Build errors with GCC 5 about afsctool HOT 9 OPEN

I believe you can fix the variably modified X at file scope errors by using enum rather than const char or const long long int: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93082. Apparently this was allowed in GCC at some point, but then they became stricter and now it fails, and the clang upstream seems to think they should follow GCC in doing this: https://bugs.llvm.org/show_bug.cgi?id=44406.

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It’s not newfangled. That it compiles at all is against the C standard. Clang allowing it is accidental. I don’t know if newer GCC supports it.

I ran into this on Linux, not Mac. Maybe it makes sense to make afsctool a Mac-only program and support zfsctool on both platforms? (though right now the code seems to suggest that they should both run on Linux)

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We actually can use GCC 11 to build in Homebrew, but the error still happens there. According to the Clang issue linked above, it seems this may have been allowed in GCC 4, and Clang followed their lead and allowed it as well. But then in GCC 5 they got stricter and didn't allow it anymore, but Clang didn't follow them in disabling it, possibly because it would break existing code.

You can disregard these errors as they go away when we use GCC 11:

/tmp/afsctool-20220303-4478-1g0rh9p/afsctool-1.7.2/src/afsctool.c:103:19: error: missing binary operator before token "("
#if !__has_builtin(__builtin_available)
^
/tmp/afsctool-20220303-4478-1g0rh9p/afsctool-1.7.2/src/afsctool.c: In function ‘afsctool’:
/tmp/afsctool-20220303-4478-1g0rh9p/afsctool-1.7.2/src/afsctool.c:2483:19: error: missing binary operator before token "("
#if !__has_builtin(__builtin_available)
^

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But which C standard?

C++17 C17, for one. http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2310.pdf Page 96.
I think it would fix the problem to replace sizeunit10_long[sizeunits] = … with sizeunit10_long[] = …. That way it’s a partial type, not a VLA.

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Sorry yes, I meant C17. It has been illegal from when VLA's were introduced in C99 (http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf Page 118)

I'm in favor of just removing sizeunits :-)

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@RJVB if it's possible for this fix to be added as a commit we can then use that commit to as a patch for our package. If you think it warrants a new release, we can also bump the version up to that new release.

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