[dev.typeparams] cmd/compile/internal/types2: use comparable bit rather than ==() method

This removes the special "==" methods from comparable interfaces in
favor of a "comparable" flag in TypeSets indicating that the interface
is or embeds comparable. Fixes various related implementation
inaccuracies.

While at it, fix setup of the predeclared error and comparable
interface types by associating their respective type name objects
with them.

For #47411.

Change-Id: I409f880c8c8f2fe345621401267e4aaabd17124d
Reviewed-on: https://go-review.googlesource.com/c/go/+/337354
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

2 files changed, 29 insertions, 3 deletions

diff --git a/src/cmd/compile/internal/types2/testdata/check/issues.go2 b/src/cmd/compile/internal/types2/testdata/check/issues.go2
index 32c4320d27..1ede383ebe 100644
--- a/src/cmd/compile/internal/types2/testdata/check/issues.go2
+++ b/src/cmd/compile/internal/types2/testdata/check/issues.go2
@@ -58,7 +58,7 @@ func _() {
 type T1[P interface{~uint}] struct{}
 
 func _[P any]() {
-    _ = T1[P /* ERROR P has no type constraints */ ]{}
+    _ = T1[P /* ERROR P has no constraints */ ]{}
 }
 
 // This is the original (simplified) program causing the same issue.
@@ -74,8 +74,8 @@ func (u T2[U]) Add1() U {
     return u.s + 1
 }
 
-func NewT2[U any]() T2[U /* ERROR U has no type constraints */ ] {
-    return T2[U /* ERROR U has no type constraints */ ]{}
+func NewT2[U any]() T2[U /* ERROR U has no constraints */ ] {
+    return T2[U /* ERROR U has no constraints */ ]{}
 }
 
 func _() {
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue47411.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue47411.go2
new file mode 100644
index 0000000000..72968f9d43
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue47411.go2
@@ -0,0 +1,26 @@
+// 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.
+
+package p
+
+func f[_ comparable]()
+func g[_ interface{interface{comparable; ~int|~string}}]()
+
+func _[P comparable,
+        Q interface{ comparable; ~int|~string },
+        R any,                               // not comparable
+        S interface{ comparable; ~func() },  // not comparable
+]() {
+        _ = f[int]
+        _ = f[P]
+        _ = f[Q]
+        _ = f[func( /* ERROR does not satisfy comparable */ )]
+        _ = f[R /* ERROR R has no constraints */ ]
+
+        _ = g[int]
+        _ = g[P /* ERROR P has no type constraints */ ]
+        _ = g[Q]
+        _ = g[func( /* ERROR does not satisfy comparable */ )]
+        _ = g[R /* ERROR R has no constraints */ ]
+}