src/cmd/compile/internal/noder/import.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package noder

 import (
 	"errors"
 	"fmt"
 	"internal/buildcfg"
 	"os"
 	pathpkg "path"
 	"runtime"
 	"sort"
 	"strconv"
 	"strings"
 	"unicode"
 	"unicode/utf8"

 	"cmd/compile/internal/base"
 	"cmd/compile/internal/importer"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/syntax"
 	"cmd/compile/internal/typecheck"
 	"cmd/compile/internal/types"
 	"cmd/compile/internal/types2"
 	"cmd/internal/archive"
 	"cmd/internal/bio"
 	"cmd/internal/goobj"
 	"cmd/internal/objabi"
 	"cmd/internal/src"
 )

 // haveLegacyImports records whether we've imported any packages
 // without a new export data section. This is useful for experimenting
 // with new export data format designs, when you need to support
 // existing tests that manually compile files with inconsistent
 // compiler flags.
 var haveLegacyImports = false

 // newReadImportFunc is an extension hook for experimenting with new
 // export data formats. If a new export data payload was written out
 // for an imported package by overloading writeNewExportFunc, then
 // that payload will be mapped into memory and passed to
 // newReadImportFunc.
 var newReadImportFunc = func(data string, pkg1 *types.Pkg, env *types2.Context, packages map[string]*types2.Package) (pkg2 *types2.Package, err error) {
 	panic("unexpected new export data payload")
 }

 type gcimports struct {
 	ctxt     *types2.Context
 	packages map[string]*types2.Package
 }

 func (m *gcimports) Import(path string) (*types2.Package, error) {
 	return m.ImportFrom(path, "" /* no vendoring */, 0)
 }

 func (m *gcimports) ImportFrom(path, srcDir string, mode types2.ImportMode) (*types2.Package, error) {
 	if mode != 0 {
 		panic("mode must be 0")
 	}

 	_, pkg, err := readImportFile(path, typecheck.Target, m.ctxt, m.packages)
 	return pkg, err
 }

 func isDriveLetter(b byte) bool {
 	return 'a' <= b && b <= 'z' || 'A' <= b && b <= 'Z'
 }

 // is this path a local name? begins with ./ or ../ or /
 func islocalname(name string) bool {
 	return strings.HasPrefix(name, "/") ||
 		runtime.GOOS == "windows" && len(name) >= 3 && isDriveLetter(name[0]) && name[1] == ':' && name[2] == '/' ||
 		strings.HasPrefix(name, "./") || name == "." ||
 		strings.HasPrefix(name, "../") || name == ".."
 }

 func openPackage(path string) (*os.File, error) {
 	if islocalname(path) {
 		if base.Flag.NoLocalImports {
 			return nil, errors.New("local imports disallowed")
 		}

 		if base.Flag.Cfg.PackageFile != nil {
 			return os.Open(base.Flag.Cfg.PackageFile[path])
 		}

 		// try .a before .o.  important for building libraries:
 		// if there is an array.o in the array.a library,
 		// want to find all of array.a, not just array.o.
 		if file, err := os.Open(fmt.Sprintf("%s.a", path)); err == nil {
 			return file, nil
 		}
 		if file, err := os.Open(fmt.Sprintf("%s.o", path)); err == nil {
 			return file, nil
 		}
 		return nil, errors.New("file not found")
 	}

 	// local imports should be canonicalized already.
 	// don't want to see "encoding/../encoding/base64"
 	// as different from "encoding/base64".
 	if q := pathpkg.Clean(path); q != path {
 		return nil, fmt.Errorf("non-canonical import path %q (should be %q)", path, q)
 	}

 	if base.Flag.Cfg.PackageFile != nil {
 		return os.Open(base.Flag.Cfg.PackageFile[path])
 	}

 	for _, dir := range base.Flag.Cfg.ImportDirs {
 		if file, err := os.Open(fmt.Sprintf("%s/%s.a", dir, path)); err == nil {
 			return file, nil
 		}
 		if file, err := os.Open(fmt.Sprintf("%s/%s.o", dir, path)); err == nil {
 			return file, nil
 		}
 	}

 	if buildcfg.GOROOT != "" {
 		suffix := ""
 		if base.Flag.InstallSuffix != "" {
 			suffix = "_" + base.Flag.InstallSuffix
 		} else if base.Flag.Race {
 			suffix = "_race"
 		} else if base.Flag.MSan {
 			suffix = "_msan"
 		} else if base.Flag.ASan {
 			suffix = "_asan"
 		}

 		if file, err := os.Open(fmt.Sprintf("%s/pkg/%s_%s%s/%s.a", buildcfg.GOROOT, buildcfg.GOOS, buildcfg.GOARCH, suffix, path)); err == nil {
 			return file, nil
 		}
 		if file, err := os.Open(fmt.Sprintf("%s/pkg/%s_%s%s/%s.o", buildcfg.GOROOT, buildcfg.GOOS, buildcfg.GOARCH, suffix, path)); err == nil {
 			return file, nil
 		}
 	}
 	return nil, errors.New("file not found")
 }

