reflect: update to Go 1.22 semantics

The IsZero function was changed slightly in Go 1.22, so we'll need to
update it.

While this could in theory break existing programs that rely on the old
behavior, they'd also break with the imminent Go 1.22 release so I don't
think this is a real problem.

3 files changed, 38 insertions, 10 deletions

diff --git a/src/reflect/all_test.go b/src/reflect/all_test.go
index 39fc7a374..ef8c7da43 100644
--- a/src/reflect/all_test.go
+++ b/src/reflect/all_test.go
@@ -1450,6 +1450,11 @@ func TestIsNil(t *testing.T) {
 	NotNil(fi, t)
 }
 
+func setField[S, V any](in S, offset uintptr, value V) (out S) {
+	*(*V)(unsafe.Add(unsafe.Pointer(&in), offset)) = value
+	return in
+}
+
 func TestIsZero(t *testing.T) {
 	for i, tt := range []struct {
 		x    any
@@ -1483,14 +1488,14 @@ func TestIsZero(t *testing.T) {
 		{float32(1.2), false},
 		{float64(0), true},
 		{float64(1.2), false},
-		{math.Copysign(0, -1), false},
+		{math.Copysign(0, -1), true},
 		{complex64(0), true},
 		{complex64(1.2), false},
 		{complex128(0), true},
 		{complex128(1.2), false},
-		{complex(math.Copysign(0, -1), 0), false},
-		{complex(0, math.Copysign(0, -1)), false},
-		{complex(math.Copysign(0, -1), math.Copysign(0, -1)), false},
+		{complex(math.Copysign(0, -1), 0), true},
+		{complex(0, math.Copysign(0, -1)), true},
+		{complex(math.Copysign(0, -1), math.Copysign(0, -1)), true},
 		{uintptr(0), true},
 		{uintptr(128), false},
 		// Array
@@ -1503,6 +1508,8 @@ func TestIsZero(t *testing.T) {
 		{[3][]int{{1}}, false},                  // incomparable array
 		{[1 << 12]byte{}, true},
 		{[1 << 12]byte{1}, false},
+		{[1]struct{ p *int }{}, true},
+		{[1]struct{ p *int }{{new(int)}}, false},
 		{[3]Value{}, true},
 		{[3]Value{{}, ValueOf(0), {}}, false},
 		// Chan
@@ -1539,6 +1546,20 @@ func TestIsZero(t *testing.T) {
 		{struct{ s []int }{[]int{1}}, false},  // incomparable struct
 		{struct{ Value }{}, true},
 		{struct{ Value }{ValueOf(0)}, false},
+		{struct{ _, a, _ uintptr }{}, true}, // comparable struct with blank fields
+		{setField(struct{ _, a, _ uintptr }{}, 0*unsafe.Sizeof(uintptr(0)), 1), true},
+		{setField(struct{ _, a, _ uintptr }{}, 1*unsafe.Sizeof(uintptr(0)), 1), false},
+		{setField(struct{ _, a, _ uintptr }{}, 2*unsafe.Sizeof(uintptr(0)), 1), true},
+		{struct{ _, a, _ func() }{}, true}, // incomparable struct with blank fields
+		{setField(struct{ _, a, _ func() }{}, 0*unsafe.Sizeof((func())(nil)), func() {}), true},
+		{setField(struct{ _, a, _ func() }{}, 1*unsafe.Sizeof((func())(nil)), func() {}), false},
+		{setField(struct{ _, a, _ func() }{}, 2*unsafe.Sizeof((func())(nil)), func() {}), true},
+		{struct{ a [256]S }{}, true},
+		{struct{ a [256]S }{a: [256]S{2: {i1: 1}}}, false},
+		{struct{ a [256]float32 }{}, true},
+		{struct{ a [256]float32 }{a: [256]float32{2: 1.0}}, false},
+		{struct{ _, a [256]S }{}, true},
+		{setField(struct{ _, a [256]S }{}, 0*unsafe.Sizeof(int64(0)), int64(1)), true},
 		// UnsafePointer
 		{(unsafe.Pointer)(nil), true},
 		{(unsafe.Pointer)(new(int)), false},
@@ -1564,9 +1585,7 @@ func TestIsZero(t *testing.T) {
 		p.SetZero()
 		if !p.IsZero() {
 			t.Errorf("%d: IsZero((%s)(%+v)) is true after SetZero", i, p.Kind(), tt.x)
-
 		}
-
 	}
 
 	/* // TODO(tinygo): panic/recover support
diff --git a/src/reflect/benchmark_test.go b/src/reflect/benchmark_test.go
new file mode 100644
index 000000000..6c080ec16
--- /dev/null
+++ b/src/reflect/benchmark_test.go
@@ -0,0 +1,10 @@
+// Copyright 2022 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 reflect_test
+
+type S struct {
+	i1 int64
+	i2 int64
+}
diff --git a/src/reflect/value.go b/src/reflect/value.go
index dc81fe66a..1227ac422 100644
--- a/src/reflect/value.go
+++ b/src/reflect/value.go
@@ -124,10 +124,9 @@ func (v Value) IsZero() bool {
 	case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
 		return v.Uint() == 0
 	case Float32, Float64:
-		return math.Float64bits(v.Float()) == 0
+		return v.Float() == 0
 	case Complex64, Complex128:
-		c := v.Complex()
-		return math.Float64bits(real(c)) == 0 && math.Float64bits(imag(c)) == 0
+		return v.Complex() == 0
 	case Array:
 		for i := 0; i < v.Len(); i++ {
 			if !v.Index(i).IsZero() {
@@ -141,7 +140,7 @@ func (v Value) IsZero() bool {
 		return v.Len() == 0
 	case Struct:
 		for i := 0; i < v.NumField(); i++ {
-			if !v.Field(i).IsZero() {
+			if !v.Field(i).IsZero() && v.Type().Field(i).Name != "_" {
 				return false
 			}
 		}