _, f := range testpkg.Files {
-			files = append(files, f)
-		}
-		for _, e := range doc.Examples(files...) {
-			name := stripExampleSuffix(e.Name)
-			if name == "" || globals[name] {
-				examples = append(examples, e)
-			} else {
-				log.Printf("skipping example Example%s: refers to unknown function or type", e.Name)
-			}
+	globals := globalNames(pkg)
+	for _, e := range doc.Examples(files...) {
+		name := stripExampleSuffix(e.Name)
+		if name == "" || globals[name] {
+			examples = append(examples, e)
+		} else {
+			log.Printf("skipping example Example%s: refers to unknown function or type", e.Name)
 		}
 	}
-	return examples, nil
+
+	return examples
 }
 
 // getPageInfo returns the PageInfo for a package directory abspath. If the
@@ -993,83 +971,56 @@ func parseExamples(fset *token.FileSet, pkgs map[string]*ast.Package, dir string
 // computed (PageInfo.PAst), otherwise package documentation (PageInfo.Doc)
 // is extracted from the AST. If there is no corresponding package in the
 // directory, PageInfo.PAst and PageInfo.PDoc are nil. If there are no sub-
-// directories, PageInfo.Dirs is nil. If a directory read error occurred,
-// PageInfo.Err is set to the respective error but the error is not logged.
+// directories, PageInfo.Dirs is nil. If an error occurred, PageInfo.Err is
+// set to the respective error but the error is not logged.
 //
-func (h *docServer) getPageInfo(abspath, relpath string, mode PageInfoMode) PageInfo {
-	var pkgFiles []string
+func (h *docServer) getPageInfo(abspath, relpath string, mode PageInfoMode) (info PageInfo) {
+	info.Dirname = abspath
 
-	// Restrict to the package files
-	// that would be used when building the package on this
-	// system.  This makes sure that if there are separate
-	// implementations for, say, Windows vs Unix, we don't
+	// Restrict to the package files that would be used when building
+	// the package on this system.  This makes sure that if there are
+	// separate implementations for, say, Windows vs Unix, we don't
 	// jumble them all together.
 	// Note: Uses current binary's GOOS/GOARCH.
-	// To use different pair, such as if we allowed the user
-	// to choose, set ctxt.GOOS and ctxt.GOARCH before
-	// calling ctxt.ScanDir.
+	// To use different pair, such as if we allowed the user to choose,
+	// set ctxt.GOOS and ctxt.GOARCH before calling ctxt.ImportDir.
 	ctxt := build.Default
 	ctxt.IsAbsPath = pathpkg.IsAbs
 	ctxt.ReadDir = fsReadDir
 	ctxt.OpenFile = fsOpenFile
-	if dir, err := ctxt.ImportDir(abspath, 0); err == nil {
-		pkgFiles = append(dir.GoFiles, dir.CgoFiles...)
+	pkginfo, err := ctxt.ImportDir(abspath, 0)
+	// continue if there are no Go source files; we still want the directory info
+	if _, nogo := err.(*build.NoGoError); err != nil && !nogo {
+		info.Err = err
+		return
 	}
 
-	// filter function to select the desired .go files
-	filter := func(d os.FileInfo) bool {
-		// Only Go files.
-		if !isPkgFile(d) {
-			return false
-		}
-		// If we are looking at cmd documentation, only accept
-		// the special fakePkgFile containing the documentation.
-		if !h.isPkg {
-			return d.Name() == fakePkgFile
-		}
-		// Also restrict file list to pkgFiles.
-		return pkgFiles == nil || inList(d.Name(), pkgFiles)
+	// collect package files
+	pkgname := pkginfo.Name
+	pkgfiles := append(pkginfo.GoFiles, pkginfo.CgoFiles...)
+	if len(pkgfiles) == 0 {
+		// Commands written in C have no .go files in the build.
+		// Instead, documentation may be found in an ignored file.
+		// The file may be ignored via an explicit +build ignore
+		// constraint (recommended), or by defining the package
+		// documentation (historic).
+		pkgname = "main" // assume package main since pkginfo.Name == ""
+		pkgfiles = pkginfo.IgnoredGoFiles
 	}
 
-	// get package ASTs
-	fset := token.NewFileSet()
-	pkgs, err := parseDir(fset, abspath, filter)
-	if err != nil {
-		return PageInfo{Dirname: abspath, Err: err}
-	}
-
-	// select package
-	var pkg *ast.Package // selected package
-	if len(pkgs) == 1 {
-		// Exactly one package - select it.
-		for _, p := range pkgs {
-			pkg = p
+	// get package information, if any
+	if len(pkgfiles) > 0 {
+		// build package AST
+		fset := token.NewFileSet()
+		files, err := parseFiles(fset, abspath, pkgfiles)
+		if err != nil {
+			info.Err = err
+			return
 		}
+		pkg := &ast.Package{Name: pkgname, Files: files}
 
