Compilation failures with clang on Fedora 37

[jiridanek]

There is multiple issues:

• First, multiple instances of https://stackoverflow.com/questions/33855949/why-is-the-compiler-showing-call-to-function-with-no-prototype. Saying void foo(void) appears to be the correct standard-compliant C, https://stackoverflow.com/questions/693788/is-it-better-to-use-c-void-arguments-void-foovoid-or-not-void-foo.

/usr/bin/clang  -I/home/jdanek/repos/skupper-router/include -I/home/jdanek/repos/skupper-router/cmake-build-relwithdebinfo-clang/include -I/usr/include/python3.11 -I/home/jdanek/repos/skupper-router/cmake-build-relwithdebinfo-clang/src -I/home/jdanek/repos/skupper-router/src -I/home/jdanek/repos/skupper-router/src/router_core -isystem /home/jdanek/repos/qpid/qpid-proton/build/install/include -O2 -g -DNDEBUG -fcolor-diagnostics -Wall -Wextra -Werror -Wpedantic -Wno-unused-parameter -Wno-missing-field-initializers -Wno-sign-compare -Wno-language-extension-token -gdwarf-aranges -std=gnu11 -MD -MT src/CMakeFiles/skupper-router.dir/adaptors/adaptor_common.c.o -MF src/CMakeFiles/skupper-router.dir/adaptors/adaptor_common.c.o.d -o src/CMakeFiles/skupper-router.dir/adaptors/adaptor_common.c.o -c /home/jdanek/repos/skupper-router/src/adaptors/adaptor_common.c
In file included from /home/jdanek/repos/skupper-router/src/adaptors/adaptor_common.c:19:
In file included from /home/jdanek/repos/skupper-router/src/adaptors/adaptor_common.h:24:
In file included from /home/jdanek/repos/skupper-router/src/entity.h:22:
/home/jdanek/repos/skupper-router/include/qpid/dispatch/error.h:83:39: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
QD_EXPORT const char* qd_error_message();
                                      ^
                                       void

• Second, some options for tests subfolders that are unknown in clang

FAILED: tests/c_unittests/CMakeFiles/c_unittests.dir/test_terminus.cpp.o 
/usr/bin/clang++ -Dc_unittests_EXPORTS -I/home/jdanek/repos/skupper-router/include -I/home/jdanek/repos/skupper-router/cmake-build-relwithdebinfo-clang/include -I/home/jdanek/repos/qpid/qpid-proton/build/install/include -I/usr/include/python3.11 -I/home/jdanek/repos/skupper-router/src -I/home/jdanek/repos/skupper-router/cmake-build-relwithdebinfo-clang/src -I/home/jdanek/repos/skupper-router/src/router_core -I/home/jdanek/repos/skupper-router/tests/cpp-stub -fno-inline -fno-builtin -fno-stack-protector -Wno-literal-suffix -O2 -g -DNDEBUG -fcolor-diagnostics -Wall -Wextra -Werror -Wpedantic -Wno-unused-parameter -Wno-missing-field-initializers -Wno-sign-compare -Wno-language-extension-token -gdwarf-aranges -std=c++17 -MD -MT tests/c_unittests/CMakeFiles/c_unittests.dir/test_terminus.cpp.o -MF tests/c_unittests/CMakeFiles/c_unittests.dir/test_terminus.cpp.o.d -o tests/c_unittests/CMakeFiles/c_unittests.dir/test_terminus.cpp.o -c /home/jdanek/repos/skupper-router/tests/c_unittests/test_terminus.cpp
error: unknown warning option '-Wno-literal-suffix'; did you mean '-Wno-literal-range'? [-Werror,-Wunknown-warning-option]

[jiridanek]

• @kgiusti, @ganeshmurthy The reason why clang might be good in CI is that Add Clang Thread Safety Annotations #212 feature. Other than that, supporting clang is clearly a chore with unclear benefits (given that users are not asking for it). I suggest fixing the issues ^^^ in one-off round of fixes and not adding clang job to ci.

Clang job in CI would require contributors to fix clang issues as they appear. There is unlikely to be many, since both GCC and Clang implement the standard, Clang implements gcc switches, CMake also helps with portability, and so differences are minor, but it is still a drain sometimes.

[jiridanek]

Consider GCC option to catch the #803 declarations in GCC as well https://stackoverflow.com/questions/50401100/compiler-warning-for-function-defined-without-prototype-in-scope

[jiridanek]

Consider GCC option to catch the #803 declarations in GCC as well https://stackoverflow.com/questions/50401100/compiler-warning-for-function-defined-without-prototype-in-scope

https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

• -Wmissing-prototypes
• -Wmissing-declarations
• -Wstrict-prototypes
• -Wold-style-definition

A definition using ‘()’ is not considered an old-style definition in C2X mode, because it is equivalent to ‘(void)’ in that case, but is considered an old-style definition for older standards.