Adding upstream version 1.21.8.upstream/1.21.8

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

16 files changed, 2664 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/importer/exportdata.go b/src/cmd/compile/internal/importer/exportdata.go
new file mode 100644
index 0000000..42fc5c9
--- /dev/null
+++ b/src/cmd/compile/internal/importer/exportdata.go
@@ -0,0 +1,95 @@
+// Copyright 2011 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.
+
+// This file implements FindExportData.
+
+package importer
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
+	// See $GOROOT/include/ar.h.
+	hdr := make([]byte, 16+12+6+6+8+10+2)
+	_, err = io.ReadFull(r, hdr)
+	if err != nil {
+		return
+	}
+	// leave for debugging
+	if false {
+		fmt.Printf("header: %s", hdr)
+	}
+	s := strings.TrimSpace(string(hdr[16+12+6+6+8:][:10]))
+	size, err = strconv.Atoi(s)
+	if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
+		err = fmt.Errorf("invalid archive header")
+		return
+	}
+	name = strings.TrimSpace(string(hdr[:16]))
+	return
+}
+
+// FindExportData positions the reader r at the beginning of the
+// export data section of an underlying GC-created object/archive
+// file by reading from it. The reader must be positioned at the
+// start of the file before calling this function. The hdr result
+// is the string before the export data, either "$$" or "$$B".
+//
+// If size is non-negative, it's the number of bytes of export data
+// still available to read from r.
+func FindExportData(r *bufio.Reader) (hdr string, size int, err error) {
+	// Read first line to make sure this is an object file.
+	line, err := r.ReadSlice('\n')
+	if err != nil {
+		err = fmt.Errorf("can't find export data (%v)", err)
+		return
+	}
+
+	if string(line) == "!<arch>\n" {
+		// Archive file. Scan to __.PKGDEF.
+		var name string
+		if name, size, err = readGopackHeader(r); err != nil {
+			return
+		}
+
+		// First entry should be __.PKGDEF.
+		if name != "__.PKGDEF" {
+			err = fmt.Errorf("go archive is missing __.PKGDEF")
+			return
+		}
+
+		// Read first line of __.PKGDEF data, so that line
+		// is once again the first line of the input.
+		if line, err = r.ReadSlice('\n'); err != nil {
+			err = fmt.Errorf("can't find export data (%v)", err)
+			return
+		}
+	}
+
+	// Now at __.PKGDEF in archive or still at beginning of file.
+	// Either way, line should begin with "go object ".
+	if !strings.HasPrefix(string(line), "go object ") {
+		err = fmt.Errorf("not a Go object file")
+		return
+	}
+	size -= len(line)
+
+	// Skip over object header to export data.
+	// Begins after first line starting with $$.
+	for line[0] != '$' {
+		if line, err = r.ReadSlice('\n'); err != nil {
+			err = fmt.Errorf("can't find export data (%v)", err)
+			return
+		}
+		size -= len(line)
+	}
+	hdr = string(line)
+
+	return
+}
diff --git a/src/cmd/compile/internal/importer/gcimporter.go b/src/cmd/compile/internal/importer/gcimporter.go
new file mode 100644
index 0000000..490cdf9
--- /dev/null
+++ b/src/cmd/compile/internal/importer/gcimporter.go
@@ -0,0 +1,243 @@
+// Copyright 2011 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 importer implements Import for gc-generated object files.
+package importer
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"go/build"
+	"internal/pkgbits"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"cmd/compile/internal/types2"
+)
+
+var exportMap sync.Map // package dir → func() (string, bool)
+
+// lookupGorootExport returns the location of the export data
+// (normally found in the build cache, but located in GOROOT/pkg
+// in prior Go releases) for the package located in pkgDir.
+//
+// (We use the package's directory instead of its import path
+// mainly to simplify handling of the packages in src/vendor
+// and cmd/vendor.)
+func lookupGorootExport(pkgDir string) (string, bool) {
+	f, ok := exportMap.Load(pkgDir)
+	if !ok {
+		var (
+			listOnce   sync.Once
+			exportPath string
+		)
+		f, _ = exportMap.LoadOrStore(pkgDir, func() (string, bool) {
+			listOnce.Do(func() {
+				cmd := exec.Command(filepath.Join(build.Default.GOROOT, "bin", "go"), "list", "-export", "-f", "{{.Export}}", pkgDir)
+				cmd.Dir = build.Default.GOROOT
+				cmd.Env = append(os.Environ(), "PWD="+cmd.Dir, "GOROOT="+build.Default.GOROOT)
+				var output []byte
+				output, err := cmd.Output()
+				if err != nil {
+					return
+				}
+
+				exports := strings.Split(string(bytes.TrimSpace(output)), "\n")
+				if len(exports) != 1 {
+					return
+				}
+
+				exportPath = exports[0]
+			})
+
+			return exportPath, exportPath != ""
+		})
+	}
+
+	return f.(func() (string, bool))()
+}
+
+var pkgExts = [...]string{".a", ".o"} // a file from the build cache will have no extension
+
+// FindPkg returns the filename and unique package id for an import
+// path based on package information provided by build.Import (using
+// the build.Default build.Context). A relative srcDir is interpreted
+// relative to the current working directory.
+// If no file was found, an empty filename is returned.
+func FindPkg(path, srcDir string) (filename, id string) {
+	if path == "" {
+		return
+	}
+
+	var noext string
+	switch {
+	default:
+		// "x" -> "$GOPATH/pkg/$GOOS_$GOARCH/x.ext", "x"
+		// Don't require the source files to be present.
+		if abs, err := filepath.Abs(srcDir); err == nil { // see issue 14282
+			srcDir = abs
+		}
+		bp, _ := build.Import(path, srcDir, build.FindOnly|build.AllowBinary)
+		if bp.PkgObj == "" {
+			var ok bool
+			if bp.Goroot && bp.Dir != "" {
+				filename, ok = lookupGorootExport(bp.Dir)
+			}
+			if !ok {
+				id = path // make sure we have an id to print in error message
+				return
+			}
+		} else {
+			noext = strings.TrimSuffix(bp.PkgObj, ".a")
+		}
+		id = bp.ImportPath
+
+	case build.IsLocalImport(path):
+		// "./x" -> "/this/directory/x.ext", "/this/directory/x"
+		noext = filepath.Join(srcDir, path)
+		id = noext
+
+	case filepath.IsAbs(path):
+		// for completeness only - go/build.Import
+		// does not support absolute imports
+		// "/x" -> "/x.ext", "/x"
+		noext = path
+		id = path
+	}
+
+	if false { // for debugging
+		if path != id {
+			fmt.Printf("%s -> %s\n", path, id)
+		}
+	}
+
+	if filename != "" {
+		if f, err := os.Stat(filename); err == nil && !f.IsDir() {
+			return
+		}
+	}
+	// try extensions
+	for _, ext := range pkgExts {
+		filename = noext + ext
+		if f, err := os.Stat(filename); err == nil && !f.IsDir() {
+			return
+		}
+	}
+
+	filename = "" // not found
+	return
+}
+
+// Import imports a gc-generated package given its import path and srcDir, adds
+// the corresponding package object to the packages map, and returns the object.
+// The packages map must contain all packages already imported.
+func Import(packages map[string]*types2.Package, path, srcDir string, lookup func(path string) (io.ReadCloser, error)) (pkg *types2.Package, err error) {
+	var rc io.ReadCloser
+	var id string
+	if lookup != nil {
+		// With custom lookup specified, assume that caller has
+		// converted path to a canonical import path for use in the map.
+		if path == "unsafe" {
+			return types2.Unsafe, nil
+		}
+		id = path
+
+		// No need to re-import if the package was imported completely before.
+		if pkg = packages[id]; pkg != nil && pkg.Complete() {
+			return
+		}
+		f, err := lookup(path)
+		if err != nil {
+			return nil, err
+		}
+		rc = f
+	} else {
+		var filename string
+		filename, id = FindPkg(path, srcDir)
+		if filename == "" {
+			if path == "unsafe" {
+				return types2.Unsafe, nil
+			}
+			return nil, fmt.Errorf("can't find import: %q", id)
+		}
+
+		// no need to re-import if the package was imported completely before
+		if pkg = packages[id]; pkg != nil && pkg.Complete() {
+			return
+		}
+
+		// open file
+		f, err := os.Open(filename)
+		if err != nil {
+			return nil, err
+		}
+		defer func() {
+			if err != nil {
+				// add file name to error
+				err = fmt.Errorf("%s: %v", filename, err)
+			}
+		}()
+		rc = f
+	}
+	defer rc.Close()
+
+	buf := bufio.NewReader(rc)
+	hdr, size, err := FindExportData(buf)
+	if err != nil {
+		return
+	}
+
+	switch hdr {
+	case "$$\n":
+		err = fmt.Errorf("import %q: old textual export format no longer supported (recompile library)", path)
+
+	case "$$B\n":
+		var data []byte
+		var r io.Reader = buf
+		if size >= 0 {
+			r = io.LimitReader(r, int64(size))
+		}
+		data, err = io.ReadAll(r)
+		if err != nil {
+			break
+		}
+
+		if len(data) == 0 {
+			err = fmt.Errorf("import %q: missing export data", path)
+			break
+		}
+		exportFormat := data[0]
+		s := string(data[1:])
+
+		// The indexed export format starts with an 'i'; the older
+		// binary export format starts with a 'c', 'd', or 'v'
+		// (from "version"). Select appropriate importer.
+		switch exportFormat {
+		case 'u':
+			s = s[:strings.Index(s, "\n$$\n")]
+			input := pkgbits.NewPkgDecoder(id, s)
+			pkg = ReadPackage(nil, packages, input)
+		case 'i':
+			pkg, err = ImportData(packages, s, id)
+		default:
+			err = fmt.Errorf("import %q: old binary export format no longer supported (recompile library)", path)
+		}
+
+	default:
+		err = fmt.Errorf("import %q: unknown export data header: %q", path, hdr)
+	}
+
+	return
+}
+
+type byPath []*types2.Package
+
+func (a byPath) Len() int           { return len(a) }
+func (a byPath) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a byPath) Less(i, j int) bool { return a[i].Path() < a[j].Path() }
diff --git a/src/cmd/compile/internal/importer/gcimporter_test.go b/src/cmd/compile/internal/importer/gcimporter_test.go
new file mode 100644
index 0000000..96c5f69
--- /dev/null
+++ b/src/cmd/compile/internal/importer/gcimporter_test.go
@@ -0,0 +1,608 @@
+// Copyright 2011 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 importer
+
+import (
+	"bytes"
+	"cmd/compile/internal/types2"
+	"fmt"
+	"go/build"
+	"internal/testenv"
+	"os"
+	"os/exec"
+	"path"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestMain(m *testing.M) {
+	build.Default.GOROOT = testenv.GOROOT(nil)
+	os.Exit(m.Run())
+}
+
+// compile runs the compiler on filename, with dirname as the working directory,
+// and writes the output file to outdirname.