-	} else if len(pkgs) > 1 {
-		// More than one package - report an error.
-		var buf bytes.Buffer
-		for _, p := range pkgs {
-			if buf.Len() > 0 {
-				fmt.Fprintf(&buf, ", ")
-			}
-			fmt.Fprintf(&buf, p.Name)
-		}
-		return PageInfo{
-			Dirname: abspath,
-			Err:     fmt.Errorf("%s contains more than one package: %s", abspath, buf.Bytes()),
-		}
-	}
-
-	examples, err := parseExamples(fset, pkgs, abspath)
-	if err != nil {
-		log.Println("parsing examples:", err)
-	}
-
-	// compute package documentation
-	var past *ast.File
-	var pdoc *doc.Package
-	if pkg != nil {
+		// extract package documentation
+		info.FSet = fset
 		if mode&showSource == 0 {
 			// show extracted documentation
 			var m doc.Mode
@@ -1079,7 +1030,15 @@ func (h *docServer) getPageInfo(abspath, relpath string, mode PageInfoMode) Page
 			if mode&allMethods != 0 {
 				m |= doc.AllMethods
 			}
-			pdoc = doc.New(pkg, pathpkg.Clean(relpath), m) // no trailing '/' in importpath
+			info.PDoc = doc.New(pkg, pathpkg.Clean(relpath), m) // no trailing '/' in importpath
+
+			// collect examples
+			testfiles := append(pkginfo.TestGoFiles, pkginfo.XTestGoFiles...)
+			files, err = parseFiles(fset, abspath, testfiles)
+			if err != nil {
+				log.Println("parsing examples:", err)
+			}
+			info.Examples = collectExamples(pkg, files)
 		} else {
 			// show source code
 			// TODO(gri) Consider eliminating export filtering in this mode,
@@ -1087,11 +1046,12 @@ func (h *docServer) getPageInfo(abspath, relpath string, mode PageInfoMode) Page
 			if mode&noFiltering == 0 {
 				packageExports(fset, pkg)
 			}
-			past = ast.MergePackageFiles(pkg, 0)
+			info.PAst = ast.MergePackageFiles(pkg, 0)
 		}
+		info.IsMain = pkgname == "main"
 	}
 
-	// get directory information
+	// get directory information, if any
 	var dir *Directory
 	var timestamp time.Time
 	if tree, ts := fsTree.get(); tree != nil && tree.(*Directory) != nil {
@@ -1109,19 +1069,11 @@ func (h *docServer) getPageInfo(abspath, relpath string, mode PageInfoMode) Page
 		dir = newDirectory(abspath, 1)
 		timestamp = time.Now()
 	}
+	info.Dirs = dir.listing(true)
+	info.DirTime = timestamp
+	info.DirFlat = mode&flatDir != 0
 
-	return PageInfo{
-		Dirname:  abspath,
-		FSet:     fset,
-		PAst:     past,
-		PDoc:     pdoc,
-		Examples: examples,
-		Dirs:     dir.listing(true),
-		DirTime:  timestamp,
-		DirFlat:  mode&flatDir != 0,
-		IsPkg:    h.isPkg,
-		Err:      nil,
-	}
+	return
 }
 
 func (h *docServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
@@ -1151,26 +1103,25 @@ func (h *docServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	switch {
 	case info.PAst != nil:
 		tabtitle = info.PAst.Name.Name
-		title = "Package " + tabtitle
 	case info.PDoc != nil:
-		if info.PDoc.Name == fakePkgName {
-			// assume that the directory name is the command name
-			_, tabtitle = pathpkg.Split(relpath)
-		} else {
-			tabtitle = info.PDoc.Name
-		}
-		if info.IsPkg {
-			title = "Package " + tabtitle
-		} else {
-			title = "Command " + tabtitle
-		}
+		tabtitle = info.PDoc.Name
 	default:
 		tabtitle = info.Dirname
-		title = "Directory " + tabtitle
+		title = "Directory "
 		if *showTimestamps {
 			subtitle = "Last update: " + info.DirTime.String()
 		}
 	}
+	if title == "" {
+		if info.IsMain {
+			// assume that the directory name is the command name
+			_, tabtitle = pathpkg.Split(relpath)
+			title = "Command "
+		} else {
+			title = "Package "
+		}
+	}
+	title += tabtitle
 
