Native extension ABI version check failing for some gems

[tomstuart]

As discussed, the native extension ABI version check in d497bae is causing failures when loading some gems on Linux (Ubuntu 20.04.2 LTS).

My current example is the semian gem:

LoadError: The native extension at truffleruby/2.7.3.4/gems/semian-0.11.4/lib/semian/semian.so has a different ABI version: "TRUFFLERUBY_ABI_VERSION" than the running TruffleRuby: "2.7.3.4"

@nirvdrum reported a similar problem with the google-protobuf gem. I’ll add more examples as I find them.

[eregon]

google-protobuf is a different case, I already have a PR to fix that (it showed nil due the the symbol being hidden).

What happens here most likely is that TRUFFLERUBY_ABI_VERSION is not defined somehow, and in that case STRINGIZE(TRUFFLERUBY_ABI_VERSION); is replaced by "TRUFFLERUBY_ABI_VERSION" (unexpectedly).
Probably best to make it a compile/preprocessor-time error if TRUFFLERUBY_ABI_VERSION is not defined for clarity.

[eregon]

https://github.com/Shopify/semian/blob/6ff4b8292038fe3f6fc785884129039d5cf3e05f/ext/semian/extconf.rb#L26 is most likely what overrides the CFLAGS and causes the error.

[tomstuart]

Makes sense. Is the suggestion that this must be fixed in the gem? Do we have no way of supporting what it’s currently doing?

[eregon]

I'll try to find a way that's more reliably to pass the define, but overriding $CFLAGS seems problematic in general and might be worth fixing in the gem anyway (appending to $CFLAGS is fine, replacing much less).

[eregon]

I found a way, I moved the define from debugflags (part of CFLAGS), to DEFS, part of CPPFLAGS (= C preprocessor flags, CPPFLAGS="cppflags_hardcoded $(DEFS) $(cppflags)") which seems better suited.
Here is to hoping nobody overrides cppflags or $CPPFLAGS.

[tomstuart]

FWIW I couldn’t find any other gems with this specific problem. All of the other failures I saw were the nil case like google-protobuf.

[eregon]

FWIW RubyInline includes CFLAGS but not CPPFLAGS when it compiles, but that's probably a bug of RubyInline (there are other known bugs with it), so doesn't matter too much.

[eregon]

Fixed by 3252693