// 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"
	"errors"
	"fmt"
	"internal/testenv"
	"reflect"
	"regexp"
	"strings"
	"testing"

	. "cmd/compile/internal/types2"
)

// brokenPkg is a source prefix for packages that are not expected to parse
// or type-check cleanly. They are always parsed assuming that they contain
// generic code.
const brokenPkg = "package broken_"

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{
		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
		{`package g1; var(j int32; s int; n = 1.0<<s == j)`, `1.0`, `int32`, `1`},        // issue #48422
	}

	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 syntax.String(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`},

		// uses of nil
		{`package n0; var _ *int = nil`, `nil`, `*int`},
		{`package n1; var _ func() = nil`, `nil`, `func()`},
		{`package n2; var _ []byte = nil`, `nil`, `[]byte`},
		{`package n3; var _ map[int]int = nil`, `nil`, `map[int]int`},
		{`package n4; var _ chan int = nil`, `nil`, `chan int`},
		{`package n5a; var _ interface{} = (*int)(nil)`, `nil`, `*int`},
		{`package n5b; var _ interface{m()} = nil`, `nil`, `interface{m()}`},
		{`package n6; import "unsafe"; var _ unsafe.Pointer = nil`, `nil`, `unsafe.Pointer`},

		{`package n10; var (x *int; _ = x == nil)`, `nil`, `*int`},
		{`package n11; var (x func(); _ = x == nil)`, `nil`, `func()`},
		{`package n12; var (x []byte; _ = x == nil)`, `nil`, `[]byte`},
		{`package n13; var (x map[int]int; _ = x == nil)`, `nil`, `map[int]int`},
		{`package n14; var (x chan int; _ = x == nil)`, `nil`, `chan int`},
		{`package n15a; var (x interface{}; _ = x == (*int)(nil))`, `nil`, `*int`},
		{`package n15b; var (x interface{m()}; _ = x == nil)`, `nil`, `interface{m()}`},
		{`package n15; import "unsafe"; var (x unsafe.Pointer; _ = x == nil)`, `nil`, `unsafe.Pointer`},

		{`package n20; var _ = (*int)(nil)`, `nil`, `*int`},
		{`package n21; var _ = (func())(nil)`, `nil`, `func()`},
		{`package n22; var _ = ([]byte)(nil)`, `nil`, `[]byte`},
		{`package n23; var _ = (map[int]int)(nil)`, `nil`, `map[int]int`},
		{`package n24; var _ = (chan int)(nil)`, `nil`, `chan int`},
		{`package n25a; var _ = (interface{})((*int)(nil))`, `nil`, `*int`},
		{`package n25b; var _ = (interface{m()})(nil)`, `nil`, `interface{m()}`},
		{`package n26; import "unsafe"; var _ = unsafe.Pointer(nil)`, `nil`, `unsafe.Pointer`},

		{`package n30; func f(*int) { f(nil) }`, `nil`, `*int`},
		{`package n31; func f(func()) { f(nil) }`, `nil`, `func()`},
		{`package n32; func f([]byte) { f(nil) }`, `nil`, `[]byte`},
		{`package n33; func f(map[int]int) { f(nil) }`, `nil`, `map[int]int`},
		{`package n34; func f(chan int) { f(nil) }`, `nil`, `chan int`},
		{`package n35a; func f(interface{}) { f((*int)(nil)) }`, `nil`, `*int`},
		{`package n35b; func f(interface{m()}) { f(nil) }`, `nil`, `interface{m()}`},
		{`package n35; import "unsafe"; func f(unsafe.Pointer) { f(nil) }`, `nil`, `unsafe.Pointer`},

		// 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
		{brokenPkg + `x0; func _() { var x struct {f string}; x.f := 0 }`, `x.f`, `string`},
		{brokenPkg + `x1; func _() { var z string; type x struct {f string}; y := &x{q: z}}`, `z`, `string`},
		{brokenPkg + `x2; func _() { var a, b string; type x struct {f string}; z := &x{f: a, f: b,}}`, `b`, `string`},
		{brokenPkg + `x3; var x = panic("");`, `panic`, `func(interface{})`},
		{`package x4; func _() { panic("") }`, `panic`, `func(interface{})`},
		{brokenPkg + `x5; func _() { var x map[string][...]int; x = map[string][...]int{"": {1,2,3}} }`, `x`, `map[string]invalid type`},