+// compile gives the resulting package a packagepath of testdata/<filebasename>.
+func compile(t *testing.T, dirname, filename, outdirname string, packagefiles map[string]string) string {
+	// filename must end with ".go"
+	basename, ok := strings.CutSuffix(filepath.Base(filename), ".go")
+	if !ok {
+		t.Helper()
+		t.Fatalf("filename doesn't end in .go: %s", filename)
+	}
+	objname := basename + ".o"
+	outname := filepath.Join(outdirname, objname)
+	pkgpath := path.Join("testdata", basename)
+
+	importcfgfile := os.DevNull
+	if len(packagefiles) > 0 {
+		importcfgfile = filepath.Join(outdirname, basename) + ".importcfg"
+		importcfg := new(bytes.Buffer)
+		for k, v := range packagefiles {
+			fmt.Fprintf(importcfg, "packagefile %s=%s\n", k, v)
+		}
+		if err := os.WriteFile(importcfgfile, importcfg.Bytes(), 0655); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	cmd := testenv.Command(t, testenv.GoToolPath(t), "tool", "compile", "-p", pkgpath, "-D", "testdata", "-importcfg", importcfgfile, "-o", outname, filename)
+	cmd.Dir = dirname
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Helper()
+		t.Logf("%s", out)
+		t.Fatalf("go tool compile %s failed: %s", filename, err)
+	}
+	return outname
+}
+
+func testPath(t *testing.T, path, srcDir string) *types2.Package {
+	t0 := time.Now()
+	pkg, err := Import(make(map[string]*types2.Package), path, srcDir, nil)
+	if err != nil {
+		t.Errorf("testPath(%s): %s", path, err)
+		return nil
+	}
+	t.Logf("testPath(%s): %v", path, time.Since(t0))
+	return pkg
+}
+
+func mktmpdir(t *testing.T) string {
+	tmpdir := t.TempDir()
+	if err := os.Mkdir(filepath.Join(tmpdir, "testdata"), 0700); err != nil {
+		t.Fatal("mktmpdir:", err)
+	}
+	return tmpdir
+}
+
+func TestImportTestdata(t *testing.T) {
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	testenv.MustHaveGoBuild(t)
+
+	testfiles := map[string][]string{
+		"exports.go":  {"go/ast", "go/token"},
+		"generics.go": nil,
+	}
+	if true /* was goexperiment.Unified */ {
+		// TODO(mdempsky): Fix test below to flatten the transitive
+		// Package.Imports graph. Unified IR is more precise about
+		// recreating the package import graph.
+		testfiles["exports.go"] = []string{"go/ast"}
+	}
+
+	for testfile, wantImports := range testfiles {
+		tmpdir := mktmpdir(t)
+
+		importMap := map[string]string{}
+		for _, pkg := range wantImports {
+			export, _ := FindPkg(pkg, "testdata")
+			if export == "" {
+				t.Fatalf("no export data found for %s", pkg)
+			}
+			importMap[pkg] = export
+		}
+
+		compile(t, "testdata", testfile, filepath.Join(tmpdir, "testdata"), importMap)
+		path := "./testdata/" + strings.TrimSuffix(testfile, ".go")
+
+		if pkg := testPath(t, path, tmpdir); pkg != nil {
+			// The package's Imports list must include all packages
+			// explicitly imported by testfile, plus all packages
+			// referenced indirectly via exported objects in testfile.
+			got := fmt.Sprint(pkg.Imports())
+			for _, want := range wantImports {
+				if !strings.Contains(got, want) {
+					t.Errorf(`Package("exports").Imports() = %s, does not contain %s`, got, want)
+				}
+			}
+		}
+	}
+}
+
+func TestVersionHandling(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	const dir = "./testdata/versions"
+	list, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tmpdir := mktmpdir(t)
+	corruptdir := filepath.Join(tmpdir, "testdata", "versions")
+	if err := os.Mkdir(corruptdir, 0700); err != nil {
+		t.Fatal(err)
+	}
+
+	for _, f := range list {
+		name := f.Name()
+		if !strings.HasSuffix(name, ".a") {
+			continue // not a package file
+		}
+		if strings.Contains(name, "corrupted") {
+			continue // don't process a leftover corrupted file
+		}
+		pkgpath := "./" + name[:len(name)-2]
+
+		if testing.Verbose() {
+			t.Logf("importing %s", name)
+		}
+
+		// test that export data can be imported
+		_, err := Import(make(map[string]*types2.Package), pkgpath, dir, nil)
+		if err != nil {
+			// ok to fail if it fails with a no longer supported error for select files
+			if strings.Contains(err.Error(), "no longer supported") {
+				switch name {
+				case "test_go1.7_0.a", "test_go1.7_1.a",
+					"test_go1.8_4.a", "test_go1.8_5.a",
+					"test_go1.11_6b.a", "test_go1.11_999b.a":
+					continue
+				}
+				// fall through
+			}
+			// ok to fail if it fails with a newer version error for select files
+			if strings.Contains(err.Error(), "newer version") {
+				switch name {
+				case "test_go1.11_999i.a":
+					continue
+				}
+				// fall through
+			}
+			t.Errorf("import %q failed: %v", pkgpath, err)
+			continue
+		}
+
+		// create file with corrupted export data
+		// 1) read file
+		data, err := os.ReadFile(filepath.Join(dir, name))
+		if err != nil {
+			t.Fatal(err)
+		}
+		// 2) find export data
+		i := bytes.Index(data, []byte("\n$$B\n")) + 5
+		j := bytes.Index(data[i:], []byte("\n$$\n")) + i
+		if i < 0 || j < 0 || i > j {
+			t.Fatalf("export data section not found (i = %d, j = %d)", i, j)
+		}
+		// 3) corrupt the data (increment every 7th byte)
+		for k := j - 13; k >= i; k -= 7 {
+			data[k]++
+		}
+		// 4) write the file
+		pkgpath += "_corrupted"
+		filename := filepath.Join(corruptdir, pkgpath) + ".a"
+		os.WriteFile(filename, data, 0666)
+
+		// test that importing the corrupted file results in an error
+		_, err = Import(make(map[string]*types2.Package), pkgpath, corruptdir, nil)
+		if err == nil {
+			t.Errorf("import corrupted %q succeeded", pkgpath)
+		} else if msg := err.Error(); !strings.Contains(msg, "version skew") {
+			t.Errorf("import %q error incorrect (%s)", pkgpath, msg)
+		}
+	}
+}
+
+func TestImportStdLib(t *testing.T) {
+	if testing.Short() {
+		t.Skip("the imports can be expensive, and this test is especially slow when the build cache is empty")
+	}
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	// Get list of packages in stdlib. Filter out test-only packages with {{if .GoFiles}} check.
+	var stderr bytes.Buffer
+	cmd := exec.Command("go", "list", "-f", "{{if .GoFiles}}{{.ImportPath}}{{end}}", "std")
+	cmd.Stderr = &stderr
+	out, err := cmd.Output()
+	if err != nil {
+		t.Fatalf("failed to run go list to determine stdlib packages: %v\nstderr:\n%v", err, stderr.String())
+	}
+	pkgs := strings.Fields(string(out))
+
+	var nimports int
+	for _, pkg := range pkgs {
+		t.Run(pkg, func(t *testing.T) {
+			if testPath(t, pkg, filepath.Join(testenv.GOROOT(t), "src", path.Dir(pkg))) != nil {
+				nimports++
+			}
+		})
+	}
+	const minPkgs = 225 // 'GOOS=plan9 go1.18 list std | wc -l' reports 228; most other platforms have more.
+	if len(pkgs) < minPkgs {
+		t.Fatalf("too few packages (%d) were imported", nimports)
+	}
+
+	t.Logf("tested %d imports", nimports)
+}
+
+var importedObjectTests = []struct {
+	name string
+	want string
+}{
+	// non-interfaces
+	{"crypto.Hash", "type Hash uint"},
+	{"go/ast.ObjKind", "type ObjKind int"},
+	{"go/types.Qualifier", "type Qualifier func(*Package) string"},
+	{"go/types.Comparable", "func Comparable(T Type) bool"},
+	{"math.Pi", "const Pi untyped float"},
+	{"math.Sin", "func Sin(x float64) float64"},
+	{"go/ast.NotNilFilter", "func NotNilFilter(_ string, v reflect.Value) bool"},
+	{"go/internal/gcimporter.FindPkg", "func FindPkg(path string, srcDir string) (filename string, id string)"},
+
+	// interfaces
+	{"context.Context", "type Context interface{Deadline() (deadline time.Time, ok bool); Done() <-chan struct{}; Err() error; Value(key any) any}"},
+	{"crypto.Decrypter", "type Decrypter interface{Decrypt(rand io.Reader, msg []byte, opts DecrypterOpts) (plaintext []byte, err error); Public() PublicKey}"},
+	{"encoding.BinaryMarshaler", "type BinaryMarshaler interface{MarshalBinary() (data []byte, err error)}"},
+	{"io.Reader", "type Reader interface{Read(p []byte) (n int, err error)}"},
+	{"io.ReadWriter", "type ReadWriter interface{Reader; Writer}"},
+	{"go/ast.Node", "type Node interface{End() go/token.Pos; Pos() go/token.Pos}"},
+	{"go/types.Type", "type Type interface{String() string; Underlying() Type}"},
+}
+
+func TestImportedTypes(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	for _, test := range importedObjectTests {
+		s := strings.Split(test.name, ".")
