[dev.typeparams] go/types: use correct type parameter list in missingMethod

This is a port of CL 321232 to go/types, adjusted to add a missing
comment and to remove optional support for method type params.

Fixes #46275

Change-Id: I63fcbb669e7607876a888fca89b9064568805448
Reviewed-on: https://go-review.googlesource.com/c/go/+/324751
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

diff --git a/src/go/types/lookup.go b/src/go/types/lookup.go
index 9c7bfd4bb97da8db276c633874c8dda8186dffda..3e89b6cc2b5b93da0c3c665c394a1f8f726d8b02 100644 (file)
--- a/src/go/types/lookup.go
+++ b/src/go/types/lookup.go
@@ -327,11 +327,15 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
                                return m, f
                        }
 
+                       // both methods must have the same number of type parameters
                        ftyp := f.typ.(*Signature)
                        mtyp := m.typ.(*Signature)
                        if len(ftyp.tparams) != len(mtyp.tparams) {
                                return m, f
                        }
+                       if len(ftyp.tparams) > 0 {
+                               panic("internal error: method with type parameters")
+                       }
 
                        // If the methods have type parameters we don't care whether they
                        // are the same or not, as long as they match up. Use unification
@@ -385,6 +389,9 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
                if len(ftyp.tparams) != len(mtyp.tparams) {
                        return m, f
                }
+               if len(ftyp.tparams) > 0 {
+                       panic("internal error: method with type parameters")
+               }
 
                // If V is a (instantiated) generic type, its methods are still
                // parameterized using the original (declaration) receiver type
@@ -412,7 +419,7 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
                // TODO(gri) is this always correct? what about type bounds?
                // (Alternative is to rename/subst type parameters and compare.)
                u := newUnifier(check, true)
-               u.x.init(ftyp.tparams)
+               u.x.init(ftyp.rparams)
                if !u.unify(ftyp, mtyp) {
                        return m, f
                }

diff --git a/src/go/types/testdata/fixedbugs/issue46275.go2 b/src/go/types/testdata/fixedbugs/issue46275.go2
new file mode 100644 (file)
index 0000000..0ebde31
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue46275.go2
@@ -0,0 +1,27 @@
+// 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 issue46275
+
+type N[T any] struct {
+        *N[T]
+        t T
+}
+
+func (n *N[T]) Elem() T {
+        return n.t
+}
+
+type I interface {
+        Elem() string
+}
+
+func _() {
+        var n1 *N[string]
+        var _ I = n1
+        type NS N[string]
+        var n2 *NS
+        var _ I = n2
+}
+