diff --git a/src/cmd/go2go/testdata/go2path/src/gsort/gsort_test.go2 b/src/cmd/go2go/testdata/go2path/src/gsort/gsort_test.go2
index 47715ed23f..412a946f73 100644
--- a/src/cmd/go2go/testdata/go2path/src/gsort/gsort_test.go2
+++ b/src/cmd/go2go/testdata/go2path/src/gsort/gsort_test.go2
@@ -17,7 +17,7 @@ import (
 
 var ints = []int{74, 59, 238, -784, 9845, 959, 905, 0, 0, 42, 7586, -5467984, 7586}
 var float64s = []float64{74.3, 59.0, math.Inf(1), 238.2, -784.0, 2.3, math.NaN(), math.NaN(), math.Inf(-1), 9845.768, -959.7485, 905, 7.8, 7.8}
-var strings = []string{"", "Hello", "foo", "bar", "foo", "f00", "%*&^*&^&", "***"}
+var strs = []string{"", "Hello", "foo", "bar", "foo", "f00", "%*&^*&^&", "***"}
 
 func TestSortOrderedInts(t *testing.T) {
 	testOrdered(t, ints, sort.Ints)
@@ -28,7 +28,7 @@ func TestSortOrderedFloat64s(t *testing.T) {
 }
 
 func TestSortOrderedStrings(t *testing.T) {
-	testOrdered(t, strings, sort.Strings)
+	testOrdered(t, strs, sort.Strings)
 }
 
