internal/gcimporter/bexport_test.go - tools.git - Git at Google

 // 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 gcimporter_test

 import (
 	"bytes"
 	"fmt"
 	"go/ast"
 	"go/parser"
 	"go/token"
 	"go/types"
 	"path/filepath"
 	"reflect"
 	"runtime"
 	"sort"
 	"strings"
 	"testing"

 	"golang.org/x/tools/internal/gcimporter"
 	"golang.org/x/tools/internal/typeparams"
 )

 var isRace = false

 func fileLine(fset *token.FileSet, obj types.Object) string {
 	posn := fset.Position(obj.Pos())
 	filename := filepath.Clean(strings.ReplaceAll(posn.Filename, "$GOROOT", runtime.GOROOT()))
 	return fmt.Sprintf("%s:%d", filename, posn.Line)
 }

 func equalType(x, y types.Type) error {
 	if reflect.TypeOf(x) != reflect.TypeOf(y) {
 		return fmt.Errorf("unequal kinds: %T vs %T", x, y)
 	}
 	switch x := x.(type) {
 	case *types.Interface:
 		y := y.(*types.Interface)
 		// TODO(gri): enable separate emission of Embedded interfaces
 		// and ExplicitMethods then use this logic.
 		// if x.NumEmbeddeds() != y.NumEmbeddeds() {
 		// 	return fmt.Errorf("unequal number of embedded interfaces: %d vs %d",
 		// 		x.NumEmbeddeds(), y.NumEmbeddeds())
 		// }
 		// for i := 0; i < x.NumEmbeddeds(); i++ {
 		// 	xi := x.Embedded(i)
 		// 	yi := y.Embedded(i)
 		// 	if xi.String() != yi.String() {
 		// 		return fmt.Errorf("mismatched %th embedded interface: %s vs %s",
 		// 			i, xi, yi)
 		// 	}
 		// }
 		// if x.NumExplicitMethods() != y.NumExplicitMethods() {
 		// 	return fmt.Errorf("unequal methods: %d vs %d",
 		// 		x.NumExplicitMethods(), y.NumExplicitMethods())
 		// }
 		// for i := 0; i < x.NumExplicitMethods(); i++ {
 		// 	xm := x.ExplicitMethod(i)
 		// 	ym := y.ExplicitMethod(i)
 		// 	if xm.Name() != ym.Name() {
 		// 		return fmt.Errorf("mismatched %th method: %s vs %s", i, xm, ym)
 		// 	}
 		// 	if err := equalType(xm.Type(), ym.Type()); err != nil {
 		// 		return fmt.Errorf("mismatched %s method: %s", xm.Name(), err)
 		// 	}
 		// }
 		if x.NumMethods() != y.NumMethods() {
 			return fmt.Errorf("unequal methods: %d vs %d",
 				x.NumMethods(), y.NumMethods())
 		}
 		for i := 0; i < x.NumMethods(); i++ {
 			xm := x.Method(i)
 			ym := y.Method(i)
 			if xm.Name() != ym.Name() {
 				return fmt.Errorf("mismatched %dth method: %s vs %s", i, xm, ym)
 			}
 			if err := equalType(xm.Type(), ym.Type()); err != nil {
 				return fmt.Errorf("mismatched %s method: %s", xm.Name(), err)
 			}
 		}
 		// Constraints are handled explicitly in the *TypeParam case below, so we
 		// don't yet need to consider embeddeds here.
 		// TODO(rfindley): consider the type set here.
 	case *types.Array:
 		y := y.(*types.Array)
 		if x.Len() != y.Len() {
 			return fmt.Errorf("unequal array lengths: %d vs %d", x.Len(), y.Len())
 		}
 		if err := equalType(x.Elem(), y.Elem()); err != nil {
 			return fmt.Errorf("array elements: %s", err)
 		}
 	case *types.Basic:
 		y := y.(*types.Basic)
 		if x.Kind() != y.Kind() {
 			return fmt.Errorf("unequal basic types: %s vs %s", x, y)
 		}
 	case *types.Chan:
 		y := y.(*types.Chan)
 		if x.Dir() != y.Dir() {
 			return fmt.Errorf("unequal channel directions: %d vs %d", x.Dir(), y.Dir())
 		}
 		if err := equalType(x.Elem(), y.Elem()); err != nil {
 			return fmt.Errorf("channel elements: %s", err)
 		}
 	case *types.Map:
 		y := y.(*types.Map)
 		if err := equalType(x.Key(), y.Key()); err != nil {
