go/types: add a test case for issue 45985

The fix for #45985 is a little subtle. Start by committing the (bad)
test case.

For #45985

Change-Id: Ia6625818e9b1c5e869b2c2f724f817c13c9944d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/317471
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/infer.go b/src/go/types/infer.go
index da3a521870244a06fc5adc16b1db8d17c3f813f5..5d49351e1f043475332fad124e73efc5b4e2f6a5 100644 (file)
--- a/src/go/types/infer.go
+++ b/src/go/types/infer.go
@@ -398,7 +398,7 @@ func (check *Checker) inferB(tparams []*TypeName, targs []Type, report bool) (ty
                if sbound != nil {
                        if !u.unify(typ, sbound) {
                                if report {
-                                       check.errorf(tpar, 0, "%s does not match %s", tpar, sbound)
+                                       check.errorf(tpar, _Todo, "%s does not match %s", tpar, sbound)
                                }
                                return nil, 0
                        }
@@ -412,7 +412,7 @@ func (check *Checker) inferB(tparams []*TypeName, targs []Type, report bool) (ty
        // was given, unification produced the type list [int, []C, *A]. We eliminate the
        // remaining type parameters by substituting the type parameters in this type list
        // until nothing changes anymore.
-       types, index = u.x.types()
+       types, _ = u.x.types()
        if debug {
                for i, targ := range targs {
                        assert(targ == nil || types[i] == targ)

diff --git a/src/go/types/testdata/fixedbugs/issue45985.go2 b/src/go/types/testdata/fixedbugs/issue45985.go2
new file mode 100644 (file)
index 0000000..550b9c6
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue45985.go2
@@ -0,0 +1,14 @@
+// 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 issue45985
+
+// TODO(rFindley): this error should be on app[int] below.
+func app[S /* ERROR "type S = S does not match" */ interface{ type []T }, T any](s S, e T) S {
+    return append(s, e)
+}
+
+func _() {
+       _ = app[int]
+}