[dev.typeparams] cmd/compile/internal/importer, types2: initial check-in of types2 and importer

This is a copy of the importer and types2 (unreviewed) prototype version
excluding the testdata directory containing tests (see below). Each file
is marked with the comment

// UNREVIEWED

on the first line. The plan is to check in this code wholesale (it runs and
passes all tests) and then review the code file-by-file via subsequent CLs
and remove the "// UNREVIEWED" comments as we review the files.

Since most tests are unchanged from the original go/types, the next CL will
commit those tests as they don't need to be reviewed again. (Eventually we
may want to factor them out and share them from a single place, e.g. the
test directory.)

The existing file fmtmap_test.go was updated.

Change-Id: I9bd0ad1a7e7188b501423483a44d18e623c0fe71
Reviewed-on: https://go-review.googlesource.com/c/go/+/263624
Trust: Robert Griesemer <gri@golang.org>
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 1741 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/types2/api_test.go b/src/cmd/compile/internal/types2/api_test.go
new file mode 100644
index 0000000000..403df3f941
--- /dev/null
+++ b/src/cmd/compile/internal/types2/api_test.go
@@ -0,0 +1,1741 @@
+// UNREVIEWED
+// Copyright 2013 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 types2_test
+
+import (
+	"bytes"
+	"cmd/compile/internal/syntax"
+	"fmt"
+	"internal/testenv"
+	"reflect"
+	"regexp"
+	"strings"
+	"testing"
+
+	. "cmd/compile/internal/types2"
+)
+
+func unimplemented() {
+	panic("unimplemented")
+}
+
+func parseSrc(path, src string) (*syntax.File, error) {
+	errh := func(error) {} // dummy error handler so that parsing continues in presence of errors
+	return syntax.Parse(syntax.NewFileBase(path), strings.NewReader(src), errh, nil, syntax.AllowGenerics)
+}
+
+func pkgFor(path, source string, info *Info) (*Package, error) {
+	f, err := parseSrc(path, source)
+	if err != nil {
+		return nil, err
+	}
+	conf := Config{Importer: defaultImporter()}
+	return conf.Check(f.PkgName.Value, []*syntax.File{f}, info)
+}
+
+func mustTypecheck(t *testing.T, path, source string, info *Info) string {
+	pkg, err := pkgFor(path, source, info)
+	if err != nil {
+		name := path
+		if pkg != nil {
+			name = "package " + pkg.Name()
+		}
+		t.Fatalf("%s: didn't type-check (%s)", name, err)
+	}
+	return pkg.Name()
+}
+
+func mayTypecheck(t *testing.T, path, source string, info *Info) (string, error) {
+	f, err := parseSrc(path, source)
+	if f == nil { // ignore errors unless f is nil
+		t.Fatalf("%s: unable to parse: %s", path, err)
+	}
+	conf := Config{
+		AcceptMethodTypeParams: true,
+		InferFromConstraints:   true,
+		Error:                  func(err error) {},
+		Importer:               defaultImporter(),
+	}
+	pkg, err := conf.Check(f.PkgName.Value, []*syntax.File{f}, info)
+	return pkg.Name(), err
+}
+
+func TestValuesInfo(t *testing.T) {
+	var tests = []struct {
+		src  string
+		expr string // constant expression
+		typ  string // constant type
+		val  string // constant value
+	}{
+		{`package a0; const _ = false`, `false`, `untyped bool`, `false`},
+		{`package a1; const _ = 0`, `0`, `untyped int`, `0`},
+		{`package a2; const _ = 'A'`, `'A'`, `untyped rune`, `65`},
+		{`package a3; const _ = 0.`, `0.`, `untyped float`, `0`},
+		{`package a4; const _ = 0i`, `0i`, `untyped complex`, `(0 + 0i)`},
+		{`package a5; const _ = "foo"`, `"foo"`, `untyped string`, `"foo"`},
+
+		{`package b0; var _ = false`, `false`, `bool`, `false`},
+		{`package b1; var _ = 0`, `0`, `int`, `0`},
+		{`package b2; var _ = 'A'`, `'A'`, `rune`, `65`},
+		{`package b3; var _ = 0.`, `0.`, `float64`, `0`},
+		{`package b4; var _ = 0i`, `0i`, `complex128`, `(0 + 0i)`},
+		{`package b5; var _ = "foo"`, `"foo"`, `string`, `"foo"`},
+
+		{`package c0a; var _ = bool(false)`, `false`, `bool`, `false`},
+		{`package c0b; var _ = bool(false)`, `bool(false)`, `bool`, `false`},
+		{`package c0c; type T bool; var _ = T(false)`, `T(false)`, `c0c.T`, `false`},
+
+		{`package c1a; var _ = int(0)`, `0`, `int`, `0`},
+		{`package c1b; var _ = int(0)`, `int(0)`, `int`, `0`},
+		{`package c1c; type T int; var _ = T(0)`, `T(0)`, `c1c.T`, `0`},
+
+		{`package c2a; var _ = rune('A')`, `'A'`, `rune`, `65`},
+		{`package c2b; var _ = rune('A')`, `rune('A')`, `rune`, `65`},
+		{`package c2c; type T rune; var _ = T('A')`, `T('A')`, `c2c.T`, `65`},
+
+		{`package c3a; var _ = float32(0.)`, `0.`, `float32`, `0`},
+		{`package c3b; var _ = float32(0.)`, `float32(0.)`, `float32`, `0`},
+		{`package c3c; type T float32; var _ = T(0.)`, `T(0.)`, `c3c.T`, `0`},
+
+		{`package c4a; var _ = complex64(0i)`, `0i`, `complex64`, `(0 + 0i)`},
+		{`package c4b; var _ = complex64(0i)`, `complex64(0i)`, `complex64`, `(0 + 0i)`},
+		{`package c4c; type T complex64; var _ = T(0i)`, `T(0i)`, `c4c.T`, `(0 + 0i)`},
+
+		{`package c5a; var _ = string("foo")`, `"foo"`, `string`, `"foo"`},
+		{`package c5b; var _ = string("foo")`, `string("foo")`, `string`, `"foo"`},
+		{`package c5c; type T string; var _ = T("foo")`, `T("foo")`, `c5c.T`, `"foo"`},
+		{`package c5d; var _ = string(65)`, `65`, `untyped int`, `65`},
+		{`package c5e; var _ = string('A')`, `'A'`, `untyped rune`, `65`},
+		{`package c5f; type T string; var _ = T('A')`, `'A'`, `untyped rune`, `65`},
+		{`package c5g; var s uint; var _ = string(1 << s)`, `1 << s`, `untyped int`, ``},
+
+		{`package d0; var _ = []byte("foo")`, `"foo"`, `string`, `"foo"`},
+		{`package d1; var _ = []byte(string("foo"))`, `"foo"`, `string`, `"foo"`},
+		{`package d2; var _ = []byte(string("foo"))`, `string("foo")`, `string`, `"foo"`},
+		{`package d3; type T []byte; var _ = T("foo")`, `"foo"`, `string`, `"foo"`},
+
+		{`package e0; const _ = float32( 1e-200)`, `float32(1e-200)`, `float32`, `0`},
+		{`package e1; const _ = float32(-1e-200)`, `float32(-1e-200)`, `float32`, `0`},
+		{`package e2; const _ = float64( 1e-2000)`, `float64(1e-2000)`, `float64`, `0`},
+		{`package e3; const _ = float64(-1e-2000)`, `float64(-1e-2000)`, `float64`, `0`},
+		{`package e4; const _ = complex64( 1e-200)`, `complex64(1e-200)`, `complex64`, `(0 + 0i)`},
+		{`package e5; const _ = complex64(-1e-200)`, `complex64(-1e-200)`, `complex64`, `(0 + 0i)`},
+		{`package e6; const _ = complex128( 1e-2000)`, `complex128(1e-2000)`, `complex128`, `(0 + 0i)`},
+		{`package e7; const _ = complex128(-1e-2000)`, `complex128(-1e-2000)`, `complex128`, `(0 + 0i)`},
+
+		{`package f0 ; var _ float32 =  1e-200`, `1e-200`, `float32`, `0`},
+		{`package f1 ; var _ float32 = -1e-200`, `-1e-200`, `float32`, `0`},
+		{`package f2a; var _ float64 =  1e-2000`, `1e-2000`, `float64`, `0`},
+		{`package f3a; var _ float64 = -1e-2000`, `-1e-2000`, `float64`, `0`},
+		{`package f2b; var _         =  1e-2000`, `1e-2000`, `float64`, `0`},
+		{`package f3b; var _         = -1e-2000`, `-1e-2000`, `float64`, `0`},
+		{`package f4 ; var _ complex64  =  1e-200 `, `1e-200`, `complex64`, `(0 + 0i)`},
+		{`package f5 ; var _ complex64  = -1e-200 `, `-1e-200`, `complex64`, `(0 + 0i)`},
+		{`package f6a; var _ complex128 =  1e-2000i`, `1e-2000i`, `complex128`, `(0 + 0i)`},