 			return fmt.Errorf("map keys: %s", err)
 		}
 		if err := equalType(x.Elem(), y.Elem()); err != nil {
 			return fmt.Errorf("map values: %s", err)
 		}
 	case *types.Named:
 		y := y.(*types.Named)
 		return cmpNamed(x, y)
 	case *types.Pointer:
 		y := y.(*types.Pointer)
 		if err := equalType(x.Elem(), y.Elem()); err != nil {
 			return fmt.Errorf("pointer elements: %s", err)
 		}
 	case *types.Signature:
 		y := y.(*types.Signature)
 		if err := equalType(x.Params(), y.Params()); err != nil {
 			return fmt.Errorf("parameters: %s", err)
 		}
 		if err := equalType(x.Results(), y.Results()); err != nil {
 			return fmt.Errorf("results: %s", err)
 		}
 		if x.Variadic() != y.Variadic() {
 			return fmt.Errorf("unequal variadicity: %t vs %t",
 				x.Variadic(), y.Variadic())
 		}
 		if (x.Recv() != nil) != (y.Recv() != nil) {
 			return fmt.Errorf("unequal receivers: %s vs %s", x.Recv(), y.Recv())
 		}
 		if x.Recv() != nil {
 			// TODO(adonovan): fix: this assertion fires for interface methods.
 			// The type of the receiver of an interface method is a named type
 			// if the Package was loaded from export data, or an unnamed (interface)
 			// type if the Package was produced by type-checking ASTs.
 			// if err := equalType(x.Recv().Type(), y.Recv().Type()); err != nil {
 			// 	return fmt.Errorf("receiver: %s", err)
 			// }
 		}
 		if err := equalTypeParams(typeparams.ForSignature(x), typeparams.ForSignature(y)); err != nil {
 			return fmt.Errorf("type params: %s", err)
 		}
 		if err := equalTypeParams(typeparams.RecvTypeParams(x), typeparams.RecvTypeParams(y)); err != nil {
 			return fmt.Errorf("recv type params: %s", err)
 		}
 	case *types.Slice:
 		y := y.(*types.Slice)
 		if err := equalType(x.Elem(), y.Elem()); err != nil {
 			return fmt.Errorf("slice elements: %s", err)
 		}
 	case *types.Struct:
 		y := y.(*types.Struct)
 		if x.NumFields() != y.NumFields() {
 			return fmt.Errorf("unequal struct fields: %d vs %d",
 				x.NumFields(), y.NumFields())
 		}
 		for i := 0; i < x.NumFields(); i++ {
 			xf := x.Field(i)
 			yf := y.Field(i)
 			if xf.Name() != yf.Name() {
 				return fmt.Errorf("mismatched fields: %s vs %s", xf, yf)
 			}
 			if err := equalType(xf.Type(), yf.Type()); err != nil {
 				return fmt.Errorf("struct field %s: %s", xf.Name(), err)
 			}
 			if x.Tag(i) != y.Tag(i) {
 				return fmt.Errorf("struct field %s has unequal tags: %q vs %q",
 					xf.Name(), x.Tag(i), y.Tag(i))
 			}
 		}
 	case *types.Tuple:
 		y := y.(*types.Tuple)
 		if x.Len() != y.Len() {
 			return fmt.Errorf("unequal tuple lengths: %d vs %d", x.Len(), y.Len())
 		}
 		for i := 0; i < x.Len(); i++ {
 			if err := equalType(x.At(i).Type(), y.At(i).Type()); err != nil {
 				return fmt.Errorf("tuple element %d: %s", i, err)
 			}
 		}
 	case *typeparams.TypeParam:
 		y := y.(*typeparams.TypeParam)
 		if x.String() != y.String() {
 			return fmt.Errorf("unequal named types: %s vs %s", x, y)
 		}
 		// For now, just compare constraints by type string to short-circuit
 		// cycles. We have to make interfaces explicit as export data currently
 		// doesn't support marking interfaces as implicit.
 		// TODO(rfindley): remove makeExplicit once export data contains an
 		// implicit bit.
 		xc := makeExplicit(x.Constraint()).String()
 		yc := makeExplicit(y.Constraint()).String()
 		if xc != yc {
 			return fmt.Errorf("unequal constraints: %s vs %s", xc, yc)
 		}

