// TestLineComments, using a simple test case, checks that consequtive line
// comments are properly terminated with a newline even if the AST position
// information is incorrect.
//
func TestLineComments(t *testing.T) {
	const src = `// comment 1
	// comment 2
	// comment 3
	package main
	`

	fset := token.NewFileSet()
	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
	if err != nil {
		panic(err) // error in test
	}

	var buf bytes.Buffer
	fset = token.NewFileSet() // use the wrong file set
	Fprint(&buf, fset, f)

	nlines := 0
	for _, ch := range buf.Bytes() {
		if ch == '\n' {
			nlines++
		}
	}

	const expected = 3
	if nlines < expected {
		t.Errorf("got %d, expected %d\n", nlines, expected)
		t.Errorf("result:\n%s", buf.Bytes())
	}
}
func TestFilterDuplicates(t *testing.T) {
	// parse input
	fset := token.NewFileSet()
	file, err := parser.ParseFile(fset, "", input, 0)
	if err != nil {
		t.Fatal(err)
	}

	// create package
	files := map[string]*ast.File{"": file}
	pkg, err := ast.NewPackage(fset, files, nil, nil)
	if err != nil {
		t.Fatal(err)
	}

	// filter
	merged := ast.MergePackageFiles(pkg, ast.FilterFuncDuplicates)

	// pretty-print
	var buf bytes.Buffer
	if err := format.Node(&buf, fset, merged); err != nil {
		t.Fatal(err)
	}
	output := buf.String()

	if output != golden {
		t.Errorf("incorrect output:\n%s", output)
	}
}
func ExampleScanner_Scan() {
	// src is the input that we want to tokenize.
	src := []byte("cos(x) + 1i*sin(x) // Euler")

	// Initialize the scanner.
	var s scanner.Scanner
	fset := token.NewFileSet()                      // positions are relative to fset
	file := fset.AddFile("", fset.Base(), len(src)) // register input "file"
	s.Init(file, src, nil /* no error handler */, scanner.ScanComments)

	// Repeated calls to Scan yield the token sequence found in the input.
	for {
		pos, tok, lit := s.Scan()
		if tok == token.EOF {
			break
		}
		fmt.Printf("%s\t%s\t%q\n", fset.Position(pos), tok, lit)
	}