 // myheight tracks the local package's height based on packages
 // imported so far.
 var myheight int

 // resolveImportPath resolves an import path as it appears in a Go
 // source file to the package's full path.
 func resolveImportPath(path string) (string, error) {
 	// The package name main is no longer reserved,
 	// but we reserve the import path "main" to identify
 	// the main package, just as we reserve the import
 	// path "math" to identify the standard math package.
 	if path == "main" {
 		return "", errors.New("cannot import \"main\"")
 	}

 	if base.Ctxt.Pkgpath != "" && path == base.Ctxt.Pkgpath {
 		return "", fmt.Errorf("import %q while compiling that package (import cycle)", path)
 	}

 	if mapped, ok := base.Flag.Cfg.ImportMap[path]; ok {
 		path = mapped
 	}

 	if islocalname(path) {
 		if path[0] == '/' {
 			return "", errors.New("import path cannot be absolute path")
 		}

 		prefix := base.Flag.D
 		if prefix == "" {
 			// Questionable, but when -D isn't specified, historically we
 			// resolve local import paths relative to the directory the
 			// compiler's current directory, not the respective source
 			// file's directory.
 			prefix = base.Ctxt.Pathname
 		}
 		path = pathpkg.Join(prefix, path)

 		if err := checkImportPath(path, true); err != nil {
 			return "", err
 		}
 	}

 	return path, nil
 }

 func importfile(decl *syntax.ImportDecl) *types.Pkg {
 	path, err := parseImportPath(decl.Path)
 	if err != nil {
 		base.Errorf("%s", err)
 		return nil
 	}

 	pkg, _, err := readImportFile(path, typecheck.Target, nil, nil)
 	if err != nil {
 		base.Errorf("%s", err)
 		return nil
 	}

 	if pkg != types.UnsafePkg && pkg.Height >= myheight {
 		myheight = pkg.Height + 1
 	}
 	return pkg
 }

 func parseImportPath(pathLit *syntax.BasicLit) (string, error) {
 	if pathLit.Kind != syntax.StringLit {
 		return "", errors.New("import path must be a string")
 	}

 	path, err := strconv.Unquote(pathLit.Value)
 	if err != nil {
 		return "", errors.New("import path must be a string")
 	}

 	if err := checkImportPath(path, false); err != nil {
 		return "", err
 	}

 	return path, err
 }

 // readImportFile reads the import file for the given package path and
 // returns its types.Pkg representation. If packages is non-nil, the
 // types2.Package representation is also returned.
 func readImportFile(path string, target *ir.Package, env *types2.Context, packages map[string]*types2.Package) (pkg1 *types.Pkg, pkg2 *types2.Package, err error) {
 	path, err = resolveImportPath(path)
 	if err != nil {
 		return
 	}

 	if path == "unsafe" {
 		pkg1, pkg2 = types.UnsafePkg, types2.Unsafe

 		// TODO(mdempsky): Investigate if this actually matters. Why would
 		// the linker or runtime care whether a package imported unsafe?
 		if !pkg1.Direct {
 			pkg1.Direct = true
 			target.Imports = append(target.Imports, pkg1)
 		}

 		return
 	}

 	pkg1 = types.NewPkg(path, "")
 	if packages != nil {
 		pkg2 = packages[path]
 		assert(pkg1.Direct == (pkg2 != nil && pkg2.Complete()))
 	}

 	if pkg1.Direct {
 		return
 	}
 	pkg1.Direct = true
 	target.Imports = append(target.Imports, pkg1)

 	f, err := openPackage(path)
 	if err != nil {
 		return
 	}
 	defer f.Close()

 	r, end, newsize, err := findExportData(f)
 	if err != nil {
 		return
 	}

 	if base.Debug.Export != 0 {
 		fmt.Printf("importing %s (%s)\n", path, f.Name())
 	}

 	if newsize != 0 {
 		// We have unified IR data. Map it, and feed to the importers.
 		end -= newsize
 		var data string
 		data, err = base.MapFile(r.File(), end, newsize)
 		if err != nil {
 			return
 		}

 		pkg2, err = newReadImportFunc(data, pkg1, env, packages)
 	} else {
 		// We only have old data. Oh well, fall back to the legacy importers.
 		haveLegacyImports = true

 		var c byte
 		switch c, err = r.ReadByte(); {
 		case err != nil:
 			return

 		case c != 'i':
 			// Indexed format is distinguished by an 'i' byte,
 			// whereas previous export formats started with 'c', 'd', or 'v'.
 			err = fmt.Errorf("unexpected package format byte: %v", c)
 			return
 		}

 		pos := r.Offset()

