[GR-14917] Ensure directory of C files being compiled is first on include path.

PullRequest: truffleruby/767

Author: aardvark179

CHANGELOG.md

@@ -10,6 +10,7 @@ Bug fixes:
 * Fixed a race condition when using the interpolate-once (`/o`) modifier in
   regular expressions.
 * Calling `StringIO#close` multiple times no longer raises an exception (#1640).
+* Fixed a bug in include file resolution when compiling C extensions.
 
 New features:
 

lib/truffle/rbconfig-for-mkmf.rb

@@ -113,8 +113,14 @@
 expanded.merge!(common)
 mkconfig.merge!(common)
 
-mkconfig['COMPILE_C']   = "ruby #{cext_dir}/preprocess.rb $< | $(CC) $(INCFLAGS) $(CPPFLAGS) $(CFLAGS) $(COUTFLAG) -xc - -o $@ && #{opt} #{opt_passes} $@ -o $@"
-mkconfig['COMPILE_CXX'] = "ruby #{cext_dir}/preprocess.rb $< | $(CXX) $(INCFLAGS) $(CPPFLAGS) $(CXXFLAGS) $(COUTFLAG) -xc++ - -o $@ && #{opt} #{opt_passes} $@ -o $@"
+# We use -I$(<D) (the directory portion of the prerequisite - i.e. the
+# C or C++ file) to add the file's path as the first entry on the
+# include path. This is to ensure that files from the source file's
+# directory are include in preference to others on the include path,
+# and is required because we are actually piping the file into the
+# compiler which disables this standard behaviour of the C preprocessor.
+mkconfig['COMPILE_C']   = "ruby #{cext_dir}/preprocess.rb $< | $(CC) -I$(<D) $(INCFLAGS) $(CPPFLAGS) $(CFLAGS) $(COUTFLAG) -xc - -o $@ && #{opt} #{opt_passes} $@ -o $@"
+mkconfig['COMPILE_CXX'] = "ruby #{cext_dir}/preprocess.rb $< | $(CXX) -I$(<D) $(INCFLAGS) $(CPPFLAGS) $(CXXFLAGS) $(COUTFLAG) -xc++ - -o $@ && #{opt} #{opt_passes} $@ -o $@"
 
 # From mkmf.rb: "$(CC) #{OUTFLAG}#{CONFTEST}#{$EXEEXT} $(INCFLAGS) $(CPPFLAGS) $(CFLAGS) $(src) $(LIBPATH) $(LDFLAGS) $(ARCH_FLAG) $(LOCAL_LIBS) $(LIBS)"
 mkconfig['TRY_LINK'] = "#{cc} -o conftest $(INCFLAGS) $(CPPFLAGS) #{base_cflags} #{link_o_files} $(src) $(LIBPATH) $(LDFLAGS) $(ARCH_FLAG) $(LOCAL_LIBS) $(LIBS)"