 	default:
 		panic(fmt.Sprintf("unexpected %T type", x))
 	}
 	return nil
 }

 // cmpNamed compares two named types x and y, returning an error for any
 // discrepancies. It does not compare their underlying types.
 func cmpNamed(x, y *types.Named) error {
 	xOrig := typeparams.NamedTypeOrigin(x)
 	yOrig := typeparams.NamedTypeOrigin(y)
 	if xOrig.String() != yOrig.String() {
 		return fmt.Errorf("unequal named types: %s vs %s", x, y)
 	}
 	if err := equalTypeParams(typeparams.ForNamed(x), typeparams.ForNamed(y)); err != nil {
 		return fmt.Errorf("type parameters: %s", err)
 	}
 	if err := equalTypeArgs(typeparams.NamedTypeArgs(x), typeparams.NamedTypeArgs(y)); err != nil {
 		return fmt.Errorf("type arguments: %s", err)
 	}
 	if x.NumMethods() != y.NumMethods() {
 		return fmt.Errorf("unequal methods: %d vs %d",
 			x.NumMethods(), y.NumMethods())
 	}
 	// Unfortunately method sorting is not canonical, so sort before comparing.
 	var xms, yms []*types.Func
 	for i := 0; i < x.NumMethods(); i++ {
 		xms = append(xms, x.Method(i))
 		yms = append(yms, y.Method(i))
 	}
 	for _, ms := range [][]*types.Func{xms, yms} {
 		sort.Slice(ms, func(i, j int) bool {
 			return ms[i].Name() < ms[j].Name()
 		})
 	}
 	for i, xm := range xms {
 		ym := yms[i]
 		if xm.Name() != ym.Name() {
 			return fmt.Errorf("mismatched %dth method: %s vs %s", i, xm, ym)
 		}
 		// Calling equalType here leads to infinite recursion, so just compare
 		// strings.
 		if xm.String() != ym.String() {
 			return fmt.Errorf("unequal methods: %s vs %s", x, y)
 		}
 	}
 	return nil
 }

 // makeExplicit returns an explicit version of typ, if typ is an implicit
 // interface. Otherwise it returns typ unmodified.
 func makeExplicit(typ types.Type) types.Type {
 	if iface, _ := typ.(*types.Interface); iface != nil && typeparams.IsImplicit(iface) {
 		var methods []*types.Func
 		for i := 0; i < iface.NumExplicitMethods(); i++ {
 			methods = append(methods, iface.Method(i))
 		}
 		var embeddeds []types.Type
 		for i := 0; i < iface.NumEmbeddeds(); i++ {
 			embeddeds = append(embeddeds, iface.EmbeddedType(i))
 		}
 		return types.NewInterfaceType(methods, embeddeds)
 	}
 	return typ
 }

 func equalTypeArgs(x, y *typeparams.TypeList) error {
 	if x.Len() != y.Len() {
 		return fmt.Errorf("unequal lengths: %d vs %d", x.Len(), y.Len())
 	}
 	for i := 0; i < x.Len(); i++ {
 		if err := equalType(x.At(i), y.At(i)); err != nil {
 			return fmt.Errorf("type %d: %s", i, err)
 		}
 	}
 	return nil
 }

 func equalTypeParams(x, y *typeparams.TypeParamList) error {
 	if x.Len() != y.Len() {
 		return fmt.Errorf("unequal lengths: %d vs %d", x.Len(), y.Len())
 	}
 	for i := 0; i < x.Len(); i++ {
 		if err := equalType(x.At(i), y.At(i)); err != nil {
 			return fmt.Errorf("type parameter %d: %s", i, err)
 		}
 	}
 	return nil
 }

