[gcc r13-2764] libstdc++: Fix accidental duplicate test [PR91456]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:5814816641389dd76153aae63e8ccb67a1a9a321

commit r13-2764-g5814816641389dd76153aae63e8ccb67a1a9a321
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Sep 21 14:59:18 2022 +0100

    libstdc++: Fix accidental duplicate test [PR91456]
    
    It looks like I committed the testcase for std::function twice, instead
    of one for std::function and one for std::is_invocable_r. This replaces
    the is_invocable_r one with the example from the PR.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/91456
            * testsuite/20_util/function/91456.cc: Add comment with PR
            number.
            * testsuite/20_util/is_invocable/91456.cc: Likewise. Replace
            std::function checks with std::is_invocable_r checks.

Diff:
---
 libstdc++-v3/testsuite/20_util/function/91456.cc     |  3 +++
 libstdc++-v3/testsuite/20_util/is_invocable/91456.cc | 10 ++++++----
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/testsuite/20_util/function/91456.cc b/libstdc++-v3/testsuite/20_util/function/91456.cc
index 6b6631c452d..081bf20e2cf 100644
--- a/libstdc++-v3/testsuite/20_util/function/91456.cc
+++ b/libstdc++-v3/testsuite/20_util/function/91456.cc
@@ -17,6 +17,9 @@
 
 // { dg-do compile { target c++17 } }
 
+// PR 91456
+// std::function and std::is_invocable_r do not understand guaranteed elision
+
 #include <functional>
 
 struct Immovable {
diff --git a/libstdc++-v3/testsuite/20_util/is_invocable/91456.cc b/libstdc++-v3/testsuite/20_util/is_invocable/91456.cc
index a946db15c55..976d257ce85 100644
--- a/libstdc++-v3/testsuite/20_util/is_invocable/91456.cc
+++ b/libstdc++-v3/testsuite/20_util/is_invocable/91456.cc
@@ -17,6 +17,9 @@
 
 // { dg-do compile { target c++17 } }
 
+// PR 91456
+// std::function and std::is_invocable_r do not understand guaranteed elision
+
 #include <type_traits>
 
 #include <functional>
@@ -27,7 +30,6 @@ struct Immovable {
   Immovable& operator=(const Immovable&) = delete;
 };
 
-Immovable get() { return {}; }
-const Immovable i = get();                      // OK
-std::function<const Immovable()> f{&get};       // fails
-const Immovable i2 = f();
+static_assert(std::is_invocable_r_v<Immovable, Immovable(*)()>);
+static_assert(std::is_invocable_r_v<const Immovable, Immovable(*)()>);
+static_assert(std::is_invocable_r_v<Immovable, const Immovable(*)()>);