go/ssa/interp: Adds reflect.DeepEqual model for interp testing

Implements reflect.DeepEqual() for testing interp packages. Adds test that exercises this.

Fixes a nil pointer dereference in ext۰reflect۰Value۰Elem in interp.

Updates golang/go#48525

Change-Id: Ib32e96d37aa5c85cefe59e9514d4e162d7f7011e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/391314
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Tim King <taking@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Trust: Tim King <taking@google.com>

go/ssa/interp/interp_test.go

@@ -111,6 +111,7 @@ var testdataTests = []string{
 	"complit.go",
 	"convert.go",
 	"coverage.go",
+	"deepequal.go",
 	"defer.go",
 	"fieldprom.go",
 	"ifaceconv.go",

go/ssa/interp/reflect.go

@@ -407,7 +407,11 @@ func ext۰reflect۰Value۰Elem(fr *frame, args []value) value {
 	case iface:
 		return makeReflectValue(x.t, x.v)
 	case *value:
-		return makeReflectValue(rV2T(args[0]).t.Underlying().(*types.Pointer).Elem(), *x)
+		var v value
+		if x != nil {
+			v = *x
+		}
+		return makeReflectValue(rV2T(args[0]).t.Underlying().(*types.Pointer).Elem(), v)
 	default:
 		panic(fmt.Sprintf("reflect.(Value).Elem(%T)", x))
 	}

go/ssa/interp/testdata/deepequal.go

@@ -0,0 +1,93 @@
+// This interpreter test is designed to test the test copy of DeepEqual.
+//
+// Validate this file with 'go run' after editing.
+
+package main
+
+import "reflect"
+
+func assert(cond bool) {
+	if !cond {
+		panic("failed")
+	}
+}
+
+type X int
+type Y struct {
+	y *Y
+	z [3]int
+}
+
+var (
+	a = []int{0, 1, 2, 3}
+	b = []X{0, 1, 2, 3}
+	c = map[int]string{0: "zero", 1: "one"}
+	d = map[X]string{0: "zero", 1: "one"}
+	e = &Y{}
+	f = (*Y)(nil)
+	g = &Y{y: e}
+	h *Y
+)
+
+func init() {
+	h = &Y{} // h->h
+	h.y = h
+}
+
+func main() {
+	assert(reflect.DeepEqual(nil, nil))
+	assert(reflect.DeepEqual((*int)(nil), (*int)(nil)))
+	assert(!reflect.DeepEqual(nil, (*int)(nil)))
+
+	assert(reflect.DeepEqual(0, 0))
+	assert(!reflect.DeepEqual(0, int64(0)))
+
+	assert(!reflect.DeepEqual("", 0))
+
+	assert(reflect.DeepEqual(a, []int{0, 1, 2, 3}))
+	assert(!reflect.DeepEqual(a, []int{0, 1, 2}))
+	assert(!reflect.DeepEqual(a, []int{0, 1, 0, 3}))
+
+	assert(reflect.DeepEqual(b, []X{0, 1, 2, 3}))
+	assert(!reflect.DeepEqual(b, []X{0, 1, 0, 3}))
+
+	assert(reflect.DeepEqual(c, map[int]string{0: "zero", 1: "one"}))
+	assert(!reflect.DeepEqual(c, map[int]string{0: "zero", 1: "one", 2: "two"}))
+	assert(!reflect.DeepEqual(c, map[int]string{1: "one", 2: "two"}))
+	assert(!reflect.DeepEqual(c, map[int]string{1: "one"}))
+
+	assert(reflect.DeepEqual(d, map[X]string{0: "zero", 1: "one"}))
+	assert(!reflect.DeepEqual(d, map[int]string{0: "zero", 1: "one"}))
+
+	assert(reflect.DeepEqual(e, &Y{}))
+	assert(reflect.DeepEqual(e, &Y{z: [3]int{0, 0, 0}}))
+	assert(!reflect.DeepEqual(e, &Y{z: [3]int{0, 1, 0}}))
+
+	assert(reflect.DeepEqual(f, (*Y)(nil)))
+	assert(!reflect.DeepEqual(f, nil))
+
+	// eq_h -> eq_h. Pointer structure and elements are equal so DeepEqual.
+	eq_h := &Y{}
+	eq_h.y = eq_h
+	assert(reflect.DeepEqual(h, eq_h))
+
+	// deepeq_h->h->h. Pointed to elem of (deepeq_h, h) are (h,h). (h,h) are deep equal so h and deepeq_h are DeepEqual.
+	deepeq_h := &Y{}
+	deepeq_h.y = h
+	assert(reflect.DeepEqual(h, deepeq_h))
+
+	distinct := []interface{}{a, b, c, d, e, f, g, h}
+	for x := range distinct {
+		for y := range distinct {
+			assert((x == y) == reflect.DeepEqual(distinct[x], distinct[y]))
+		}
+	}
+
+	// anonymous struct types.
+	assert(reflect.DeepEqual(struct{}{}, struct{}{}))
+	assert(reflect.DeepEqual(struct{ x int }{1}, struct{ x int }{1}))
+	assert(!reflect.DeepEqual(struct{ x int }{}, struct{ x int }{5}))
+	assert(!reflect.DeepEqual(struct{ x, y int }{0, 1}, struct{ x int }{0}))
+	assert(reflect.DeepEqual(struct{ x, y int }{2, 3}, struct{ x, y int }{2, 3}))
+	assert(!reflect.DeepEqual(struct{ x, y int }{4, 5}, struct{ x, y int }{4, 6}))
+}

