Bug #19778
closed
mkmf.rb pkg_config() interaction with RbConfig::CONFIG["cflags"]
Description
(This was first reported at https://github.com/ruby/openssl/issues/650: The extension's build breaks in a strange way if RbConfig::CONFIG["*flags"] contains the path of an OpenSSL installation but pkg-config returns the path of a different OpenSSL installation)
Commit 097c3e9cbbf23718371f08c24b2d2297b039f63f ("mkmf.rb: -I flags to $INCFLAGS", Ruby 2.2) changed how mkmf's pkg_config() handles the result of the pkg-config command. It now stores the -I flags in $INCFLAGS and others in $CFLAGS.
mkmf generates a Makefile that compiles source files with:
$(CC) $(INCFLAGS) $(CPPFLAGS) $(CFLAGS)
and link the final library with:
$(LDSHARED) -o $@ $(OBJS) $(LIBPATH) $(DLDFLAGS) $(LOCAL_LIBS) $(LIBS)
This "new" behavior of pkg_config() is problematic when RbConfig::CONFIG["{C,CPP}FLAGS"] also provide -I flags and RbConfig::CONFIG["LDFLAGS"] provides the matching -L flags -- for example, if Ruby is compiled with ./configure --with-opt-dir=<dir>. This would end up with compiling sources with
[...] -I<from pkg-config> -I<from RbConfig> [...]
and then linking with
[...] -L<from RbConfig> -L<from pkg-config> [...]
This doesn't seem right. I don't know which should come earlier, but the order should be consistent. The commit in question clearly describes the change in the commit message, but it doesn't have a linked issue. What is it intended for? Also, what is $INCFLAGS?
On the other hand, dir_config() would prepend -I flags to $CPPFLAGS and -L flags to $LIBPATH, so it doesn't have issues with flags from RbConfig, albeit in a differently way.
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