	// output:
	// 1:1	IDENT	"cos"
	// 1:4	(	""
	// 1:5	IDENT	"x"
	// 1:6	)	""
	// 1:8	+	""
	// 1:10	IMAG	"1i"
	// 1:12	*	""
	// 1:13	IDENT	"sin"
	// 1:16	(	""
	// 1:17	IDENT	"x"
	// 1:18	)	""
	// 1:20	;	"\n"
	// 1:20	COMMENT	"// Euler"
}
func TestExamples(t *testing.T) {
	fset := token.NewFileSet()
	file, err := parser.ParseFile(fset, "test.go", strings.NewReader(exampleTestFile), parser.ParseComments)
	if err != nil {
		t.Fatal(err)
	}
	for i, e := range doc.Examples(file) {
		c := exampleTestCases[i]
		if e.Name != c.Name {
			t.Errorf("got Name == %q, want %q", e.Name, c.Name)
		}
		if w := c.Play; w != "" {
			var g string // hah
			if e.Play == nil {
				g = "<nil>"
			} else {
				var buf bytes.Buffer
				if err := format.Node(&buf, fset, e.Play); err != nil {
					t.Fatal(err)
				}
				g = buf.String()
			}
			if g != w {
				t.Errorf("%s: got Play == %q, want %q", c.Name, g, w)
			}
		}
		if g, w := e.Output, c.Output; g != w {
			t.Errorf("%s: got Output == %q, want %q", c.Name, g, w)
		}
	}
}
Exemple #5
0
// Read reads the index from r into x; x must not be nil.
// If r does not also implement io.ByteReader, it will be wrapped in a bufio.Reader.
func (x *Index) Read(r io.Reader) error {
	// We use the ability to read bytes as a plausible surrogate for buffering.
	if _, ok := r.(io.ByteReader); !ok {
		r = bufio.NewReader(r)
	}
	var fx fileIndex
	if err := fx.Read(r); err != nil {
		return err
	}
	x.words = fx.Words
	x.alts = fx.Alts
	x.snippets = fx.Snippets
	if fx.Fulltext {
		x.fset = token.NewFileSet()
		decode := func(x interface{}) error {
			return gob.NewDecoder(r).Decode(x)
		}
		if err := x.fset.Read(decode); err != nil {
			return err
		}
		x.suffixes = new(suffixarray.Index)
		if err := x.suffixes.Read(r); err != nil {
			return err
		}
	}
	return nil
}
func BenchmarkParse(b *testing.B) {
	b.SetBytes(int64(len(src)))
	for i := 0; i < b.N; i++ {
		if _, err := ParseFile(token.NewFileSet(), "", src, ParseComments); err != nil {
			b.Fatalf("benchmark failed due to parse error: %s", err)
		}
	}
}
Exemple #7
0
func pkgName(filename string) string {
	// use a new file set each time in order to not pollute the indexer's
	// file set (which must stay in sync with the concatenated source code)
	file, err := parser.ParseFile(token.NewFileSet(), filename, nil, parser.PackageClauseOnly)
	if err != nil || file == nil {
		return ""
	}
	return file.Name.Name
}
func parseFunc(filename, functionname string) (fun *ast.FuncDecl, fset *token.FileSet) {
	fset = token.NewFileSet()
	if file, err := parser.ParseFile(fset, filename, nil, 0); err == nil {
		for _, d := range file.Decls {
			if f, ok := d.(*ast.FuncDecl); ok && f.Name.Name == functionname {
				fun = f
				return
			}
		}
	}
	panic("function not found")
}
Exemple #9
0
func TestErrors(t *testing.T) {
	fsetErrs = token.NewFileSet()
	list, err := ioutil.ReadDir(testdata)
	if err != nil {
		t.Fatal(err)
	}
	for _, fi := range list {
		name := fi.Name()
		if !fi.IsDir() && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".src") {
			checkErrors(t, filepath.Join(testdata, name), nil)
		}
	}
}
Exemple #10
0
func main() {
	flag.Parse()
	fset := token.NewFileSet()
	nheadings := 0
	err := filepath.Walk(*root, func(path string, fi os.FileInfo, err error) error {
		if !fi.IsDir() {
			return nil
		}
		pkgs, err := parser.ParseDir(fset, path, isGoFile, parser.ParseComments)
		if err != nil {
			if *verbose {
				fmt.Fprintln(os.Stderr, err)
			}
			return nil
		}
		for _, pkg := range pkgs {
			d := doc.New(pkg, path, doc.Mode(0))
			list := appendHeadings(nil, d.Doc)
			for _, d := range d.Consts {
				list = appendHeadings(list, d.Doc)
			}
			for _, d := range d.Types {
				list = appendHeadings(list, d.Doc)
			}
			for _, d := range d.Vars {
				list = appendHeadings(list, d.Doc)
			}
			for _, d := range d.Funcs {
				list = appendHeadings(list, d.Doc)
			}
			if len(list) > 0 {
				// directories may contain multiple packages;
				// print path and package name
				fmt.Printf("%s (package %s)\n", path, pkg.Name)
				for _, h := range list {
					fmt.Printf("\t%s\n", h)
				}
				nheadings += len(list)
			}
		}
		return nil
	})
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	fmt.Println(nheadings, "headings found")
}
func BenchmarkScan(b *testing.B) {
	b.StopTimer()
	fset := token.NewFileSet()
	file := fset.AddFile("", fset.Base(), len(source))
	var s Scanner
	b.StartTimer()
	for i := 0; i < b.N; i++ {
		s.Init(file, source, nil, ScanComments)
		for {
			_, tok, _ := s.Scan()
			if tok == token.EOF {
				break
			}
		}
	}
}
Exemple #12
0
// tokenSelection returns, as a selection, the sequence of
// consecutive occurrences of token sel in the Go src text.
//
func tokenSelection(src []byte, sel token.Token) Selection {
	var s scanner.Scanner
	fset := token.NewFileSet()
	file := fset.AddFile("", fset.Base(), len(src))
	s.Init(file, src, nil, scanner.ScanComments)
	return func() (seg Segment) {
		for {
			pos, tok, lit := s.Scan()
			if tok == token.EOF {
				break
			}
			offs := file.Offset(pos)
			if tok == sel {
				seg = Segment{offs, offs + len(lit)}
				break
			}
		}
		return
	}
}
Exemple #13
0
// newDirectory creates a new package directory tree with at most maxDepth
// levels, anchored at root. The result tree is pruned such that it only
// contains directories that contain package files or that contain
// subdirectories containing package files (transitively). If a non-nil
// pathFilter is provided, directory paths additionally must be accepted
// by the filter (i.e., pathFilter(path) must be true). If a value >= 0 is
// provided for maxDepth, nodes at larger depths are pruned as well; they
// are assumed to contain package files even if their contents are not known
// (i.e., in this case the tree may contain directories w/o any package files).
//
func newDirectory(root string, maxDepth int) *Directory {
	// The root could be a symbolic link so use Stat not Lstat.
	d, err := fs.Stat(root)
	// If we fail here, report detailed error messages; otherwise
	// is is hard to see why a directory tree was not built.
	switch {
	case err != nil:
		log.Printf("newDirectory(%s): %s", root, err)
		return nil
	case !isPkgDir(d):
		log.Printf("newDirectory(%s): not a package directory", root)
		return nil
	}
	if maxDepth < 0 {
		maxDepth = 1e6 // "infinity"
	}
	b := treeBuilder{maxDepth}
	// the file set provided is only for local parsing, no position
	// information escapes and thus we don't need to save the set
	return b.newDirTree(token.NewFileSet(), root, d.Name(), 0)
}
Exemple #14
0
// ParseExpr is a convenience function for obtaining the AST of an expression x.
// The position information recorded in the AST is undefined. The filename used
// in error messages is the empty string.
//
func ParseExpr(x string) (ast.Expr, error) {
	var p parser
	p.init(token.NewFileSet(), "", []byte(x), 0)