 		// Map string (and data) section into memory as a single large
 		// string. This reduces heap fragmentation and allows
 		// returning individual substrings very efficiently.
 		var data string
 		data, err = base.MapFile(r.File(), pos, end-pos)
 		if err != nil {
 			return
 		}

 		typecheck.ReadImports(pkg1, data)

 		if packages != nil {
 			pkg2, err = importer.ImportData(packages, data, path)
 			if err != nil {
 				return
 			}
 		}
 	}

 	err = addFingerprint(path, f, end)
 	return
 }

 // findExportData returns a *bio.Reader positioned at the start of the
 // binary export data section, and a file offset for where to stop
 // reading.
 func findExportData(f *os.File) (r *bio.Reader, end, newsize int64, err error) {
 	r = bio.NewReader(f)

 	// check object header
 	line, err := r.ReadString('\n')
 	if err != nil {
 		return
 	}

 	if line == "!<arch>\n" { // package archive
 		// package export block should be first
 		sz := int64(archive.ReadHeader(r.Reader, "__.PKGDEF"))
 		if sz <= 0 {
 			err = errors.New("not a package file")
 			return
 		}
 		end = r.Offset() + sz
 		line, err = r.ReadString('\n')
 		if err != nil {
 			return
 		}
 	} else {
 		// Not an archive; provide end of file instead.
 		// TODO(mdempsky): I don't think this happens anymore.
 		var fi os.FileInfo
 		fi, err = f.Stat()
 		if err != nil {
 			return
 		}
 		end = fi.Size()
 	}

 	if !strings.HasPrefix(line, "go object ") {
 		err = fmt.Errorf("not a go object file: %s", line)
 		return
 	}
 	if expect := objabi.HeaderString(); line != expect {
 		err = fmt.Errorf("object is [%s] expected [%s]", line, expect)
 		return
 	}

 	// process header lines
 	for !strings.HasPrefix(line, "$$") {
 		if strings.HasPrefix(line, "newexportsize ") {
 			fields := strings.Fields(line)
 			newsize, err = strconv.ParseInt(fields[1], 10, 64)
 			if err != nil {
 				return
 			}
 		}

 		line, err = r.ReadString('\n')
 		if err != nil {
 			return
 		}
 	}

 	// Expect $$B\n to signal binary import format.
 	if line != "$$B\n" {
 		err = errors.New("old export format no longer supported (recompile library)")
 		return
 	}

 	return
 }

 // addFingerprint reads the linker fingerprint included at the end of
 // the exportdata.
 func addFingerprint(path string, f *os.File, end int64) error {
 	const eom = "\n$$\n"
 	var fingerprint goobj.FingerprintType

 	var buf [len(fingerprint) + len(eom)]byte
 	if _, err := f.ReadAt(buf[:], end-int64(len(buf))); err != nil {
 		return err
 	}

 	// Caller should have given us the end position of the export data,
 	// which should end with the "\n$$\n" marker. As a consistency check
 	// to make sure we're reading at the right offset, make sure we
 	// found the marker.
 	if s := string(buf[len(fingerprint):]); s != eom {
 		return fmt.Errorf("expected $$ marker, but found %q", s)
 	}

 	copy(fingerprint[:], buf[:])

 	// assume files move (get installed) so don't record the full path
 	if base.Flag.Cfg.PackageFile != nil {
 		// If using a packageFile map, assume path_ can be recorded directly.
 		base.Ctxt.AddImport(path, fingerprint)
 	} else {
 		// For file "/Users/foo/go/pkg/darwin_amd64/math.a" record "math.a".
 		file := f.Name()
 		base.Ctxt.AddImport(file[len(file)-len(path)-len(".a"):], fingerprint)
 	}
 	return nil
 }