+		if len(s) != 2 {
+			t.Fatal("inconsistent test data")
+		}
+		importPath := s[0]
+		objName := s[1]
+
+		pkg, err := Import(make(map[string]*types2.Package), importPath, ".", nil)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+
+		obj := pkg.Scope().Lookup(objName)
+		if obj == nil {
+			t.Errorf("%s: object not found", test.name)
+			continue
+		}
+
+		got := types2.ObjectString(obj, types2.RelativeTo(pkg))
+		if got != test.want {
+			t.Errorf("%s: got %q; want %q", test.name, got, test.want)
+		}
+
+		if named, _ := obj.Type().(*types2.Named); named != nil {
+			verifyInterfaceMethodRecvs(t, named, 0)
+		}
+	}
+}
+
+// verifyInterfaceMethodRecvs verifies that method receiver types
+// are named if the methods belong to a named interface type.
+func verifyInterfaceMethodRecvs(t *testing.T, named *types2.Named, level int) {
+	// avoid endless recursion in case of an embedding bug that lead to a cycle
+	if level > 10 {
+		t.Errorf("%s: embeds itself", named)
+		return
+	}
+
+	iface, _ := named.Underlying().(*types2.Interface)
+	if iface == nil {
+		return // not an interface
+	}
+
+	// The unified IR importer always sets interface method receiver
+	// parameters to point to the Interface type, rather than the Named.
+	// See #49906.
+	//
+	// TODO(mdempsky): This is only true for the types2 importer. For
+	// the go/types importer, we duplicate the Interface and rewrite its
+	// receiver methods to match historical behavior.
+	var want types2.Type = named
+	if true /* was goexperiment.Unified */ {
+		want = iface
+	}
+
+	// check explicitly declared methods
+	for i := 0; i < iface.NumExplicitMethods(); i++ {
+		m := iface.ExplicitMethod(i)
+		recv := m.Type().(*types2.Signature).Recv()
+		if recv == nil {
+			t.Errorf("%s: missing receiver type", m)
+			continue
+		}
+		if recv.Type() != want {
+			t.Errorf("%s: got recv type %s; want %s", m, recv.Type(), named)
+		}
+	}
+
+	// check embedded interfaces (if they are named, too)
+	for i := 0; i < iface.NumEmbeddeds(); i++ {
+		// embedding of interfaces cannot have cycles; recursion will terminate
+		if etype, _ := iface.EmbeddedType(i).(*types2.Named); etype != nil {
+			verifyInterfaceMethodRecvs(t, etype, level+1)
+		}
+	}
+}
+
+func TestIssue5815(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	pkg := importPkg(t, "strings", ".")
+
+	scope := pkg.Scope()
+	for _, name := range scope.Names() {
+		obj := scope.Lookup(name)
+		if obj.Pkg() == nil {
+			t.Errorf("no pkg for %s", obj)
+		}
+		if tname, _ := obj.(*types2.TypeName); tname != nil {
+			named := tname.Type().(*types2.Named)
+			for i := 0; i < named.NumMethods(); i++ {
+				m := named.Method(i)
+				if m.Pkg() == nil {
+					t.Errorf("no pkg for %s", m)
+				}
+			}
+		}
+	}
+}
+
+// Smoke test to ensure that imported methods get the correct package.
+func TestCorrectMethodPackage(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	imports := make(map[string]*types2.Package)
+	_, err := Import(imports, "net/http", ".", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	mutex := imports["sync"].Scope().Lookup("Mutex").(*types2.TypeName).Type()
+	obj, _, _ := types2.LookupFieldOrMethod(types2.NewPointer(mutex), false, nil, "Lock")
+	lock := obj.(*types2.Func)
+	if got, want := lock.Pkg().Path(), "sync"; got != want {
+		t.Errorf("got package path %q; want %q", got, want)
+	}
+}
+
+func TestIssue13566(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	tmpdir := mktmpdir(t)
+	testoutdir := filepath.Join(tmpdir, "testdata")
+
+	// b.go needs to be compiled from the output directory so that the compiler can
+	// find the compiled package a. We pass the full path to compile() so that we
+	// don't have to copy the file to that directory.
+	bpath, err := filepath.Abs(filepath.Join("testdata", "b.go"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	jsonExport, _ := FindPkg("encoding/json", "testdata")
+	if jsonExport == "" {
+		t.Fatalf("no export data found for encoding/json")
+	}
+
+	compile(t, "testdata", "a.go", testoutdir, map[string]string{"encoding/json": jsonExport})
+	compile(t, testoutdir, bpath, testoutdir, map[string]string{"testdata/a": filepath.Join(testoutdir, "a.o")})
+
+	// import must succeed (test for issue at hand)
+	pkg := importPkg(t, "./testdata/b", tmpdir)
+
+	// make sure all indirectly imported packages have names
+	for _, imp := range pkg.Imports() {
+		if imp.Name() == "" {
+			t.Errorf("no name for %s package", imp.Path())
+		}
+	}
+}
+
+func TestIssue13898(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	// import go/internal/gcimporter which imports go/types partially
+	imports := make(map[string]*types2.Package)
+	_, err := Import(imports, "go/internal/gcimporter", ".", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// look for go/types package
+	var goTypesPkg *types2.Package
+	for path, pkg := range imports {
+		if path == "go/types" {
+			goTypesPkg = pkg
+			break
+		}
+	}
+	if goTypesPkg == nil {
+		t.Fatal("go/types not found")
+	}
+
+	// look for go/types.Object type
+	obj := lookupObj(t, goTypesPkg.Scope(), "Object")
+	typ, ok := obj.Type().(*types2.Named)
+	if !ok {
+		t.Fatalf("go/types.Object type is %v; wanted named type", typ)
+	}
+
+	// lookup go/types.Object.Pkg method
+	m, index, indirect := types2.LookupFieldOrMethod(typ, false, nil, "Pkg")
+	if m == nil {
+		t.Fatalf("go/types.Object.Pkg not found (index = %v, indirect = %v)", index, indirect)
+	}
+
+	// the method must belong to go/types
+	if m.Pkg().Path() != "go/types" {
+		t.Fatalf("found %v; want go/types", m.Pkg())
+	}
+}
+
+func TestIssue15517(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	tmpdir := mktmpdir(t)
+
+	compile(t, "testdata", "p.go", filepath.Join(tmpdir, "testdata"), nil)
+
+	// Multiple imports of p must succeed without redeclaration errors.
+	// We use an import path that's not cleaned up so that the eventual
+	// file path for the package is different from the package path; this
+	// will expose the error if it is present.
+	//
+	// (Issue: Both the textual and the binary importer used the file path
+	// of the package to be imported as key into the shared packages map.
+	// However, the binary importer then used the package path to identify
+	// the imported package to mark it as complete; effectively marking the
+	// wrong package as complete. By using an "unclean" package path, the
+	// file and package path are different, exposing the problem if present.
+	// The same issue occurs with vendoring.)
+	imports := make(map[string]*types2.Package)
+	for i := 0; i < 3; i++ {
+		if _, err := Import(imports, "./././testdata/p", tmpdir, nil); err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+func TestIssue15920(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	compileAndImportPkg(t, "issue15920")
+}
+
+func TestIssue20046(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	// "./issue20046".V.M must exist
+	pkg := compileAndImportPkg(t, "issue20046")
+	obj := lookupObj(t, pkg.Scope(), "V")
+	if m, index, indirect := types2.LookupFieldOrMethod(obj.Type(), false, nil, "M"); m == nil {
+		t.Fatalf("V.M not found (index = %v, indirect = %v)", index, indirect)
+	}
+}
+func TestIssue25301(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	compileAndImportPkg(t, "issue25301")
+}
+
+func TestIssue25596(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	compileAndImportPkg(t, "issue25596")
+}
+
+func importPkg(t *testing.T, path, srcDir string) *types2.Package {
+	pkg, err := Import(make(map[string]*types2.Package), path, srcDir, nil)
+	if err != nil {
+		t.Helper()
+		t.Fatal(err)
+	}
+	return pkg
+}
+
+func compileAndImportPkg(t *testing.T, name string) *types2.Package {
+	t.Helper()
+	tmpdir := mktmpdir(t)
+	compile(t, "testdata", name+".go", filepath.Join(tmpdir, "testdata"), nil)
+	return importPkg(t, "./testdata/"+name, tmpdir)
+}
+
+func lookupObj(t *testing.T, scope *types2.Scope, name string) types2.Object {
+	if obj := scope.Lookup(name); obj != nil {
+		return obj
+	}
+	t.Helper()
+	t.Fatalf("%s not found", name)
+	return nil
+}
diff --git a/src/cmd/compile/internal/importer/iimport.go b/src/cmd/compile/internal/importer/iimport.go
new file mode 100644
index 0000000..24d3d4b
--- /dev/null
+++ b/src/cmd/compile/internal/importer/iimport.go
@@ -0,0 +1,795 @@
+// Copyright 2018 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.
+
+// Indexed package import.
+// See cmd/compile/internal/typecheck/iexport.go for the export data format.
+
+package importer
+
+import (
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types2"
+	"encoding/binary"
+	"fmt"
+	"go/constant"
+	"go/token"
+	"io"
+	"math/big"
+	"sort"
+	"strings"
+)
+
+type intReader struct {
+	*strings.Reader
+	path string
+}
+
+func (r *intReader) int64() int64 {
+	i, err := binary.ReadVarint(r.Reader)
+	if err != nil {
+		errorf("import %q: read varint error: %v", r.path, err)
+	}
+	return i
+}
+
+func (r *intReader) uint64() uint64 {
+	i, err := binary.ReadUvarint(r.Reader)
+	if err != nil {
+		errorf("import %q: read varint error: %v", r.path, err)
+	}
+	return i
+}
+
+// Keep this in sync with constants in iexport.go.
+const (
+	iexportVersionGo1_11   = 0
+	iexportVersionPosCol   = 1
+	iexportVersionGenerics = 2
+	iexportVersionGo1_18   = 2
+
+	iexportVersionCurrent = 2
+)
+
+type ident struct {
+	pkg  *types2.Package
+	name string
+}
+
+const predeclReserved = 32
+
+type itag uint64
+
+const (
+	// Types
+	definedType itag = iota
+	pointerType
+	sliceType
+	arrayType
+	chanType
+	mapType
+	signatureType
+	structType
+	interfaceType
+	typeParamType
+	instanceType
+	unionType
+)
+
+const io_SeekCurrent = 1 // io.SeekCurrent (not defined in Go 1.4)
+
+// ImportData imports a package from the serialized package data
+// and returns the number of bytes consumed and a reference to the package.
