Allow disabling use of __builtin_constant_p in internal macros

Turns out that even in GCC, the expression in `__builtin_cosntant_p`
can end up evaluated and side-effects executed. To allow users to
work around this bug, I added a configuration option to disable its
use in internal macros.

Related to catchorg#2925

BUILD.bazel

@@ -56,6 +56,8 @@ expand_template(
         "#cmakedefine CATCH_CONFIG_WCHAR": "",
         "#cmakedefine CATCH_CONFIG_WINDOWS_CRTDBG": "",
         "#cmakedefine CATCH_CONFIG_WINDOWS_SEH": "",
+        "#cmakedefine CATCH_CONFIG_USE_BUILTIN_CONSTANT_P": "",
+        "#cmakedefine CATCH_CONFIG_NO_USE_BUILTIN_CONSTANT_P": "",
     },
     template = "src/catch2/catch_user_config.hpp.in",
 )

CMake/CatchConfigOptions.cmake

@@ -44,6 +44,7 @@ set(_OverridableOptions
   "WINDOWS_SEH"
   "GETENV"
   "EXPERIMENTAL_STATIC_ANALYSIS_SUPPORT"
+  "USE_BUILTIN_CONSTANT_P"
 )
 
 foreach(OptionName ${_OverridableOptions})

docs/configuration.md

@@ -158,11 +158,14 @@ by using `_NO_` in the macro, e.g. `CATCH_CONFIG_NO_CPP17_UNCAUGHT_EXCEPTIONS`.
     CATCH_CONFIG_ANDROID_LOGWRITE           // Use android's logging system for debug output
     CATCH_CONFIG_GLOBAL_NEXTAFTER           // Use nextafter{,f,l} instead of std::nextafter
     CATCH_CONFIG_GETENV                     // System has a working `getenv`
+    CATCH_CONFIG_USE_BUILTIN_CONSTANT_P     // Use __builtin_constant_p to trigger warnings
 
 > [`CATCH_CONFIG_ANDROID_LOGWRITE`](https://github.com/catchorg/Catch2/issues/1743) and [`CATCH_CONFIG_GLOBAL_NEXTAFTER`](https://github.com/catchorg/Catch2/pull/1739) were introduced in Catch2 2.10.0
 
 > `CATCH_CONFIG_GETENV` was [introduced](https://github.com/catchorg/Catch2/pull/2562) in Catch2 3.2.0
 
+> `CATCH_CONFIG_USE_BUILTIN_CONSTANT_P` was introduced in Catch2 vX.Y.Z
+
 Currently Catch enables `CATCH_CONFIG_WINDOWS_SEH` only when compiled with MSVC, because some versions of MinGW do not have the necessary Win32 API support.
 
 `CATCH_CONFIG_POSIX_SIGNALS` is on by default, except when Catch is compiled under `Cygwin`, where it is disabled by default (but can be force-enabled by defining `CATCH_CONFIG_POSIX_SIGNALS`).
@@ -183,6 +186,12 @@ With the exception of `CATCH_CONFIG_EXPERIMENTAL_REDIRECT`,
 these toggles can be disabled by using `_NO_` form of the toggle,
 e.g. `CATCH_CONFIG_NO_WINDOWS_SEH`.
 
+`CATCH_CONFIG_USE_BUILTIN_CONSTANT_P` is ON by default for Clang and GCC
+(but as far as possible, not for other compilers masquerading for these
+two). However, it can cause bugs where the enclosed code is evaluated, even
+though it should not be, e.g. in [#2925](https://github.com/catchorg/Catch2/issues/2925).
+
+
 ### `CATCH_CONFIG_FAST_COMPILE`
 This compile-time flag speeds up compilation of assertion macros by ~20%,
 by disabling the generation of assertion-local try-catch blocks for

src/catch2/catch_user_config.hpp.in

@@ -178,6 +178,15 @@
 #endif
 
 
+#cmakedefine CATCH_CONFIG_USE_BUILTIN_CONSTANT_P
+#cmakedefine CATCH_CONFIG_NO_USE_BUILTIN_CONSTANT_P
+
+#if defined( CATCH_CONFIG_USE_BUILTIN_CONSTANT_P ) && \
+    defined( CATCH_CONFIG_NO_USE_BUILTIN_CONSTANT_P )
+#    error Cannot force USE_BUILTIN_CONSTANT_P to both ON and OFF
+#endif
+
+
 // ------
 // Simple toggle defines
 // their value is never used and they cannot be overridden

src/catch2/internal/catch_compiler_capabilities.hpp

@@ -62,7 +62,7 @@
 #    define CATCH_INTERNAL_SUPPRESS_SHADOW_WARNINGS \
          _Pragma( "GCC diagnostic ignored \"-Wshadow\"" )
 
-#    define CATCH_INTERNAL_IGNORE_BUT_WARN(...) (void)__builtin_constant_p(__VA_ARGS__)
+#    define CATCH_INTERNAL_CONFIG_USE_BUILTIN_CONSTANT_P
 