 // The linker uses the magic symbol prefixes "go." and "type."
 // Avoid potential confusion between import paths and symbols
 // by rejecting these reserved imports for now. Also, people
 // "can do weird things in GOPATH and we'd prefer they didn't
 // do _that_ weird thing" (per rsc). See also #4257.
 var reservedimports = []string{
 	"go",
 	"type",
 }

 func checkImportPath(path string, allowSpace bool) error {
 	if path == "" {
 		return errors.New("import path is empty")
 	}

 	if strings.Contains(path, "\x00") {
 		return errors.New("import path contains NUL")
 	}

 	for _, ri := range reservedimports {
 		if path == ri {
 			return fmt.Errorf("import path %q is reserved and cannot be used", path)
 		}
 	}

 	for _, r := range path {
 		switch {
 		case r == utf8.RuneError:
 			return fmt.Errorf("import path contains invalid UTF-8 sequence: %q", path)
 		case r < 0x20 || r == 0x7f:
 			return fmt.Errorf("import path contains control character: %q", path)
 		case r == '\\':
 			return fmt.Errorf("import path contains backslash; use slash: %q", path)
 		case !allowSpace && unicode.IsSpace(r):
 			return fmt.Errorf("import path contains space character: %q", path)
 		case strings.ContainsRune("!\"#$%&'()*,:;<=>?[]^`{|}", r):
 			return fmt.Errorf("import path contains invalid character '%c': %q", r, path)
 		}
 	}

 	return nil
 }

 func pkgnotused(lineno src.XPos, path string, name string) {
 	// If the package was imported with a name other than the final
 	// import path element, show it explicitly in the error message.
 	// Note that this handles both renamed imports and imports of
 	// packages containing unconventional package declarations.
 	// Note that this uses / always, even on Windows, because Go import
 	// paths always use forward slashes.
 	elem := path
 	if i := strings.LastIndex(elem, "/"); i >= 0 {
 		elem = elem[i+1:]
 	}
 	if name == "" || elem == name {
 		base.ErrorfAt(lineno, "imported and not used: %q", path)
 	} else {
 		base.ErrorfAt(lineno, "imported and not used: %q as %s", path, name)
 	}
 }

 func mkpackage(pkgname string) {
 	if types.LocalPkg.Name == "" {
 		if pkgname == "_" {
 			base.Errorf("invalid package name _")
 		}
 		types.LocalPkg.Name = pkgname
 	} else {
 		if pkgname != types.LocalPkg.Name {
 			base.Errorf("package %s; expected %s", pkgname, types.LocalPkg.Name)
 		}
 	}
 }

 func clearImports() {
 	type importedPkg struct {
 		pos  src.XPos
 		path string
 		name string
 	}
 	var unused []importedPkg

 	for _, s := range types.LocalPkg.Syms {
 		n := ir.AsNode(s.Def)
 		if n == nil {
 			continue
 		}
 		if n.Op() == ir.OPACK {
 			// throw away top-level package name left over
 			// from previous file.
 			// leave s->block set to cause redeclaration
 			// errors if a conflicting top-level name is
 			// introduced by a different file.
 			p := n.(*ir.PkgName)
 			if !p.Used && base.SyntaxErrors() == 0 {
 				unused = append(unused, importedPkg{p.Pos(), p.Pkg.Path, s.Name})
 			}
 			s.Def = nil
 			continue
 		}
 		if s.Def != nil && s.Def.Sym() != s {
 			// throw away top-level name left over
 			// from previous import . "x"
 			// We'll report errors after type checking in CheckDotImports.
 			s.Def = nil
 			continue
 		}
 	}

 	sort.Slice(unused, func(i, j int) bool { return unused[i].pos.Before(unused[j].pos) })
 	for _, pkg := range unused {
 		pkgnotused(pkg.pos, pkg.path, pkg.name)
 	}
 }

 // CheckDotImports reports errors for any unused dot imports.
 func CheckDotImports() {
 	for _, pack := range dotImports {
 		if !pack.Used {
 			base.ErrorfAt(pack.Pos(), "imported and not used: %q", pack.Pkg.Path)
 		}
 	}

 	// No longer needed; release memory.
 	dotImports = nil
 	typecheck.DotImportRefs = nil
 }

 // dotImports tracks all PkgNames that have been dot-imported.
 var dotImports []*ir.PkgName

 // find all the exported symbols in package referenced by PkgName,
 // and make them available in the current package
 func importDot(pack *ir.PkgName) {
 	if typecheck.DotImportRefs == nil {
 		typecheck.DotImportRefs = make(map[*ir.Ident]*ir.PkgName)
 	}

 	opkg := pack.Pkg
 	for _, s := range opkg.Syms {
 		if s.Def == nil {
 			if _, ok := typecheck.DeclImporter[s]; !ok {
 				continue
 			}
 		}
 		if !types.IsExported(s.Name) || strings.ContainsRune(s.Name, 0xb7) { // 0xb7 = center dot
 			continue
 		}
 		s1 := typecheck.Lookup(s.Name)
 		if s1.Def != nil {
 			pkgerror := fmt.Sprintf("during import %q", opkg.Path)
 			typecheck.Redeclared(base.Pos, s1, pkgerror)
 			continue
 		}

 		id := ir.NewIdent(src.NoXPos, s)
 		typecheck.DotImportRefs[id] = pack
 		s1.Def = id
 		s1.Block = 1
 	}