+		{`package f7a; var _ complex128 = -1e-2000i`, `-1e-2000i`, `complex128`, `(0 + 0i)`},
+		{`package f6b; var _            =  1e-2000i`, `1e-2000i`, `complex128`, `(0 + 0i)`},
+		{`package f7b; var _            = -1e-2000i`, `-1e-2000i`, `complex128`, `(0 + 0i)`},
+
+		{`package g0; const (a = len([iota]int{}); b; c); const _ = c`, `c`, `int`, `2`}, // issue #22341
+	}
+
+	for _, test := range tests {
+		info := Info{
+			Types: make(map[syntax.Expr]TypeAndValue),
+		}
+		name := mustTypecheck(t, "ValuesInfo", test.src, &info)
+
+		// look for expression
+		var expr syntax.Expr
+		for e := range info.Types {
+			if ExprString(e) == test.expr {
+				expr = e
+				break
+			}
+		}
+		if expr == nil {
+			t.Errorf("package %s: no expression found for %s", name, test.expr)
+			continue
+		}
+		tv := info.Types[expr]
+
+		// check that type is correct
+		if got := tv.Type.String(); got != test.typ {
+			t.Errorf("package %s: got type %s; want %s", name, got, test.typ)
+			continue
+		}
+
+		// if we have a constant, check that value is correct
+		if tv.Value != nil {
+			if got := tv.Value.ExactString(); got != test.val {
+				t.Errorf("package %s: got value %s; want %s", name, got, test.val)
+			}
+		} else {
+			if test.val != "" {
+				t.Errorf("package %s: no constant found; want %s", name, test.val)
+			}
+		}
+	}
+}
+
+func TestTypesInfo(t *testing.T) {
+	var tests = []struct {
+		src  string
+		expr string // expression
+		typ  string // value type
+	}{
+		// single-valued expressions of untyped constants
+		{`package b0; var x interface{} = false`, `false`, `bool`},
+		{`package b1; var x interface{} = 0`, `0`, `int`},
+		{`package b2; var x interface{} = 0.`, `0.`, `float64`},
+		{`package b3; var x interface{} = 0i`, `0i`, `complex128`},
+		{`package b4; var x interface{} = "foo"`, `"foo"`, `string`},
+
+		// comma-ok expressions
+		{`package p0; var x interface{}; var _, _ = x.(int)`,
+			`x.(int)`,
+			`(int, bool)`,
+		},
+		{`package p1; var x interface{}; func _() { _, _ = x.(int) }`,
+			`x.(int)`,
+			`(int, bool)`,
+		},
+		{`package p2a; type mybool bool; var m map[string]complex128; var b mybool; func _() { _, b = m["foo"] }`,
+			`m["foo"]`,
+			`(complex128, p2a.mybool)`,
+		},
+		{`package p2b; var m map[string]complex128; var b bool; func _() { _, b = m["foo"] }`,
+			`m["foo"]`,
+			`(complex128, bool)`,
+		},
+		{`package p3; var c chan string; var _, _ = <-c`,
+			`<-c`,
+			`(string, bool)`,
+		},
+
+		// issue 6796
+		{`package issue6796_a; var x interface{}; var _, _ = (x.(int))`,
+			`x.(int)`,
+			`(int, bool)`,
+		},
+		{`package issue6796_b; var c chan string; var _, _ = (<-c)`,
+			`(<-c)`,
+			`(string, bool)`,
+		},
+		{`package issue6796_c; var c chan string; var _, _ = (<-c)`,
+			`<-c`,
+			`(string, bool)`,
+		},
+		{`package issue6796_d; var c chan string; var _, _ = ((<-c))`,
+			`(<-c)`,
+			`(string, bool)`,
+		},
+		{`package issue6796_e; func f(c chan string) { _, _ = ((<-c)) }`,
+			`(<-c)`,
+			`(string, bool)`,
+		},
+
+		// issue 7060
+		{`package issue7060_a; var ( m map[int]string; x, ok = m[0] )`,
+			`m[0]`,
+			`(string, bool)`,
+		},
+		{`package issue7060_b; var ( m map[int]string; x, ok interface{} = m[0] )`,
+			`m[0]`,
+			`(string, bool)`,
+		},
+		{`package issue7060_c; func f(x interface{}, ok bool, m map[int]string) { x, ok = m[0] }`,
+			`m[0]`,
+			`(string, bool)`,
+		},
+		{`package issue7060_d; var ( ch chan string; x, ok = <-ch )`,
+			`<-ch`,
+			`(string, bool)`,
+		},
+		{`package issue7060_e; var ( ch chan string; x, ok interface{} = <-ch )`,
+			`<-ch`,
+			`(string, bool)`,
+		},
+		{`package issue7060_f; func f(x interface{}, ok bool, ch chan string) { x, ok = <-ch }`,
+			`<-ch`,
+			`(string, bool)`,
+		},
+
+		// issue 28277
+		{`package issue28277_a; func f(...int)`,
+			`...int`,
+			`[]int`,
+		},
+		{`package issue28277_b; func f(a, b int, c ...[]struct{})`,
+			`...[]struct{}`,
+			`[][]struct{}`,
+		},
+
+		// tests for broken code that doesn't parse or type-check
+		{`package x0; func _() { var x struct {f string}; x.f := 0 }`, `x.f`, `string`},
+		{`package x1; func _() { var z string; type x struct {f string}; y := &x{q: z}}`, `z`, `string`},
+		{`package x2; func _() { var a, b string; type x struct {f string}; z := &x{f: a, f: b,}}`, `b`, `string`},
+		{`package x3; var x = panic("");`, `panic`, `func(interface{})`},
+		{`package x4; func _() { panic("") }`, `panic`, `func(interface{})`},
+		{`package x5; func _() { var x map[string][...]int; x = map[string][...]int{"": {1,2,3}} }`, `x`, `map[string][-1]int`},
+
+		// parameterized functions
+		{`package p0; func f[T any](T); var _ = f[int]`, `f`, `func[T₁ any](T₁)`},
+		{`package p1; func f[T any](T); var _ = f[int]`, `f[int]`, `func(int)`},
+		{`package p2; func f[T any](T); var _ = f(42)`, `f`, `func[T₁ any](T₁)`},
+		{`package p2; func f[T any](T); var _ = f(42)`, `f(42)`, `()`},
+
+		// type parameters
+		{`package t0; type t[] int; var _ t`, `t`, `t0.t`}, // t[] is a syntax error that is ignored in this test in favor of t
+		{`package t1; type t[P any] int; var _ t[int]`, `t`, `t1.t[P₁ any]`},
+		{`package t2; type t[P interface{}] int; var _ t[int]`, `t`, `t2.t[P₁ interface{}]`},
+		{`package t3; type t[P, Q interface{}] int; var _ t[int, int]`, `t`, `t3.t[P₁, Q₂ interface{}]`},
+		{`package t4; type t[P, Q interface{ m() }] int; var _ t[int, int]`, `t`, `t4.t[P₁, Q₂ interface{m()}]`},
+
+		// instantiated types must be sanitized
+		{`package g0; type t[P any] int; var x struct{ f t[int] }; var _ = x.f`, `x.f`, `g0.t[int]`},
+	}
+
+	for _, test := range tests {
+		info := Info{Types: make(map[syntax.Expr]TypeAndValue)}
+		name, _ := mayTypecheck(t, "TypesInfo", test.src, &info)
+
+		// look for expression type
+		var typ Type
+		for e, tv := range info.Types {
+			if ExprString(e) == test.expr {
+				typ = tv.Type
+				break
+			}
+		}
+		if typ == nil {
+			t.Errorf("package %s: no type found for %s", name, test.expr)
+			continue
+		}
+
+		// check that type is correct
+		if got := typ.String(); got != test.typ {
+			t.Errorf("package %s: got %s; want %s", name, got, test.typ)
+		}
+	}
+}
+
+func TestInferredInfo(t *testing.T) {
+	var tests = []struct {
+		src   string
+		fun   string
+		targs []string
+		sig   string
+	}{
+		{`package p0; func f[T any](T); func _() { f(42) }`,
+			`f`,
+			[]string{`int`},
+			`func(int)`,
+		},
+		{`package p1; func f[T any](T) T; func _() { f('@') }`,
+			`f`,
+			[]string{`rune`},
+			`func(rune) rune`,
+		},
+		{`package p2; func f[T any](...T) T; func _() { f(0i) }`,
+			`f`,
+			[]string{`complex128`},
+			`func(...complex128) complex128`,
+		},
+		{`package p3; func f[A, B, C any](A, *B, []C); func _() { f(1.2, new(string), []byte{}) }`,
+			`f`,
+			[]string{`float64`, `string`, `byte`},
+			`func(float64, *string, []byte)`,
+		},
+		{`package p4; func f[A, B any](A, *B, ...[]B); func _() { f(1.2, new(byte)) }`,
+			`f`,
+			[]string{`float64`, `byte`},
+			`func(float64, *byte, ...[]byte)`,
+		},
+
+		// we don't know how to translate these but we can type-check them