	// Set up pkg-level scopes to avoid nil-pointer errors.
	// This is not needed for a correct expression x as the
	// parser will be ok with a nil topScope, but be cautious
	// in case of an erroneous x.
	p.openScope()
	p.pkgScope = p.topScope
	e := p.parseRhsOrType()
	p.closeScope()
	assert(p.topScope == nil, "unbalanced scopes")

	if p.errors.Len() > 0 {
		p.errors.Sort()
		return nil, p.errors.Err()
	}

	return e, nil
}
// This example demonstrates how to inspect the AST of a Go program.
func ExampleInspect() {
	// src is the input for which we want to inspect the AST.
	src := `
package p
const c = 1.0
var X = f(3.14)*2 + c
`

	// Create the AST by parsing src.
	fset := token.NewFileSet() // positions are relative to fset
	f, err := parser.ParseFile(fset, "src.go", src, 0)
	if err != nil {
		panic(err)
	}

	// Inspect the AST and print all identifiers and literals.
	ast.Inspect(f, func(n ast.Node) bool {
		var s string
		switch x := n.(type) {
		case *ast.BasicLit:
			s = x.Value
		case *ast.Ident:
			s = x.Name
		}
		if s != "" {
			fmt.Printf("%s:\t%s\n", fset.Position(n.Pos()), s)
		}
		return true
	})

	// output:
	// src.go:2:9:	p
	// src.go:3:7:	c
	// src.go:3:11:	1.0
	// src.go:4:5:	X
	// src.go:4:9:	f
	// src.go:4:11:	3.14
	// src.go:4:17:	2
	// src.go:4:21:	c
}
func ExampleParseFile() {
	fset := token.NewFileSet() // positions are relative to fset

	// Parse the file containing this very example
	// but stop after processing the imports.
	f, err := parser.ParseFile(fset, "example_test.go", nil, parser.ImportsOnly)
	if err != nil {
		fmt.Println(err)
		return
	}

	// Print the imports from the file's AST.
	for _, s := range f.Imports {
		fmt.Println(s.Path.Value)
	}

	// output:
	//
	// "fmt"
	// "go/parser"
	// "go/token"
}
func BenchmarkScanFile(b *testing.B) {
	b.StopTimer()
	const filename = "scanner.go"
	src, err := ioutil.ReadFile(filename)
	if err != nil {
		panic(err)
	}
	fset := token.NewFileSet()
	file := fset.AddFile(filename, fset.Base(), len(src))
	b.SetBytes(int64(len(src)))
	var s Scanner
	b.StartTimer()
	for i := 0; i < b.N; i++ {
		s.Init(file, src, nil, ScanComments)
		for {
			_, tok, _ := s.Scan()
			if tok == token.EOF {
				break
			}
		}
	}
}
func TestCommentMap(t *testing.T) {
	fset := token.NewFileSet()
	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
	if err != nil {
		t.Fatal(err)
	}
	cmap := NewCommentMap(fset, f, f.Comments)

	// very correct association of comments
	for n, list := range cmap {
		key := fmt.Sprintf("%2d: %T", fset.Position(n.Pos()).Line, n)
		got := ctext(list)
		want := res[key]
		if got != want {
			t.Errorf("%s: got %q; want %q", key, got, want)
		}
	}

	// verify that no comments got lost
	if n := len(cmap.Comments()); n != len(f.Comments) {
		t.Errorf("got %d comment groups in map; want %d", n, len(f.Comments))
	}

	// support code to update test:
	// set genMap to true to generate res map
	const genMap = false
	if genMap {
		out := make([]string, 0, len(cmap))
		for n, list := range cmap {
			out = append(out, fmt.Sprintf("\t\"%2d: %T\":\t%q,", fset.Position(n.Pos()).Line, n, ctext(list)))
		}
		sort.Strings(out)
		for _, s := range out {
			fmt.Println(s)
		}
	}
}
Exemple #19
0
func test(t *testing.T, mode Mode) {
	// determine file filter
	filter := isGoFile
	if *files != "" {
		rx, err := regexp.Compile(*files)
		if err != nil {
			t.Fatal(err)
		}
		filter = func(fi os.FileInfo) bool {
			return isGoFile(fi) && rx.MatchString(fi.Name())
		}
	}