 	dotImports = append(dotImports, pack)
 }

 // importName is like oldname,
 // but it reports an error if sym is from another package and not exported.
 func importName(sym *types.Sym) ir.Node {
 	n := oldname(sym)
 	if !types.IsExported(sym.Name) && sym.Pkg != types.LocalPkg {
 		n.SetDiag(true)
 		base.Errorf("cannot refer to unexported name %s.%s", sym.Pkg.Name, sym.Name)
 	}
 	return n
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package noder

	import (
	"errors"
	"fmt"
	"internal/buildcfg"
	"os"
	pathpkg "path"
	"runtime"
	"sort"
	"strconv"
	"strings"
	"unicode"
	"unicode/utf8"

	"cmd/compile/internal/base"
	"cmd/compile/internal/importer"
	"cmd/compile/internal/ir"
	"cmd/compile/internal/syntax"
	"cmd/compile/internal/typecheck"
	"cmd/compile/internal/types"
	"cmd/compile/internal/types2"
	"cmd/internal/archive"
	"cmd/internal/bio"
	"cmd/internal/goobj"
	"cmd/internal/objabi"
	"cmd/internal/src"
	)

	// haveLegacyImports records whether we've imported any packages
	// without a new export data section. This is useful for experimenting
	// with new export data format designs, when you need to support
	// existing tests that manually compile files with inconsistent
	// compiler flags.
	var haveLegacyImports = false

	// newReadImportFunc is an extension hook for experimenting with new
	// export data formats. If a new export data payload was written out
	// for an imported package by overloading writeNewExportFunc, then
	// that payload will be mapped into memory and passed to
	// newReadImportFunc.
	var newReadImportFunc = func(data string, pkg1 types.Pkg, env types2.Context, packages map[string]types2.Package) (pkg2 types2.Package, err error) {
	panic("unexpected new export data payload")
	}

	type gcimports struct {
	ctxt *types2.Context
	packages map[string]*types2.Package
	}

	func (m gcimports) Import(path string) (types2.Package, error) {
	return m.ImportFrom(path, "" /* no vendoring */, 0)
	}

	func (m gcimports) ImportFrom(path, srcDir string, mode types2.ImportMode) (types2.Package, error) {
	if mode != 0 {
	panic("mode must be 0")
	}

	_, pkg, err := readImportFile(path, typecheck.Target, m.ctxt, m.packages)
	return pkg, err
	}

	func isDriveLetter(b byte) bool {
	return 'a' <= b && b <= 'z' \|\| 'A' <= b && b <= 'Z'
	}

	// is this path a local name? begins with ./ or ../ or /
	func islocalname(name string) bool {
	return strings.HasPrefix(name, "/") \|\|
	runtime.GOOS == "windows" && len(name) >= 3 && isDriveLetter(name[0]) && name[1] == ':' && name[2] == '/' \|\|
	strings.HasPrefix(name, "./") \|\| name == "." \|\|
	strings.HasPrefix(name, "../") \|\| name == ".."
	}

	func openPackage(path string) (*os.File, error) {
	if islocalname(path) {
	if base.Flag.NoLocalImports {
	return nil, errors.New("local imports disallowed")
	}

	if base.Flag.Cfg.PackageFile != nil {
	return os.Open(base.Flag.Cfg.PackageFile[path])
	}

	// try .a before .o. important for building libraries:
	// if there is an array.o in the array.a library,
	// want to find all of array.a, not just array.o.
	if file, err := os.Open(fmt.Sprintf("%s.a", path)); err == nil {
	return file, nil
	}
	if file, err := os.Open(fmt.Sprintf("%s.o", path)); err == nil {
	return file, nil
	}
	return nil, errors.New("file not found")
	}

	// local imports should be canonicalized already.
	// don't want to see "encoding/../encoding/base64"
	// as different from "encoding/base64".
	if q := pathpkg.Clean(path); q != path {
	return nil, fmt.Errorf("non-canonical import path %q (should be %q)", path, q)
	}

	if base.Flag.Cfg.PackageFile != nil {
	return os.Open(base.Flag.Cfg.PackageFile[path])
	}

	for _, dir := range base.Flag.Cfg.ImportDirs {
	if file, err := os.Open(fmt.Sprintf("%s/%s.a", dir, path)); err == nil {
	return file, nil
	}
	if file, err := os.Open(fmt.Sprintf("%s/%s.o", dir, path)); err == nil {
	return file, nil
	}
	}

	if buildcfg.GOROOT != "" {
	suffix := ""
	if base.Flag.InstallSuffix != "" {
	suffix = "_" + base.Flag.InstallSuffix
	} else if base.Flag.Race {
	suffix = "_race"
	} else if base.Flag.MSan {
	suffix = "_msan"
	} else if base.Flag.ASan {
	suffix = "_asan"
	}

