reflect: add Overflow methods to Type

This CL adds new methods synonymous with the method of the same name
in reflect.Value to reflect.Type: OverflowComplex, OverflowFloat, OverflowInt, OverflowUint.

Fixes #60427

Change-Id: I7a0bb35629e59a7429820f13fcd3a6f120194bc6
GitHub-Last-Rev: 26c11bcffe
GitHub-Pull-Request: golang/go#65955
Reviewed-on: https://go-review.googlesource.com/c/go/+/567296
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

api/next/60427.txt

@@ -0,0 +1,4 @@
+pkg reflect, type Type interface, OverflowComplex(complex128) bool #60427
+pkg reflect, type Type interface, OverflowFloat(float64) bool #60427
+pkg reflect, type Type interface, OverflowInt(int64) bool #60427
+pkg reflect, type Type interface, OverflowUint(uint64) bool #60427

doc/next/6-stdlib/99-minor/reflect/60427.md

@@ -0,0 +1,6 @@
+The new methods synonymous with the method of the same name in [`reflect.Value`](/pkg/reflect#Value)
+are added to [`reflect.Type`](/pkg/reflect#Type):
+1. [`OverflowComplex`](/pkg/reflect#Type.OverflowComplex)
+2. [`OverflowFloat`](/pkg/reflect#Type.OverflowFloat)
+3. [`OverflowInt`](/pkg/reflect#Type.OverflowInt)
+4. [`OverflowUint`](/pkg/reflect#Type.OverflowUint)

src/reflect/all_test.go

@@ -4827,7 +4827,7 @@ func TestComparable(t *testing.T) {
 	}
 }
 
-func TestOverflow(t *testing.T) {
+func TestValueOverflow(t *testing.T) {
 	if ovf := V(float64(0)).OverflowFloat(1e300); ovf {
 		t.Errorf("%v wrongly overflows float64", 1e300)
 	}
@@ -4866,6 +4866,45 @@ func TestOverflow(t *testing.T) {
 	}
 }
 
+func TestTypeOverflow(t *testing.T) {
+	if ovf := TypeFor[float64]().OverflowFloat(1e300); ovf {
+		t.Errorf("%v wrongly overflows float64", 1e300)
+	}
+
+	maxFloat32 := float64((1<<24 - 1) << (127 - 23))
+	if ovf := TypeFor[float32]().OverflowFloat(maxFloat32); ovf {
+		t.Errorf("%v wrongly overflows float32", maxFloat32)
+	}
+	ovfFloat32 := float64((1<<24-1)<<(127-23) + 1<<(127-52))
+	if ovf := TypeFor[float32]().OverflowFloat(ovfFloat32); !ovf {
+		t.Errorf("%v should overflow float32", ovfFloat32)
+	}
+	if ovf := TypeFor[float32]().OverflowFloat(-ovfFloat32); !ovf {
+		t.Errorf("%v should overflow float32", -ovfFloat32)
+	}
+
+	maxInt32 := int64(0x7fffffff)
+	if ovf := TypeFor[int32]().OverflowInt(maxInt32); ovf {
+		t.Errorf("%v wrongly overflows int32", maxInt32)
+	}
+	if ovf := TypeFor[int32]().OverflowInt(-1 << 31); ovf {
+		t.Errorf("%v wrongly overflows int32", -int64(1)<<31)
+	}
+	ovfInt32 := int64(1 << 31)
+	if ovf := TypeFor[int32]().OverflowInt(ovfInt32); !ovf {
+		t.Errorf("%v should overflow int32", ovfInt32)
+	}
+
+	maxUint32 := uint64(0xffffffff)
+	if ovf := TypeFor[uint32]().OverflowUint(maxUint32); ovf {
+		t.Errorf("%v wrongly overflows uint32", maxUint32)
+	}
+	ovfUint32 := uint64(1 << 32)
+	if ovf := TypeFor[uint32]().OverflowUint(ovfUint32); !ovf {
+		t.Errorf("%v should overflow uint32", ovfUint32)
+	}
+}
+
 func checkSameType(t *testing.T, x Type, y any) {
 	if x != TypeOf(y) || TypeOf(Zero(x).Interface()) != TypeOf(y) {
 		t.Errorf("did not find preexisting type for %s (vs %s)", TypeOf(x), TypeOf(y))

src/reflect/type.go

@@ -225,6 +225,22 @@ type Type interface {
 	// It panics if i is not in the range [0, NumOut()).
 	Out(i int) Type
 
+	// OverflowComplex reports whether the complex128 x cannot be represented by type t.
+	// It panics if t's Kind is not Complex64 or Complex128.
+	OverflowComplex(x complex128) bool
+
+	// OverflowFloat reports whether the float64 x cannot be represented by type t.
+	// It panics if t's Kind is not Float32 or Float64.
+	OverflowFloat(x float64) bool
+
+	// OverflowInt reports whether the int64 x cannot be represented by type t.
+	// It panics if t's Kind is not Int, Int8, Int16, Int32, or Int64.
+	OverflowInt(x int64) bool
+
+	// OverflowUint reports whether the uint64 x cannot be represented by type t.
+	// It panics if t's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
+	OverflowUint(x uint64) bool
+
 	common() *abi.Type
 	uncommon() *uncommonType
 }
@@ -297,6 +313,58 @@ type rtype struct {
 	t abi.Type
 }
 
+// OverflowComplex reports whether the complex128 x cannot be represented by type t.
+// It panics if t's Kind is not Complex64 or Complex128.
+func (t *rtype) OverflowComplex(x complex128) bool {
+	k := t.Kind()
+	switch k {
+	case Complex64:
+		return overflowFloat32(real(x)) || overflowFloat32(imag(x))
+	case Complex128:
+		return false
+	}
+	panic("reflect: OverflowComplex of non-complex type " + t.String())
+}
+
+// OverflowFloat reports whether the float64 x cannot be represented by type t.
+// It panics if t's Kind is not Float32 or Float64.
+func (t *rtype) OverflowFloat(x float64) bool {
+	k := t.Kind()
+	switch k {
+	case Float32:
+		return overflowFloat32(x)
+	case Float64:
+		return false
+	}
+	panic("reflect: OverflowFloat of non-float type " + t.String())
+}
+
+// OverflowInt reports whether the int64 x cannot be represented by type t.
+// It panics if t's Kind is not Int, Int8, Int16, Int32, or Int64.
+func (t *rtype) OverflowInt(x int64) bool {
+	k := t.Kind()
+	switch k {
+	case Int, Int8, Int16, Int32, Int64:
+		bitSize := t.Size() * 8
+		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
+		return x != trunc
+	}
+	panic("reflect: OverflowInt of non-int type " + t.String())
+}
+
+// OverflowUint reports whether the uint64 x cannot be represented by type t.
+// It panics if t's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
+func (t *rtype) OverflowUint(x uint64) bool {
+	k := t.Kind()
+	switch k {
+	case Uint, Uintptr, Uint8, Uint16, Uint32, Uint64:
+		bitSize := t.Size() * 8
+		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
+		return x != trunc
+	}
+	panic("reflect: OverflowUint of non-uint type " + t.String())
+}
+
 func (t *rtype) common() *abi.Type {
 	return &t.t
 }