From: Samuel Just <sjust@redhat.com>
Date: Mon, 18 May 2020 18:03:36 +0000 (-0700)
Subject: errorator: don't rely on non-evaluation of static_assert in constexpr branch
X-Git-Tag: v17.0.0~2328^2~4
X-Git-Url: http://git.apps.os.sepia.ceph.com/?a=commitdiff_plain;h=eecc61f3c9be13aa9dadf3f0790ab757d8ac7779;p=ceph.git

errorator: don't rely on non-evaluation of static_assert in constexpr branch

At least in clang, we appear to fail that static assert even with another
branch taken.  Instead, assert that one of the other conditions is true.

Signed-off-by: Samuel Just <sjust@redhat.com>
---

diff --git a/src/crimson/common/errorator.h b/src/crimson/common/errorator.h
index b7a7c8eff0031..15fffbb0a4165 100644
--- a/src/crimson/common/errorator.h
+++ b/src/crimson/common/errorator.h
@@ -299,7 +299,9 @@ static constexpr auto composer(FuncHead&& head, FuncTail&&... tail) {
                          std::forward<decltype(args)>(args)...);
     } else {
       static_assert(
-        _impl::always_false<FuncHead>::value, "composition is not exhaustive");
+	std::is_invocable_v<FuncHead, decltype(args)...> ||
+	(sizeof...(FuncTail) > 0),
+      "composition is not exhaustive");
     }
   };
 }