	if file, err := os.Open(fmt.Sprintf("%s/pkg/%s_%s%s/%s.a", buildcfg.GOROOT, buildcfg.GOOS, buildcfg.GOARCH, suffix, path)); err == nil {
	return file, nil
	}
	if file, err := os.Open(fmt.Sprintf("%s/pkg/%s_%s%s/%s.o", buildcfg.GOROOT, buildcfg.GOOS, buildcfg.GOARCH, suffix, path)); err == nil {
	return file, nil
	}
	}
	return nil, errors.New("file not found")
	}

	// myheight tracks the local package's height based on packages
	// imported so far.
	var myheight int

	// resolveImportPath resolves an import path as it appears in a Go
	// source file to the package's full path.
	func resolveImportPath(path string) (string, error) {
	// The package name main is no longer reserved,
	// but we reserve the import path "main" to identify
	// the main package, just as we reserve the import
	// path "math" to identify the standard math package.
	if path == "main" {
	return "", errors.New("cannot import \"main\"")
	}

	if base.Ctxt.Pkgpath != "" && path == base.Ctxt.Pkgpath {
	return "", fmt.Errorf("import %q while compiling that package (import cycle)", path)
	}

	if mapped, ok := base.Flag.Cfg.ImportMap[path]; ok {
	path = mapped
	}

	if islocalname(path) {
	if path[0] == '/' {
	return "", errors.New("import path cannot be absolute path")
	}

	prefix := base.Flag.D
	if prefix == "" {
	// Questionable, but when -D isn't specified, historically we
	// resolve local import paths relative to the directory the
	// compiler's current directory, not the respective source
	// file's directory.
	prefix = base.Ctxt.Pathname
	}
	path = pathpkg.Join(prefix, path)

	if err := checkImportPath(path, true); err != nil {
	return "", err
	}
	}

	return path, nil
	}

	func importfile(decl syntax.ImportDecl) types.Pkg {
	path, err := parseImportPath(decl.Path)
	if err != nil {
	base.Errorf("%s", err)
	return nil
	}

	pkg, _, err := readImportFile(path, typecheck.Target, nil, nil)
	if err != nil {
	base.Errorf("%s", err)
	return nil
	}

	if pkg != types.UnsafePkg && pkg.Height >= myheight {
	myheight = pkg.Height + 1
	}
	return pkg
	}

	func parseImportPath(pathLit *syntax.BasicLit) (string, error) {
	if pathLit.Kind != syntax.StringLit {
	return "", errors.New("import path must be a string")
	}

	path, err := strconv.Unquote(pathLit.Value)
	if err != nil {
	return "", errors.New("import path must be a string")
	}

	if err := checkImportPath(path, false); err != nil {
	return "", err
	}

	return path, err
	}

	// readImportFile reads the import file for the given package path and
	// returns its types.Pkg representation. If packages is non-nil, the
	// types2.Package representation is also returned.
	func readImportFile(path string, target ir.Package, env types2.Context, packages map[string]types2.Package) (pkg1 types.Pkg, pkg2 *types2.Package, err error) {
	path, err = resolveImportPath(path)
	if err != nil {
	return
	}

	if path == "unsafe" {
	pkg1, pkg2 = types.UnsafePkg, types2.Unsafe

	// TODO(mdempsky): Investigate if this actually matters. Why would
	// the linker or runtime care whether a package imported unsafe?
	if !pkg1.Direct {
	pkg1.Direct = true
	target.Imports = append(target.Imports, pkg1)
	}

	return
	}

	pkg1 = types.NewPkg(path, "")
	if packages != nil {
	pkg2 = packages[path]
	assert(pkg1.Direct == (pkg2 != nil && pkg2.Complete()))
	}

	if pkg1.Direct {
	return
	}
	pkg1.Direct = true
	target.Imports = append(target.Imports, pkg1)

	f, err := openPackage(path)
	if err != nil {
	return
	}
	defer f.Close()

	r, end, newsize, err := findExportData(f)
	if err != nil {
	return
	}

	if base.Debug.Export != 0 {
	fmt.Printf("importing %s (%s)\n", path, f.Name())
	}

	if newsize != 0 {
	// We have unified IR data. Map it, and feed to the importers.
	end -= newsize
	var data string
	data, err = base.MapFile(r.File(), end, newsize)
	if err != nil {
	return
	}

	pkg2, err = newReadImportFunc(data, pkg1, env, packages)
	} else {
	// We only have old data. Oh well, fall back to the legacy importers.
	haveLegacyImports = true

	var c byte
	switch c, err = r.ReadByte(); {
	case err != nil:
	return

	case c != 'i':
	// Indexed format is distinguished by an 'i' byte,
	// whereas previous export formats started with 'c', 'd', or 'v'.
	err = fmt.Errorf("unexpected package format byte: %v", c)
	return
	}

	pos := r.Offset()

