cmd/compile: unexpected error from constraint type inference

[RelicOfTesla]

What version of Go are you using (go version)?

$ go version
go version go1.18.3 windows/amd64

What did you do?

type BaseT interface {
	Type1 | Type2
}
type BaseType int
type Type1 BaseType
type Type2 BaseType // float64

type ValueT[T BaseT] struct {
	A1 T
}

func NewType1() *ValueT[Type1] {
	r := NewT[Type1]()
	return r
}
func NewType2() *ValueT[Type2] {
	r := NewT[Type2]()
	return r
}

func NewT[TBase BaseT, TVal ValueT[TBase]]() *TVal {
	ret := TVal{}
	return &ret
}
func TestGoType(t *testing.T) {
	r1 := NewType1()
	r2 := NewType2()
	t.Log(r1, r2)
	t.Log(reflect.TypeOf(r1), reflect.TypeOf(r2))
	fooT1(r1.A1)
	fooT2(r2.A1)
}

func fooT1(t1 Type1) {

}
func fooT2(t2 Type2) {

}

What did you expect to see?

Compile success

What did you see instead?

error:

TBase does not match int
TBase does not match int

[ianlancetaylor]

CC @griesemer

Standalone reproducer:

package p

type BaseT interface {
	Type1 | Type2
}
type BaseType int
type Type1 BaseType
type Type2 BaseType

type ValueT[T BaseT] struct {
	A1 T
}

func NewType1() *ValueT[Type1] {
	r := NewT[Type1]()
	return r
}

func NewT[TInt BaseT, TVal ValueT[TInt]]() *TVal {
	ret := TVal{}
	return &ret
}

foo.go:15:18: TInt does not match int