From b7ced159dbb789c70d4c502393e06ffac8c0e23d Mon Sep 17 00:00:00 2001
From: Niclas Larsson <niclas@edgesystems.se>
Date: Thu, 4 Jun 2026 19:45:38 +0200
Subject: [PATCH] Avoid is_constructible recursion in OnceAction

Both OnceAction compatibility traits, IsDirectlyCompatible and
IsCompatibleAfterIgnoringArguments, check std::is_constructible before
is_callable_r.

On libc++ that order breaks. Evaluating
is_constructible<std::tuple<OnceAction&&>, ...> drives libc++'s tuple
constructor SFINAE, which calls back into OnceAction's converting
constructor and re-enters the conjunction while it is still incomplete.
GCC <= 8 (e.g. QNX 7.1's gcc 8.3) rejects this with:

    incomplete type ... used in nested name specifier

so EXPECT_CALL(m, f()).WillOnce(Return(...)) fails to compile. GCC >= 9
and every Clang accept the original order; libstdc++ is unaffected.

Swapping the two checks fixes it: is_callable_r is cheap and
non-recursive, so the conjunction short-circuits to false for the
non-callable tuple before is_constructible is instantiated.

Fixes #3947.
---
 googlemock/include/gmock/gmock-actions.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/googlemock/include/gmock/gmock-actions.h b/googlemock/include/gmock/gmock-actions.h
index 94552cea2..4a3904f64 100644
--- a/googlemock/include/gmock/gmock-actions.h
+++ b/googlemock/include/gmock/gmock-actions.h
@@ -427,21 +427,21 @@ class [[nodiscard]] OnceAction<Result(Args...)> final {
   // via StdFunctionAdaptor.
   template <typename Callable>
   using IsDirectlyCompatible = internal::conjunction<
-      // It must be possible to capture the callable in StdFunctionAdaptor.
-      std::is_constructible<typename std::decay<Callable>::type, Callable>,
       // The callable must be compatible with our signature.
       internal::is_callable_r<Result, typename std::decay<Callable>::type,
-                              Args...>>;
+                              Args...>,
+      // It must be possible to capture the callable in StdFunctionAdaptor.
+      std::is_constructible<typename std::decay<Callable>::type, Callable>>;
 
   // True iff we can use the given callable type via StdFunctionAdaptor once we
   // ignore incoming arguments.
   template <typename Callable>
   using IsCompatibleAfterIgnoringArguments = internal::conjunction<
-      // It must be possible to capture the callable in a lambda.
-      std::is_constructible<typename std::decay<Callable>::type, Callable>,
       // The callable must be invocable with zero arguments, returning something
       // convertible to Result.
-      internal::is_callable_r<Result, typename std::decay<Callable>::type>>;
+      internal::is_callable_r<Result, typename std::decay<Callable>::type>,
+      // It must be possible to capture the callable in a lambda.
+      std::is_constructible<typename std::decay<Callable>::type, Callable>>;
 
  public:
   // Construct from a callable that is directly compatible with our mocked