+// If the export data version is not recognized or the format is otherwise
+// compromised, an error is returned.
+func ImportData(imports map[string]*types2.Package, data, path string) (pkg *types2.Package, err error) {
+	const currentVersion = iexportVersionCurrent
+	version := int64(-1)
+	defer func() {
+		if e := recover(); e != nil {
+			if version > currentVersion {
+				err = fmt.Errorf("cannot import %q (%v), export data is newer version - update tool", path, e)
+			} else {
+				err = fmt.Errorf("cannot import %q (%v), possibly version skew - reinstall package", path, e)
+			}
+		}
+	}()
+
+	r := &intReader{strings.NewReader(data), path}
+
+	version = int64(r.uint64())
+	switch version {
+	case iexportVersionGo1_18, iexportVersionPosCol, iexportVersionGo1_11:
+	default:
+		errorf("unknown iexport format version %d", version)
+	}
+
+	sLen := int64(r.uint64())
+	dLen := int64(r.uint64())
+
+	whence, _ := r.Seek(0, io_SeekCurrent)
+	stringData := data[whence : whence+sLen]
+	declData := data[whence+sLen : whence+sLen+dLen]
+	r.Seek(sLen+dLen, io_SeekCurrent)
+
+	p := iimporter{
+		exportVersion: version,
+		ipath:         path,
+		version:       int(version),
+
+		stringData:   stringData,
+		pkgCache:     make(map[uint64]*types2.Package),
+		posBaseCache: make(map[uint64]*syntax.PosBase),
+
+		declData: declData,
+		pkgIndex: make(map[*types2.Package]map[string]uint64),
+		typCache: make(map[uint64]types2.Type),
+		// Separate map for typeparams, keyed by their package and unique
+		// name (name with subscript).
+		tparamIndex: make(map[ident]*types2.TypeParam),
+	}
+
+	for i, pt := range predeclared {
+		p.typCache[uint64(i)] = pt
+	}
+
+	pkgList := make([]*types2.Package, r.uint64())
+	for i := range pkgList {
+		pkgPathOff := r.uint64()
+		pkgPath := p.stringAt(pkgPathOff)
+		pkgName := p.stringAt(r.uint64())
+		_ = int(r.uint64()) // was package height, but not necessary anymore.
+
+		if pkgPath == "" {
+			pkgPath = path
+		}
+		pkg := imports[pkgPath]
+		if pkg == nil {
+			pkg = types2.NewPackage(pkgPath, pkgName)
+			imports[pkgPath] = pkg
+		} else {
+			if pkg.Name() != pkgName {
+				errorf("conflicting names %s and %s for package %q", pkg.Name(), pkgName, path)
+			}
+		}
+
+		p.pkgCache[pkgPathOff] = pkg
+
+		nameIndex := make(map[string]uint64)
+		for nSyms := r.uint64(); nSyms > 0; nSyms-- {
+			name := p.stringAt(r.uint64())
+			nameIndex[name] = r.uint64()
+		}
+
+		p.pkgIndex[pkg] = nameIndex
+		pkgList[i] = pkg
+	}
+
+	localpkg := pkgList[0]
+
+	names := make([]string, 0, len(p.pkgIndex[localpkg]))
+	for name := range p.pkgIndex[localpkg] {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	for _, name := range names {
+		p.doDecl(localpkg, name)
+	}
+
+	// SetConstraint can't be called if the constraint type is not yet complete.
+	// When type params are created in the 'P' case of (*importReader).obj(),
+	// the associated constraint type may not be complete due to recursion.
+	// Therefore, we defer calling SetConstraint there, and call it here instead
+	// after all types are complete.
+	for _, d := range p.later {
+		d.t.SetConstraint(d.constraint)
+	}
+	// record all referenced packages as imports
+	list := append(([]*types2.Package)(nil), pkgList[1:]...)
+	sort.Sort(byPath(list))
+	localpkg.SetImports(list)
+
+	// package was imported completely and without errors
+	localpkg.MarkComplete()
+
+	return localpkg, nil
+}
+
+type setConstraintArgs struct {
+	t          *types2.TypeParam
+	constraint types2.Type
+}
+
+type iimporter struct {
+	exportVersion int64
+	ipath         string
+	version       int
+
+	stringData   string
+	pkgCache     map[uint64]*types2.Package
+	posBaseCache map[uint64]*syntax.PosBase
+
+	declData    string
+	pkgIndex    map[*types2.Package]map[string]uint64
+	typCache    map[uint64]types2.Type
+	tparamIndex map[ident]*types2.TypeParam
+
+	interfaceList []*types2.Interface
+
+	// Arguments for calls to SetConstraint that are deferred due to recursive types
+	later []setConstraintArgs
+}
+
+func (p *iimporter) doDecl(pkg *types2.Package, name string) {
+	// See if we've already imported this declaration.
+	if obj := pkg.Scope().Lookup(name); obj != nil {
+		return
+	}
+
+	off, ok := p.pkgIndex[pkg][name]
+	if !ok {
+		errorf("%v.%v not in index", pkg, name)
+	}
+
+	r := &importReader{p: p, currPkg: pkg}
+	r.declReader.Reset(p.declData[off:])
+
+	r.obj(name)
+}
+
+func (p *iimporter) stringAt(off uint64) string {
+	var x [binary.MaxVarintLen64]byte
+	n := copy(x[:], p.stringData[off:])
+
+	slen, n := binary.Uvarint(x[:n])
+	if n <= 0 {
+		errorf("varint failed")
+	}
+	spos := off + uint64(n)
+	return p.stringData[spos : spos+slen]
+}
+
+func (p *iimporter) pkgAt(off uint64) *types2.Package {
+	if pkg, ok := p.pkgCache[off]; ok {
+		return pkg
+	}
+	path := p.stringAt(off)
+	errorf("missing package %q in %q", path, p.ipath)
+	return nil
+}
+
+func (p *iimporter) posBaseAt(off uint64) *syntax.PosBase {
+	if posBase, ok := p.posBaseCache[off]; ok {
+		return posBase
+	}
+	filename := p.stringAt(off)
+	posBase := syntax.NewTrimmedFileBase(filename, true)
+	p.posBaseCache[off] = posBase
+	return posBase
+}
+
+func (p *iimporter) typAt(off uint64, base *types2.Named) types2.Type {
+	if t, ok := p.typCache[off]; ok && canReuse(base, t) {
+		return t
+	}
+
+	if off < predeclReserved {
+		errorf("predeclared type missing from cache: %v", off)
+	}
+
+	r := &importReader{p: p}
+	r.declReader.Reset(p.declData[off-predeclReserved:])
+	t := r.doType(base)
+
+	if canReuse(base, t) {
+		p.typCache[off] = t
+	}
+	return t
+}
+
+// canReuse reports whether the type rhs on the RHS of the declaration for def
+// may be re-used.
+//
+// Specifically, if def is non-nil and rhs is an interface type with methods, it
+// may not be re-used because we have a convention of setting the receiver type
+// for interface methods to def.
+func canReuse(def *types2.Named, rhs types2.Type) bool {
+	if def == nil {
+		return true
+	}
+	iface, _ := rhs.(*types2.Interface)
+	if iface == nil {
+		return true
+	}
+	// Don't use iface.Empty() here as iface may not be complete.
+	return iface.NumEmbeddeds() == 0 && iface.NumExplicitMethods() == 0
+}
+
+type importReader struct {
+	p           *iimporter
+	declReader  strings.Reader
+	currPkg     *types2.Package
+	prevPosBase *syntax.PosBase
+	prevLine    int64
+	prevColumn  int64
+}
+
+func (r *importReader) obj(name string) {
+	tag := r.byte()
+	pos := r.pos()
+
+	switch tag {
+	case 'A':
+		typ := r.typ()
+
+		r.declare(types2.NewTypeName(pos, r.currPkg, name, typ))
+
+	case 'C':
+		typ, val := r.value()
+
+		r.declare(types2.NewConst(pos, r.currPkg, name, typ, val))
+
+	case 'F', 'G':
+		var tparams []*types2.TypeParam
+		if tag == 'G' {
+			tparams = r.tparamList()
+		}
+		sig := r.signature(nil, nil, tparams)
+		r.declare(types2.NewFunc(pos, r.currPkg, name, sig))
+
+	case 'T', 'U':
+		// Types can be recursive. We need to setup a stub
+		// declaration before recursing.
+		obj := types2.NewTypeName(pos, r.currPkg, name, nil)
+		named := types2.NewNamed(obj, nil, nil)
+		// Declare obj before calling r.tparamList, so the new type name is recognized
+		// if used in the constraint of one of its own typeparams (see #48280).
+		r.declare(obj)
+		if tag == 'U' {
+			tparams := r.tparamList()
+			named.SetTypeParams(tparams)
+		}
+
+		underlying := r.p.typAt(r.uint64(), named).Underlying()
+		named.SetUnderlying(underlying)
+
+		if !isInterface(underlying) {
+			for n := r.uint64(); n > 0; n-- {
+				mpos := r.pos()
+				mname := r.ident()
+				recv := r.param()
+
+				// If the receiver has any targs, set those as the
+				// rparams of the method (since those are the
+				// typeparams being used in the method sig/body).
+				targs := baseType(recv.Type()).TypeArgs()
+				var rparams []*types2.TypeParam
+				if targs.Len() > 0 {
+					rparams = make([]*types2.TypeParam, targs.Len())
+					for i := range rparams {
+						rparams[i], _ = targs.At(i).(*types2.TypeParam)
+					}
+				}
+				msig := r.signature(recv, rparams, nil)
+
+				named.AddMethod(types2.NewFunc(mpos, r.currPkg, mname, msig))
+			}
+		}
+
+	case 'P':
+		// We need to "declare" a typeparam in order to have a name that
+		// can be referenced recursively (if needed) in the type param's
+		// bound.
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected type param type")
+		}
+		name0 := typecheck.TparamName(name)
+		if name0 == "" {
+			errorf("malformed type parameter export name %s: missing prefix", name)
+		}
+
+		tn := types2.NewTypeName(pos, r.currPkg, name0, nil)
+		t := types2.NewTypeParam(tn, nil)
+		// To handle recursive references to the typeparam within its
+		// bound, save the partial type in tparamIndex before reading the bounds.