 // TestVeryLongFile tests the position of an import object declared in
 // a very long input file.  Line numbers greater than maxlines are
 // reported as line 1, not garbage or token.NoPos.
 func TestVeryLongFile(t *testing.T) {
 	// parse and typecheck
 	longFile := "package foo" + strings.Repeat("\n", 123456) + "var X int"
 	fset1 := token.NewFileSet()
 	f, err := parser.ParseFile(fset1, "foo.go", longFile, 0)
 	if err != nil {
 		t.Fatal(err)
 	}
 	var conf types.Config
 	pkg, err := conf.Check("foo", fset1, []*ast.File{f}, nil)
 	if err != nil {
 		t.Fatal(err)
 	}

 	// export
 	var out bytes.Buffer
 	if err := gcimporter.IExportData(&out, fset1, pkg); err != nil {
 		t.Fatal(err)
 	}
 	exportdata := out.Bytes()

 	// import
 	imports := make(map[string]*types.Package)
 	fset2 := token.NewFileSet()
 	_, pkg2, err := gcimporter.IImportData(fset2, imports, exportdata, pkg.Path())
 	if err != nil {
 		t.Fatalf("BImportData(%s): %v", pkg.Path(), err)
 	}

 	// compare
 	posn1 := fset1.Position(pkg.Scope().Lookup("X").Pos())
 	posn2 := fset2.Position(pkg2.Scope().Lookup("X").Pos())
 	if want := "foo.go:1:1"; posn2.String() != want {
 		t.Errorf("X position = %s, want %s (orig was %s)",
 			posn2, want, posn1)
 	}
 }

 const src = `
 package p

 type (
 	T0 = int32
 	T1 = struct{}
 	T2 = struct{ T1 }
 	Invalid = foo // foo is undeclared
 )
 `

 func checkPkg(t *testing.T, pkg *types.Package, label string) {
 	T1 := types.NewStruct(nil, nil)
 	T2 := types.NewStruct([]*types.Var{types.NewField(0, pkg, "T1", T1, true)}, nil)

 	for _, test := range []struct {
 		name string
 		typ  types.Type
 	}{
 		{"T0", types.Typ[types.Int32]},
 		{"T1", T1},
 		{"T2", T2},
 		{"Invalid", types.Typ[types.Invalid]},
 	} {
 		obj := pkg.Scope().Lookup(test.name)
 		if obj == nil {
 			t.Errorf("%s: %s not found", label, test.name)
 			continue
 		}
 		tname, _ := obj.(*types.TypeName)
 		if tname == nil {
 			t.Errorf("%s: %v not a type name", label, obj)
 			continue
 		}
 		if !tname.IsAlias() {
 			t.Errorf("%s: %v: not marked as alias", label, tname)
 			continue
 		}
 		if got := tname.Type(); !types.Identical(got, test.typ) {
 			t.Errorf("%s: %v: got %v; want %v", label, tname, got, test.typ)
 		}
 	}
 }
	// 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 gcimporter_test

	import (
	"bytes"
	"fmt"
	"go/ast"
	"go/parser"
	"go/token"
	"go/types"
	"path/filepath"
	"reflect"
	"runtime"
	"sort"
	"strings"
	"testing"

	"golang.org/x/tools/internal/gcimporter"
	"golang.org/x/tools/internal/typeparams"
	)

	var isRace = false

	func fileLine(fset *token.FileSet, obj types.Object) string {
	posn := fset.Position(obj.Pos())
	filename := filepath.Clean(strings.ReplaceAll(posn.Filename, "$GOROOT", runtime.GOROOT()))
	return fmt.Sprintf("%s:%d", filename, posn.Line)
	}