		// parameterized functions
		{`package p0; func f[T any](T) {}; var _ = f[int]`, `f`, `func[T any](T)`},
		{`package p1; func f[T any](T) {}; var _ = f[int]`, `f[int]`, `func(int)`},
		{`package p2; func f[T any](T) {}; func _() { f(42) }`, `f`, `func(int)`},
		{`package p3; func f[T any](T) {}; func _() { f[int](42) }`, `f[int]`, `func(int)`},
		{`package p4; func f[T any](T) {}; func _() { f[int](42) }`, `f`, `func[T any](T)`},
		{`package p5; func f[T any](T) {}; func _() { 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[P any]`},
		{`package t2; type t[P interface{}] int; var _ t[int]`, `t`, `t2.t[P interface{}]`},
		{`package t3; type t[P, Q interface{}] int; var _ t[int, int]`, `t`, `t3.t[P, Q interface{}]`},
		{brokenPkg + `t4; type t[P, Q interface{ m() }] int; var _ t[int, int]`, `t`, `broken_t4.t[P, Q 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]`},

		// issue 45096
		{`package issue45096; func _[T interface{ ~int8 | ~int16 | ~int32 }](x T) { _ = x < 0 }`, `0`, `T`},

		// issue 47895
		{`package p; import "unsafe"; type S struct { f int }; var s S; var _ = unsafe.Offsetof(s.f)`, `s.f`, `int`},
	}

	for _, test := range tests {
		info := Info{Types: make(map[syntax.Expr]TypeAndValue)}
		var name string
		if strings.HasPrefix(test.src, brokenPkg) {
			var err error
			name, err = mayTypecheck(t, "TypesInfo", test.src, &info)
			if err == nil {
				t.Errorf("package %s: expected to fail but passed", name)
				continue
			}
		} else {
			name = mustTypecheck(t, "TypesInfo", test.src, &info)
		}

		// look for expression type
		var typ Type
		for e, tv := range info.Types {
			if syntax.String(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 TestInstanceInfo(t *testing.T) {
	var tests = []struct {
		src   string
		name  string
		targs []string
		typ   string
	}{
		{`package p0; func f[T any](T) {}; func _() { f(42) }`,
			`f`,
			[]string{`int`},
			`func(int)`,
		},
		{`package p1; func f[T any](T) T { panic(0) }; func _() { f('@') }`,
			`f`,
			[]string{`rune`},
			`func(rune) rune`,
		},
		{`package p2; func f[T any](...T) T { panic(0) }; 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) }`,
			`m`,
			[]string{`int`},
			`func(int)`,
		},
		{`package q1; type T struct{}; func (T) m[P any](P) P { panic(0) }; func _(x T) { x.m(42) }`,
			`m`,
			[]string{`int`},
			`func(int) int`,
		},
		{`package q2; type T struct{}; func (T) m[P any](...P) P { panic(0) }; func _(x T) { x.m(42) }`,
			`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{}) }`,
			`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)) }`,
			`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) }`,
			`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{~*T}](x T) {}; func _(x string) { f(x) }`,
			`f`,
			[]string{`string`, `*string`},
			`func(x string)`,
		},
		{`package s2; func f[T any, P interface{~*T}](x []T) {}; func _(x []int) { f(x) }`,
			`f`,
			[]string{`int`, `*int`},
			`func(x []int)`,
		},
		{`package s3; type C[T any] interface{~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{~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{~*T}]() T { panic(0) }; func _() { _ = f[string] }`,
			`f`,
			[]string{`string`, `*string`},
			`func() string`,
		},
		{`package t2; func f[T any, P interface{~*T}]() T { panic(0) }; func _() { _ = (f[string]) }`,
			`f`,
			[]string{`string`, `*string`},
			`func() string`,
		},
		{`package t3; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T { return nil }; func _() { _ = f[int] }`,
			`f`,
			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
			`func() []int`,
		},
		{`package t4; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T { return nil }; func _() { _ = f[int] }`,
			`f`,
			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
			`func() []int`,
		},
		{`package i0; import lib "generic_lib"; func _() { lib.F(42) }`,
			`F`,
			[]string{`int`},
			`func(int)`,
		},
		{`package type0; type T[P interface{~int}] struct{ x P }; var _ T[int]`,
			`T`,
			[]string{`int`},
			`struct{x int}`,
		},
		{`package type1; type T[P interface{~int}] struct{ x P }; var _ (T[int])`,
			`T`,
			[]string{`int`},
			`struct{x int}`,
		},
		{`package type2; type T[P interface{~int}] struct{ x P }; var _ T[(int)]`,
			`T`,
			[]string{`int`},
			`struct{x int}`,
		},
		{`package type3; type T[P1 interface{~[]P2}, P2 any] struct{ x P1; y P2 }; var _ T[[]int, int]`,
			`T`,
			[]string{`[]int`, `int`},
			`struct{x []int; y int}`,
		},
		{`package type4; import lib "generic_lib"; var _ lib.T[int]`,
			`T`,
			[]string{`int`},
			`[]int`,
		},
	}

