[gcc r14-11387] c++: disable -Wnonnull in unevaluated context [PR115580]

[Marek Polacek]

https://gcc.gnu.org/g:8c635072ae68f60f14333cf113e75fa25a55becf

commit r14-11387-g8c635072ae68f60f14333cf113e75fa25a55becf
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Mar 4 13:07:27 2025 -0500

    c++: disable -Wnonnull in unevaluated context [PR115580]
    
    This PR complains that we issue a -Wnonnull even in a decltype.
    This fix disables even -Wformat and -Wrestrict.  I think that's fine.
    
            PR c++/115580
    
    gcc/c-family/ChangeLog:
    
            * c-common.cc (check_function_arguments): Return early if
            c_inhibit_evaluation_warnings.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/Wnonnull16.C: New test.
    
    Reviewed-by: Jason Merrill <jason@redhat.com>
    (cherry picked from commit 459c8a55567b06522e4b9cc0a4ef62f9d3024526)

Diff:
---
 gcc/c-family/c-common.cc               |  3 +++
 gcc/testsuite/g++.dg/warn/Wnonnull16.C | 16 ++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index d5b28efd6db4..0d05694b6d04 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -6160,6 +6160,9 @@ check_function_arguments (location_t loc, const_tree fndecl, const_tree fntype,
 {
   bool warned_p = false;
 
+  if (c_inhibit_evaluation_warnings)
+    return warned_p;
+
   /* Check for null being passed in a pointer argument that must be
      non-null.  In C++, this includes the this pointer.  We also need
      to do this if format checking is enabled.  */
diff --git a/gcc/testsuite/g++.dg/warn/Wnonnull16.C b/gcc/testsuite/g++.dg/warn/Wnonnull16.C
new file mode 100644
index 000000000000..8740f351ac76
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wnonnull16.C
@@ -0,0 +1,16 @@
+// PR c++/115580
+// { dg-do compile { target c++11 } }
+
+class WithMember {
+public:
+  int foo();
+};
+
+decltype(((WithMember*)nullptr)->foo()) footype; // { dg-bogus "pointer is null" }
+
+int f(void*) __attribute__((nonnull));
+
+void g()
+{
+  [[maybe_unused]] decltype(f(nullptr)) b; // { dg-bogus "non-null" }
+}