go/ssa/interp/testdata/src/reflect/deepequal.go

@@ -0,0 +1,109 @@
+package reflect
+
+// Not an actual implementation of DeepEqual. This is a model that supports
+// the bare minimum needed to get through testing interp.
+//
+// Does not handle cycles.
+//
+// Note: unclear if reflect.go can support this.
+func DeepEqual(x, y interface{}) bool {
+	if x == nil || y == nil {
+		return x == y
+	}
+	v1 := ValueOf(x)
+	v2 := ValueOf(y)
+
+	return deepValueEqual(v1, v2, make(map[visit]bool))
+}
+
+// Key for the visitedMap in deepValueEqual.
+type visit struct {
+	a1, a2 uintptr
+	typ    Type
+}
+
+func deepValueEqual(v1, v2 Value, visited map[visit]bool) bool {
+	if !v1.IsValid() || !v2.IsValid() {
+		return v1.IsValid() == v2.IsValid()
+	}
+	if v1.Type() != v2.Type() {
+		return false
+	}
+
+	// Short circuit on reference types that can lead to cycles in comparison.
+	switch v1.Kind() {
+	case Pointer, Map, Slice, Interface:
+		k := visit{v1.Pointer(), v2.Pointer(), v1.Type()} // Not safe for moving GC.
+		if visited[k] {
+			// The comparison algorithm assumes that all checks in progress are true when it reencounters them.
+			return true
+		}
+		visited[k] = true
+	}
+
+	switch v1.Kind() {
+	case Array:
+		for i := 0; i < v1.Len(); i++ {
+			if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
+				return false
+			}
+		}
+		return true
+	case Slice:
+		if v1.IsNil() != v2.IsNil() {
+			return false
+		}
+		if v1.Len() != v2.Len() {
+			return false
+		}
+		if v1.Pointer() == v2.Pointer() {
+			return true
+		}
+		for i := 0; i < v1.Len(); i++ {
+			if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
+				return false
+			}
+		}
+		return true
+	case Interface:
+		if v1.IsNil() || v2.IsNil() {
+			return v1.IsNil() == v2.IsNil()
+		}
+		return deepValueEqual(v1.Elem(), v2.Elem(), visited)
+	case Ptr:
+		if v1.Pointer() == v2.Pointer() {
+			return true
+		}
+		return deepValueEqual(v1.Elem(), v2.Elem(), visited)
+	case Struct:
+		for i, n := 0, v1.NumField(); i < n; i++ {
+			if !deepValueEqual(v1.Field(i), v2.Field(i), visited) {
+				return false
+			}
+		}
+		return true
+	case Map:
+		if v1.IsNil() != v2.IsNil() {
+			return false
+		}
+		if v1.Len() != v2.Len() {
+			return false
+		}
+		if v1.Pointer() == v2.Pointer() {
+			return true
+		}
+		for _, k := range v1.MapKeys() {
+			val1 := v1.MapIndex(k)
+			val2 := v2.MapIndex(k)
+			if !val1.IsValid() || !val2.IsValid() || !deepValueEqual(val1, val2, visited) {
+				return false
+			}
+		}
+		return true
+	case Func:
+		return v1.IsNil() && v2.IsNil()
+	default:
+		// Normal equality suffices
+		return v1.Interface() == v2.Interface() // try interface comparison as a fallback.
+	}
+}

go/ssa/interp/testdata/src/reflect/reflect.go

@@ -11,9 +11,20 @@ type Value struct {
 
 func (Value) String() string
 
-func (Value) Elem() string
+func (Value) Elem() Value
 func (Value) Kind() Kind
 func (Value) Int() int64
+func (Value) IsValid() bool
+func (Value) IsNil() bool
+func (Value) Len() int
+func (Value) Pointer() uintptr
+func (Value) Index(i int) Value
+func (Value) Type() Type
+func (Value) Field(int) Value
+func (Value) MapIndex(Value) Value
+func (Value) MapKeys() []Value
+func (Value) NumField() int
+func (Value) Interface() interface{}
 
 func SliceOf(Type) Type