	for _, test := range tests {
		const lib = `package generic_lib

func F[P any](P) {}

type T[P any] []P
`

		imports := make(testImporter)
		conf := Config{Importer: imports}
		instances := make(map[*syntax.Name]Instance)
		uses := make(map[*syntax.Name]Object)
		makePkg := func(src string) *Package {
			f, err := parseSrc("p.go", src)
			if err != nil {
				t.Fatal(err)
			}
			pkg, err := conf.Check("", []*syntax.File{f}, &Info{Instances: instances, Uses: uses})
			if err != nil {
				t.Fatal(err)
			}
			imports[pkg.Name()] = pkg
			return pkg
		}
		makePkg(lib)
		pkg := makePkg(test.src)

		// look for instance information
		var targs []Type
		var typ Type
		for ident, inst := range instances {
			if syntax.String(ident) == test.name {
				for i := 0; i < inst.TypeArgs.Len(); i++ {
					targs = append(targs, inst.TypeArgs.At(i))
				}
				typ = inst.Type

				// Check that we can find the corresponding parameterized type.
				ptype := uses[ident].Type()
				lister, _ := ptype.(interface{ TypeParams() *TypeParamList })
				if lister == nil || lister.TypeParams().Len() == 0 {
					t.Errorf("package %s: info.Types[%v] = %v, want parameterized type", pkg.Name(), ident, ptype)
					continue
				}

				// Verify the invariant that re-instantiating the generic type with
				// TypeArgs results in an equivalent type.
				inst2, err := Instantiate(nil, ptype, targs, true)
				if err != nil {
					t.Errorf("Instantiate(%v, %v) failed: %v", ptype, targs, err)
				}
				if !Identical(inst.Type, inst2) {
					t.Errorf("%v and %v are not identical", inst.Type, inst2)
				}
				break
			}
		}
		if targs == nil {
			t.Errorf("package %s: no instance information found for %s", pkg.Name(), test.name)
			continue
		}

		// check that type arguments are correct
		if len(targs) != len(test.targs) {
			t.Errorf("package %s: got %d type arguments; want %d", pkg.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", pkg.Name(), i, got, test.targs[i])
				continue
			}
		}

		// check that the types match
		if got := typ.Underlying().String(); got != test.typ {
			t.Errorf("package %s: got %s; want %s", pkg.Name(), got, test.typ)
		}
	}
}

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()`},
		{`package p5; func f() int { x, _ := 1, 2; return x }`, `_`, `var _ int`},
	}

	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()`},
	}

	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{…}`, `value`},
		{`package v2; var _ = func(){}`, `func() {}`, `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, syntax.String(e))
			if syntax.String(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", "comm:",
		}},
		{`package p16; func _(c chan int) { select{ case i := <-c: x := i; _ = x} }`, []string{
			"file:", "func:c", "comm: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 {…}()",
		}},
		{`package p8; var (a, b = func() (_, _ int) { return c, c }(); c = 1)`, []string{
			"c = 1", "a, b = func() (_, _ int) {…}()",
		}},
		{`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) {
	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

		start := indexFor(mainSrc, syntax.StartPos(e))
		end := indexFor(mainSrc, syntax.EndPos(e))
		segment := 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()),
		}
		want := wantOut[segment]
		if want != got {
			t.Errorf("%s: got %q; want %q", segment, got, want)
		}
		delete(wantOut, segment)