	func equalType(x, y types.Type) error {
	if reflect.TypeOf(x) != reflect.TypeOf(y) {
	return fmt.Errorf("unequal kinds: %T vs %T", x, y)
	}
	switch x := x.(type) {
	case *types.Interface:
	y := y.(*types.Interface)
	// TODO(gri): enable separate emission of Embedded interfaces
	// and ExplicitMethods then use this logic.
	// if x.NumEmbeddeds() != y.NumEmbeddeds() {
	// return fmt.Errorf("unequal number of embedded interfaces: %d vs %d",
	// x.NumEmbeddeds(), y.NumEmbeddeds())
	// }
	// for i := 0; i < x.NumEmbeddeds(); i++ {
	// xi := x.Embedded(i)
	// yi := y.Embedded(i)
	// if xi.String() != yi.String() {
	// return fmt.Errorf("mismatched %th embedded interface: %s vs %s",
	// i, xi, yi)
	// }
	// }
	// if x.NumExplicitMethods() != y.NumExplicitMethods() {
	// return fmt.Errorf("unequal methods: %d vs %d",
	// x.NumExplicitMethods(), y.NumExplicitMethods())
	// }
	// for i := 0; i < x.NumExplicitMethods(); i++ {
	// xm := x.ExplicitMethod(i)
	// ym := y.ExplicitMethod(i)
	// if xm.Name() != ym.Name() {
	// return fmt.Errorf("mismatched %th method: %s vs %s", i, xm, ym)
	// }
	// if err := equalType(xm.Type(), ym.Type()); err != nil {
	// return fmt.Errorf("mismatched %s method: %s", xm.Name(), err)
	// }
	// }
	if x.NumMethods() != y.NumMethods() {
	return fmt.Errorf("unequal methods: %d vs %d",
	x.NumMethods(), y.NumMethods())
	}
	for i := 0; i < x.NumMethods(); i++ {
	xm := x.Method(i)
	ym := y.Method(i)
	if xm.Name() != ym.Name() {
	return fmt.Errorf("mismatched %dth method: %s vs %s", i, xm, ym)
	}
	if err := equalType(xm.Type(), ym.Type()); err != nil {
	return fmt.Errorf("mismatched %s method: %s", xm.Name(), err)
	}
	}
	// Constraints are handled explicitly in the *TypeParam case below, so we
	// don't yet need to consider embeddeds here.
	// TODO(rfindley): consider the type set here.
	case *types.Array:
	y := y.(*types.Array)
	if x.Len() != y.Len() {
	return fmt.Errorf("unequal array lengths: %d vs %d", x.Len(), y.Len())
	}
	if err := equalType(x.Elem(), y.Elem()); err != nil {
	return fmt.Errorf("array elements: %s", err)
	}
	case *types.Basic:
	y := y.(*types.Basic)
	if x.Kind() != y.Kind() {
	return fmt.Errorf("unequal basic types: %s vs %s", x, y)
	}
	case *types.Chan:
	y := y.(*types.Chan)
	if x.Dir() != y.Dir() {
	return fmt.Errorf("unequal channel directions: %d vs %d", x.Dir(), y.Dir())
	}
	if err := equalType(x.Elem(), y.Elem()); err != nil {
	return fmt.Errorf("channel elements: %s", err)
	}
	case *types.Map:
	y := y.(*types.Map)
	if err := equalType(x.Key(), y.Key()); err != nil {
	return fmt.Errorf("map keys: %s", err)
	}
	if err := equalType(x.Elem(), y.Elem()); err != nil {
	return fmt.Errorf("map values: %s", err)
	}
	case *types.Named:
	y := y.(*types.Named)
	return cmpNamed(x, y)
	case *types.Pointer:
	y := y.(*types.Pointer)
	if err := equalType(x.Elem(), y.Elem()); err != nil {
	return fmt.Errorf("pointer elements: %s", err)
	}
	case *types.Signature:
	y := y.(*types.Signature)
	if err := equalType(x.Params(), y.Params()); err != nil {
	return fmt.Errorf("parameters: %s", err)
	}
	if err := equalType(x.Results(), y.Results()); err != nil {
	return fmt.Errorf("results: %s", err)
	}
	if x.Variadic() != y.Variadic() {
	return fmt.Errorf("unequal variadicity: %t vs %t",
	x.Variadic(), y.Variadic())
	}
	if (x.Recv() != nil) != (y.Recv() != nil) {
	return fmt.Errorf("unequal receivers: %s vs %s", x.Recv(), y.Recv())
	}
	if x.Recv() != nil {
	// TODO(adonovan): fix: this assertion fires for interface methods.
	// The type of the receiver of an interface method is a named type
	// if the Package was loaded from export data, or an unnamed (interface)
	// type if the Package was produced by type-checking ASTs.
	// if err := equalType(x.Recv().Type(), y.Recv().Type()); err != nil {
	// return fmt.Errorf("receiver: %s", err)
	// }
	}
	if err := equalTypeParams(typeparams.ForSignature(x), typeparams.ForSignature(y)); err != nil {
	return fmt.Errorf("type params: %s", err)
	}
	if err := equalTypeParams(typeparams.RecvTypeParams(x), typeparams.RecvTypeParams(y)); err != nil {
	return fmt.Errorf("recv type params: %s", err)
	}
	case *types.Slice:
	y := y.(*types.Slice)
	if err := equalType(x.Elem(), y.Elem()); err != nil {
	return fmt.Errorf("slice elements: %s", err)
	}
	case *types.Struct:
	y := y.(*types.Struct)
	if x.NumFields() != y.NumFields() {
	return fmt.Errorf("unequal struct fields: %d vs %d",
	x.NumFields(), y.NumFields())
	}
	for i := 0; i < x.NumFields(); i++ {
	xf := x.Field(i)
	yf := y.Field(i)
	if xf.Name() != yf.Name() {
	return fmt.Errorf("mismatched fields: %s vs %s", xf, yf)
	}
	if err := equalType(xf.Type(), yf.Type()); err != nil {
	return fmt.Errorf("struct field %s: %s", xf.Name(), err)
	}
	if x.Tag(i) != y.Tag(i) {
	return fmt.Errorf("struct field %s has unequal tags: %q vs %q",
	xf.Name(), x.Tag(i), y.Tag(i))
	}
	}
	case *types.Tuple:
	y := y.(*types.Tuple)
	if x.Len() != y.Len() {
	return fmt.Errorf("unequal tuple lengths: %d vs %d", x.Len(), y.Len())
	}
	for i := 0; i < x.Len(); i++ {
	if err := equalType(x.At(i).Type(), y.At(i).Type()); err != nil {
	return fmt.Errorf("tuple element %d: %s", i, err)
	}
	}
	case *typeparams.TypeParam:
	y := y.(*typeparams.TypeParam)
	if x.String() != y.String() {
	return fmt.Errorf("unequal named types: %s vs %s", x, y)
	}
	// For now, just compare constraints by type string to short-circuit
	// cycles. We have to make interfaces explicit as export data currently
	// doesn't support marking interfaces as implicit.
	// TODO(rfindley): remove makeExplicit once export data contains an
	// implicit bit.
	xc := makeExplicit(x.Constraint()).String()
	yc := makeExplicit(y.Constraint()).String()
	if xc != yc {
	return fmt.Errorf("unequal constraints: %s vs %s", xc, yc)
	}