+		id := ident{r.currPkg, name}
+		r.p.tparamIndex[id] = t
+
+		var implicit bool
+		if r.p.exportVersion >= iexportVersionGo1_18 {
+			implicit = r.bool()
+		}
+		constraint := r.typ()
+		if implicit {
+			iface, _ := constraint.(*types2.Interface)
+			if iface == nil {
+				errorf("non-interface constraint marked implicit")
+			}
+			iface.MarkImplicit()
+		}
+		// The constraint type may not be complete, if we
+		// are in the middle of a type recursion involving type
+		// constraints. So, we defer SetConstraint until we have
+		// completely set up all types in ImportData.
+		r.p.later = append(r.p.later, setConstraintArgs{t: t, constraint: constraint})
+
+	case 'V':
+		typ := r.typ()
+
+		r.declare(types2.NewVar(pos, r.currPkg, name, typ))
+
+	default:
+		errorf("unexpected tag: %v", tag)
+	}
+}
+
+func (r *importReader) declare(obj types2.Object) {
+	obj.Pkg().Scope().Insert(obj)
+}
+
+func (r *importReader) value() (typ types2.Type, val constant.Value) {
+	typ = r.typ()
+	if r.p.exportVersion >= iexportVersionGo1_18 {
+		// TODO: add support for using the kind
+		_ = constant.Kind(r.int64())
+	}
+
+	switch b := typ.Underlying().(*types2.Basic); b.Info() & types2.IsConstType {
+	case types2.IsBoolean:
+		val = constant.MakeBool(r.bool())
+
+	case types2.IsString:
+		val = constant.MakeString(r.string())
+
+	case types2.IsInteger:
+		var x big.Int
+		r.mpint(&x, b)
+		val = constant.Make(&x)
+
+	case types2.IsFloat:
+		val = r.mpfloat(b)
+
+	case types2.IsComplex:
+		re := r.mpfloat(b)
+		im := r.mpfloat(b)
+		val = constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
+
+	default:
+		errorf("unexpected type %v", typ) // panics
+		panic("unreachable")
+	}
+
+	return
+}
+
+func intSize(b *types2.Basic) (signed bool, maxBytes uint) {
+	if (b.Info() & types2.IsUntyped) != 0 {
+		return true, 64
+	}
+
+	switch b.Kind() {
+	case types2.Float32, types2.Complex64:
+		return true, 3
+	case types2.Float64, types2.Complex128:
+		return true, 7
+	}
+
+	signed = (b.Info() & types2.IsUnsigned) == 0
+	switch b.Kind() {
+	case types2.Int8, types2.Uint8:
+		maxBytes = 1
+	case types2.Int16, types2.Uint16:
+		maxBytes = 2
+	case types2.Int32, types2.Uint32:
+		maxBytes = 4
+	default:
+		maxBytes = 8
+	}
+
+	return
+}
+
+func (r *importReader) mpint(x *big.Int, typ *types2.Basic) {
+	signed, maxBytes := intSize(typ)
+
+	maxSmall := 256 - maxBytes
+	if signed {
+		maxSmall = 256 - 2*maxBytes
+	}
+	if maxBytes == 1 {
+		maxSmall = 256
+	}
+
+	n, _ := r.declReader.ReadByte()
+	if uint(n) < maxSmall {
+		v := int64(n)
+		if signed {
+			v >>= 1
+			if n&1 != 0 {
+				v = ^v
+			}
+		}
+		x.SetInt64(v)
+		return
+	}
+
+	v := -n
+	if signed {
+		v = -(n &^ 1) >> 1
+	}
+	if v < 1 || uint(v) > maxBytes {
+		errorf("weird decoding: %v, %v => %v", n, signed, v)
+	}
+	b := make([]byte, v)
+	io.ReadFull(&r.declReader, b)
+	x.SetBytes(b)
+	if signed && n&1 != 0 {
+		x.Neg(x)
+	}
+}
+
+func (r *importReader) mpfloat(typ *types2.Basic) constant.Value {
+	var mant big.Int
+	r.mpint(&mant, typ)
+	var f big.Float
+	f.SetInt(&mant)
+	if f.Sign() != 0 {
+		f.SetMantExp(&f, int(r.int64()))
+	}
+	return constant.Make(&f)
+}
+
+func (r *importReader) ident() string {
+	return r.string()
+}
+
+func (r *importReader) qualifiedIdent() (*types2.Package, string) {
+	name := r.string()
+	pkg := r.pkg()
+	return pkg, name
+}
+
+func (r *importReader) pos() syntax.Pos {
+	if r.p.version >= 1 {
+		r.posv1()
+	} else {
+		r.posv0()
+	}
+
+	if (r.prevPosBase == nil || r.prevPosBase.Filename() == "") && r.prevLine == 0 && r.prevColumn == 0 {
+		return syntax.Pos{}
+	}
+
+	return syntax.MakePos(r.prevPosBase, uint(r.prevLine), uint(r.prevColumn))
+}
+
+func (r *importReader) posv0() {
+	delta := r.int64()
+	if delta != deltaNewFile {
+		r.prevLine += delta
+	} else if l := r.int64(); l == -1 {
+		r.prevLine += deltaNewFile
+	} else {
+		r.prevPosBase = r.posBase()
+		r.prevLine = l
+	}
+}
+
+func (r *importReader) posv1() {
+	delta := r.int64()
+	r.prevColumn += delta >> 1
+	if delta&1 != 0 {
+		delta = r.int64()
+		r.prevLine += delta >> 1
+		if delta&1 != 0 {
+			r.prevPosBase = r.posBase()
+		}
+	}
+}
+
+func (r *importReader) typ() types2.Type {
+	return r.p.typAt(r.uint64(), nil)
+}
+
+func isInterface(t types2.Type) bool {
+	_, ok := t.(*types2.Interface)
+	return ok
+}
+
+func (r *importReader) pkg() *types2.Package     { return r.p.pkgAt(r.uint64()) }
+func (r *importReader) string() string           { return r.p.stringAt(r.uint64()) }
+func (r *importReader) posBase() *syntax.PosBase { return r.p.posBaseAt(r.uint64()) }
+
+func (r *importReader) doType(base *types2.Named) types2.Type {
+	switch k := r.kind(); k {
+	default:
+		errorf("unexpected kind tag in %q: %v", r.p.ipath, k)
+		return nil
+
+	case definedType:
+		pkg, name := r.qualifiedIdent()
+		r.p.doDecl(pkg, name)
+		return pkg.Scope().Lookup(name).(*types2.TypeName).Type()
+	case pointerType:
+		return types2.NewPointer(r.typ())
+	case sliceType:
+		return types2.NewSlice(r.typ())
+	case arrayType:
+		n := r.uint64()
+		return types2.NewArray(r.typ(), int64(n))
+	case chanType:
+		dir := chanDir(int(r.uint64()))
+		return types2.NewChan(dir, r.typ())
+	case mapType:
+		return types2.NewMap(r.typ(), r.typ())
+	case signatureType:
+		r.currPkg = r.pkg()
+		return r.signature(nil, nil, nil)
+
+	case structType:
+		r.currPkg = r.pkg()
+
+		fields := make([]*types2.Var, r.uint64())
+		tags := make([]string, len(fields))
+		for i := range fields {
+			fpos := r.pos()
+			fname := r.ident()
+			ftyp := r.typ()
+			emb := r.bool()
+			tag := r.string()
+
+			fields[i] = types2.NewField(fpos, r.currPkg, fname, ftyp, emb)
+			tags[i] = tag
+		}
+		return types2.NewStruct(fields, tags)
+
+	case interfaceType:
+		r.currPkg = r.pkg()
+
+		embeddeds := make([]types2.Type, r.uint64())
+		for i := range embeddeds {
+			_ = r.pos()
+			embeddeds[i] = r.typ()
+		}
+
+		methods := make([]*types2.Func, r.uint64())
+		for i := range methods {
+			mpos := r.pos()
+			mname := r.ident()
+
+			// TODO(mdempsky): Matches bimport.go, but I
+			// don't agree with this.
+			var recv *types2.Var
+			if base != nil {
+				recv = types2.NewVar(syntax.Pos{}, r.currPkg, "", base)
+			}
+
+			msig := r.signature(recv, nil, nil)
+			methods[i] = types2.NewFunc(mpos, r.currPkg, mname, msig)
+		}
+
+		typ := types2.NewInterfaceType(methods, embeddeds)
+		r.p.interfaceList = append(r.p.interfaceList, typ)
+		return typ
+
+	case typeParamType:
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected type param type")
+		}
+		pkg, name := r.qualifiedIdent()
+		id := ident{pkg, name}
+		if t, ok := r.p.tparamIndex[id]; ok {
+			// We're already in the process of importing this typeparam.
+			return t
+		}
+		// Otherwise, import the definition of the typeparam now.
+		r.p.doDecl(pkg, name)
+		return r.p.tparamIndex[id]
+
+	case instanceType:
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected instantiation type")
+		}
+		// pos does not matter for instances: they are positioned on the original
+		// type.
+		_ = r.pos()
+		len := r.uint64()
+		targs := make([]types2.Type, len)
+		for i := range targs {
+			targs[i] = r.typ()
+		}
+		baseType := r.typ()
+		// The imported instantiated type doesn't include any methods, so
+		// we must always use the methods of the base (orig) type.
+		// TODO provide a non-nil *Context
+		t, _ := types2.Instantiate(nil, baseType, targs, false)
+		return t
+
+	case unionType:
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected instantiation type")
+		}
+		terms := make([]*types2.Term, r.uint64())
+		for i := range terms {
+			terms[i] = types2.NewTerm(r.bool(), r.typ())
+		}
+		return types2.NewUnion(terms)
+	}
+}
+
+func (r *importReader) kind() itag {
+	return itag(r.uint64())
+}
+
+func (r *importReader) signature(recv *types2.Var, rparams, tparams []*types2.TypeParam) *types2.Signature {
+	params := r.paramList()
+	results := r.paramList()
+	variadic := params.Len() > 0 && r.bool()
+	return types2.NewSignatureType(recv, rparams, tparams, params, results, variadic)
+}
+
+func (r *importReader) tparamList() []*types2.TypeParam {
+	n := r.uint64()
+	if n == 0 {
+		return nil
+	}
+	xs := make([]*types2.TypeParam, n)
+	for i := range xs {
+		xs[i] = r.typ().(*types2.TypeParam)
+	}
+	return xs
+}
+
+func (r *importReader) paramList() *types2.Tuple {
+	xs := make([]*types2.Var, r.uint64())
+	for i := range xs {
+		xs[i] = r.param()
+	}
+	return types2.NewTuple(xs...)
