go/types, types2: better error message for invalid use of constraint type

Fixes #42881.

Change-Id: If800c5f90c0034d192bf8b6649e5cfda96df48cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/410954
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue42881.go b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue42881.go
new file mode 100644 (file)
index 0000000..7122d1c
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue42881.go
@@ -0,0 +1,16 @@
+// Copyright 2022 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
+
+type (
+       T1 interface{ comparable }
+       T2 interface{ int }
+)
+
+var (
+       _ comparable // ERROR cannot use type comparable outside a type constraint: interface is \(or embeds\) comparable
+       _ T1         // ERROR cannot use type T1 outside a type constraint: interface is \(or embeds\) comparable
+       _ T2         // ERROR cannot use type T2 outside a type constraint: interface contains type constraints
+)

diff --git a/src/cmd/compile/internal/types2/typexpr.go b/src/cmd/compile/internal/types2/typexpr.go
index f0cd236050fd215c5698b6b382f90bfb1281292d..692feb975186af55dac0bf76fdbe2c71b5a0deaa 100644 (file)
--- a/src/cmd/compile/internal/types2/typexpr.go
+++ b/src/cmd/compile/internal/types2/typexpr.go
@@ -167,9 +167,9 @@ func (check *Checker) validVarType(e syntax.Expr, typ Type) {
                        tset := computeInterfaceTypeSet(check, pos, t) // TODO(gri) is this the correct position?
                        if !tset.IsMethodSet() {
                                if tset.comparable {
-                                       check.softErrorf(pos, "interface is (or embeds) comparable")
+                                       check.softErrorf(pos, "cannot use type %s outside a type constraint: interface is (or embeds) comparable", typ)
                                } else {
-                                       check.softErrorf(pos, "interface contains type constraints")
+                                       check.softErrorf(pos, "cannot use type %s outside a type constraint: interface contains type constraints", typ)
                                }
                        }
                }

diff --git a/src/go/types/testdata/fixedbugs/issue42881.go b/src/go/types/testdata/fixedbugs/issue42881.go
new file mode 100644 (file)
index 0000000..7122d1c
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue42881.go
@@ -0,0 +1,16 @@
+// Copyright 2022 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
+
+type (
+       T1 interface{ comparable }
+       T2 interface{ int }
+)
+
+var (
+       _ comparable // ERROR cannot use type comparable outside a type constraint: interface is \(or embeds\) comparable
+       _ T1         // ERROR cannot use type T1 outside a type constraint: interface is \(or embeds\) comparable
+       _ T2         // ERROR cannot use type T2 outside a type constraint: interface contains type constraints
+)

diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index a881d33654c4ffd5aabaf8f7aac74dce7ffcc516..b02929df224725d9b5555ed496460c956de02614 100644 (file)
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -163,9 +163,9 @@ func (check *Checker) validVarType(e ast.Expr, typ Type) {
                        tset := computeInterfaceTypeSet(check, e.Pos(), t) // TODO(gri) is this the correct position?
                        if !tset.IsMethodSet() {
                                if tset.comparable {
-                                       check.softErrorf(e, _MisplacedConstraintIface, "interface is (or embeds) comparable")
+                                       check.softErrorf(e, _MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface is (or embeds) comparable", typ)
                                } else {
-                                       check.softErrorf(e, _MisplacedConstraintIface, "interface contains type constraints")
+                                       check.softErrorf(e, _MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface contains type constraints", typ)
                                }
                        }
                }