	default:
	panic(fmt.Sprintf("unexpected %T type", x))
	}
	return nil
	}

	// cmpNamed compares two named types x and y, returning an error for any
	// discrepancies. It does not compare their underlying types.
	func cmpNamed(x, y *types.Named) error {
	xOrig := typeparams.NamedTypeOrigin(x)
	yOrig := typeparams.NamedTypeOrigin(y)
	if xOrig.String() != yOrig.String() {
	return fmt.Errorf("unequal named types: %s vs %s", x, y)
	}
	if err := equalTypeParams(typeparams.ForNamed(x), typeparams.ForNamed(y)); err != nil {
	return fmt.Errorf("type parameters: %s", err)
	}
	if err := equalTypeArgs(typeparams.NamedTypeArgs(x), typeparams.NamedTypeArgs(y)); err != nil {
	return fmt.Errorf("type arguments: %s", err)
	}
	if x.NumMethods() != y.NumMethods() {
	return fmt.Errorf("unequal methods: %d vs %d",
	x.NumMethods(), y.NumMethods())
	}
	// Unfortunately method sorting is not canonical, so sort before comparing.
	var xms, yms []*types.Func
	for i := 0; i < x.NumMethods(); i++ {
	xms = append(xms, x.Method(i))
	yms = append(yms, y.Method(i))
	}
	for _, ms := range [][]*types.Func{xms, yms} {
	sort.Slice(ms, func(i, j int) bool {
	return ms[i].Name() < ms[j].Name()
	})
	}
	for i, xm := range xms {
	ym := yms[i]
	if xm.Name() != ym.Name() {
	return fmt.Errorf("mismatched %dth method: %s vs %s", i, xm, ym)
	}
	// Calling equalType here leads to infinite recursion, so just compare
	// strings.
	if xm.String() != ym.String() {
	return fmt.Errorf("unequal methods: %s vs %s", x, y)
	}
	}
	return nil
	}

