[dev.typeparams] cmd/compile/internal/types2: embedding stand-alone type parameters is not permitted

For #47127.

Change-Id: Ie979ff56ae7c2dd0e5ce0ff39588f98ae68b5ee9
Reviewed-on: https://go-review.googlesource.com/c/go/+/334151
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

6 files changed, 70 insertions, 32 deletions

diff --git a/src/cmd/compile/internal/types2/testdata/check/issues.go2 b/src/cmd/compile/internal/types2/testdata/check/issues.go2
index 88ae294d7c..32c4320d27 100644
--- a/src/cmd/compile/internal/types2/testdata/check/issues.go2
+++ b/src/cmd/compile/internal/types2/testdata/check/issues.go2
@@ -232,7 +232,7 @@ func _[T interface{ ~func() }](f T) {
 
 type sliceOf[E any] interface{ ~[]E }
 
-func append[T interface{}, S sliceOf[T], T2 interface{ T }](s S, t ...T2) S
+func append[T interface{}, S sliceOf[T], T2 interface{}](s S, t ...T2) S
 
 var f           func()
 var cancelSlice []context.CancelFunc
diff --git a/src/cmd/compile/internal/types2/testdata/check/tinference.go2 b/src/cmd/compile/internal/types2/testdata/check/tinference.go2
index 2fdb39ca7a..1b70981759 100644
--- a/src/cmd/compile/internal/types2/testdata/check/tinference.go2
+++ b/src/cmd/compile/internal/types2/testdata/check/tinference.go2
@@ -8,19 +8,20 @@ import "strconv"
 
 type any interface{}
 
-func f0[A any, B interface{~C}, C interface{~D}, D interface{~A}](A, B, C, D)
-func _() {
-	f := f0[string]
-	f("a", "b", "c", "d")
-	f0("a", "b", "c", "d")
-}
-
-func f1[A any, B interface{~A}](A, B)
-func _() {
-	f := f1[int]
-	f(int(0), int(0))
-	f1(int(0), int(0))
-}
+// Embedding stand-alone type parameters is not permitted for now. Disabled.
+// func f0[A any, B interface{~C}, C interface{~D}, D interface{~A}](A, B, C, D)
+// func _() {
+// 	f := f0[string]
+// 	f("a", "b", "c", "d")
+// 	f0("a", "b", "c", "d")
+// }
+// 
+// func f1[A any, B interface{~A}](A, B)
+// func _() {
+// 	f := f1[int]
+// 	f(int(0), int(0))
+// 	f1(int(0), int(0))
+// }
 
 func f2[A any, B interface{~[]A}](A, B)
 func _() {
@@ -29,13 +30,14 @@ func _() {
 	f2(byte(0), []byte{})
 }
 
-func f3[A any, B interface{~C}, C interface{~*A}](A, B, C)
-func _() {
-	f := f3[int]
-	var x int
-	f(x, &x, &x)
-	f3(x, &x, &x)
-}
+// Embedding stand-alone type parameters is not permitted for now. Disabled.
+// func f3[A any, B interface{~C}, C interface{~*A}](A, B, C)
+// func _() {
+// 	f := f3[int]
+// 	var x int
+// 	f(x, &x, &x)
+// 	f3(x, &x, &x)
+// }
 
 func f4[A any, B interface{~[]C}, C interface{~*A}](A, B, C)
 func _() {
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39634.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39634.go2
index 6d002f5d2f..5cb15e7e58 100644
--- a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39634.go2
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39634.go2
@@ -31,9 +31,10 @@ type x7[A any] struct{ foo7 }
 func main7() { var _ foo7 = x7[int]{} }
 
 // crash 8
-type foo8[A any] interface { ~A }
-func bar8[A foo8[A]](a A) {}
-func main8() {}
+// Embedding stand-alone type parameters is not permitted for now. Disabled.
+// type foo8[A any] interface { ~A }
+// func bar8[A foo8[A]](a A) {}
+// func main8() {}
 
 // crash 9
 type foo9[A any] interface { foo9 /* ERROR illegal cycle */ [A] }
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39680.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39680.go2
index 01eadd2dbf..e56bc35475 100644
--- a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39680.go2
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39680.go2
@@ -4,6 +4,9 @@
 
 package p
 
+// Embedding stand-alone type parameters is not permitted for now. Disabled.
+
+/*
 import "fmt"
 
 // Minimal test case.
@@ -25,3 +28,4 @@ func Print[T constr[T]](s []T) {
 func f() {
 	Print([]string{"Hello, ", "playground\n"})
 }
+*/
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39948.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39948.go2
index 6372397ed9..e38e57268d 100644
--- a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39948.go2
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39948.go2
@@ -2,14 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// TODO(gri) Eventually, once we disallow type lists, we need to
-//           adjust this code: for 1.17 we don't accept type parameters,
-//           and for 1.18 this code is valid.
-//           Leaving for now so we can see that existing errors
-//           are being reported.
-
-package go1_17 // don't permit non-interface elements in interfaces
+package p
 
 type T[P any] interface{
-	P // ERROR P is a type parameter, not an interface
+	P // ERROR cannot embed a type parameter
 }
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue47127.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue47127.go2
new file mode 100644
index 0000000000..387c946957
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue47127.go2
@@ -0,0 +1,37 @@
+// Copyright 2021 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.
+
+// Embedding of stand-alone type parameters is not permitted.
+
+package p
+
+type (
+        _[P any] interface{ *P | []P | chan P | map[string]P }
+        _[P any] interface{ P /* ERROR "cannot embed a type parameter" */ }
+        _[P any] interface{ ~P /* ERROR "cannot embed a type parameter" */ }
+        _[P any] interface{ int | P /* ERROR "cannot embed a type parameter" */ }
+        _[P any] interface{ int | ~P /* ERROR "cannot embed a type parameter" */ }
+)
+
+func _[P any]() {
+        type (
+                _[P any] interface{ *P | []P | chan P | map[string]P }
+                _[P any] interface{ P /* ERROR "cannot embed a type parameter" */ }
+                _[P any] interface{ ~P /* ERROR "cannot embed a type parameter" */ }
+                _[P any] interface{ int | P /* ERROR "cannot embed a type parameter" */ }
+                _[P any] interface{ int | ~P /* ERROR "cannot embed a type parameter" */ }
+
+                _ interface{ *P | []P | chan P | map[string]P }
+                _ interface{ P /* ERROR "cannot embed a type parameter" */ }
+                _ interface{ ~P /* ERROR "cannot embed a type parameter" */ }
+                _ interface{ int | P /* ERROR "cannot embed a type parameter" */ }
+                _ interface{ int | ~P /* ERROR "cannot embed a type parameter" */ }
+        )
+}
+
+func _[P any, Q interface{ *P | []P | chan P | map[string]P }]()
+func _[P any, Q interface{ P /* ERROR "cannot embed a type parameter" */ }]()
+func _[P any, Q interface{ ~P /* ERROR "cannot embed a type parameter" */ }]()
+func _[P any, Q interface{ int | P /* ERROR "cannot embed a type parameter" */ }]()
+func _[P any, Q interface{ int | ~P /* ERROR "cannot embed a type parameter" */ }]()