	// get packages
	fset := token.NewFileSet()
	pkgs, err := parser.ParseDir(fset, dataDir, filter, parser.ParseComments)
	if err != nil {
		t.Fatal(err)
	}

	// test packages
	for _, pkg := range pkgs {
		importpath := dataDir + "/" + pkg.Name
		doc := New(pkg, importpath, mode)

		// golden files always use / in filenames - canonicalize them
		for i, filename := range doc.Filenames {
			doc.Filenames[i] = filepath.ToSlash(filename)
		}

		// print documentation
		var buf bytes.Buffer
		if err := templateTxt.Execute(&buf, bundle{doc, fset}); err != nil {
			t.Error(err)
			continue
		}
		got := buf.Bytes()

		// update golden file if necessary
		golden := filepath.Join(dataDir, fmt.Sprintf("%s.%d.golden", pkg.Name, mode))
		if *update {
			err := ioutil.WriteFile(golden, got, 0644)
			if err != nil {
				t.Error(err)
			}
			continue
		}

		// get golden file
		want, err := ioutil.ReadFile(golden)
		if err != nil {
			t.Error(err)
			continue
		}

		// compare
		if !bytes.Equal(got, want) {
			t.Errorf("package %s\n\tgot:\n%s\n\twant:\n%s", pkg.Name, got, want)
		}
	}
}
Exemple #20
0
// NewIndex creates a new index for the .go files
// in the directories given by dirnames.
//
func NewIndex(dirnames <-chan string, fulltextIndex bool, throttle float64) *Index {
	var x Indexer
	th := NewThrottle(throttle, 100*time.Millisecond) // run at least 0.1s at a time

	// initialize Indexer
	// (use some reasonably sized maps to start)
	x.fset = token.NewFileSet()
	x.packages = make(map[string]*Pak, 256)
	x.words = make(map[string]*IndexResult, 8192)

	// index all files in the directories given by dirnames
	for dirname := range dirnames {
		list, err := fs.ReadDir(dirname)
		if err != nil {
			continue // ignore this directory
		}
		for _, f := range list {
			if !f.IsDir() {
				x.visitFile(dirname, f, fulltextIndex)
			}
			th.Throttle()
		}
	}

	if !fulltextIndex {
		// the file set, the current file, and the sources are
		// not needed after indexing if no text index is built -
		// help GC and clear them
		x.fset = nil
		x.sources.Reset()
		x.current = nil // contains reference to fset!
	}

	// for each word, reduce the RunLists into a LookupResult;
	// also collect the word with its canonical spelling in a
	// word list for later computation of alternative spellings
	words := make(map[string]*LookupResult)
	var wlist RunList
	for w, h := range x.words {
		decls := reduce(h.Decls)
		others := reduce(h.Others)
		words[w] = &LookupResult{
			Decls:  decls,
			Others: others,
		}
		wlist = append(wlist, &wordPair{canonical(w), w})
		th.Throttle()
	}
	x.stats.Words = len(words)

	// reduce the word list {canonical(w), w} into
	// a list of AltWords runs {canonical(w), {w}}
	alist := wlist.reduce(lessWordPair, newAltWords)

	// convert alist into a map of alternative spellings
	alts := make(map[string]*AltWords)
	for i := 0; i < len(alist); i++ {
		a := alist[i].(*AltWords)
		alts[a.Canon] = a
	}

	// create text index
	var suffixes *suffixarray.Index
	if fulltextIndex {
		suffixes = suffixarray.New(x.sources.Bytes())
	}

	return &Index{x.fset, suffixes, words, alts, x.snippets, x.stats}
}
	"newgo/ast"
	"newgo/parser"
	"newgo/token"
	"path/filepath"
	"testing"
	"time"
)

const (
	dataDir  = "testdata"
	tabwidth = 8
)

var update = flag.Bool("update", false, "update golden files")

var fset = token.NewFileSet()

type checkMode uint

const (
	export checkMode = 1 << iota
	rawFormat
	idempotent
)

// format parses src, prints the corresponding AST, verifies the resulting
// src is syntactically correct, and returns the resulting src or an error
// if any.
func format(src []byte, mode checkMode) ([]byte, error) {
	// parse src
	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
Exemple #22
0
// getPageInfo returns the PageInfo for a package directory abspath. If the
// parameter genAST is set, an AST containing only the package exports is
// 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 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 {
	info := &PageInfo{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
	// 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.ImportDir.
	ctxt := build.Default
	ctxt.IsAbsPath = pathpkg.IsAbs
	ctxt.ReadDir = fsReadDir
	ctxt.OpenFile = fsOpenFile
	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 info
	}