	// Map string (and data) section into memory as a single large
	// string. This reduces heap fragmentation and allows
	// returning individual substrings very efficiently.
	var data string
	data, err = base.MapFile(r.File(), pos, end-pos)
	if err != nil {
	return
	}

	typecheck.ReadImports(pkg1, data)

	if packages != nil {
	pkg2, err = importer.ImportData(packages, data, path)
	if err != nil {
	return
	}
	}
	}

	err = addFingerprint(path, f, end)
	return
	}

	// findExportData returns a *bio.Reader positioned at the start of the
	// binary export data section, and a file offset for where to stop
	// reading.
	func findExportData(f os.File) (r bio.Reader, end, newsize int64, err error) {
	r = bio.NewReader(f)

	// check object header
	line, err := r.ReadString('\n')
	if err != nil {
	return
	}

	if line == "!<arch>\n" { // package archive
	// package export block should be first
	sz := int64(archive.ReadHeader(r.Reader, "__.PKGDEF"))
	if sz <= 0 {
	err = errors.New("not a package file")
	return
	}
	end = r.Offset() + sz
	line, err = r.ReadString('\n')
	if err != nil {
	return
	}
	} else {
	// Not an archive; provide end of file instead.
	// TODO(mdempsky): I don't think this happens anymore.
	var fi os.FileInfo
	fi, err = f.Stat()
	if err != nil {
	return
	}
	end = fi.Size()
	}

	if !strings.HasPrefix(line, "go object ") {
	err = fmt.Errorf("not a go object file: %s", line)
	return
	}
	if expect := objabi.HeaderString(); line != expect {
	err = fmt.Errorf("object is [%s] expected [%s]", line, expect)
	return
	}

	// process header lines
	for !strings.HasPrefix(line, "$$") {
	if strings.HasPrefix(line, "newexportsize ") {
	fields := strings.Fields(line)
	newsize, err = strconv.ParseInt(fields[1], 10, 64)
	if err != nil {
	return
	}
	}

	line, err = r.ReadString('\n')
	if err != nil {
	return
	}
	}

	// Expect $$B\n to signal binary import format.
	if line != "$$B\n" {
	err = errors.New("old export format no longer supported (recompile library)")
	return
	}

	return
	}

	// addFingerprint reads the linker fingerprint included at the end of
	// the exportdata.
	func addFingerprint(path string, f *os.File, end int64) error {
	const eom = "\n$$\n"
	var fingerprint goobj.FingerprintType

	var buf [len(fingerprint) + len(eom)]byte
	if _, err := f.ReadAt(buf[:], end-int64(len(buf))); err != nil {
	return err
	}

	// Caller should have given us the end position of the export data,
	// which should end with the "\n$$\n" marker. As a consistency check
	// to make sure we're reading at the right offset, make sure we
	// found the marker.
	if s := string(buf[len(fingerprint):]); s != eom {
	return fmt.Errorf("expected $$ marker, but found %q", s)
	}

	copy(fingerprint[:], buf[:])

	// assume files move (get installed) so don't record the full path
	if base.Flag.Cfg.PackageFile != nil {
	// If using a packageFile map, assume path_ can be recorded directly.
	base.Ctxt.AddImport(path, fingerprint)
	} else {
	// For file "/Users/foo/go/pkg/darwin_amd64/math.a" record "math.a".
	file := f.Name()
	base.Ctxt.AddImport(file[len(file)-len(path)-len(".a"):], fingerprint)
	}
	return nil
	}

	// The linker uses the magic symbol prefixes "go." and "type."
	// Avoid potential confusion between import paths and symbols
	// by rejecting these reserved imports for now. Also, people
	// "can do weird things in GOPATH and we'd prefer they didn't
	// do _that_ weird thing" (per rsc). See also #4257.
	var reservedimports = []string{
	"go",
	"type",
	}

	func checkImportPath(path string, allowSpace bool) error {
	if path == "" {
	return errors.New("import path is empty")
	}

	if strings.Contains(path, "\x00") {
	return errors.New("import path contains NUL")
	}

	for _, ri := range reservedimports {
	if path == ri {
	return fmt.Errorf("import path %q is reserved and cannot be used", path)
	}
	}

