[Bug 255910] lang/ruby26 lang/ruby27: Fix clang 12 -Wcompound-token-split-by-macro warning in ruby.h

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=255910

            Bug ID: 255910
           Summary: lang/ruby26 lang/ruby27: Fix clang 12
                    -Wcompound-token-split-by-macro warning in ruby.h
           Product: Ports & Packages
           Version: Latest
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: Individual Port(s)
          Assignee: ruby at FreeBSD.org
          Reporter: dim at FreeBSD.org
             Flags: maintainer-feedback?(ruby at FreeBSD.org)
          Assignee: ruby at FreeBSD.org

Created attachment 224976
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=224976&action=edit
Fix -Wcompound-token-split-by-macro warning in ruby26's ruby.h

During an exp-run for llvm 12 (see bug 255570), it turned out that several ruby
gem extensions do not build with clang 12.0.0, for example devel/rubygem-thrift
[1]:

compiling binary_protocol_accelerated.c
binary_protocol_accelerated.c:404:68: error: '(' and '{' tokens introducing
statement expression appear in different macro expansion contexts
[-Werror,-Wcompound-token-split-by-macro]
  VALUE thrift_binary_protocol_class = rb_const_get(thrift_module,
rb_intern("BinaryProtocol"));
                                                                  
^~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1847:23: note: expanded from macro
'rb_intern'
        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
                      ^
binary_protocol_accelerated.c:404:68: note: '{' token is here
  VALUE thrift_binary_protocol_class = rb_const_get(thrift_module,
rb_intern("BinaryProtocol"));
                                                                  
^~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1847:24: note: expanded from macro
'rb_intern'
        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1832:5: note: expanded from macro
'RUBY_CONST_ID_CACHE'
    {                                                   \
    ^

and similarly www/unit-ruby [2]:

src/ruby/nxt_ruby.c:242:21: error: '(' and '{' tokens introducing statement
expression appear in different macro expansion contexts
[-Werror,-Wcompound-token-split-by-macro]
    nxt_ruby_call = rb_intern("call");
                    ^~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1847:23: note: expanded from macro
'rb_intern'
        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
                      ^
src/ruby/nxt_ruby.c:242:21: note: '{' token is here
    nxt_ruby_call = rb_intern("call");
                    ^~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1847:24: note: expanded from macro
'rb_intern'
        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1832:5: note: expanded from macro
'RUBY_CONST_ID_CACHE'
    {                                                   \
    ^

The gem extensions appear to purposefully compile using -Werror, and this new
-Wcompound-token-split-by-macro is enabled by default in clang 12 and later
(see [3]). Of course we could go over all these extensions, and either remove
-Werror or add -Wno-compound-token-split-by-macro, but that seems quite a lot
of effort.

Instead, I have submitted a pull request to ruby's GitHub, which fixes this by
modifying the main ruby.h header:
* Add RUBY_CONST_ID_CACHE_NB() (i.e. no-brace) which contains the code itself,
without any braces
* RUBY_CONST_ID_CACHE() which uses RUBY_CONST_ID_CACHE_NB(), but puts braces
around it (so no existing code using this macro breaks)
* Finally, change rb_intern() so the __extension__ directly creates a gcc
statement expression, using the RUBY_CONST_ID_CACHE_NB() macro

I am attaching a patch that adds these changes to the lang/ruby26 and
lang/ruby27 ports.

Also noted in the pull request is that ruby 3.0 does not need these changes, as
they have refactored ruby.h, so that it avoids emitting this warning.

[1]
http://package22.nyi.freebsd.org/data/mainamd64PR255570-default/2021-05-08_16h02m24s/logs/errors/rubygem-thrift-0.14.0,1.log
[2]
http://package22.nyi.freebsd.org/data/mainamd64PR255570-default/2021-05-08_16h02m24s/logs/errors/unit-ruby2.7-1.23.0.log
[3]
https://github.com/llvm/llvm-project/commit/0e00a95b4fad5e72851de012d3a0b2c2d01f8685
[4] https://github.com/ruby/ruby/pull/4504

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