	// 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 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 info
		}

		// ignore any errors - they are due to unresolved identifiers
		pkg, _ := ast.NewPackage(fset, files, poorMansImporter, nil)

		// extract package documentation
		info.FSet = fset
		if mode&showSource == 0 {
			// show extracted documentation
			var m doc.Mode
			if mode&noFiltering != 0 {
				m = doc.AllDecls
			}
			if mode&allMethods != 0 {
				m |= doc.AllMethods
			}
			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)

			// collect any notes that we want to show
			if info.PDoc.Notes != nil {
				// could regexp.Compile only once per godoc, but probably not worth it
				if rx, err := regexp.Compile(*notes); err == nil {
					for m, n := range info.PDoc.Notes {
						if rx.MatchString(m) {
							if info.Notes == nil {
								info.Notes = make(map[string][]*doc.Note)
							}
							info.Notes[m] = n
						}
					}
				}
			}

		} else {
			// show source code
			// TODO(gri) Consider eliminating export filtering in this mode,
			//           or perhaps eliminating the mode altogether.
			if mode&noFiltering == 0 {
				packageExports(fset, pkg)
			}
			info.PAst = ast.MergePackageFiles(pkg, 0)
		}
		info.IsMain = pkgname == "main"
	}

	// get directory information, if any
	var dir *Directory
	var timestamp time.Time
	if tree, ts := fsTree.get(); tree != nil && tree.(*Directory) != nil {
		// directory tree is present; lookup respective directory
		// (may still fail if the file system was updated and the
		// new directory tree has not yet been computed)
		dir = tree.(*Directory).lookup(abspath)
		timestamp = ts
	}
	if dir == nil {
		// no directory tree present (too early after startup or
		// command-line mode); compute one level for this page
		// note: cannot use path filter here because in general
		//       it doesn't contain the fsTree path
		dir = newDirectory(abspath, 1)
		timestamp = time.Now()
	}
	info.Dirs = dir.listing(true)
	info.DirTime = timestamp
	info.DirFlat = mode&flatDir != 0

	return info
}
Exemple #23
0
// Source formats src in canonical gofmt style and returns the result
// or an (I/O or syntax) error. src is expected to be a syntactically
// correct Go source file, or a list of Go declarations or statements.
//
// If src is a partial source file, the leading and trailing space of src
// is applied to the result (such that it has the same leading and trailing
// space as src), and the result is indented by the same amount as the first
// line of src containing code. Imports are not sorted for partial source files.
//
func Source(src []byte) ([]byte, error) {
	fset := token.NewFileSet()
	node, err := parse(fset, src)
	if err != nil {
		return nil, err
	}

	var buf bytes.Buffer
	if file, ok := node.(*ast.File); ok {
		// Complete source file.
		ast.SortImports(fset, file)
		err := config.Fprint(&buf, fset, file)
		if err != nil {
			return nil, err
		}

	} else {
		// Partial source file.
		// Determine and prepend leading space.
		i, j := 0, 0
		for j < len(src) && isSpace(src[j]) {
			if src[j] == '\n' {
				i = j + 1 // index of last line in leading space
			}
			j++
		}
		buf.Write(src[:i])

		// Determine indentation of first code line.
		// Spaces are ignored unless there are no tabs,
		// in which case spaces count as one tab.
		indent := 0
		hasSpace := false
		for _, b := range src[i:j] {
			switch b {
			case ' ':
				hasSpace = true
			case '\t':
				indent++
			}
		}
		if indent == 0 && hasSpace {
			indent = 1
		}

		// Format the source.
		cfg := config
		cfg.Indent = indent
		err := cfg.Fprint(&buf, fset, node)
		if err != nil {
			return nil, err
		}

		// Determine and append trailing space.
		i = len(src)
		for i > 0 && isSpace(src[i-1]) {
			i--
		}
		buf.Write(src[i:])
	}

	return buf.Bytes(), nil
}
Exemple #24
0
// Import returns details about the Go package named by the import path,
// interpreting local import paths relative to the srcDir directory.
// If the path is a local import path naming a package that can be imported
// using a standard import path, the returned package will set p.ImportPath
// to that path.
//
// In the directory containing the package, .go, .c, .h, and .s files are
// considered part of the package except for:
//
//	- .go files in package documentation
//	- files starting with _ or . (likely editor temporary files)
//	- files with build constraints not satisfied by the context
//
// If an error occurs, Import returns a non-nil error and a non-nil
// *Package containing partial information.
//
func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Package, error) {
	p := &Package{
		ImportPath: path,
	}
	if path == "" {
		return p, fmt.Errorf("import %q: invalid import path", path)
	}