 func testOrdered(type Elem contracts.Ordered)(t *testing.T, s []Elem, sorter func([]Elem)) {
diff --git a/src/cmd/go2go/testdata/go2path/src/orderedmap/orderedmap.go2 b/src/cmd/go2go/testdata/go2path/src/orderedmap/orderedmap.go2
new file mode 100644
index 0000000000..684250f41d
--- /dev/null
+++ b/src/cmd/go2go/testdata/go2path/src/orderedmap/orderedmap.go2
@@ -0,0 +1,136 @@
+// Copyright 2020 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 orderedmap provides an ordered map, implemented as a binary tree.
+package orderedmap
+
+// FIXME: This should probably be container/orderedmap.
+
+import (
+	"context"
+
+	"chans"
+	"contracts"
+)
+
+// Map is an ordered map.
+type Map(type K, V) struct {
+	root    *node(K, V)
+	compare func(K, K) int
+}
+
+// node is the type of a node in the binary tree.
+type node(type K, V) struct {
+	key         K
+	val         V
+	left, right *node(K, V)
+}
+
+// New returns a new map. It takes a comparison function that compares two
+// keys and returns < 0 if the first is less, == 0 if they are equal,
+// > 0 if the first is greater.
+func New(type K, V)(compare func(K, K) int) *Map(K, V) {
+	return &Map(K, V){compare: compare}
+}
+
+// NewOrdered returns a new map whose key is an ordered type.
+// This is like New, but does not require providing a compare function.
+// The map compare function uses the obvious key ordering.
+func NewOrdered(type K, V contracts.Ordered(K))() *Map(K, V) {
+	return New(K, V)(func(k1, k2 K) int {
+		switch {
+		case k1 < k2:
+			return -1
+		case k1 == k2:
+			return 0
+		default:
+			return -1
+		}
+	})
+}
+
+// find looks up key in the map, returning either a pointer to the slot of the
+// node holding key, or a pointer to the slot where should a node would go.
+func (m *Map(K, V)) find(key K) **node(K, V) {
+	pn := &m.root
+	for *pn != nil {
+		switch cmp := m.compare(key, (*pn).key); {
+		case cmp < 0:
+			pn = &(*pn).left
+		case cmp > 0:
+			pn = &(*pn).right
+		default:
+			return pn
+		}
+	}
+	return pn
+}
+
+// Insert inserts a new key/value into the map.
+// If the key is already present, the value is replaced.
+// Reports whether this is a new key.
+func (m *Map(K, V)) Insert(key K, val V) bool {
+	pn := m.find(key)
+	if *pn != nil {
+		(*pn).val = val
+		return false
+	}
+	*pn = &node(K, V){key: key, val: val}
+	return true
+}
+
+// Find returns the value associated with a key, or the zero value
+// if not present. The found result reports whether the key was found.
+func (m *Map(K, V)) Find(key K) (V, bool) {
+	pn := m.find(key)
+	if *pn == nil {
+		var zero V
+		return zero, false
+	}
+	return (*pn).val, true
+}
+
+// keyValue is a pair of key and value used while iterating.
+type keyValue(type K, V) struct {
+	key K
+	val V
+}
+
+// iterate returns an iterator that traverses the map.
+func (m *Map(K, V)) Iterate() *Iterator(K, V) {
+	sender, receiver := chans.Ranger(keyValue(K, V))()
+	var f func(*node(K, V)) bool
+	f = func(n *node(K, V)) bool {
+		if n == nil {
+			return true
+		}
+		// Stop the traversal if Send fails, which means that
+		// nothing is listening to the receiver.
+		return f(n.left) &&
+			sender.Send(context.Background(), keyValue(K, V){n.key, n.val}) &&
+			f(n.right)
+	}
+	go func() {
+		f(m.root)
+		sender.Close()
+	}()
+	return &Iterator(K, V){receiver}
+}
+
+// Iterator is used to iterate over the map.
+type Iterator(type K, V) struct {
+	r *chans.Receiver(keyValue(K, V))
+}
+
+// Next returns the next key and value pair, and a boolean that reports
+// whether they are valid. If not valid, we have reached the end of the map.
+func (it *Iterator(K, V)) Next() (K, V, bool) {
+	keyval, ok := it.r.Next(context.Background())
+	if !ok {
+		var zerok K
+		var zerov V
+		return zerok, zerov, false
+	}
+	return keyval.key, keyval.val, true
+}
diff --git a/src/cmd/go2go/testdata/go2path/src/orderedmap/orderedmap_test.go2 b/src/cmd/go2go/testdata/go2path/src/orderedmap/orderedmap_test.go2
new file mode 100644
index 0000000000..b51ac0a7f3
--- /dev/null
+++ b/src/cmd/go2go/testdata/go2path/src/orderedmap/orderedmap_test.go2
@@ -0,0 +1,63 @@
+// Copyright 2020 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 orderedmap
+
+import (
+	"bytes"
+	"testing"
+
+	"slices"
+)
+
+func TestMap(t *testing.T) {
+	m := New([]byte, int)(bytes.Compare)
+
+	if _, found := m.Find([]byte("a")); found {
+		t.Errorf("unexpectedly found %q in empty map", []byte("a"))
+	}
+	if !m.Insert([]byte("a"), 'a') {
+		t.Errorf("key %q unexpectedly already present", []byte("a"))
+	}
+	if !m.Insert([]byte("c"), 'c') {
+		t.Errorf("key %q unexpectedly already present", []byte("c"))
+	}
+	if !m.Insert([]byte("b"), 'b') {
+		t.Errorf("key %q unexpectedly already present", []byte("b"))
+	}
+	if m.Insert([]byte("c"), 'x') {
+		t.Errorf("key %q unexpectedly not present", []byte("c"))
+	}
+
+	if v, found := m.Find([]byte("a")); !found {
+		t.Errorf("did not find %q", []byte("a"))
+	} else if v != 'a' {
+		t.Errorf("key %q returned wrong value %c, expected %c", []byte("a"), v, 'a')
+	}
+	if v, found := m.Find([]byte("c")); !found {
+		t.Errorf("did not find %q", []byte("c"))
+	} else if v != 'x' {
+		t.Errorf("key %q returned wrong value %c, expected %c", []byte("c"), v, 'x')
+	}
+
+	if _, found := m.Find([]byte("d")); found {
+		t.Errorf("unexpectedly found %q", []byte("d"))
+	}
+
+	gather := func(it *Iterator([]byte, int)) []int {
+		var r []int
+		for {
+			_, v, ok := it.Next()
+			if !ok {
+				return r
+			}
+			r = append(r, v)
+		}
+	}
+	got := gather(m.Iterate())
+	want := []int{'a', 'b', 'x'}
+	if !slices.Equal(got, want) {
+		t.Errorf("Iterate returned %v, want %v", got, want)
+	}
+}
diff --git a/src/go/go2go/go2go.go b/src/go/go2go/go2go.go
index 1c47560680..6d44ebaa15 100644
--- a/src/go/go2go/go2go.go
+++ b/src/go/go2go/go2go.go
@@ -92,7 +92,7 @@ func rewriteFilesInPath(importer *Importer, importPath, dir string, go2files []s
 		}
 
 		if !strings.HasSuffix(pkg.Name, "_test") {
-			importer.record(pkgfiles, importPath, tpkg)
+			importer.record(pkgfiles, importPath, tpkg, asts)
 		}
 
 		rpkgs = append(rpkgs, tpkg)
@@ -101,7 +101,7 @@ func rewriteFilesInPath(importer *Importer, importPath, dir string, go2files []s
 