+}
+
+func (r *importReader) param() *types2.Var {
+	pos := r.pos()
+	name := r.ident()
+	typ := r.typ()
+	return types2.NewParam(pos, r.currPkg, name, typ)
+}
+
+func (r *importReader) bool() bool {
+	return r.uint64() != 0
+}
+
+func (r *importReader) int64() int64 {
+	n, err := binary.ReadVarint(&r.declReader)
+	if err != nil {
+		errorf("readVarint: %v", err)
+	}
+	return n
+}
+
+func (r *importReader) uint64() uint64 {
+	n, err := binary.ReadUvarint(&r.declReader)
+	if err != nil {
+		errorf("readUvarint: %v", err)
+	}
+	return n
+}
+
+func (r *importReader) byte() byte {
+	x, err := r.declReader.ReadByte()
+	if err != nil {
+		errorf("declReader.ReadByte: %v", err)
+	}
+	return x
+}
+
+func baseType(typ types2.Type) *types2.Named {
+	// pointer receivers are never types2.Named types
+	if p, _ := typ.(*types2.Pointer); p != nil {
+		typ = p.Elem()
+	}
+	// receiver base types are always (possibly generic) types2.Named types
+	n, _ := typ.(*types2.Named)
+	return n
+}
diff --git a/src/cmd/compile/internal/importer/support.go b/src/cmd/compile/internal/importer/support.go
new file mode 100644
index 0000000..5810f5e
--- /dev/null
+++ b/src/cmd/compile/internal/importer/support.go
@@ -0,0 +1,152 @@
+// Copyright 2015 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.
+
+// This file implements support functionality for iimport.go.
+
+package importer
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/types2"
+	"fmt"
+	"go/token"
+	"internal/pkgbits"
+	"sync"
+)
+
+func assert(p bool) {
+	base.Assert(p)
+}
+
+func errorf(format string, args ...interface{}) {
+	panic(fmt.Sprintf(format, args...))
+}
+
+const deltaNewFile = -64 // see cmd/compile/internal/gc/bexport.go
+
+// Synthesize a token.Pos
+type fakeFileSet struct {
+	fset  *token.FileSet
+	files map[string]*token.File
+}
+
+func (s *fakeFileSet) pos(file string, line, column int) token.Pos {
+	// TODO(mdempsky): Make use of column.
+
+	// Since we don't know the set of needed file positions, we
+	// reserve maxlines positions per file.
+	const maxlines = 64 * 1024
+	f := s.files[file]
+	if f == nil {
+		f = s.fset.AddFile(file, -1, maxlines)
+		s.files[file] = f
+		// Allocate the fake linebreak indices on first use.
+		// TODO(adonovan): opt: save ~512KB using a more complex scheme?
+		fakeLinesOnce.Do(func() {
+			fakeLines = make([]int, maxlines)
+			for i := range fakeLines {
+				fakeLines[i] = i
+			}
+		})
+		f.SetLines(fakeLines)
+	}
+
+	if line > maxlines {
+		line = 1
+	}
+
+	// Treat the file as if it contained only newlines
+	// and column=1: use the line number as the offset.
+	return f.Pos(line - 1)
+}
+
+var (
+	fakeLines     []int
+	fakeLinesOnce sync.Once
+)
+
+func chanDir(d int) types2.ChanDir {
+	// tag values must match the constants in cmd/compile/internal/gc/go.go
+	switch d {
+	case 1 /* Crecv */ :
+		return types2.RecvOnly
+	case 2 /* Csend */ :
+		return types2.SendOnly
+	case 3 /* Cboth */ :
+		return types2.SendRecv
+	default:
+		errorf("unexpected channel dir %d", d)
+		return 0
+	}
+}
+
+var predeclared = []types2.Type{
+	// basic types
+	types2.Typ[types2.Bool],
+	types2.Typ[types2.Int],
+	types2.Typ[types2.Int8],
+	types2.Typ[types2.Int16],
+	types2.Typ[types2.Int32],
+	types2.Typ[types2.Int64],
+	types2.Typ[types2.Uint],
+	types2.Typ[types2.Uint8],
+	types2.Typ[types2.Uint16],
+	types2.Typ[types2.Uint32],
+	types2.Typ[types2.Uint64],
+	types2.Typ[types2.Uintptr],
+	types2.Typ[types2.Float32],
+	types2.Typ[types2.Float64],
+	types2.Typ[types2.Complex64],
+	types2.Typ[types2.Complex128],
+	types2.Typ[types2.String],
+
+	// basic type aliases
+	types2.Universe.Lookup("byte").Type(),
+	types2.Universe.Lookup("rune").Type(),
+
+	// error
+	types2.Universe.Lookup("error").Type(),
+
+	// untyped types
+	types2.Typ[types2.UntypedBool],
+	types2.Typ[types2.UntypedInt],
+	types2.Typ[types2.UntypedRune],
+	types2.Typ[types2.UntypedFloat],
+	types2.Typ[types2.UntypedComplex],
+	types2.Typ[types2.UntypedString],
+	types2.Typ[types2.UntypedNil],
+
+	// package unsafe
+	types2.Typ[types2.UnsafePointer],
+
+	// invalid type
+	types2.Typ[types2.Invalid], // only appears in packages with errors
+
+	// used internally by gc; never used by this package or in .a files
+	// not to be confused with the universe any
+	anyType{},
+
+	// comparable
+	types2.Universe.Lookup("comparable").Type(),
+
+	// any
+	types2.Universe.Lookup("any").Type(),
+}
+
+type anyType struct{}
+
+func (t anyType) Underlying() types2.Type { return t }
+func (t anyType) String() string          { return "any" }
+
+// See cmd/compile/internal/noder.derivedInfo.
+type derivedInfo struct {
+	idx    pkgbits.Index
+	needed bool
+}
+
+// See cmd/compile/internal/noder.typeInfo.
+type typeInfo struct {
+	idx     pkgbits.Index
+	derived bool
+}
diff --git a/src/cmd/compile/internal/importer/testdata/a.go b/src/cmd/compile/internal/importer/testdata/a.go
new file mode 100644
index 0000000..56e4292
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/a.go
@@ -0,0 +1,14 @@
+// Copyright 2016 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.
+
+// Input for TestIssue13566
+
+package a
+
+import "encoding/json"
+
+type A struct {
+	a    *A
+	json json.RawMessage
+}
diff --git a/src/cmd/compile/internal/importer/testdata/b.go b/src/cmd/compile/internal/importer/testdata/b.go
new file mode 100644
index 0000000..4196678
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/b.go
@@ -0,0 +1,11 @@
+// Copyright 2016 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.
+
+// Input for TestIssue13566
+
+package b
+
+import "./a"
+
+type A a.A
diff --git a/src/cmd/compile/internal/importer/testdata/exports.go b/src/cmd/compile/internal/importer/testdata/exports.go
new file mode 100644
index 0000000..91598c0
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/exports.go
@@ -0,0 +1,91 @@
+// Copyright 2011 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.
+
+// This file is used to generate an object file which
+// serves as test file for gcimporter_test.go.
+
+package exports
+
+import "go/ast"
+
+// Issue 3682: Correctly read dotted identifiers from export data.
+const init1 = 0
+
+func init() {}
+
+const (
+	C0  int     = 0
+	C1          = 3.14159265
+	C2          = 2.718281828i
+	C3          = -123.456e-789
+	C4          = +123.456e+789
+	C5          = 1234i
+	C6          = "foo\n"
+	C7          = `bar\n`
+	C8          = 42
+	C9  int     = 42
+	C10 float64 = 42
+)
+
+type (
+	T1  int
+	T2  [10]int
+	T3  []int
+	T4  *int
+	T5  chan int
+	T6a chan<- int
+	T6b chan (<-chan int)
+	T6c chan<- (chan int)
+	T7  <-chan *ast.File
+	T8  struct{}
+	T9  struct {
+		a    int
+		b, c float32
+		d    []string `go:"tag"`
+	}
+	T10 struct {
+		T8
+		T9
+		_ *T10
+	}
+	T11 map[int]string
+	T12 interface{}
+	T13 interface {
+		m1()
+		m2(int) float32
+	}
+	T14 interface {
+		T12
+		T13
+		m3(x ...struct{}) []T9
+	}
+	T15 func()
+	T16 func(int)
+	T17 func(x int)
+	T18 func() float32
+	T19 func() (x float32)
+	T20 func(...interface{})
+	T21 struct{ next *T21 }
+	T22 struct{ link *T23 }
+	T23 struct{ link *T22 }
+	T24 *T24
+	T25 *T26
+	T26 *T27
+	T27 *T25
+	T28 func(T28) T28
+)
+
+var (
+	V0 int
+	V1         = -991.0
+	V2 float32 = 1.2
+)
+
+func F1()         {}
+func F2(x int)    {}
+func F3() int     { return 0 }
+func F4() float32 { return 0 }
+func F5(a, b, c int, u, v, w struct{ x, y T1 }, more ...interface{}) (p, q, r chan<- T10)
+
+func (p *T1) M1()
diff --git a/src/cmd/compile/internal/importer/testdata/generics.go b/src/cmd/compile/internal/importer/testdata/generics.go
new file mode 100644
index 0000000..00bf040
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/generics.go
@@ -0,0 +1,29 @@
+// Copyright 2021 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.
+
+// This file is used to generate an object file which
+// serves as test file for gcimporter_test.go.