	var pkga string
	var pkgerr error
	switch ctxt.Compiler {
	case "gccgo":
		dir, elem := pathpkg.Split(p.ImportPath)
		pkga = "pkg/gccgo_" + ctxt.GOOS + "_" + ctxt.GOARCH + "/" + dir + "lib" + elem + ".a"
	case "gc":
		suffix := ""
		if ctxt.InstallSuffix != "" {
			suffix = "_" + ctxt.InstallSuffix
		}
		pkga = "pkg/" + ctxt.GOOS + "_" + ctxt.GOARCH + suffix + "/" + p.ImportPath + ".a"
	default:
		// Save error for end of function.
		pkgerr = fmt.Errorf("import %q: unknown compiler %q", path, ctxt.Compiler)
	}

	binaryOnly := false
	if IsLocalImport(path) {
		pkga = "" // local imports have no installed path
		if srcDir == "" {
			return p, fmt.Errorf("import %q: import relative to unknown directory", path)
		}
		if !ctxt.isAbsPath(path) {
			p.Dir = ctxt.joinPath(srcDir, path)
		}
		// Determine canonical import path, if any.
		if ctxt.GOROOT != "" {
			root := ctxt.joinPath(ctxt.GOROOT, "src", "pkg")
			if sub, ok := ctxt.hasSubdir(root, p.Dir); ok {
				p.Goroot = true
				p.ImportPath = sub
				p.Root = ctxt.GOROOT
				goto Found
			}
		}
		all := ctxt.gopath()
		for i, root := range all {
			rootsrc := ctxt.joinPath(root, "src")
			if sub, ok := ctxt.hasSubdir(rootsrc, p.Dir); ok {
				// We found a potential import path for dir,
				// but check that using it wouldn't find something
				// else first.
				if ctxt.GOROOT != "" {
					if dir := ctxt.joinPath(ctxt.GOROOT, "src", "pkg", sub); ctxt.isDir(dir) {
						p.ConflictDir = dir
						goto Found
					}
				}
				for _, earlyRoot := range all[:i] {
					if dir := ctxt.joinPath(earlyRoot, "src", sub); ctxt.isDir(dir) {
						p.ConflictDir = dir
						goto Found
					}
				}

				// sub would not name some other directory instead of this one.
				// Record it.
				p.ImportPath = sub
				p.Root = root
				goto Found
			}
		}
		// It's okay that we didn't find a root containing dir.
		// Keep going with the information we have.
	} else {
		if strings.HasPrefix(path, "/") {
			return p, fmt.Errorf("import %q: cannot import absolute path", path)
		}

		// tried records the location of unsuccessful package lookups
		var tried struct {
			goroot string
			gopath []string
		}

		// Determine directory from import path.
		if ctxt.GOROOT != "" {
			dir := ctxt.joinPath(ctxt.GOROOT, "src", "pkg", path)
			isDir := ctxt.isDir(dir)
			binaryOnly = !isDir && mode&AllowBinary != 0 && pkga != "" && ctxt.isFile(ctxt.joinPath(ctxt.GOROOT, pkga))
			if isDir || binaryOnly {
				p.Dir = dir
				p.Goroot = true
				p.Root = ctxt.GOROOT
				goto Found
			}
			tried.goroot = dir
		}
		for _, root := range ctxt.gopath() {
			dir := ctxt.joinPath(root, "src", path)
			isDir := ctxt.isDir(dir)
			binaryOnly = !isDir && mode&AllowBinary != 0 && pkga != "" && ctxt.isFile(ctxt.joinPath(root, pkga))
			if isDir || binaryOnly {
				p.Dir = dir
				p.Root = root
				goto Found
			}
			tried.gopath = append(tried.gopath, dir)
		}

		// package was not found
		var paths []string
		if tried.goroot != "" {
			paths = append(paths, fmt.Sprintf("\t%s (from $GOROOT)", tried.goroot))
		} else {
			paths = append(paths, "\t($GOROOT not set)")
		}
		var i int
		var format = "\t%s (from $GOPATH)"
		for ; i < len(tried.gopath); i++ {
			if i > 0 {
				format = "\t%s"
			}
			paths = append(paths, fmt.Sprintf(format, tried.gopath[i]))
		}
		if i == 0 {
			paths = append(paths, "\t($GOPATH not set)")
		}
		return p, fmt.Errorf("cannot find package %q in any of:\n%s", path, strings.Join(paths, "\n"))
	}

