From cf51fb5d680a9a1ca98af3361e65722d07bff111 Mon Sep 17 00:00:00 2001 From: Robert Griesemer Date: Sat, 16 Oct 2021 20:30:12 -0700 Subject: [PATCH] cmd/compile, types2: avoid confusing follow-on error in invalid type assertion This CL avoids a useless follow-on error (that gets reported before the actual error due to source position). This addresses the first part of the issue below. Thanks to @cuonglm for the suggestion for the fix. For #49005. Change-Id: Ifdd83072a05c32e115dc58a0233868a64f336f3f Reviewed-on: https://go-review.googlesource.com/c/go/+/356449 Trust: Robert Griesemer Run-TryBot: Robert Griesemer TryBot-Result: Go Bot Reviewed-by: Cuong Manh Le --- src/cmd/compile/internal/types2/typexpr.go | 7 +++++++ test/fixedbugs/issue49005a.go | 13 +++++++++++++ 2 files changed, 20 insertions(+) create mode 100644 test/fixedbugs/issue49005a.go diff --git a/src/cmd/compile/internal/types2/typexpr.go b/src/cmd/compile/internal/types2/typexpr.go index 646becbdae0..eae93309147 100644 --- a/src/cmd/compile/internal/types2/typexpr.go +++ b/src/cmd/compile/internal/types2/typexpr.go @@ -312,6 +312,13 @@ func (check *Checker) typInternal(e0 syntax.Expr, def *Named) (T Type) { typ := new(Pointer) def.setUnderlying(typ) typ.base = check.varType(e.X) + // If typ.base is invalid, it's unlikely that *base is particularly + // useful - even a valid dereferenciation will lead to an invalid + // type again, and in some cases we get unexpected follow-on errors + // (e.g., see #49005). Return an invalid type instead. + if typ.base == Typ[Invalid] { + return Typ[Invalid] + } return typ } diff --git a/test/fixedbugs/issue49005a.go b/test/fixedbugs/issue49005a.go new file mode 100644 index 00000000000..55d92c4650b --- /dev/null +++ b/test/fixedbugs/issue49005a.go @@ -0,0 +1,13 @@ +// errorcheck + +// 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 + +type T interface{ M() } + +func F() T + +var _ = F().(*X) // ERROR "undefined: X"