		// 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) {
				t.Errorf("%s: Recv() = %s, want %s", segment, 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 segment := range wantOut {
		t.Errorf("no syntax.Selection found with syntax %q", segment)
	}
}

// indexFor returns the index into s corresponding to the position pos.
func indexFor(s string, pos syntax.Pos) int {
	i, line := 0, 1 // string index and corresponding line
	target := int(pos.Line())
	for line < target && i < len(s) {
		if s[i] == '\n' {
			line++
		}
		i++
	}
	return i + int(pos.Col()-1) // columns are 1-based
}

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
		}
	}
}

var nopos syntax.Pos

// newDefined creates a new defined type named T with the given underlying type.
func newDefined(underlying Type) *Named {
	tname := NewTypeName(nopos, nil, "T", nil)
	return NewNamed(tname, underlying, nil)
}

func TestConvertibleTo(t *testing.T) {
	for _, test := range []struct {
		v, t Type
		want bool
	}{
		{Typ[Int], Typ[Int], true},
		{Typ[Int], Typ[Float32], true},
		{Typ[Int], Typ[String], true},
		{newDefined(Typ[Int]), Typ[Int], true},
		{newDefined(new(Struct)), new(Struct), true},
		{newDefined(Typ[Int]), new(Struct), false},
		{Typ[UntypedInt], Typ[Int], true},
		{NewSlice(Typ[Int]), NewPointer(NewArray(Typ[Int], 10)), true},
		{NewSlice(Typ[Int]), NewArray(Typ[Int], 10), false},
		{NewSlice(Typ[Int]), NewPointer(NewArray(Typ[Uint], 10)), false},
		// Untyped string values are not permitted by the spec, so the behavior below is undefined.
		{Typ[UntypedString], Typ[String], true},
	} {
		if got := ConvertibleTo(test.v, test.t); got != test.want {
			t.Errorf("ConvertibleTo(%v, %v) = %t, want %t", test.v, test.t, got, test.want)
		}
	}
}

func TestAssignableTo(t *testing.T) {
	for _, test := range []struct {
		v, t Type
		want bool
	}{
		{Typ[Int], Typ[Int], true},
		{Typ[Int], Typ[Float32], false},
		{newDefined(Typ[Int]), Typ[Int], false},
		{newDefined(new(Struct)), new(Struct), true},
		{Typ[UntypedBool], Typ[Bool], true},
		{Typ[UntypedString], Typ[Bool], false},
		// Neither untyped string nor untyped numeric assignments arise during
		// normal type checking, so the below behavior is technically undefined by
		// the spec.
		{Typ[UntypedString], Typ[String], true},
		{Typ[UntypedInt], Typ[Int], true},
	} {
		if got := AssignableTo(test.v, test.t); got != test.want {
			t.Errorf("AssignableTo(%v, %v) = %t, want %t", test.v, test.t, got, test.want)
		}
	}
}

func TestIdentical(t *testing.T) {
	// For each test, we compare the types of objects X and Y in the source.
	tests := []struct {
		src  string
		want bool
	}{
		// Basic types.
		{"var X int; var Y int", true},
		{"var X int; var Y string", false},

		// TODO: add more tests for complex types.

		// Named types.
		{"type X int; type Y int", false},

		// Aliases.
		{"type X = int; type Y = int", true},

		// Functions.
		{`func X(int) string { return "" }; func Y(int) string { return "" }`, true},
		{`func X() string { return "" }; func Y(int) string { return "" }`, false},
		{`func X(int) string { return "" }; func Y(int) {}`, false},