 	for _, tpkg := range tpkgs {
 		for i, pkgfile := range tpkg {
-			if err := rewriteFile(dir, fset, importer, pkgfile.name, pkgfile.ast, i == 0); err != nil {
+			if err := rewriteFile(dir, fset, importer, importPath, pkgfile.name, pkgfile.ast, i == 0); err != nil {
 				return nil, err
 			}
 		}
@@ -128,7 +128,7 @@ func RewriteBuffer(importer *Importer, filename string, file []byte) ([]byte, er
 		return nil, fmt.Errorf("type checking failed for %s\n%v", pf.Name.Name, merr)
 	}
 	importer.addIDs(pf)
-	if err := rewriteAST(fset, importer, pf, true); err != nil {
+	if err := rewriteAST(fset, importer, "", pf, true); err != nil {
 		return nil, err
 	}
 	var buf bytes.Buffer
diff --git a/src/go/go2go/importer.go b/src/go/go2go/importer.go
index 49a166887e..ce50fa66f9 100644
--- a/src/go/go2go/importer.go
+++ b/src/go/go2go/importer.go
@@ -15,6 +15,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 )
 
@@ -35,6 +36,9 @@ type Importer struct {
 	// Map from import path to package information.
 	packages map[string]*types.Package
 
+	// Map from import path to list of import paths that it imports.
+	imports map[string][]string
+
 	// Map from Object to AST function declaration for
 	// parameterized functions.
 	idToFunc map[types.Object]*ast.FuncDecl
@@ -59,6 +63,7 @@ func NewImporter(tmpdir string) *Importer {
 		info:         info,
 		translated:   make(map[string]string),
 		packages:     make(map[string]*types.Package),
+		imports:      make(map[string][]string),
 		idToFunc:     make(map[types.Object]*ast.FuncDecl),
 		idToTypeSpec: make(map[types.Object]*ast.TypeSpec),
 	}
@@ -216,13 +221,42 @@ func (imp *Importer) localImport(importPath, dir string) (*types.Package, error)
 
 // record records information for a package, for use when working
 // with packages that import this one.
-func (imp *Importer) record(pkgfiles []namedAST, importPath string, tpkg *types.Package) {
+func (imp *Importer) record(pkgfiles []namedAST, importPath string, tpkg *types.Package, asts []*ast.File) {
 	if importPath != "" {
 		imp.packages[importPath] = tpkg
 	}
-       for _, nast := range pkgfiles {
-               imp.addIDs(nast.ast)
-       }
+	imp.imports[importPath] = imp.collectImports(asts)
+	for _, nast := range pkgfiles {
+		imp.addIDs(nast.ast)
+	}
+}
+
+// collectImports returns all the imports paths imported by any of the ASTs.
+func (imp *Importer) collectImports(asts []*ast.File) []string {
+	m := make(map[string]bool)
+	for _, a := range asts {
+		for _, decl := range a.Decls {
+			gen, ok := decl.(*ast.GenDecl)
+			if !ok || gen.Tok != token.IMPORT {
+				continue
+			}
+			for _, spec := range gen.Specs {
+				imp := spec.(*ast.ImportSpec)
+				if imp.Name != nil {
+					// We don't try to handle import aliases.
+					continue
+				}
+				path := strings.TrimPrefix(strings.TrimSuffix(imp.Path.Value, `"`), `"`)
+				m[path] = true
+			}
+		}
+	}
+	s := make([]string, 0, len(m))
+	for p := range m {
+		s = append(s, p)
+	}
+	sort.Strings(s)
+	return s
 }
 
 // addIDs finds IDs for generic functions and types and adds them to a map.
@@ -269,3 +303,35 @@ func (imp *Importer) lookupTypeSpec(obj types.Object) (*ast.TypeSpec, bool) {
 	ts, ok := imp.idToTypeSpec[obj]
 	return ts, ok
 }
+
+// transitiveImports returns all the transitive imports of an import path.
+func (imp *Importer) transitiveImports(path string) []string {
+	return imp.gatherTransitiveImports(path, make(map[string]bool))
+}
+
+// gatherTransitiveImports returns all the transitive imports of an import path,
+// using a map to avoid duplicate work.
+func (imp *Importer) gatherTransitiveImports(path string, m map[string]bool) []string {
+	imports := imp.imports[path]
+	if len(imports) == 0 {
+		return nil
+	}
+	var r []string
+	for _, im := range imports {
+		r = append(r, im)
+		if !m[im] {
+			m[im] = true
+			r = append(r, imp.gatherTransitiveImports(im, m)...)
+		}
+	}
+	dup := make(map[string]bool)
+	for _, p := range r {
+		dup[p] = true
+	}
+	r = make([]string, 0, len(dup))
+	for p := range dup {
+		r = append(r, p)
+	}
+	sort.Strings(r)
+	return r
+}
diff --git a/src/go/go2go/instantiate.go b/src/go/go2go/instantiate.go
index 5eba7355b9..f508eb9606 100644
--- a/src/go/go2go/instantiate.go
+++ b/src/go/go2go/instantiate.go
@@ -171,6 +171,8 @@ func (t *translator) instantiateTypeDecl(qid qualifiedIdent, typ *types.Named, a
 
 	instType := t.instantiateType(ta, typ.Underlying())
 
