cmd/compile: fix ICE with recursive alias type parameter

CL 585399 fixed an initialization loop during IR contruction that
involving alias type, by avoiding publishing alias declarations until
the RHS type expression has been constructed.

There's an assertion to ensure that the alias's type must be the same
during the initialization. However, that assertion is too strict, since
we may construct different instances of the same type, if the type is an
instantination of generic type.

To fix this, we could use types.IdenticalStrict to ensure that these
types matching exactly.

Updates golang#66873.
Updates golang#73309.

Change-Id: I2559bed37e21615854333fb1057d7349406e6a1b
Reviewed-on: https://go-review.googlesource.com/c/go/+/668175
Reviewed-by: David Chase <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Auto-Submit: Cuong Manh Le <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: cuonglm

src/cmd/compile/internal/noder/reader.go

@@ -762,7 +762,7 @@ func (pr *pkgReader) objIdxMayFail(idx index, implicits, explicits []*types.Type
 		if hack {
 			if sym.Def != nil {
 				name = sym.Def.(*ir.Name)
-				assert(name.Type() == typ)
+				assert(types.IdenticalStrict(name.Type(), typ))
 				return name, nil
 			}
 			sym.Def = name

src/cmd/compile/internal/types2/stdlib_test.go

@@ -332,6 +332,7 @@ func TestStdFixed(t *testing.T) {
 		"issue49814.go",  // go/types does not have constraints on array size
 		"issue56103.go",  // anonymous interface cycles; will be a type checker error in 1.22
 		"issue52697.go",  // types2 does not have constraints on stack size
+		"issue73309.go",  // this test requires GODEBUG=gotypesalias=1
 
 		// These tests requires runtime/cgo.Incomplete, which is only available on some platforms.
 		// However, types2 does not know about build constraints.

src/go/types/stdlib_test.go

@@ -334,6 +334,7 @@ func TestStdFixed(t *testing.T) {
 		"issue49814.go",  // go/types does not have constraints on array size
 		"issue56103.go",  // anonymous interface cycles; will be a type checker error in 1.22
 		"issue52697.go",  // go/types does not have constraints on stack size
+		"issue73309.go",  // this test requires GODEBUG=gotypesalias=1
 
 		// These tests requires runtime/cgo.Incomplete, which is only available on some platforms.
 		// However, go/types does not know about build constraints.

test/fixedbugs/issue73309.go

@@ -0,0 +1,18 @@
+// compile
+
+// Copyright 2025 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 main
+
+type B[T any] struct {
+	a A[T]
+}
+
+type A[T any] = func(B[T]) bool
+
+func main() {
+	var s A[int]
+	println(s)
+}