+
+package generics
+
+type Any any
+
+var x any
+
+type T[A, B any] struct {
+	Left  A
+	Right B
+}
+
+var X T[int, string] = T[int, string]{1, "hi"}
+
+func ToInt[P interface{ ~int }](p P) int { return int(p) }
+
+var IntID = ToInt[int]
+
+type G[C comparable] int
+
+func ImplicitFunc[T ~int]() {}
+
+type ImplicitType[T ~int] int
diff --git a/src/cmd/compile/internal/importer/testdata/issue15920.go b/src/cmd/compile/internal/importer/testdata/issue15920.go
new file mode 100644
index 0000000..c70f7d8
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/issue15920.go
@@ -0,0 +1,11 @@
+// Copyright 2016 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 p
+
+// The underlying type of Error is the underlying type of error.
+// Make sure we can import this again without problems.
+type Error error
+
+func F() Error { return nil }
diff --git a/src/cmd/compile/internal/importer/testdata/issue20046.go b/src/cmd/compile/internal/importer/testdata/issue20046.go
new file mode 100644
index 0000000..c63ee82
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/issue20046.go
@@ -0,0 +1,9 @@
+// Copyright 2017 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 p
+
+var V interface {
+	M()
+}
diff --git a/src/cmd/compile/internal/importer/testdata/issue25301.go b/src/cmd/compile/internal/importer/testdata/issue25301.go
new file mode 100644
index 0000000..e3dc98b
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/issue25301.go
@@ -0,0 +1,17 @@
+// Copyright 2018 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 issue25301
+
+type (
+	A = interface {
+		M()
+	}
+	T interface {
+		A
+	}
+	S struct{}
+)
+
+func (S) M() { println("m") }
diff --git a/src/cmd/compile/internal/importer/testdata/issue25596.go b/src/cmd/compile/internal/importer/testdata/issue25596.go
new file mode 100644
index 0000000..8923373
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/issue25596.go
@@ -0,0 +1,13 @@
+// Copyright 2018 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 issue25596
+
+type E interface {
+	M() T
+}
+
+type T interface {
+	E
+}
diff --git a/src/cmd/compile/internal/importer/testdata/p.go b/src/cmd/compile/internal/importer/testdata/p.go
new file mode 100644
index 0000000..9e2e705
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/p.go
@@ -0,0 +1,13 @@
+// Copyright 2016 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.
+
+// Input for TestIssue15517
+
+package p
+
+const C = 0
+
+var V int
+
+func F() {}
diff --git a/src/cmd/compile/internal/importer/testdata/versions/test.go b/src/cmd/compile/internal/importer/testdata/versions/test.go
new file mode 100644
index 0000000..227fc09
--- /dev/null
+++ b/src/cmd/compile/internal/importer/testdata/versions/test.go
@@ -0,0 +1,28 @@
+// Copyright 2016 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.
+
+// To create a test case for a new export format version,
+// build this package with the latest compiler and store
+// the resulting .a file appropriately named in the versions
+// directory. The VersionHandling test will pick it up.
+//
+// In the testdata/versions:
+//
+// go build -o test_go1.$X_$Y.a test.go
+//
+// with $X = Go version and $Y = export format version
+// (add 'b' or 'i' to distinguish between binary and
+// indexed format starting with 1.11 as long as both
+// formats are supported).
+//
+// Make sure this source is extended such that it exercises
+// whatever export format change has taken place.
+
+package test
+
+// Any release before and including Go 1.7 didn't encode
+// the package for a blank struct field.
+type BlankField struct {
+	_ int
+}
diff --git a/src/cmd/compile/internal/importer/ureader.go b/src/cmd/compile/internal/importer/ureader.go
new file mode 100644
index 0000000..f5c2f41
--- /dev/null
+++ b/src/cmd/compile/internal/importer/ureader.go
@@ -0,0 +1,535 @@
+// Copyright 2021 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 importer
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/types2"
+	"cmd/internal/src"
+	"internal/pkgbits"
+)
+
+type pkgReader struct {
+	pkgbits.PkgDecoder
+
+	ctxt    *types2.Context
+	imports map[string]*types2.Package
+
+	posBases []*syntax.PosBase
+	pkgs     []*types2.Package
+	typs     []types2.Type
+}
+
+func ReadPackage(ctxt *types2.Context, imports map[string]*types2.Package, input pkgbits.PkgDecoder) *types2.Package {
+	pr := pkgReader{
+		PkgDecoder: input,
+
+		ctxt:    ctxt,
+		imports: imports,
+
+		posBases: make([]*syntax.PosBase, input.NumElems(pkgbits.RelocPosBase)),
+		pkgs:     make([]*types2.Package, input.NumElems(pkgbits.RelocPkg)),
+		typs:     make([]types2.Type, input.NumElems(pkgbits.RelocType)),
+	}
+
+	r := pr.newReader(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)
+	pkg := r.pkg()
+	r.Bool() // TODO(mdempsky): Remove; was "has init"
+
+	for i, n := 0, r.Len(); i < n; i++ {
+		// As if r.obj(), but avoiding the Scope.Lookup call,
+		// to avoid eager loading of imports.
+		r.Sync(pkgbits.SyncObject)
+		assert(!r.Bool())
+		r.p.objIdx(r.Reloc(pkgbits.RelocObj))
+		assert(r.Len() == 0)
+	}
+
+	r.Sync(pkgbits.SyncEOF)
+
+	pkg.MarkComplete()
+	return pkg
+}
+
+type reader struct {
+	pkgbits.Decoder
+
+	p *pkgReader
+
+	dict *readerDict
+}
+
+type readerDict struct {
+	bounds []typeInfo
+
+	tparams []*types2.TypeParam
+
+	derived      []derivedInfo
+	derivedTypes []types2.Type
+}
+
+type readerTypeBound struct {
+	derived  bool
+	boundIdx int
+}
+
+func (pr *pkgReader) newReader(k pkgbits.RelocKind, idx pkgbits.Index, marker pkgbits.SyncMarker) *reader {
+	return &reader{
+		Decoder: pr.NewDecoder(k, idx, marker),
+		p:       pr,
+	}
+}
+
+func (pr *pkgReader) tempReader(k pkgbits.RelocKind, idx pkgbits.Index, marker pkgbits.SyncMarker) *reader {
+	return &reader{
+		Decoder: pr.TempDecoder(k, idx, marker),
+		p:       pr,
+	}
+}
+
+func (pr *pkgReader) retireReader(r *reader) {
+	pr.RetireDecoder(&r.Decoder)
+}
+
+// @@@ Positions
+
+func (r *reader) pos() syntax.Pos {
+	r.Sync(pkgbits.SyncPos)
+	if !r.Bool() {
+		return syntax.Pos{}
+	}
+
+	// TODO(mdempsky): Delta encoding.
+	posBase := r.posBase()
+	line := r.Uint()
+	col := r.Uint()
+	return syntax.MakePos(posBase, line, col)
+}
+
+func (r *reader) posBase() *syntax.PosBase {
+	return r.p.posBaseIdx(r.Reloc(pkgbits.RelocPosBase))
+}
+
+func (pr *pkgReader) posBaseIdx(idx pkgbits.Index) *syntax.PosBase {
+	if b := pr.posBases[idx]; b != nil {
+		return b
+	}
+	var b *syntax.PosBase
+	{
+		r := pr.tempReader(pkgbits.RelocPosBase, idx, pkgbits.SyncPosBase)
+
+		filename := r.String()
+
+		if r.Bool() {
+			b = syntax.NewTrimmedFileBase(filename, true)
+		} else {
+			pos := r.pos()
+			line := r.Uint()
+			col := r.Uint()
+			b = syntax.NewLineBase(pos, filename, true, line, col)
+		}
+		pr.retireReader(r)
+	}
+
+	pr.posBases[idx] = b
+	return b
+}
+
+// @@@ Packages
+
+func (r *reader) pkg() *types2.Package {
+	r.Sync(pkgbits.SyncPkg)
+	return r.p.pkgIdx(r.Reloc(pkgbits.RelocPkg))
+}
+
+func (pr *pkgReader) pkgIdx(idx pkgbits.Index) *types2.Package {
+	// TODO(mdempsky): Consider using some non-nil pointer to indicate
+	// the universe scope, so we don't need to keep re-reading it.
+	if pkg := pr.pkgs[idx]; pkg != nil {
+		return pkg
+	}
+
+	pkg := pr.newReader(pkgbits.RelocPkg, idx, pkgbits.SyncPkgDef).doPkg()
+	pr.pkgs[idx] = pkg
+	return pkg
+}
+
+func (r *reader) doPkg() *types2.Package {
+	path := r.String()
+	switch path {
+	case "":
+		path = r.p.PkgPath()
+	case "builtin":
+		return nil // universe
+	case "unsafe":
+		return types2.Unsafe
+	}
+
+	if pkg := r.p.imports[path]; pkg != nil {
+		return pkg
+	}
+
+	name := r.String()
+	pkg := types2.NewPackage(path, name)
+	r.p.imports[path] = pkg
+
+	// TODO(mdempsky): The list of imported packages is important for
+	// go/types, but we could probably skip populating it for types2.
+	imports := make([]*types2.Package, r.Len())
+	for i := range imports {
+		imports[i] = r.pkg()
+	}
+	pkg.SetImports(imports)
+
+	return pkg
+}
+
+// @@@ Types
+
+func (r *reader) typ() types2.Type {
+	return r.p.typIdx(r.typInfo(), r.dict)
+}
+
+func (r *reader) typInfo() typeInfo {
+	r.Sync(pkgbits.SyncType)
+	if r.Bool() {
+		return typeInfo{idx: pkgbits.Index(r.Len()), derived: true}
+	}
+	return typeInfo{idx: r.Reloc(pkgbits.RelocType), derived: false}
+}
+
+func (pr *pkgReader) typIdx(info typeInfo, dict *readerDict) types2.Type {
+	idx := info.idx
+	var where *types2.Type
+	if info.derived {
+		where = &dict.derivedTypes[idx]
+		idx = dict.derived[idx].idx
+	} else {
+		where = &pr.typs[idx]
+	}
+
+	if typ := *where; typ != nil {
+		return typ
+	}
+
+	var typ types2.Type
+	{
+		r := pr.tempReader(pkgbits.RelocType, idx, pkgbits.SyncTypeIdx)
+		r.dict = dict
+
+		typ = r.doTyp()
+		assert(typ != nil)
+		pr.retireReader(r)
+	}
+
+	// See comment in pkgReader.typIdx explaining how this happens.