 	// special cases for top-level package/command directories
 	switch tabtitle {

src/cmd/godoc/parser.go

@@ -2,10 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This file contains support functions for parsing .go files.
-// Similar functionality is found in package go/parser but the
-// functions here operate using godoc's file system fs instead
-// of calling the OS's file operations directly.
+// This file contains support functions for parsing .go files
+// accessed via godoc's file system fs.
 
 package main
 
@@ -13,7 +11,6 @@ import (
 	"go/ast"
 	"go/parser"
 	"go/token"
-	"os"
 	pathpkg "path"
 )
 
@@ -25,44 +22,16 @@ func parseFile(fset *token.FileSet, filename string, mode parser.Mode) (*ast.Fil
 	return parser.ParseFile(fset, filename, src, mode)
 }
 
-func parseFiles(fset *token.FileSet, filenames []string) (pkgs map[string]*ast.Package, first error) {
-	pkgs = make(map[string]*ast.Package)
-	for _, filename := range filenames {
-		file, err := parseFile(fset, filename, parser.ParseComments)
+func parseFiles(fset *token.FileSet, abspath string, localnames []string) (map[string]*ast.File, error) {
+	files := make(map[string]*ast.File)
+	for _, f := range localnames {
+		absname := pathpkg.Join(abspath, f)
+		file, err := parseFile(fset, absname, parser.ParseComments)
 		if err != nil {
-			if first == nil {
-				first = err
-			}
-			continue
+			return nil, err
 		}
-
-		name := file.Name.Name
-		pkg, found := pkgs[name]
-		if !found {
-			// TODO(gri) Use NewPackage here; reconsider ParseFiles API.
-			pkg = &ast.Package{Name: name, Files: make(map[string]*ast.File)}
-			pkgs[name] = pkg
-		}
-		pkg.Files[filename] = file
+		files[absname] = file
 	}
-	return
-}
-
-func parseDir(fset *token.FileSet, path string, filter func(os.FileInfo) bool) (map[string]*ast.Package, error) {
-	list, err := fs.ReadDir(path)
-	if err != nil {
-		return nil, err
-	}
-
-	filenames := make([]string, len(list))
-	i := 0
-	for _, d := range list {
-		if filter == nil || filter(d) {
-			filenames[i] = pathpkg.Join(path, d.Name())
-			i++
-		}
-	}
-	filenames = filenames[0:i]
-
-	return parseFiles(fset, filenames)
+
+	return files, nil
 }

src/cmd/gofmt/doc.go

@@ -72,6 +72,6 @@ To convert the package tree from explicit slice upper bounds to implicit ones:
 
 	gofmt -r 'α[β:len(α)] -> α[β:]' -w $GOROOT/src/pkg
 */
-package documentation
+package main
 
 // BUG(rsc): The implementation of -r is a bit slow.

src/cmd/ld/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 Ld is the portable code for a modified version of the Plan 9 linker.  The original is documented at
@@ -70,4 +72,4 @@ Options new in this version:
 		calls, not false positives caused by dead temporaries stored in
 		the current function call.
 */
-package documentation
+package main

src/cmd/nm/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 Nm is a version of the Plan 9 nm command.  The original is documented at
@@ -18,4 +20,4 @@ Usage:
 	go tool nm [-aghnsTu] file
 
 */
-package documentation
+package main

src/cmd/pack/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 Pack is a variant of the Plan 9 ar tool.  The original is documented at
@@ -24,4 +26,4 @@ The new option 'P' causes pack to remove the given prefix
 from file names in the line number information in object files
 that are already stored in or added to the archive.
 */
-package documentation
+package main

src/cmd/prof/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 
 Prof is a rudimentary real-time profiler.
@@ -44,4 +46,4 @@ every 100ms until the program completes.
 It is installed as go tool prof and is architecture-independent.
 
 */
-package documentation
+package main

src/cmd/vet/doc.go

@@ -67,4 +67,4 @@ The other flags are:
 			-printfuncs=Warn:1,Warnf:1
 
 */
-package documentation
+package main

src/cmd/yacc/doc.go

@@ -48,4 +48,4 @@ referenced by yacc's generated code.  Setting it to distinct values
 allows multiple grammars to be placed in a single package.
 
 */
-package documentation
+package main

src/pkg/exp/ebnflint/doc.go

@@ -19,4 +19,4 @@ The --start flag specifies the name of the start production for
 the grammar; it defaults to "Start".
 
 */
-package documentation
+package main

src/pkg/exp/gotype/doc.go

@@ -58,6 +58,6 @@ To verify the output of a pipe:
 	echo "package foo" | gotype
 
 */
-package documentation
+package main
 
 // BUG(gri): At the moment, only single-file scope analysis is performed.