 #endif
 
@@ -86,35 +86,13 @@
 // clang-cl defines _MSC_VER as well as __clang__, which could cause the
 // start/stop internal suppression macros to be double defined.
 #if defined(__clang__) && !defined(_MSC_VER)
-
+#    define CATCH_INTERNAL_CONFIG_USE_BUILTIN_CONSTANT_P
 #    define CATCH_INTERNAL_START_WARNINGS_SUPPRESSION _Pragma( "clang diagnostic push" )
 #    define CATCH_INTERNAL_STOP_WARNINGS_SUPPRESSION  _Pragma( "clang diagnostic pop" )
-
 #endif // __clang__ && !_MSC_VER
 
 #if defined(__clang__)
 
-// As of this writing, IBM XL's implementation of __builtin_constant_p has a bug
-// which results in calls to destructors being emitted for each temporary,
-// without a matching initialization. In practice, this can result in something
-// like `std::string::~string` being called on an uninitialized value.
-//
-// For example, this code will likely segfault under IBM XL:
-// ```
-// REQUIRE(std::string("12") + "34" == "1234")
-// ```
-//
-// Similarly, NVHPC's implementation of `__builtin_constant_p` has a bug which
-// results in calls to the immediately evaluated lambda expressions to be
-// reported as unevaluated lambdas.
-// https://developer.nvidia.com/nvidia_bug/3321845.
-//
-// Therefore, `CATCH_INTERNAL_IGNORE_BUT_WARN` is not implemented.
-#  if !defined(__ibmxl__) && !defined(__CUDACC__) && !defined( __NVCOMPILER )
-#    define CATCH_INTERNAL_IGNORE_BUT_WARN(...) (void)__builtin_constant_p(__VA_ARGS__) /* NOLINT(cppcoreguidelines-pro-type-vararg, hicpp-vararg) */
-#  endif
-
-
 #    define CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS \
          _Pragma( "clang diagnostic ignored \"-Wexit-time-destructors\"" ) \
          _Pragma( "clang diagnostic ignored \"-Wglobal-constructors\"")
@@ -139,6 +117,27 @@
 
 #endif // __clang__
 
+// As of this writing, IBM XL's implementation of __builtin_constant_p has a bug
+// which results in calls to destructors being emitted for each temporary,
+// without a matching initialization. In practice, this can result in something
+// like `std::string::~string` being called on an uninitialized value.
+//
+// For example, this code will likely segfault under IBM XL:
+// ```
+// REQUIRE(std::string("12") + "34" == "1234")
+// ```
+//
+// Similarly, NVHPC's implementation of `__builtin_constant_p` has a bug which
+// results in calls to the immediately evaluated lambda expressions to be
+// reported as unevaluated lambdas.
+// https://developer.nvidia.com/nvidia_bug/3321845.
+//
+// Therefore, `CATCH_INTERNAL_IGNORE_BUT_WARN` is not implemented.
+#if defined( __ibmxl__ ) || defined( __CUDACC__ ) || defined( __NVCOMPILER )
+#    define CATCH_INTERNAL_CONFIG_NO_USE_BUILTIN_CONSTANT_P
+#endif
+
+
 
 ////////////////////////////////////////////////////////////////////////////////
 // We know some environments not to support full POSIX signals
@@ -362,6 +361,22 @@
 #endif
 
 
+// The goal of this macro is to avoid evaluation of the arguments, but
+// still have the compiler warn on problems inside...
+#if defined( CATCH_INTERNAL_CONFIG_USE_BUILTIN_CONSTANT_P ) && \
+    !defined( CATCH_INTERNAL_CONFIG_NO_USE_BUILTIN_CONSTANT_P ) && !defined(CATCH_CONFIG_USE_BUILTIN_CONSTANT_P)
+#define CATCH_CONFIG_USE_BUILTIN_CONSTANT_P
+#endif
+
+#if defined( CATCH_CONFIG_USE_BUILTIN_CONSTANT_P ) && \
+    !defined( CATCH_CONFIG_NO_USE_BUILTIN_CONSTANT_P )
+#    define CATCH_INTERNAL_IGNORE_BUT_WARN( ... )                                              \
+        (void)__builtin_constant_p( __VA_ARGS__ ) /* NOLINT(cppcoreguidelines-pro-type-vararg, \
+                                                     hicpp-vararg) */
+#else
+#    define CATCH_INTERNAL_IGNORE_BUT_WARN( ... )
+#endif
+
 // Even if we do not think the compiler has that warning, we still have
 // to provide a macro that can be used by the code.
 #if !defined(CATCH_INTERNAL_START_WARNINGS_SUPPRESSION)
@@ -398,13 +413,6 @@
 #    define CATCH_INTERNAL_SUPPRESS_SHADOW_WARNINGS
 #endif
 
-
-// The goal of this macro is to avoid evaluation of the arguments, but
-// still have the compiler warn on problems inside...
-#if !defined(CATCH_INTERNAL_IGNORE_BUT_WARN)
-#   define CATCH_INTERNAL_IGNORE_BUT_WARN(...)
-#endif
-
 #if defined(__APPLE__) && defined(__apple_build_version__) && (__clang_major__ < 10)
 #   undef CATCH_INTERNAL_SUPPRESS_UNUSED_TEMPLATE_WARNINGS
 #elif defined(__clang__) && (__clang_major__ < 5)