+		{`package q0; type T struct{}; func (T) m[P any](P); func _(x T) { x.m(42) }`,
+			`x.m`,
+			[]string{`int`},
+			`func(int)`,
+		},
+		{`package q1; type T struct{}; func (T) m[P any](P) P; func _(x T) { x.m(42) }`,
+			`x.m`,
+			[]string{`int`},
+			`func(int) int`,
+		},
+		{`package q2; type T struct{}; func (T) m[P any](...P) P; func _(x T) { x.m(42) }`,
+			`x.m`,
+			[]string{`int`},
+			`func(...int) int`,
+		},
+		{`package q3; type T struct{}; func (T) m[A, B, C any](A, *B, []C); func _(x T) { x.m(1.2, new(string), []byte{}) }`,
+			`x.m`,
+			[]string{`float64`, `string`, `byte`},
+			`func(float64, *string, []byte)`,
+		},
+		{`package q4; type T struct{}; func (T) m[A, B any](A, *B, ...[]B); func _(x T) { x.m(1.2, new(byte)) }`,
+			`x.m`,
+			[]string{`float64`, `byte`},
+			`func(float64, *byte, ...[]byte)`,
+		},
+
+		{`package r0; type T[P any] struct{}; func (_ T[P]) m[Q any](Q); func _[P any](x T[P]) { x.m(42) }`,
+			`x.m`,
+			[]string{`int`},
+			`func(int)`,
+		},
+		// TODO(gri) record method type parameters in syntax.FuncType so we can check this
+		// {`package r1; type T interface{ m[P any](P) }; func _(x T) { x.m(4.2) }`,
+		// 	`x.m`,
+		// 	[]string{`float64`},
+		// 	`func(float64)`,
+		// },
+
+		{`package s1; func f[T any, P interface{type *T}](x T); func _(x string) { f(x) }`,
+			`f`,
+			[]string{`string`, `*string`},
+			`func(x string)`,
+		},
+		{`package s2; func f[T any, P interface{type *T}](x []T); func _(x []int) { f(x) }`,
+			`f`,
+			[]string{`int`, `*int`},
+			`func(x []int)`,
+		},
+		{`package s3; type C[T any] interface{type chan<- T}; func f[T any, P C[T]](x []T); func _(x []int) { f(x) }`,
+			`f`,
+			[]string{`int`, `chan<- int`},
+			`func(x []int)`,
+		},
+		{`package s4; type C[T any] interface{type chan<- T}; func f[T any, P C[T], Q C[[]*P]](x []T); func _(x []int) { f(x) }`,
+			`f`,
+			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
+			`func(x []int)`,
+		},
+
+		{`package t1; func f[T any, P interface{type *T}]() T; func _() { _ = f[string] }`,
+			`f`,
+			[]string{`string`, `*string`},
+			`func() string`,
+		},
+		{`package t2; type C[T any] interface{type chan<- T}; func f[T any, P C[T]]() []T; func _() { _ = f[int] }`,
+			`f`,
+			[]string{`int`, `chan<- int`},
+			`func() []int`,
+		},
+		{`package t3; type C[T any] interface{type chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T; func _() { _ = f[int] }`,
+			`f`,
+			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
+			`func() []int`,
+		},
+	}
+
+	for _, test := range tests {
+		info := Info{Inferred: make(map[syntax.Expr]Inferred)}
+		name, err := mayTypecheck(t, "InferredInfo", test.src, &info)
+		if err != nil {
+			t.Errorf("package %s: %v", name, err)
+			continue
+		}
+
+		// look for inferred type arguments and signature
+		var targs []Type
+		var sig *Signature
+		for call, inf := range info.Inferred {
+			var fun syntax.Expr
+			switch x := call.(type) {
+			case *syntax.CallExpr:
+				fun = x.Fun
+			case *syntax.IndexExpr:
+				fun = x.X
+			default:
+				panic(fmt.Sprintf("unexpected call expression type %T", call))
+			}
+			if ExprString(fun) == test.fun {
+				targs = inf.Targs
+				sig = inf.Sig
+				break
+			}
+		}
+		if targs == nil {
+			t.Errorf("package %s: no inferred information found for %s", name, test.fun)
+			continue
+		}
+
+		// check that type arguments are correct
+		if len(targs) != len(test.targs) {
+			t.Errorf("package %s: got %d type arguments; want %d", name, len(targs), len(test.targs))
+			continue
+		}
+		for i, targ := range targs {
+			if got := targ.String(); got != test.targs[i] {
+				t.Errorf("package %s, %d. type argument: got %s; want %s", name, i, got, test.targs[i])
+				continue
+			}
+		}
+
+		// check that signature is correct
+		if got := sig.String(); got != test.sig {
+			t.Errorf("package %s: got %s; want %s", name, got, test.sig)
+		}
+	}
+}
+
+func TestDefsInfo(t *testing.T) {
+	var tests = []struct {
+		src  string
+		obj  string
+		want string
+	}{
+		{`package p0; const x = 42`, `x`, `const p0.x untyped int`},
+		{`package p1; const x int = 42`, `x`, `const p1.x int`},
+		{`package p2; var x int`, `x`, `var p2.x int`},
+		{`package p3; type x int`, `x`, `type p3.x int`},
+		{`package p4; func f()`, `f`, `func p4.f()`},
+
+		// generic types must be sanitized
+		// (need to use sufficiently nested types to provoke unexpanded types)
+		{`package g0; type t[P any] P; const x = t[int](42)`, `x`, `const g0.x g0.t[int]`},
+		{`package g1; type t[P any] P; var x = t[int](42)`, `x`, `var g1.x g1.t[int]`},
+		{`package g2; type t[P any] P; type x struct{ f t[int] }`, `x`, `type g2.x struct{f g2.t[int]}`},
+		{`package g3; type t[P any] P; func f(x struct{ f t[string] }); var g = f`, `g`, `var g3.g func(x struct{f g3.t[string]})`},
+	}
+
+	for _, test := range tests {
+		info := Info{
+			Defs: make(map[*syntax.Name]Object),
+		}
+		name := mustTypecheck(t, "DefsInfo", test.src, &info)
+
+		// find object
+		var def Object
+		for id, obj := range info.Defs {
+			if id.Value == test.obj {
+				def = obj
+				break
+			}
+		}
+		if def == nil {
+			t.Errorf("package %s: %s not found", name, test.obj)
+			continue
+		}
+
+		if got := def.String(); got != test.want {
+			t.Errorf("package %s: got %s; want %s", name, got, test.want)
+		}
+	}
+}
+
+func TestUsesInfo(t *testing.T) {
+	var tests = []struct {
+		src  string
+		obj  string
+		want string
+	}{
+		{`package p0; func _() { _ = x }; const x = 42`, `x`, `const p0.x untyped int`},
+		{`package p1; func _() { _ = x }; const x int = 42`, `x`, `const p1.x int`},
+		{`package p2; func _() { _ = x }; var x int`, `x`, `var p2.x int`},
+		{`package p3; func _() { type _ x }; type x int`, `x`, `type p3.x int`},
+		{`package p4; func _() { _ = f }; func f()`, `f`, `func p4.f()`},
+
+		// generic types must be sanitized
+		// (need to use sufficiently nested types to provoke unexpanded types)
+		{`package g0; func _() { _ = x }; type t[P any] P; const x = t[int](42)`, `x`, `const g0.x g0.t[int]`},
+		{`package g1; func _() { _ = x }; type t[P any] P; var x = t[int](42)`, `x`, `var g1.x g1.t[int]`},
+		{`package g2; func _() { type _ x }; type t[P any] P; type x struct{ f t[int] }`, `x`, `type g2.x struct{f g2.t[int]}`},
+		{`package g3; func _() { _ = f }; type t[P any] P; func f(x struct{ f t[string] })`, `f`, `func g3.f(x struct{f g3.t[string]})`},
+	}
+
+	for _, test := range tests {
+		info := Info{
+			Uses: make(map[*syntax.Name]Object),
+		}
+		name := mustTypecheck(t, "UsesInfo", test.src, &info)
+
+		// find object
+		var use Object
+		for id, obj := range info.Uses {
+			if id.Value == test.obj {
+				use = obj
+				break
+			}
+		}
+		if use == nil {
+			t.Errorf("package %s: %s not found", name, test.obj)
+			continue
+		}
+
+		if got := use.String(); got != test.want {
+			t.Errorf("package %s: got %s; want %s", name, got, test.want)
+		}
+	}
+}
+
+func TestImplicitsInfo(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	var tests = []struct {
+		src  string
+		want string
+	}{
+		{`package p2; import . "fmt"; var _ = Println`, ""},           // no Implicits entry