Found:
	if p.Root != "" {
		if p.Goroot {
			p.SrcRoot = ctxt.joinPath(p.Root, "src", "pkg")
		} else {
			p.SrcRoot = ctxt.joinPath(p.Root, "src")
		}
		p.PkgRoot = ctxt.joinPath(p.Root, "pkg")
		p.BinDir = ctxt.joinPath(p.Root, "bin")
		if pkga != "" {
			p.PkgObj = ctxt.joinPath(p.Root, pkga)
		}
	}

	if mode&FindOnly != 0 {
		return p, pkgerr
	}
	if binaryOnly && (mode&AllowBinary) != 0 {
		return p, pkgerr
	}

	dirs, err := ctxt.readDir(p.Dir)
	if err != nil {
		return p, err
	}

	var Sfiles []string // files with ".S" (capital S)
	var firstFile string
	imported := make(map[string][]token.Position)
	testImported := make(map[string][]token.Position)
	xTestImported := make(map[string][]token.Position)
	allTags := make(map[string]bool)
	fset := token.NewFileSet()
	for _, d := range dirs {
		if d.IsDir() {
			continue
		}

		name := d.Name()
		ext := nameExt(name)

		match, data, filename, err := ctxt.matchFile(p.Dir, name, true, allTags)
		if err != nil {
			return p, err
		}
		if !match {
			if ext == ".go" {
				p.IgnoredGoFiles = append(p.IgnoredGoFiles, name)
			}
			continue
		}

		// Going to save the file.  For non-Go files, can stop here.
		switch ext {
		case ".c":
			p.CFiles = append(p.CFiles, name)
			continue
		case ".cc", ".cpp", ".cxx":
			p.CXXFiles = append(p.CXXFiles, name)
			continue
		case ".h", ".hh", ".hpp", ".hxx":
			p.HFiles = append(p.HFiles, name)
			continue
		case ".s":
			p.SFiles = append(p.SFiles, name)
			continue
		case ".S":
			Sfiles = append(Sfiles, name)
			continue
		case ".swig":
			p.SwigFiles = append(p.SwigFiles, name)
			continue
		case ".swigcxx":
			p.SwigCXXFiles = append(p.SwigCXXFiles, name)
			continue
		case ".syso":
			// binary objects to add to package archive
			// Likely of the form foo_windows.syso, but
			// the name was vetted above with goodOSArchFile.
			p.SysoFiles = append(p.SysoFiles, name)
			continue
		}

		pf, err := parser.ParseFile(fset, filename, data, parser.ImportsOnly|parser.ParseComments)
		if err != nil {
			return p, err
		}

		pkg := pf.Name.Name
		if pkg == "documentation" {
			p.IgnoredGoFiles = append(p.IgnoredGoFiles, name)
			continue
		}

		isTest := strings.HasSuffix(name, "_test.go")
		isXTest := false
		if isTest && strings.HasSuffix(pkg, "_test") {
			isXTest = true
			pkg = pkg[:len(pkg)-len("_test")]
		}

		if p.Name == "" {
			p.Name = pkg
			firstFile = name
		} else if pkg != p.Name {
			return p, fmt.Errorf("found packages %s (%s) and %s (%s) in %s", p.Name, firstFile, pkg, name, p.Dir)
		}
		if pf.Doc != nil && p.Doc == "" {
			p.Doc = doc.Synopsis(pf.Doc.Text())
		}

		// Record imports and information about cgo.
		isCgo := false
		for _, decl := range pf.Decls {
			d, ok := decl.(*ast.GenDecl)
			if !ok {
				continue
			}
			for _, dspec := range d.Specs {
				spec, ok := dspec.(*ast.ImportSpec)
				if !ok {
					continue
				}
				quoted := spec.Path.Value
				path, err := strconv.Unquote(quoted)
				if err != nil {
					log.Panicf("%s: parser returned invalid quoted string: <%s>", filename, quoted)
				}
				if isXTest {
					xTestImported[path] = append(xTestImported[path], fset.Position(spec.Pos()))
				} else if isTest {
					testImported[path] = append(testImported[path], fset.Position(spec.Pos()))
				} else {
					imported[path] = append(imported[path], fset.Position(spec.Pos()))
				}
				if path == "C" {
					if isTest {
						return p, fmt.Errorf("use of cgo in test %s not supported", filename)
					}
					cg := spec.Doc
					if cg == nil && len(d.Specs) == 1 {
						cg = d.Doc
					}
					if cg != nil {
						if err := ctxt.saveCgo(filename, p, cg); err != nil {
							return p, err
						}
					}
					isCgo = true
				}
			}
		}
		if isCgo {
			allTags["cgo"] = true
			if ctxt.CgoEnabled {
				p.CgoFiles = append(p.CgoFiles, name)
			} else {
				p.IgnoredGoFiles = append(p.IgnoredGoFiles, name)
			}
		} else if isXTest {
			p.XTestGoFiles = append(p.XTestGoFiles, name)
		} else if isTest {
			p.TestGoFiles = append(p.TestGoFiles, name)
		} else {
			p.GoFiles = append(p.GoFiles, name)
		}
	}
	if len(p.GoFiles)+len(p.CgoFiles)+len(p.TestGoFiles)+len(p.XTestGoFiles) == 0 {
		return p, &NoGoError{p.Dir}
	}

	for tag := range allTags {
		p.AllTags = append(p.AllTags, tag)
	}
	sort.Strings(p.AllTags)

	p.Imports, p.ImportPos = cleanImports(imported)
	p.TestImports, p.TestImportPos = cleanImports(testImported)
	p.XTestImports, p.XTestImportPos = cleanImports(xTestImported)