		// Generic functions. Type parameters should be considered identical modulo
		// renaming. See also issue #49722.
		{`func X[P ~int](){}; func Y[Q ~int]() {}`, true},
		{`func X[P1 any, P2 ~*P1](){}; func Y[Q1 any, Q2 ~*Q1]() {}`, true},
		{`func X[P1 any, P2 ~[]P1](){}; func Y[Q1 any, Q2 ~*Q1]() {}`, false},
		{`func X[P ~int](P){}; func Y[Q ~int](Q) {}`, true},
		{`func X[P ~string](P){}; func Y[Q ~int](Q) {}`, false},
		{`func X[P ~int]([]P){}; func Y[Q ~int]([]Q) {}`, 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
		}
		X := pkg.Scope().Lookup("X")
		Y := pkg.Scope().Lookup("Y")
		if X == nil || Y == nil {
			t.Fatal("test must declare both X and Y")
		}
		if got := Identical(X.Type(), Y.Type()); got != test.want {
			t.Errorf("Identical(%s, %s) = %t, want %t", X.Type(), Y.Type(), got, test.want)
		}
	}
}

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 TestIdenticalUnions(t *testing.T) {
	tname := NewTypeName(nopos, nil, "myInt", nil)
	myInt := NewNamed(tname, Typ[Int], nil)
	tmap := map[string]*Term{
		"int":     NewTerm(false, Typ[Int]),
		"~int":    NewTerm(true, Typ[Int]),
		"string":  NewTerm(false, Typ[String]),
		"~string": NewTerm(true, Typ[String]),
		"myInt":   NewTerm(false, myInt),
	}
	makeUnion := func(s string) *Union {
		parts := strings.Split(s, "|")
		var terms []*Term
		for _, p := range parts {
			term := tmap[p]
			if term == nil {
				t.Fatalf("missing term %q", p)
			}
			terms = append(terms, term)
		}
		return NewUnion(terms)
	}
	for _, test := range []struct {
		x, y string
		want bool
	}{
		// These tests are just sanity checks. The tests for type sets and
		// interfaces provide much more test coverage.
		{"int|~int", "~int", true},
		{"myInt|~int", "~int", true},
		{"int|string", "string|int", true},
		{"int|int|string", "string|int", true},
		{"myInt|string", "int|string", false},
	} {
		x := makeUnion(test.x)
		y := makeUnion(test.y)
		if got := Identical(x, 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)
				}
			}
		}
	}
}

func TestInstantiate(t *testing.T) {
	// eventually we like more tests but this is a start
	const src = "package p; type T[P any] *T[P]"
	pkg, err := pkgFor(".", src, nil)
	if err != nil {
		t.Fatal(err)
	}

	// type T should have one type parameter
	T := pkg.Scope().Lookup("T").Type().(*Named)
	if n := T.TypeParams().Len(); n != 1 {
		t.Fatalf("expected 1 type parameter; found %d", n)
	}

	// instantiation should succeed (no endless recursion)
	// even with a nil *Checker
	res, err := Instantiate(nil, T, []Type{Typ[Int]}, false)
	if err != nil {
		t.Fatal(err)
	}

	// instantiated type should point to itself
	if p := res.Underlying().(*Pointer).Elem(); p != res {
		t.Fatalf("unexpected result type: %s points to %s", res, p)
	}
}

func TestInstantiateErrors(t *testing.T) {
	tests := []struct {
		src    string // by convention, T must be the type being instantiated
		targs  []Type
		wantAt int // -1 indicates no error
	}{
		{"type T[P interface{~string}] int", []Type{Typ[Int]}, 0},
		{"type T[P1 interface{int}, P2 interface{~string}] int", []Type{Typ[Int], Typ[Int]}, 1},
		{"type T[P1 any, P2 interface{~[]P1}] int", []Type{Typ[Int], NewSlice(Typ[String])}, 1},
		{"type T[P1 interface{~[]P2}, P2 any] int", []Type{NewSlice(Typ[String]), Typ[Int]}, 0},
	}

	for _, test := range tests {
		src := "package p; " + test.src
		pkg, err := pkgFor(".", src, nil)
		if err != nil {
			t.Fatal(err)
		}

		T := pkg.Scope().Lookup("T").Type().(*Named)