+		{`package p0; import local "fmt"; var _ = local.Println`, ""}, // no Implicits entry
+		{`package p1; import "fmt"; var _ = fmt.Println`, "importSpec: package fmt"},
+
+		{`package p3; func f(x interface{}) { switch x.(type) { case int: } }`, ""}, // no Implicits entry
+		{`package p4; func f(x interface{}) { switch t := x.(type) { case int: _ = t } }`, "caseClause: var t int"},
+		{`package p5; func f(x interface{}) { switch t := x.(type) { case int, uint: _ = t } }`, "caseClause: var t interface{}"},
+		{`package p6; func f(x interface{}) { switch t := x.(type) { default: _ = t } }`, "caseClause: var t interface{}"},
+
+		{`package p7; func f(x int) {}`, ""}, // no Implicits entry
+		{`package p8; func f(int) {}`, "field: var  int"},
+		{`package p9; func f() (complex64) { return 0 }`, "field: var  complex64"},
+		{`package p10; type T struct{}; func (*T) f() {}`, "field: var  *p10.T"},
+	}
+
+	for _, test := range tests {
+		info := Info{
+			Implicits: make(map[syntax.Node]Object),
+		}
+		name := mustTypecheck(t, "ImplicitsInfo", test.src, &info)
+
+		// the test cases expect at most one Implicits entry
+		if len(info.Implicits) > 1 {
+			t.Errorf("package %s: %d Implicits entries found", name, len(info.Implicits))
+			continue
+		}
+
+		// extract Implicits entry, if any
+		var got string
+		for n, obj := range info.Implicits {
+			switch x := n.(type) {
+			case *syntax.ImportDecl:
+				got = "importSpec"
+			case *syntax.CaseClause:
+				got = "caseClause"
+			case *syntax.Field:
+				got = "field"
+			default:
+				t.Fatalf("package %s: unexpected %T", name, x)
+			}
+			got += ": " + obj.String()
+		}
+
+		// verify entry
+		if got != test.want {
+			t.Errorf("package %s: got %q; want %q", name, got, test.want)
+		}
+	}
+}
+
+func predString(tv TypeAndValue) string {
+	var buf bytes.Buffer
+	pred := func(b bool, s string) {
+		if b {
+			if buf.Len() > 0 {
+				buf.WriteString(", ")
+			}
+			buf.WriteString(s)
+		}
+	}
+
+	pred(tv.IsVoid(), "void")
+	pred(tv.IsType(), "type")
+	pred(tv.IsBuiltin(), "builtin")
+	pred(tv.IsValue() && tv.Value != nil, "const")
+	pred(tv.IsValue() && tv.Value == nil, "value")
+	pred(tv.IsNil(), "nil")
+	pred(tv.Addressable(), "addressable")
+	pred(tv.Assignable(), "assignable")
+	pred(tv.HasOk(), "hasOk")
+
+	if buf.Len() == 0 {
+		return "invalid"
+	}
+	return buf.String()
+}
+
+func TestPredicatesInfo(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	var tests = []struct {
+		src  string
+		expr string
+		pred string
+	}{
+		// void
+		{`package n0; func f() { f() }`, `f()`, `void`},
+
+		// types
+		{`package t0; type _ int`, `int`, `type`},
+		{`package t1; type _ []int`, `[]int`, `type`},
+		{`package t2; type _ func()`, `func()`, `type`},
+		{`package t3; type _ func(int)`, `int`, `type`},
+		{`package t3; type _ func(...int)`, `...int`, `type`},
+
+		// built-ins
+		{`package b0; var _ = len("")`, `len`, `builtin`},
+		{`package b1; var _ = (len)("")`, `(len)`, `builtin`},
+
+		// constants
+		{`package c0; var _ = 42`, `42`, `const`},
+		{`package c1; var _ = "foo" + "bar"`, `"foo" + "bar"`, `const`},
+		{`package c2; const (i = 1i; _ = i)`, `i`, `const`},
+
+		// values
+		{`package v0; var (a, b int; _ = a + b)`, `a + b`, `value`},
+		{`package v1; var _ = &[]int{1}`, `([]int literal)`, `value`},
+		{`package v2; var _ = func(){}`, `(func() literal)`, `value`},
+		{`package v4; func f() { _ = f }`, `f`, `value`},
+		{`package v3; var _ *int = nil`, `nil`, `value, nil`},
+		{`package v3; var _ *int = (nil)`, `(nil)`, `value, nil`},
+
+		// addressable (and thus assignable) operands
+		{`package a0; var (x int; _ = x)`, `x`, `value, addressable, assignable`},
+		{`package a1; var (p *int; _ = *p)`, `*p`, `value, addressable, assignable`},
+		{`package a2; var (s []int; _ = s[0])`, `s[0]`, `value, addressable, assignable`},
+		{`package a3; var (s struct{f int}; _ = s.f)`, `s.f`, `value, addressable, assignable`},
+		{`package a4; var (a [10]int; _ = a[0])`, `a[0]`, `value, addressable, assignable`},
+		{`package a5; func _(x int) { _ = x }`, `x`, `value, addressable, assignable`},
+		{`package a6; func _()(x int) { _ = x; return }`, `x`, `value, addressable, assignable`},
+		{`package a7; type T int; func (x T) _() { _ = x }`, `x`, `value, addressable, assignable`},
+		// composite literals are not addressable
+
+		// assignable but not addressable values
+		{`package s0; var (m map[int]int; _ = m[0])`, `m[0]`, `value, assignable, hasOk`},
+		{`package s1; var (m map[int]int; _, _ = m[0])`, `m[0]`, `value, assignable, hasOk`},
+
+		// hasOk expressions
+		{`package k0; var (ch chan int; _ = <-ch)`, `<-ch`, `value, hasOk`},
+		{`package k1; var (ch chan int; _, _ = <-ch)`, `<-ch`, `value, hasOk`},
+
+		// missing entries
+		// - package names are collected in the Uses map
+		// - identifiers being declared are collected in the Defs map
+		{`package m0; import "os"; func _() { _ = os.Stdout }`, `os`, `<missing>`},
+		{`package m1; import p "os"; func _() { _ = p.Stdout }`, `p`, `<missing>`},
+		{`package m2; const c = 0`, `c`, `<missing>`},
+		{`package m3; type T int`, `T`, `<missing>`},
+		{`package m4; var v int`, `v`, `<missing>`},
+		{`package m5; func f() {}`, `f`, `<missing>`},
+		{`package m6; func _(x int) {}`, `x`, `<missing>`},
+		{`package m6; func _()(x int) { return }`, `x`, `<missing>`},
+		{`package m6; type T int; func (x T) _() {}`, `x`, `<missing>`},
+	}
+
+	for _, test := range tests {
+		info := Info{Types: make(map[syntax.Expr]TypeAndValue)}
+		name := mustTypecheck(t, "PredicatesInfo", test.src, &info)
+
+		// look for expression predicates
+		got := "<missing>"
+		for e, tv := range info.Types {
+			//println(name, ExprString(e))
+			if ExprString(e) == test.expr {
+				got = predString(tv)
+				break
+			}
+		}
+
+		if got != test.pred {
+			t.Errorf("package %s: got %s; want %s", name, got, test.pred)
+		}
+	}
+}
+
+func TestScopesInfo(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	var tests = []struct {
+		src    string
+		scopes []string // list of scope descriptors of the form kind:varlist
+	}{
+		{`package p0`, []string{
+			"file:",
+		}},
+		{`package p1; import ( "fmt"; m "math"; _ "os" ); var ( _ = fmt.Println; _ = m.Pi )`, []string{
+			"file:fmt m",
+		}},
+		{`package p2; func _() {}`, []string{
+			"file:", "func:",
+		}},
+		{`package p3; func _(x, y int) {}`, []string{
+			"file:", "func:x y",
+		}},
+		{`package p4; func _(x, y int) { x, z := 1, 2; _ = z }`, []string{
+			"file:", "func:x y z", // redeclaration of x
+		}},
+		{`package p5; func _(x, y int) (u, _ int) { return }`, []string{
+			"file:", "func:u x y",
+		}},
+		{`package p6; func _() { { var x int; _ = x } }`, []string{
+			"file:", "func:", "block:x",
+		}},
+		{`package p7; func _() { if true {} }`, []string{
+			"file:", "func:", "if:", "block:",
+		}},
+		{`package p8; func _() { if x := 0; x < 0 { y := x; _ = y } }`, []string{
+			"file:", "func:", "if:x", "block:y",
+		}},
+		{`package p9; func _() { switch x := 0; x {} }`, []string{
+			"file:", "func:", "switch:x",
+		}},
