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unique: use TypeFor instead of TypeOf to get type in Make

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Currently the first thing Make does it get the abi.Type of its argument,
and uses abi.TypeOf to do it. However, this has a problem for interface
types, since the type of the value stored in the interface value will
bleed through. This is a classic reflection mistake.

Fix this by implementing and using a generic TypeFor which matches
reflect.TypeFor. This gets the type of the type parameter, which is far
less ambiguous and error-prone.

Fixes #68990.

Change-Id: Idd8d9a1095ef017e9cd7c7779314f7d4034f01a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/607355
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Michael Anthony Knyszek 2024-08-21 14:38:30 +00:00 committed by Michael Knyszek
parent f38d42f2c4
commit 755c18ecdf
4 changed files with 13 additions and 3 deletions
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9
src/internal/abi/type.go
View File

@ -177,6 +177,15 @@ func TypeOf(a any) *Type {
return (*Type)(NoEscape(unsafe.Pointer(eface.Type)))
}
// TypeFor returns the abi.Type for a type parameter.
func TypeFor[T any]() *Type {
var v T
if t := TypeOf(v); t != nil {
return t // optimize for T being a non-interface kind
}
return TypeOf((*T)(nil)).Elem() // only for an interface kind
}
func (t *Type) Kind() Kind { return t.Kind_ & KindMask }
func (t *Type) HasName() bool {

2
src/unique/clone_test.go
View File

@ -27,7 +27,7 @@ func cSeq(stringOffsets ...uintptr) cloneSeq {
func testCloneSeq[T any](t *testing.T, want cloneSeq) {
typName := reflect.TypeFor[T]().Name()
typ := abi.TypeOf(*new(T))
typ := abi.TypeFor[T]()
t.Run(typName, func(t *testing.T) {
got := makeCloneSeq(typ)
if !reflect.DeepEqual(got, want) {

2
src/unique/handle.go
View File

@ -31,7 +31,7 @@ func (h Handle[T]) Value() T {
// are equal if and only if the values used to produce them are equal.
func Make[T comparable](value T) Handle[T] {
// Find the map for type T.
typ := abi.TypeOf(value)
typ := abi.TypeFor[T]()
ma, ok := uniqueMaps.Load(typ)
if !ok {
// This is a good time to initialize cleanup, since we must go through

3
src/unique/handle_test.go
View File

@ -41,6 +41,7 @@ func TestHandle(t *testing.T) {
s: [2]testStringStruct{testStringStruct{"y"}, testStringStruct{"z"}},
})
testHandle[testStruct](t, testStruct{0.5, "184"})
testHandle[testEface](t, testEface("hello"))
}
func testHandle[T comparable](t *testing.T, value T) {
@ -93,7 +94,7 @@ func drainMaps(t *testing.T) {
func checkMapsFor[T comparable](t *testing.T, value T) {
// Manually load the value out of the map.
typ := abi.TypeOf(value)
typ := abi.TypeFor[T]()
a, ok := uniqueMaps.Load(typ)
if !ok {
return