		_, err = Instantiate(nil, T, test.targs, true)
		if err == nil {
			t.Fatalf("Instantiate(%v, %v) returned nil error, want non-nil", T, test.targs)
		}

		var argErr *ArgumentError
		if !errors.As(err, &argErr) {
			t.Fatalf("Instantiate(%v, %v): error is not an *ArgumentError", T, test.targs)
		}

		if argErr.Index != test.wantAt {
			t.Errorf("Instantate(%v, %v): error at index %d, want index %d", T, test.targs, argErr.Index, test.wantAt)
		}
	}
}

func TestArgumentErrorUnwrapping(t *testing.T) {
	var err error = &ArgumentError{
		Index: 1,
		Err:   Error{Msg: "test"},
	}
	var e Error
	if !errors.As(err, &e) {
		t.Fatalf("error %v does not wrap types.Error", err)
	}
	if e.Msg != "test" {
		t.Errorf("e.Msg = %q, want %q", e.Msg, "test")
	}
}

func TestInstanceIdentity(t *testing.T) {
	imports := make(testImporter)
	conf := Config{Importer: imports}
	makePkg := func(src string) {
		f, err := parseSrc("", src)
		if err != nil {
			t.Fatal(err)
		}
		name := f.PkgName.Value
		pkg, err := conf.Check(name, []*syntax.File{f}, nil)
		if err != nil {
			t.Fatal(err)
		}
		imports[name] = pkg
	}
	makePkg(`package lib; type T[P any] struct{}`)
	makePkg(`package a; import "lib"; var A lib.T[int]`)
	makePkg(`package b; import "lib"; var B lib.T[int]`)
	a := imports["a"].Scope().Lookup("A")
	b := imports["b"].Scope().Lookup("B")
	if !Identical(a.Type(), b.Type()) {
		t.Errorf("mismatching types: a.A: %s, b.B: %s", a.Type(), b.Type())
	}
}

func TestImplements(t *testing.T) {
	const src = `
package p

type EmptyIface interface{}

type I interface {
	m()
}

type C interface {
	m()
	~int
}

type Integer interface{
	int8 | int16 | int32 | int64
}

type EmptyTypeSet interface{
	Integer
	~string
}

type N1 int
func (N1) m() {}

type N2 int
func (*N2) m() {}

type N3 int
func (N3) m(int) {}

type N4 string
func (N4) m()

type Bad Bad // invalid type
`

	f, err := parseSrc("p.go", src)
	if err != nil {
		t.Fatal(err)
	}
	conf := Config{Error: func(error) {}}
	pkg, _ := conf.Check(f.PkgName.Value, []*syntax.File{f}, nil)

	scope := pkg.Scope()
	var (
		EmptyIface   = scope.Lookup("EmptyIface").Type().Underlying().(*Interface)
		I            = scope.Lookup("I").Type().(*Named)
		II           = I.Underlying().(*Interface)
		C            = scope.Lookup("C").Type().(*Named)
		CI           = C.Underlying().(*Interface)
		Integer      = scope.Lookup("Integer").Type().Underlying().(*Interface)
		EmptyTypeSet = scope.Lookup("EmptyTypeSet").Type().Underlying().(*Interface)
		N1           = scope.Lookup("N1").Type()
		N1p          = NewPointer(N1)
		N2           = scope.Lookup("N2").Type()
		N2p          = NewPointer(N2)
		N3           = scope.Lookup("N3").Type()
		N4           = scope.Lookup("N4").Type()
		Bad          = scope.Lookup("Bad").Type()
	)

	tests := []struct {
		t    Type
		i    *Interface
		want bool
	}{
		{I, II, true},
		{I, CI, false},
		{C, II, true},
		{C, CI, true},
		{Typ[Int8], Integer, true},
		{Typ[Int64], Integer, true},
		{Typ[String], Integer, false},
		{EmptyTypeSet, II, true},
		{EmptyTypeSet, EmptyTypeSet, true},
		{Typ[Int], EmptyTypeSet, false},
		{N1, II, true},
		{N1, CI, true},
		{N1p, II, true},
		{N1p, CI, false},
		{N2, II, false},
		{N2, CI, false},
		{N2p, II, true},
		{N2p, CI, false},
		{N3, II, false},
		{N3, CI, false},
		{N4, II, true},
		{N4, CI, false},
		{Bad, II, false},
		{Bad, CI, false},
		{Bad, EmptyIface, true},
	}

	for _, test := range tests {
		if got := Implements(test.t, test.i); got != test.want {
			t.Errorf("Implements(%s, %s) = %t, want %t", test.t, test.i, got, test.want)
		}
	}
}