	for _, r := range path {
	switch {
	case r == utf8.RuneError:
	return fmt.Errorf("import path contains invalid UTF-8 sequence: %q", path)
	case r < 0x20 \|\| r == 0x7f:
	return fmt.Errorf("import path contains control character: %q", path)
	case r == '\\':
	return fmt.Errorf("import path contains backslash; use slash: %q", path)
	case !allowSpace && unicode.IsSpace(r):
	return fmt.Errorf("import path contains space character: %q", path)
	case strings.ContainsRune("!\"#$%&'()*,:;<=>?[]^`{\|}", r):
	return fmt.Errorf("import path contains invalid character '%c': %q", r, path)
	}
	}

	return nil
	}

	func pkgnotused(lineno src.XPos, path string, name string) {
	// If the package was imported with a name other than the final
	// import path element, show it explicitly in the error message.
	// Note that this handles both renamed imports and imports of
	// packages containing unconventional package declarations.
	// Note that this uses / always, even on Windows, because Go import
	// paths always use forward slashes.
	elem := path
	if i := strings.LastIndex(elem, "/"); i >= 0 {
	elem = elem[i+1:]
	}
	if name == "" \|\| elem == name {
	base.ErrorfAt(lineno, "imported and not used: %q", path)
	} else {
	base.ErrorfAt(lineno, "imported and not used: %q as %s", path, name)
	}
	}

	func mkpackage(pkgname string) {
	if types.LocalPkg.Name == "" {
	if pkgname == "_" {
	base.Errorf("invalid package name _")
	}
	types.LocalPkg.Name = pkgname
	} else {
	if pkgname != types.LocalPkg.Name {
	base.Errorf("package %s; expected %s", pkgname, types.LocalPkg.Name)
	}
	}
	}

	func clearImports() {
	type importedPkg struct {
	pos src.XPos
	path string
	name string
	}
	var unused []importedPkg

	for _, s := range types.LocalPkg.Syms {
	n := ir.AsNode(s.Def)
	if n == nil {
	continue
	}
	if n.Op() == ir.OPACK {
	// throw away top-level package name left over
	// from previous file.
	// leave s->block set to cause redeclaration
	// errors if a conflicting top-level name is
	// introduced by a different file.
	p := n.(*ir.PkgName)
	if !p.Used && base.SyntaxErrors() == 0 {
	unused = append(unused, importedPkg{p.Pos(), p.Pkg.Path, s.Name})
	}
	s.Def = nil
	continue
	}
	if s.Def != nil && s.Def.Sym() != s {
	// throw away top-level name left over
	// from previous import . "x"
	// We'll report errors after type checking in CheckDotImports.
	s.Def = nil
	continue
	}
	}

	sort.Slice(unused, func(i, j int) bool { return unused[i].pos.Before(unused[j].pos) })
	for _, pkg := range unused {
	pkgnotused(pkg.pos, pkg.path, pkg.name)
	}
	}

	// CheckDotImports reports errors for any unused dot imports.
	func CheckDotImports() {
	for _, pack := range dotImports {
	if !pack.Used {
	base.ErrorfAt(pack.Pos(), "imported and not used: %q", pack.Pkg.Path)
	}
	}

	// No longer needed; release memory.
	dotImports = nil
	typecheck.DotImportRefs = nil
	}

	// dotImports tracks all PkgNames that have been dot-imported.
	var dotImports []*ir.PkgName

	// find all the exported symbols in package referenced by PkgName,
	// and make them available in the current package
	func importDot(pack *ir.PkgName) {
	if typecheck.DotImportRefs == nil {
	typecheck.DotImportRefs = make(map[ir.Ident]ir.PkgName)
	}

	opkg := pack.Pkg
	for _, s := range opkg.Syms {
	if s.Def == nil {
	if _, ok := typecheck.DeclImporter[s]; !ok {
	continue
	}
	}
	if !types.IsExported(s.Name) \|\| strings.ContainsRune(s.Name, 0xb7) { // 0xb7 = center dot
	continue
	}
	s1 := typecheck.Lookup(s.Name)
	if s1.Def != nil {
	pkgerror := fmt.Sprintf("during import %q", opkg.Path)
	typecheck.Redeclared(base.Pos, s1, pkgerror)
	continue
	}

	id := ir.NewIdent(src.NoXPos, s)
	typecheck.DotImportRefs[id] = pack
	s1.Def = id
	s1.Block = 1
	}

	dotImports = append(dotImports, pack)
	}

	// importName is like oldname,
	// but it reports an error if sym is from another package and not exported.
	func importName(sym *types.Sym) ir.Node {
	n := oldname(sym)
	if !types.IsExported(sym.Name) && sym.Pkg != types.LocalPkg {
	n.SetDiag(true)
	base.Errorf("cannot refer to unexported name %s.%s", sym.Pkg.Name, sym.Name)
	}
	return n
	}