GCC 10 is not covered by the TinyCBOR fallthrough compatibility workaround

[FightingLittleBird]

Description

The TinyCBOR wrapper currently applies the following workaround:

if(CMAKE_C_COMPILER_ID STREQUAL "GNU"
   AND CMAKE_C_COMPILER_VERSION VERSION_LESS 10)
    target_compile_options(tinycbor PRIVATE
        "-D__has_cpp_attribute(x)=0")
endif()

However, the corresponding upstream TinyCBOR issue affects GCC versions
earlier than GCC 11, including GCC 10:

#293
#294
With GCC < 11 in C99 mode, __has_cpp_attribute(fallthrough) evaluates
as supported, but the C compiler cannot parse the resulting
[[fallthrough]] attribute.

The compilation error is similar to:

compilersupport_p.h:57:41: error: expected expression before '[' token
    #define CBOR_FALLTHROUGH [[fallthrough]]

This was reproduced locally with Arm GNU Toolchain 9.3.1 using -std=c99.

Problem
The condition VERSION_LESS 10 excludes GCC 10 even though GCC 10 is
also affected.

Defining __has_cpp_attribute from the command line is also only a
workaround and can produce a macro redefinition warning.

Expected behavior
TinyCBOR should compile in C99 mode with GCC 9 and GCC 10 without
overriding compiler feature-test macros.

Suggested solution
Preferred solution:

Update the bundled TinyCBOR source to v7.0 or later; or
Backport upstream commit:
45e4641
The upstream fix distinguishes C and C++ attribute detection:

#if defined(__has_cpp_attribute) && defined(__cplusplus)
    /* C++ attribute detection */
#elif defined(__has_c_attribute) && !defined(__cplusplus)
    /* C23 attribute detection */
#endif

[thiagomacieira]

Sorry, I don't understand what the problem is. As far as I can tell, TinyCBOR does compile just fine with GCC 9 and 10 in C99 mode.
https://c.godbolt.org/z/zqWEs9YTe

You're talking about a TinyCBOR wrapper. I don't know what that is and the snippet of code you've provided does not exist in the repository.

Are you sure you've reported to the right project?