+		{`package p10; func _() { switch x := 0; x { case 1: y := x; _ = y; default: }}`, []string{
+			"file:", "func:", "switch:x", "case:y", "case:",
+		}},
+		{`package p11; func _(t interface{}) { switch t.(type) {} }`, []string{
+			"file:", "func:t", "switch:",
+		}},
+		{`package p12; func _(t interface{}) { switch t := t; t.(type) {} }`, []string{
+			"file:", "func:t", "switch:t",
+		}},
+		{`package p13; func _(t interface{}) { switch x := t.(type) { case int: _ = x } }`, []string{
+			"file:", "func:t", "switch:", "case:x", // x implicitly declared
+		}},
+		{`package p14; func _() { select{} }`, []string{
+			"file:", "func:",
+		}},
+		{`package p15; func _(c chan int) { select{ case <-c: } }`, []string{
+			"file:", "func:c", "select:",
+		}},
+		{`package p16; func _(c chan int) { select{ case i := <-c: x := i; _ = x} }`, []string{
+			"file:", "func:c", "select:i x",
+		}},
+		{`package p17; func _() { for{} }`, []string{
+			"file:", "func:", "for:", "block:",
+		}},
+		{`package p18; func _(n int) { for i := 0; i < n; i++ { _ = i } }`, []string{
+			"file:", "func:n", "for:i", "block:",
+		}},
+		{`package p19; func _(a []int) { for i := range a { _ = i} }`, []string{
+			"file:", "func:a", "for:i", "block:",
+		}},
+		{`package p20; var s int; func _(a []int) { for i, x := range a { s += x; _ = i } }`, []string{
+			"file:", "func:a", "for:i x", "block:",
+		}},
+	}
+
+	for _, test := range tests {
+		info := Info{Scopes: make(map[syntax.Node]*Scope)}
+		name := mustTypecheck(t, "ScopesInfo", test.src, &info)
+
+		// number of scopes must match
+		if len(info.Scopes) != len(test.scopes) {
+			t.Errorf("package %s: got %d scopes; want %d", name, len(info.Scopes), len(test.scopes))
+		}
+
+		// scope descriptions must match
+		for node, scope := range info.Scopes {
+			var kind string
+			switch node.(type) {
+			case *syntax.File:
+				kind = "file"
+			case *syntax.FuncType:
+				kind = "func"
+			case *syntax.BlockStmt:
+				kind = "block"
+			case *syntax.IfStmt:
+				kind = "if"
+			case *syntax.SwitchStmt:
+				kind = "switch"
+			case *syntax.SelectStmt:
+				kind = "select"
+			case *syntax.CaseClause:
+				kind = "case"
+			case *syntax.CommClause:
+				kind = "comm"
+			case *syntax.ForStmt:
+				kind = "for"
+			default:
+				kind = fmt.Sprintf("%T", node)
+			}
+
+			// look for matching scope description
+			desc := kind + ":" + strings.Join(scope.Names(), " ")
+			found := false
+			for _, d := range test.scopes {
+				if desc == d {
+					found = true
+					break
+				}
+			}
+			if !found {
+				t.Errorf("package %s: no matching scope found for %s", name, desc)
+			}
+		}
+	}
+}
+
+func TestInitOrderInfo(t *testing.T) {
+	var tests = []struct {
+		src   string
+		inits []string
+	}{
+		{`package p0; var (x = 1; y = x)`, []string{
+			"x = 1", "y = x",
+		}},
+		{`package p1; var (a = 1; b = 2; c = 3)`, []string{
+			"a = 1", "b = 2", "c = 3",
+		}},
+		{`package p2; var (a, b, c = 1, 2, 3)`, []string{
+			"a = 1", "b = 2", "c = 3",
+		}},
+		{`package p3; var _ = f(); func f() int { return 1 }`, []string{
+			"_ = f()", // blank var
+		}},
+		{`package p4; var (a = 0; x = y; y = z; z = 0)`, []string{
+			"a = 0", "z = 0", "y = z", "x = y",
+		}},
+		{`package p5; var (a, _ = m[0]; m map[int]string)`, []string{
+			"a, _ = m[0]", // blank var
+		}},
+		{`package p6; var a, b = f(); func f() (_, _ int) { return z, z }; var z = 0`, []string{
+			"z = 0", "a, b = f()",
+		}},
+		{`package p7; var (a = func() int { return b }(); b = 1)`, []string{
+			"b = 1", "a = (func() int literal)()",
+		}},
+		{`package p8; var (a, b = func() (_, _ int) { return c, c }(); c = 1)`, []string{
+			"c = 1", "a, b = (func() (_, _ int) literal)()",
+		}},
+		{`package p9; type T struct{}; func (T) m() int { _ = y; return 0 }; var x, y = T.m, 1`, []string{
+			"y = 1", "x = T.m",
+		}},
+		{`package p10; var (d = c + b; a = 0; b = 0; c = 0)`, []string{
+			"a = 0", "b = 0", "c = 0", "d = c + b",
+		}},
+		{`package p11; var (a = e + c; b = d + c; c = 0; d = 0; e = 0)`, []string{
+			"c = 0", "d = 0", "b = d + c", "e = 0", "a = e + c",
+		}},
+		// emit an initializer for n:1 initializations only once (not for each node
+		// on the lhs which may appear in different order in the dependency graph)
+		{`package p12; var (a = x; b = 0; x, y = m[0]; m map[int]int)`, []string{
+			"b = 0", "x, y = m[0]", "a = x",
+		}},
+		// test case from spec section on package initialization
+		{`package p12
+
+		var (
+			a = c + b
+			b = f()
+			c = f()
+			d = 3
+		)
+
+		func f() int {
+			d++
+			return d
+		}`, []string{
+			"d = 3", "b = f()", "c = f()", "a = c + b",
+		}},
+		// test case for issue 7131
+		{`package main
+
+		var counter int
+		func next() int { counter++; return counter }
+
+		var _ = makeOrder()
+		func makeOrder() []int { return []int{f, b, d, e, c, a} }
+
+		var a       = next()
+		var b, c    = next(), next()
+		var d, e, f = next(), next(), next()
+		`, []string{
+			"a = next()", "b = next()", "c = next()", "d = next()", "e = next()", "f = next()", "_ = makeOrder()",
+		}},
+		// test case for issue 10709
+		{`package p13
+
+		var (
+		    v = t.m()
+		    t = makeT(0)
+		)
+
+		type T struct{}
+
+		func (T) m() int { return 0 }
+
+		func makeT(n int) T {
+		    if n > 0 {
+		        return makeT(n-1)
+		    }
+		    return T{}
+		}`, []string{
+			"t = makeT(0)", "v = t.m()",
+		}},
+		// test case for issue 10709: same as test before, but variable decls swapped
+		{`package p14
+
+		var (
+		    t = makeT(0)
+		    v = t.m()
+		)
+
+		type T struct{}
+
+		func (T) m() int { return 0 }
+
+		func makeT(n int) T {
+		    if n > 0 {
+		        return makeT(n-1)
+		    }
+		    return T{}
+		}`, []string{
+			"t = makeT(0)", "v = t.m()",
+		}},
+		// another candidate possibly causing problems with issue 10709
+		{`package p15
+
+		var y1 = f1()
+
+		func f1() int { return g1() }
+		func g1() int { f1(); return x1 }
+
+		var x1 = 0
+
+		var y2 = f2()
+
+		func f2() int { return g2() }
+		func g2() int { return x2 }
+
+		var x2 = 0`, []string{
+			"x1 = 0", "y1 = f1()", "x2 = 0", "y2 = f2()",
+		}},
+	}
+
+	for _, test := range tests {
+		info := Info{}
+		name := mustTypecheck(t, "InitOrderInfo", test.src, &info)
+
+		// number of initializers must match
+		if len(info.InitOrder) != len(test.inits) {
+			t.Errorf("package %s: got %d initializers; want %d", name, len(info.InitOrder), len(test.inits))
+			continue
+		}
+
+		// initializers must match
+		for i, want := range test.inits {
+			got := info.InitOrder[i].String()
+			if got != want {
+				t.Errorf("package %s, init %d: got %s; want %s", name, i, got, want)
+				continue
+			}
+		}
+	}
+}
+
+func TestMultiFileInitOrder(t *testing.T) {
+	mustParse := func(src string) *syntax.File {
+		f, err := parseSrc("main", src)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return f
+	}
+
+	fileA := mustParse(`package main; var a = 1`)
+	fileB := mustParse(`package main; var b = 2`)
+
+	// The initialization order must not depend on the parse
+	// order of the files, only on the presentation order to
+	// the type-checker.