	// add the .S files only if we are using cgo
	// (which means gcc will compile them).
	// The standard assemblers expect .s files.
	if len(p.CgoFiles) > 0 {
		p.SFiles = append(p.SFiles, Sfiles...)
		sort.Strings(p.SFiles)
	}

	return p, pkgerr
}
// This example shows what an AST looks like when printed for debugging.
func ExamplePrint() {
	// src is the input for which we want to print the AST.
	src := `
package main
func main() {
	println("Hello, World!")
}
`

	// Create the AST by parsing src.
	fset := token.NewFileSet() // positions are relative to fset
	f, err := parser.ParseFile(fset, "", src, 0)
	if err != nil {
		panic(err)
	}

	// Print the AST.
	ast.Print(fset, f)

	// output:
	//      0  *ast.File {
	//      1  .  Package: 2:1
	//      2  .  Name: *ast.Ident {
	//      3  .  .  NamePos: 2:9
	//      4  .  .  Name: "main"
	//      5  .  }
	//      6  .  Decls: []ast.Decl (len = 1) {
	//      7  .  .  0: *ast.FuncDecl {
	//      8  .  .  .  Name: *ast.Ident {
	//      9  .  .  .  .  NamePos: 3:6
	//     10  .  .  .  .  Name: "main"
	//     11  .  .  .  .  Obj: *ast.Object {
	//     12  .  .  .  .  .  Kind: func
	//     13  .  .  .  .  .  Name: "main"
	//     14  .  .  .  .  .  Decl: *(obj @ 7)
	//     15  .  .  .  .  }
	//     16  .  .  .  }
	//     17  .  .  .  Type: *ast.FuncType {
	//     18  .  .  .  .  Func: 3:1
	//     19  .  .  .  .  Params: *ast.FieldList {
	//     20  .  .  .  .  .  Opening: 3:10
	//     21  .  .  .  .  .  Closing: 3:11
	//     22  .  .  .  .  }
	//     23  .  .  .  }
	//     24  .  .  .  Body: *ast.BlockStmt {
	//     25  .  .  .  .  Lbrace: 3:13
	//     26  .  .  .  .  List: []ast.Stmt (len = 1) {
	//     27  .  .  .  .  .  0: *ast.ExprStmt {
	//     28  .  .  .  .  .  .  X: *ast.CallExpr {
	//     29  .  .  .  .  .  .  .  Fun: *ast.Ident {
	//     30  .  .  .  .  .  .  .  .  NamePos: 4:2
	//     31  .  .  .  .  .  .  .  .  Name: "println"
	//     32  .  .  .  .  .  .  .  }
	//     33  .  .  .  .  .  .  .  Lparen: 4:9
	//     34  .  .  .  .  .  .  .  Args: []ast.Expr (len = 1) {
	//     35  .  .  .  .  .  .  .  .  0: *ast.BasicLit {
	//     36  .  .  .  .  .  .  .  .  .  ValuePos: 4:10
	//     37  .  .  .  .  .  .  .  .  .  Kind: STRING
	//     38  .  .  .  .  .  .  .  .  .  Value: "\"Hello, World!\""
	//     39  .  .  .  .  .  .  .  .  }
	//     40  .  .  .  .  .  .  .  }
	//     41  .  .  .  .  .  .  .  Ellipsis: -
	//     42  .  .  .  .  .  .  .  Rparen: 4:25
	//     43  .  .  .  .  .  .  }
	//     44  .  .  .  .  .  }
	//     45  .  .  .  .  }
	//     46  .  .  .  .  Rbrace: 5:1
	//     47  .  .  .  }
	//     48  .  .  }
	//     49  .  }
	//     50  .  Scope: *ast.Scope {
	//     51  .  .  Objects: map[string]*ast.Object (len = 1) {
	//     52  .  .  .  "main": *(obj @ 11)
	//     53  .  .  }
	//     54  .  }
	//     55  .  Unresolved: []*ast.Ident (len = 1) {
	//     56  .  .  0: *(obj @ 29)
	//     57  .  }
	//     58  }
}