+	if prev := *where; prev != nil {
+		return prev
+	}
+
+	*where = typ
+	return typ
+}
+
+func (r *reader) doTyp() (res types2.Type) {
+	switch tag := pkgbits.CodeType(r.Code(pkgbits.SyncType)); tag {
+	default:
+		base.FatalfAt(src.NoXPos, "unhandled type tag: %v", tag)
+		panic("unreachable")
+
+	case pkgbits.TypeBasic:
+		return types2.Typ[r.Len()]
+
+	case pkgbits.TypeNamed:
+		obj, targs := r.obj()
+		name := obj.(*types2.TypeName)
+		if len(targs) != 0 {
+			t, _ := types2.Instantiate(r.p.ctxt, name.Type(), targs, false)
+			return t
+		}
+		return name.Type()
+
+	case pkgbits.TypeTypeParam:
+		return r.dict.tparams[r.Len()]
+
+	case pkgbits.TypeArray:
+		len := int64(r.Uint64())
+		return types2.NewArray(r.typ(), len)
+	case pkgbits.TypeChan:
+		dir := types2.ChanDir(r.Len())
+		return types2.NewChan(dir, r.typ())
+	case pkgbits.TypeMap:
+		return types2.NewMap(r.typ(), r.typ())
+	case pkgbits.TypePointer:
+		return types2.NewPointer(r.typ())
+	case pkgbits.TypeSignature:
+		return r.signature(nil, nil, nil)
+	case pkgbits.TypeSlice:
+		return types2.NewSlice(r.typ())
+	case pkgbits.TypeStruct:
+		return r.structType()
+	case pkgbits.TypeInterface:
+		return r.interfaceType()
+	case pkgbits.TypeUnion:
+		return r.unionType()
+	}
+}
+
+func (r *reader) structType() *types2.Struct {
+	fields := make([]*types2.Var, r.Len())
+	var tags []string
+	for i := range fields {
+		pos := r.pos()
+		pkg, name := r.selector()
+		ftyp := r.typ()
+		tag := r.String()
+		embedded := r.Bool()
+
+		fields[i] = types2.NewField(pos, pkg, name, ftyp, embedded)
+		if tag != "" {
+			for len(tags) < i {
+				tags = append(tags, "")
+			}
+			tags = append(tags, tag)
+		}
+	}
+	return types2.NewStruct(fields, tags)
+}
+
+func (r *reader) unionType() *types2.Union {
+	terms := make([]*types2.Term, r.Len())
+	for i := range terms {
+		terms[i] = types2.NewTerm(r.Bool(), r.typ())
+	}
+	return types2.NewUnion(terms)
+}
+
+func (r *reader) interfaceType() *types2.Interface {
+	methods := make([]*types2.Func, r.Len())
+	embeddeds := make([]types2.Type, r.Len())
+	implicit := len(methods) == 0 && len(embeddeds) == 1 && r.Bool()
+
+	for i := range methods {
+		pos := r.pos()
+		pkg, name := r.selector()
+		mtyp := r.signature(nil, nil, nil)
+		methods[i] = types2.NewFunc(pos, pkg, name, mtyp)
+	}
+
+	for i := range embeddeds {
+		embeddeds[i] = r.typ()
+	}
+
+	iface := types2.NewInterfaceType(methods, embeddeds)
+	if implicit {
+		iface.MarkImplicit()
+	}
+	return iface
+}
+
+func (r *reader) signature(recv *types2.Var, rtparams, tparams []*types2.TypeParam) *types2.Signature {
+	r.Sync(pkgbits.SyncSignature)
+
+	params := r.params()
+	results := r.params()
+	variadic := r.Bool()
+
+	return types2.NewSignatureType(recv, rtparams, tparams, params, results, variadic)
+}
+
+func (r *reader) params() *types2.Tuple {
+	r.Sync(pkgbits.SyncParams)
+	params := make([]*types2.Var, r.Len())
+	for i := range params {
+		params[i] = r.param()
+	}
+	return types2.NewTuple(params...)
+}
+
+func (r *reader) param() *types2.Var {
+	r.Sync(pkgbits.SyncParam)
+
+	pos := r.pos()
+	pkg, name := r.localIdent()
+	typ := r.typ()
+
+	return types2.NewParam(pos, pkg, name, typ)
+}
+
+// @@@ Objects
+
+func (r *reader) obj() (types2.Object, []types2.Type) {
+	r.Sync(pkgbits.SyncObject)
+
+	assert(!r.Bool())
+
+	pkg, name := r.p.objIdx(r.Reloc(pkgbits.RelocObj))
+	obj := pkg.Scope().Lookup(name)
+
+	targs := make([]types2.Type, r.Len())
+	for i := range targs {
+		targs[i] = r.typ()
+	}
+
+	return obj, targs
+}
+
+func (pr *pkgReader) objIdx(idx pkgbits.Index) (*types2.Package, string) {
+	var objPkg *types2.Package
+	var objName string
+	var tag pkgbits.CodeObj
+	{
+		rname := pr.tempReader(pkgbits.RelocName, idx, pkgbits.SyncObject1)
+
+		objPkg, objName = rname.qualifiedIdent()
+		assert(objName != "")
+
+		tag = pkgbits.CodeObj(rname.Code(pkgbits.SyncCodeObj))
+		pr.retireReader(rname)
+	}
+
+	if tag == pkgbits.ObjStub {
+		base.Assertf(objPkg == nil || objPkg == types2.Unsafe, "unexpected stub package: %v", objPkg)
+		return objPkg, objName
+	}
+
+	objPkg.Scope().InsertLazy(objName, func() types2.Object {
+		dict := pr.objDictIdx(idx)
+
+		r := pr.newReader(pkgbits.RelocObj, idx, pkgbits.SyncObject1)
+		r.dict = dict
+
+		switch tag {
+		default:
+			panic("weird")
+
+		case pkgbits.ObjAlias:
+			pos := r.pos()
+			typ := r.typ()
+			return types2.NewTypeName(pos, objPkg, objName, typ)
+
+		case pkgbits.ObjConst:
+			pos := r.pos()
+			typ := r.typ()
+			val := r.Value()
+			return types2.NewConst(pos, objPkg, objName, typ, val)
+
+		case pkgbits.ObjFunc:
+			pos := r.pos()
+			tparams := r.typeParamNames()
+			sig := r.signature(nil, nil, tparams)
+			return types2.NewFunc(pos, objPkg, objName, sig)
+
+		case pkgbits.ObjType:
+			pos := r.pos()
+
+			return types2.NewTypeNameLazy(pos, objPkg, objName, func(named *types2.Named) (tparams []*types2.TypeParam, underlying types2.Type, methods []*types2.Func) {
+				tparams = r.typeParamNames()
+
+				// TODO(mdempsky): Rewrite receiver types to underlying is an
+				// Interface? The go/types importer does this (I think because
+				// unit tests expected that), but cmd/compile doesn't care
+				// about it, so maybe we can avoid worrying about that here.
+				underlying = r.typ().Underlying()
+
+				methods = make([]*types2.Func, r.Len())
+				for i := range methods {
+					methods[i] = r.method()
+				}
+
+				return
+			})
+
+		case pkgbits.ObjVar:
+			pos := r.pos()
+			typ := r.typ()
+			return types2.NewVar(pos, objPkg, objName, typ)
+		}
+	})
+
+	return objPkg, objName
+}
+
+func (pr *pkgReader) objDictIdx(idx pkgbits.Index) *readerDict {
+	var dict readerDict
+	{
+		r := pr.tempReader(pkgbits.RelocObjDict, idx, pkgbits.SyncObject1)
+
+		if implicits := r.Len(); implicits != 0 {
+			base.Fatalf("unexpected object with %v implicit type parameter(s)", implicits)
+		}
+
+		dict.bounds = make([]typeInfo, r.Len())
+		for i := range dict.bounds {
+			dict.bounds[i] = r.typInfo()
+		}
+
+		dict.derived = make([]derivedInfo, r.Len())
+		dict.derivedTypes = make([]types2.Type, len(dict.derived))
+		for i := range dict.derived {
+			dict.derived[i] = derivedInfo{r.Reloc(pkgbits.RelocType), r.Bool()}
+		}
+
+		pr.retireReader(r)
+	}
+	// function references follow, but reader doesn't need those
+
+	return &dict
+}
+
+func (r *reader) typeParamNames() []*types2.TypeParam {
+	r.Sync(pkgbits.SyncTypeParamNames)
+
+	// Note: This code assumes it only processes objects without
+	// implement type parameters. This is currently fine, because
+	// reader is only used to read in exported declarations, which are
+	// always package scoped.
+
+	if len(r.dict.bounds) == 0 {
+		return nil
+	}
+
+	// Careful: Type parameter lists may have cycles. To allow for this,
+	// we construct the type parameter list in two passes: first we
+	// create all the TypeNames and TypeParams, then we construct and
+	// set the bound type.
+
+	r.dict.tparams = make([]*types2.TypeParam, len(r.dict.bounds))
+	for i := range r.dict.bounds {
+		pos := r.pos()
+		pkg, name := r.localIdent()
+
+		tname := types2.NewTypeName(pos, pkg, name, nil)
+		r.dict.tparams[i] = types2.NewTypeParam(tname, nil)
+	}
+
+	for i, bound := range r.dict.bounds {
+		r.dict.tparams[i].SetConstraint(r.p.typIdx(bound, r.dict))
+	}
+
+	return r.dict.tparams
+}
+
+func (r *reader) method() *types2.Func {
+	r.Sync(pkgbits.SyncMethod)
+	pos := r.pos()
+	pkg, name := r.selector()
+
+	rtparams := r.typeParamNames()
+	sig := r.signature(r.param(), rtparams, nil)
+
+	_ = r.pos() // TODO(mdempsky): Remove; this is a hacker for linker.go.
+	return types2.NewFunc(pos, pkg, name, sig)
+}
+
+func (r *reader) qualifiedIdent() (*types2.Package, string) { return r.ident(pkgbits.SyncSym) }
+func (r *reader) localIdent() (*types2.Package, string)     { return r.ident(pkgbits.SyncLocalIdent) }
+func (r *reader) selector() (*types2.Package, string)       { return r.ident(pkgbits.SyncSelector) }
+
+func (r *reader) ident(marker pkgbits.SyncMarker) (*types2.Package, string) {
+	r.Sync(marker)
+	return r.pkg(), r.String()
+}