+	for _, test := range []struct {
+		files []*syntax.File
+		want  string
+	}{
+		{[]*syntax.File{fileA, fileB}, "[a = 1 b = 2]"},
+		{[]*syntax.File{fileB, fileA}, "[b = 2 a = 1]"},
+	} {
+		var info Info
+		if _, err := new(Config).Check("main", test.files, &info); err != nil {
+			t.Fatal(err)
+		}
+		if got := fmt.Sprint(info.InitOrder); got != test.want {
+			t.Fatalf("got %s; want %s", got, test.want)
+		}
+	}
+}
+
+func TestFiles(t *testing.T) {
+	var sources = []string{
+		"package p; type T struct{}; func (T) m1() {}",
+		"package p; func (T) m2() {}; var x interface{ m1(); m2() } = T{}",
+		"package p; func (T) m3() {}; var y interface{ m1(); m2(); m3() } = T{}",
+		"package p",
+	}
+
+	var conf Config
+	pkg := NewPackage("p", "p")
+	var info Info
+	check := NewChecker(&conf, pkg, &info)
+
+	for i, src := range sources {
+		filename := fmt.Sprintf("sources%d", i)
+		f, err := parseSrc(filename, src)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := check.Files([]*syntax.File{f}); err != nil {
+			t.Error(err)
+		}
+	}
+
+	// check InitOrder is [x y]
+	var vars []string
+	for _, init := range info.InitOrder {
+		for _, v := range init.Lhs {
+			vars = append(vars, v.Name())
+		}
+	}
+	if got, want := fmt.Sprint(vars), "[x y]"; got != want {
+		t.Errorf("InitOrder == %s, want %s", got, want)
+	}
+}
+
+type testImporter map[string]*Package
+
+func (m testImporter) Import(path string) (*Package, error) {
+	if pkg := m[path]; pkg != nil {
+		return pkg, nil
+	}
+	return nil, fmt.Errorf("package %q not found", path)
+}
+
+func TestSelection(t *testing.T) {
+	t.Skip("requires fixes around source positions")
+
+	selections := make(map[*syntax.SelectorExpr]*Selection)
+
+	imports := make(testImporter)
+	conf := Config{Importer: imports}
+	makePkg := func(path, src string) {
+		f, err := parseSrc(path+".go", src)
+		if err != nil {
+			t.Fatal(err)
+		}
+		pkg, err := conf.Check(path, []*syntax.File{f}, &Info{Selections: selections})
+		if err != nil {
+			t.Fatal(err)
+		}
+		imports[path] = pkg
+	}
+
+	const libSrc = `
+package lib
+type T float64
+const C T = 3
+var V T
+func F() {}
+func (T) M() {}
+`
+	const mainSrc = `
+package main
+import "lib"
+
+type A struct {
+	*B
+	C
+}
+
+type B struct {
+	b int
+}
+
+func (B) f(int)
+
+type C struct {
+	c int
+}
+
+func (C) g()
+func (*C) h()
+
+func main() {
+	// qualified identifiers
+	var _ lib.T
+        _ = lib.C
+        _ = lib.F
+        _ = lib.V
+	_ = lib.T.M
+
+	// fields
+	_ = A{}.B
+	_ = new(A).B
+
+	_ = A{}.C
+	_ = new(A).C
+
+	_ = A{}.b
+	_ = new(A).b
+
+	_ = A{}.c
+	_ = new(A).c
+
+	// methods
+        _ = A{}.f
+        _ = new(A).f
+        _ = A{}.g
+        _ = new(A).g
+        _ = new(A).h
+
+        _ = B{}.f
+        _ = new(B).f
+
+        _ = C{}.g
+        _ = new(C).g
+        _ = new(C).h
+
+	// method expressions
+        _ = A.f
+        _ = (*A).f
+        _ = B.f
+        _ = (*B).f
+}`
+
+	wantOut := map[string][2]string{
+		"lib.T.M": {"method expr (lib.T) M(lib.T)", ".[0]"},
+
+		"A{}.B":    {"field (main.A) B *main.B", ".[0]"},
+		"new(A).B": {"field (*main.A) B *main.B", "->[0]"},
+		"A{}.C":    {"field (main.A) C main.C", ".[1]"},
+		"new(A).C": {"field (*main.A) C main.C", "->[1]"},
+		"A{}.b":    {"field (main.A) b int", "->[0 0]"},
+		"new(A).b": {"field (*main.A) b int", "->[0 0]"},
+		"A{}.c":    {"field (main.A) c int", ".[1 0]"},
+		"new(A).c": {"field (*main.A) c int", "->[1 0]"},
+
+		"A{}.f":    {"method (main.A) f(int)", "->[0 0]"},
+		"new(A).f": {"method (*main.A) f(int)", "->[0 0]"},
+		"A{}.g":    {"method (main.A) g()", ".[1 0]"},
+		"new(A).g": {"method (*main.A) g()", "->[1 0]"},
+		"new(A).h": {"method (*main.A) h()", "->[1 1]"}, // TODO(gri) should this report .[1 1] ?
+		"B{}.f":    {"method (main.B) f(int)", ".[0]"},
+		"new(B).f": {"method (*main.B) f(int)", "->[0]"},
+		"C{}.g":    {"method (main.C) g()", ".[0]"},
+		"new(C).g": {"method (*main.C) g()", "->[0]"},
+		"new(C).h": {"method (*main.C) h()", "->[1]"}, // TODO(gri) should this report .[1] ?
+
+		"A.f":    {"method expr (main.A) f(main.A, int)", "->[0 0]"},
+		"(*A).f": {"method expr (*main.A) f(*main.A, int)", "->[0 0]"},
+		"B.f":    {"method expr (main.B) f(main.B, int)", ".[0]"},
+		"(*B).f": {"method expr (*main.B) f(*main.B, int)", "->[0]"},
+	}
+
+	makePkg("lib", libSrc)
+	makePkg("main", mainSrc)
+
+	for e, sel := range selections {
+		_ = sel.String() // assertion: must not panic
+
+		unimplemented()
+		_ = e
+		// start := fset.Position(e.Pos()).Offset
+		// end := fset.Position(e.End()).Offset
+		// syntax := mainSrc[start:end] // (all SelectorExprs are in main, not lib)
+
+		direct := "."