	// makeExplicit returns an explicit version of typ, if typ is an implicit
	// interface. Otherwise it returns typ unmodified.
	func makeExplicit(typ types.Type) types.Type {
	if iface, _ := typ.(*types.Interface); iface != nil && typeparams.IsImplicit(iface) {
	var methods []*types.Func
	for i := 0; i < iface.NumExplicitMethods(); i++ {
	methods = append(methods, iface.Method(i))
	}
	var embeddeds []types.Type
	for i := 0; i < iface.NumEmbeddeds(); i++ {
	embeddeds = append(embeddeds, iface.EmbeddedType(i))
	}
	return types.NewInterfaceType(methods, embeddeds)
	}
	return typ
	}

	func equalTypeArgs(x, y *typeparams.TypeList) error {
	if x.Len() != y.Len() {
	return fmt.Errorf("unequal lengths: %d vs %d", x.Len(), y.Len())
	}
	for i := 0; i < x.Len(); i++ {
	if err := equalType(x.At(i), y.At(i)); err != nil {
	return fmt.Errorf("type %d: %s", i, err)
	}
	}
	return nil
	}

	func equalTypeParams(x, y *typeparams.TypeParamList) error {
	if x.Len() != y.Len() {
	return fmt.Errorf("unequal lengths: %d vs %d", x.Len(), y.Len())
	}
	for i := 0; i < x.Len(); i++ {
	if err := equalType(x.At(i), y.At(i)); err != nil {
	return fmt.Errorf("type parameter %d: %s", i, err)
	}
	}
	return nil
	}

	// TestVeryLongFile tests the position of an import object declared in
	// a very long input file. Line numbers greater than maxlines are
	// reported as line 1, not garbage or token.NoPos.
	func TestVeryLongFile(t *testing.T) {
	// parse and typecheck
	longFile := "package foo" + strings.Repeat("\n", 123456) + "var X int"
	fset1 := token.NewFileSet()
	f, err := parser.ParseFile(fset1, "foo.go", longFile, 0)
	if err != nil {
	t.Fatal(err)
	}
	var conf types.Config
	pkg, err := conf.Check("foo", fset1, []*ast.File{f}, nil)
	if err != nil {
	t.Fatal(err)
	}

	// export
	var out bytes.Buffer
	if err := gcimporter.IExportData(&out, fset1, pkg); err != nil {
	t.Fatal(err)
	}
	exportdata := out.Bytes()

	// import
	imports := make(map[string]*types.Package)
	fset2 := token.NewFileSet()
	_, pkg2, err := gcimporter.IImportData(fset2, imports, exportdata, pkg.Path())
	if err != nil {
	t.Fatalf("BImportData(%s): %v", pkg.Path(), err)
	}

	// compare
	posn1 := fset1.Position(pkg.Scope().Lookup("X").Pos())
	posn2 := fset2.Position(pkg2.Scope().Lookup("X").Pos())
	if want := "foo.go:1:1"; posn2.String() != want {
	t.Errorf("X position = %s, want %s (orig was %s)",
	posn2, want, posn1)
	}
	}

	const src = `
	package p

	type (
	T0 = int32
	T1 = struct{}
	T2 = struct{ T1 }
	Invalid = foo // foo is undeclared
	)
	`

	func checkPkg(t testing.T, pkg types.Package, label string) {
	T1 := types.NewStruct(nil, nil)
	T2 := types.NewStruct([]*types.Var{types.NewField(0, pkg, "T1", T1, true)}, nil)

	for _, test := range []struct {
	name string
	typ types.Type
	}{
	{"T0", types.Typ[types.Int32]},
	{"T1", T1},
	{"T2", T2},
	{"Invalid", types.Typ[types.Invalid]},
	} {
	obj := pkg.Scope().Lookup(test.name)
	if obj == nil {
	t.Errorf("%s: %s not found", label, test.name)
	continue
	}
	tname, _ := obj.(*types.TypeName)
	if tname == nil {
	t.Errorf("%s: %v not a type name", label, obj)
	continue
	}
	if !tname.IsAlias() {
	t.Errorf("%s: %v: not marked as alias", label, tname)
	continue
	}
	if got := tname.Type(); !types.Identical(got, test.typ) {
	t.Errorf("%s: %v: got %v; want %v", label, tname, got, test.typ)
	}
	}
	}