+	t.setType(instIdent, instType)
+
 	nm := typ.NumMethods()
 	for i := 0; i < nm; i++ {
 		method := typ.Method(i)
diff --git a/src/go/go2go/rewrite.go b/src/go/go2go/rewrite.go
index 2d519a1488..f9a65c14a9 100644
--- a/src/go/go2go/rewrite.go
+++ b/src/go/go2go/rewrite.go
@@ -13,6 +13,8 @@ import (
 	"go/types"
 	"os"
 	"path/filepath"
+	"sort"
+	"strconv"
 	"strings"
 )
 
@@ -79,8 +81,8 @@ type typeInstantiation struct {
 }
 
 // rewrite rewrites the contents of one file.
-func rewriteFile(dir string, fset *token.FileSet, importer *Importer, filename string, file *ast.File, addImportableName bool) (err error) {
-	if err := rewriteAST(fset, importer, file, addImportableName); err != nil {
+func rewriteFile(dir string, fset *token.FileSet, importer *Importer, importPath, filename string, file *ast.File, addImportableName bool) (err error) {
+	if err := rewriteAST(fset, importer, importPath, file, addImportableName); err != nil {
 		return err
 	}
 
@@ -108,7 +110,7 @@ func rewriteFile(dir string, fset *token.FileSet, importer *Importer, filename s
 }
 
 // rewriteAST rewrites the AST for a file.
-func rewriteAST(fset *token.FileSet, importer *Importer, file *ast.File, addImportableName bool) (err error) {
+func rewriteAST(fset *token.FileSet, importer *Importer, importPath string, file *ast.File, addImportableName bool) (err error) {
 	t := translator{
 		fset:               fset,
 		importer:           importer,
@@ -118,6 +120,63 @@ func rewriteAST(fset *token.FileSet, importer *Importer, file *ast.File, addImpo
 	}
 	t.translate(file)
 
+	// Add all the transitive imports. This is more than we need,
+	// but we're not trying to be elegant here.
+	imps := make(map[string]bool)
+
+	for _, p := range importer.transitiveImports(importPath) {
+		imps[p] = true
+	}
+
+	decls := make([]ast.Decl, 0, len(file.Decls))
+	var specs []ast.Spec
+	for _, decl := range file.Decls {
+		gen, ok := decl.(*ast.GenDecl)
+		if !ok || gen.Tok != token.IMPORT {
+			decls = append(decls, decl)
+			continue
+		}
+		for _, spec := range gen.Specs {
+			imp := spec.(*ast.ImportSpec)
+			if imp.Name != nil {
+				specs = append(specs, imp)
+			}
+			// We picked up Go 2 imports above, but we still
+			// need to pick up Go 1 imports here.
+			path := strings.TrimPrefix(strings.TrimSuffix(imp.Path.Value, `"`), `"`)
+			if imps[path] {
+				continue
+			}
+			imps[path] = true
+			for _, p := range importer.transitiveImports(path) {
+				imps[p] = true
+			}
+		}
+	}
+	file.Decls = decls
+
+	paths := make([]string, 0, len(imps))
+	for p := range imps {
+		paths = append(paths, p)
+	}
+	sort.Strings(paths)
+
+	for _, p := range paths {
+		specs = append(specs, ast.Spec(&ast.ImportSpec{
+			Path: &ast.BasicLit{
+				Kind:  token.STRING,
+				Value: strconv.Quote(p),
+			},
+		}))
+	}
+	if len(specs) > 0 {
+		first := &ast.GenDecl{
+			Tok:   token.IMPORT,
+			Specs: specs,
+		}
+		file.Decls = append([]ast.Decl{first}, file.Decls...)
+	}
+
 	// Add a name that other packages can reference to avoid an error
 	// about an unused package.
 	if addImportableName {
@@ -622,7 +681,7 @@ func (t *translator) instantiationTypes(call *ast.CallExpr) (argList []ast.Expr,
 		typeList = make([]types.Type, 0, len(argList))
 		for _, arg := range argList {
 			if at := t.lookupType(arg); at == nil {
-				panic(fmt.Sprintf("no type found for %T %v", arg, arg))
+				panic(fmt.Sprintf("%s: no type found for %T %v", t.fset.Position(arg.Pos()), arg, arg))
 			} else {
 				typeList = append(typeList, at)
 			}