+		if sel.Indirect() {
+			direct = "->"
+		}
+		got := [2]string{
+			sel.String(),
+			fmt.Sprintf("%s%v", direct, sel.Index()),
+		}
+		unimplemented()
+		_ = got
+		// want := wantOut[syntax]
+		// if want != got {
+		// 	t.Errorf("%s: got %q; want %q", syntax, got, want)
+		// }
+		// delete(wantOut, syntax)
+
+		// We must explicitly assert properties of the
+		// Signature's receiver since it doesn't participate
+		// in Identical() or String().
+		sig, _ := sel.Type().(*Signature)
+		if sel.Kind() == MethodVal {
+			got := sig.Recv().Type()
+			want := sel.Recv()
+			if !Identical(got, want) {
+				unimplemented()
+				// t.Errorf("%s: Recv() = %s, want %s", syntax, got, want)
+			}
+		} else if sig != nil && sig.Recv() != nil {
+			t.Errorf("%s: signature has receiver %s", sig, sig.Recv().Type())
+		}
+	}
+	// Assert that all wantOut entries were used exactly once.
+	for syntax := range wantOut {
+		t.Errorf("no syntax.Selection found with syntax %q", syntax)
+	}
+}
+
+func TestIssue8518(t *testing.T) {
+	imports := make(testImporter)
+	conf := Config{
+		Error:    func(err error) { t.Log(err) }, // don't exit after first error
+		Importer: imports,
+	}
+	makePkg := func(path, src string) {
+		f, err := parseSrc(path, src)
+		if err != nil {
+			t.Fatal(err)
+		}
+		pkg, _ := conf.Check(path, []*syntax.File{f}, nil) // errors logged via conf.Error
+		imports[path] = pkg
+	}
+
+	const libSrc = `
+package a
+import "missing"
+const C1 = foo
+const C2 = missing.C
+`
+
+	const mainSrc = `
+package main
+import "a"
+var _ = a.C1
+var _ = a.C2
+`
+
+	makePkg("a", libSrc)
+	makePkg("main", mainSrc) // don't crash when type-checking this package
+}
+
+func TestLookupFieldOrMethod(t *testing.T) {
+	// Test cases assume a lookup of the form a.f or x.f, where a stands for an
+	// addressable value, and x for a non-addressable value (even though a variable
+	// for ease of test case writing).
+	var tests = []struct {
+		src      string
+		found    bool
+		index    []int
+		indirect bool
+	}{
+		// field lookups
+		{"var x T; type T struct{}", false, nil, false},
+		{"var x T; type T struct{ f int }", true, []int{0}, false},
+		{"var x T; type T struct{ a, b, f, c int }", true, []int{2}, false},
+
+		// method lookups
+		{"var a T; type T struct{}; func (T) f() {}", true, []int{0}, false},
+		{"var a *T; type T struct{}; func (T) f() {}", true, []int{0}, true},
+		{"var a T; type T struct{}; func (*T) f() {}", true, []int{0}, false},
+		{"var a *T; type T struct{}; func (*T) f() {}", true, []int{0}, true}, // TODO(gri) should this report indirect = false?
+
+		// collisions
+		{"type ( E1 struct{ f int }; E2 struct{ f int }; x struct{ E1; *E2 })", false, []int{1, 0}, false},
+		{"type ( E1 struct{ f int }; E2 struct{}; x struct{ E1; *E2 }); func (E2) f() {}", false, []int{1, 0}, false},
+
+		// outside methodset
+		// (*T).f method exists, but value of type T is not addressable
+		{"var x T; type T struct{}; func (*T) f() {}", false, nil, true},
+	}
+
+	for _, test := range tests {
+		pkg, err := pkgFor("test", "package p;"+test.src, nil)
+		if err != nil {
+			t.Errorf("%s: incorrect test case: %s", test.src, err)
+			continue
+		}
+
+		obj := pkg.Scope().Lookup("a")
+		if obj == nil {
+			if obj = pkg.Scope().Lookup("x"); obj == nil {
+				t.Errorf("%s: incorrect test case - no object a or x", test.src)
+				continue
+			}
+		}
+
+		f, index, indirect := LookupFieldOrMethod(obj.Type(), obj.Name() == "a", pkg, "f")
+		if (f != nil) != test.found {
+			if f == nil {
+				t.Errorf("%s: got no object; want one", test.src)
+			} else {
+				t.Errorf("%s: got object = %v; want none", test.src, f)
+			}
+		}
+		if !sameSlice(index, test.index) {
+			t.Errorf("%s: got index = %v; want %v", test.src, index, test.index)
+		}
+		if indirect != test.indirect {
+			t.Errorf("%s: got indirect = %v; want %v", test.src, indirect, test.indirect)
+		}
+	}
+}
+
+func sameSlice(a, b []int) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i, x := range a {
+		if x != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+// TestScopeLookupParent ensures that (*Scope).LookupParent returns
+// the correct result at various positions within the source.
+func TestScopeLookupParent(t *testing.T) {
+	imports := make(testImporter)
+	conf := Config{Importer: imports}
+	var info Info
+	makePkg := func(path, src string) {
+		f, err := parseSrc(path, src)
+		if err != nil {
+			t.Fatal(err)
+		}
+		imports[path], err = conf.Check(path, []*syntax.File{f}, &info)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	makePkg("lib", "package lib; var X int")
+	// Each /*name=kind:line*/ comment makes the test look up the
+	// name at that point and checks that it resolves to a decl of
+	// the specified kind and line number.  "undef" means undefined.
+	mainSrc := `
+/*lib=pkgname:5*/ /*X=var:1*/ /*Pi=const:8*/ /*T=typename:9*/ /*Y=var:10*/ /*F=func:12*/
+package main
+
+import "lib"
+import . "lib"
+
+const Pi = 3.1415
+type T struct{}
+var Y, _ = lib.X, X
+
+func F(){
+	const pi, e = 3.1415, /*pi=undef*/ 2.71828 /*pi=const:13*/ /*e=const:13*/
+	type /*t=undef*/ t /*t=typename:14*/ *t
+	print(Y) /*Y=var:10*/
+	x, Y := Y, /*x=undef*/ /*Y=var:10*/ Pi /*x=var:16*/ /*Y=var:16*/ ; _ = x; _ = Y
+	var F = /*F=func:12*/ F /*F=var:17*/ ; _ = F
+
+	var a []int
+	for i, x := range /*i=undef*/ /*x=var:16*/ a /*i=var:20*/ /*x=var:20*/ { _ = i; _ = x }
+
+	var i interface{}
+	switch y := i.(type) { /*y=undef*/
+	case /*y=undef*/ int /*y=var:23*/ :
+	case float32, /*y=undef*/ float64 /*y=var:23*/ :
+	default /*y=var:23*/:
+		println(y)
+	}
+	/*y=undef*/
+
+        switch int := i.(type) {
+        case /*int=typename:0*/ int /*int=var:31*/ :
+        	println(int)
+        default /*int=var:31*/ :
+        }
+}
+/*main=undef*/
+`
+
+	info.Uses = make(map[*syntax.Name]Object)
+	makePkg("main", mainSrc)
+	mainScope := imports["main"].Scope()
+
+	rx := regexp.MustCompile(`^/\*(\w*)=([\w:]*)\*/$`)
+
+	base := syntax.NewFileBase("main")
+	syntax.CommentsDo(strings.NewReader(mainSrc), func(line, col uint, text string) {
+		pos := syntax.MakePos(base, line, col)
+
+		// Syntax errors are not comments.
+		if text[0] != '/' {
+			t.Errorf("%s: %s", pos, text)
+			return
+		}
+
+		// Parse the assertion in the comment.
+		m := rx.FindStringSubmatch(text)
+		if m == nil {
+			t.Errorf("%s: bad comment: %s", pos, text)
+			return
+		}
+		name, want := m[1], m[2]
+
+		// Look up the name in the innermost enclosing scope.
+		inner := mainScope.Innermost(pos)
+		if inner == nil {
+			t.Errorf("%s: at %s: can't find innermost scope", pos, text)
+			return
+		}
+		got := "undef"
+		if _, obj := inner.LookupParent(name, pos); obj != nil {
+			kind := strings.ToLower(strings.TrimPrefix(reflect.TypeOf(obj).String(), "*types2."))
+			got = fmt.Sprintf("%s:%d", kind, obj.Pos().Line())
+		}
+		if got != want {
+			t.Errorf("%s: at %s: %s resolved to %s, want %s", pos, text, name, got, want)
+		}
+	})
+
+	// Check that for each referring identifier,
+	// a lookup of its name on the innermost
+	// enclosing scope returns the correct object.
+
+	for id, wantObj := range info.Uses {
+		inner := mainScope.Innermost(id.Pos())
+		if inner == nil {
+			t.Errorf("%s: can't find innermost scope enclosing %q", id.Pos(), id.Value)
+			continue
+		}
+
+		// Exclude selectors and qualified identifiers---lexical
+		// refs only.  (Ideally, we'd see if the AST parent is a
+		// SelectorExpr, but that requires PathEnclosingInterval
+		// from golang.org/x/tools/go/ast/astutil.)
+		if id.Value == "X" {
+			continue
+		}
+
+		_, gotObj := inner.LookupParent(id.Value, id.Pos())
+		if gotObj != wantObj {
+			t.Errorf("%s: got %v, want %v", id.Pos(), gotObj, wantObj)
+			continue
+		}
+	}
+}
+
+func TestIdentical_issue15173(t *testing.T) {
+	// Identical should allow nil arguments and be symmetric.
+	for _, test := range []struct {
+		x, y Type
+		want bool
+	}{
+		{Typ[Int], Typ[Int], true},
+		{Typ[Int], nil, false},
+		{nil, Typ[Int], false},
+		{nil, nil, true},
+	} {
+		if got := Identical(test.x, test.y); got != test.want {
+			t.Errorf("Identical(%v, %v) = %t", test.x, test.y, got)
+		}
+	}
+}
+
+func TestIssue15305(t *testing.T) {
+	const src = "package p; func f() int16; var _ = f(undef)"
+	f, err := parseSrc("issue15305.go", src)
+	if err != nil {
+		t.Fatal(err)
+	}
+	conf := Config{
+		Error: func(err error) {}, // allow errors
+	}
+	info := &Info{
+		Types: make(map[syntax.Expr]TypeAndValue),
+	}
+	conf.Check("p", []*syntax.File{f}, info) // ignore result
+	for e, tv := range info.Types {
+		if _, ok := e.(*syntax.CallExpr); ok {
+			if tv.Type != Typ[Int16] {
+				t.Errorf("CallExpr has type %v, want int16", tv.Type)
+			}
+			return
+		}
+	}
+	t.Errorf("CallExpr has no type")
+}
+
+// TestCompositeLitTypes verifies that Info.Types registers the correct
+// types for composite literal expressions and composite literal type
+// expressions.
+func TestCompositeLitTypes(t *testing.T) {
+	for _, test := range []struct {
+		lit, typ string
+	}{
+		{`[16]byte{}`, `[16]byte`},
+		{`[...]byte{}`, `[0]byte`},                // test for issue #14092
+		{`[...]int{1, 2, 3}`, `[3]int`},           // test for issue #14092
+		{`[...]int{90: 0, 98: 1, 2}`, `[100]int`}, // test for issue #14092
+		{`[]int{}`, `[]int`},
+		{`map[string]bool{"foo": true}`, `map[string]bool`},
+		{`struct{}{}`, `struct{}`},
+		{`struct{x, y int; z complex128}{}`, `struct{x int; y int; z complex128}`},
+	} {
+		f, err := parseSrc(test.lit, "package p; var _ = "+test.lit)
+		if err != nil {
+			t.Fatalf("%s: %v", test.lit, err)
+		}
+
+		info := &Info{
+			Types: make(map[syntax.Expr]TypeAndValue),
+		}
+		if _, err = new(Config).Check("p", []*syntax.File{f}, info); err != nil {
+			t.Fatalf("%s: %v", test.lit, err)
+		}
+
+		cmptype := func(x syntax.Expr, want string) {
+			tv, ok := info.Types[x]
+			if !ok {
+				t.Errorf("%s: no Types entry found", test.lit)
+				return
+			}
+			if tv.Type == nil {
+				t.Errorf("%s: type is nil", test.lit)
+				return
+			}
+			if got := tv.Type.String(); got != want {
+				t.Errorf("%s: got %v, want %s", test.lit, got, want)
+			}
+		}
+
+		// test type of composite literal expression
+		rhs := f.DeclList[0].(*syntax.VarDecl).Values
+		cmptype(rhs, test.typ)
+
+		// test type of composite literal type expression
+		cmptype(rhs.(*syntax.CompositeLit).Type, test.typ)
+	}
+}
+
+// TestObjectParents verifies that objects have parent scopes or not
+// as specified by the Object interface.
+func TestObjectParents(t *testing.T) {
+	const src = `
+package p
+
+const C = 0
+
+type T1 struct {
+	a, b int
+	T2
+}
+
+type T2 interface {
+	im1()
+	im2()
+}
+
+func (T1) m1() {}
+func (*T1) m2() {}
+
+func f(x int) { y := x; print(y) }
+`
+
+	f, err := parseSrc("src", src)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	info := &Info{
+		Defs: make(map[*syntax.Name]Object),
+	}
+	if _, err = new(Config).Check("p", []*syntax.File{f}, info); err != nil {
+		t.Fatal(err)
+	}
+
+	for ident, obj := range info.Defs {
+		if obj == nil {
+			// only package names and implicit vars have a nil object
+			// (in this test we only need to handle the package name)
+			if ident.Value != "p" {
+				t.Errorf("%v has nil object", ident)
+			}
+			continue
+		}
+
+		// struct fields, type-associated and interface methods
+		// have no parent scope
+		wantParent := true
+		switch obj := obj.(type) {
+		case *Var:
+			if obj.IsField() {
+				wantParent = false
+			}
+		case *Func:
+			if obj.Type().(*Signature).Recv() != nil { // method
+				wantParent = false
+			}
+		}
+
+		gotParent := obj.Parent() != nil
+		switch {
+		case gotParent && !wantParent:
+			t.Errorf("%v: want no parent, got %s", ident, obj.Parent())
+		case !gotParent && wantParent:
+			t.Errorf("%v: no parent found", ident)
+		}
+	}
+}
+
+// TestFailedImport tests that we don't get follow-on errors
+// elsewhere in a package due to failing to import a package.
+func TestFailedImport(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	const src = `
+package p
+
+import foo "go/types/thisdirectorymustnotexistotherwisethistestmayfail/foo" // should only see an error here
+
+const c = foo.C
+type T = foo.T
+var v T = c
+func f(x T) T { return foo.F(x) }
+`
+	f, err := parseSrc("src", src)
+	if err != nil {
+		t.Fatal(err)
+	}
+	files := []*syntax.File{f}
+
+	// type-check using all possible importers
+	for _, compiler := range []string{"gc", "gccgo", "source"} {
+		errcount := 0
+		conf := Config{
+			Error: func(err error) {
+				// we should only see the import error
+				if errcount > 0 || !strings.Contains(err.Error(), "could not import") {
+					t.Errorf("for %s importer, got unexpected error: %v", compiler, err)
+				}
+				errcount++
+			},
+			//Importer: importer.For(compiler, nil),
+		}
+
+		info := &Info{
+			Uses: make(map[*syntax.Name]Object),
+		}
+		pkg, _ := conf.Check("p", files, info)
+		if pkg == nil {
+			t.Errorf("for %s importer, type-checking failed to return a package", compiler)
+			continue
+		}
+
+		imports := pkg.Imports()
+		if len(imports) != 1 {
+			t.Errorf("for %s importer, got %d imports, want 1", compiler, len(imports))
+			continue
+		}
+		imp := imports[0]
+		if imp.Name() != "foo" {
+			t.Errorf(`for %s importer, got %q, want "foo"`, compiler, imp.Name())
+			continue
+		}
+
+		// verify that all uses of foo refer to the imported package foo (imp)
+		for ident, obj := range info.Uses {
+			if ident.Value == "foo" {
+				if obj, ok := obj.(*PkgName); ok {
+					if obj.Imported() != imp {
+						t.Errorf("%s resolved to %v; want %v", ident.Value, obj.Imported(), imp)
+					}
+				} else {
+					t.Errorf("%s resolved to %v; want package name", ident.Value, obj)
+				}
+			}
+		}
+	}
+}