Re: Howto write GNUmakefile.preamble with using C API

[David Chisnall]

On 22 Jul 2008, at 11:01, Nicola Pero wrote:

> > If you want to migrate it to Objective-C, then rename your test.c  
> > file to
> > test.m, and slightly modify your GNUmakefile:
> > include $(GNUSTEP_MAKEFILES)/common.make
> > TOOL_NAME = test
> > test_OBJC_FILES = test.m
> > ADDITIONAL_OBJCFLAGS += $(shell mysql_config --cflags)
> > ADDITIONAL_TOOL_LIBS += $(shell mysql_config --libs)
> > include $(GNUSTEP_MAKEFILES)/tool.make
> >
> > It doesn't work
> > [...]
> > test.c:1:19: warning: mysql.h: No such file or directory
> > [...]
>
> Something is going wrong here - it was supposed to be compiling  
> test.m here,
> not test.c ;-)

This is a bug in GNUstep Make which I've encountered before.  It is  
due to the convoluted way in which it builds dependency chains.

When GS Make parses the _OBJC_FILES and _C_FILES lists, it performs a  
substitution of .c or .m to .o and then DISCARDS the information  
about the source.  It then uses implicit make rules to compile.  This  
is a really horrible way of doing things, because it means that  
having .c and .m (or .cpp) files with the same prefix, or renaming a  
file and changing its extension gives really unexpected results.

Possibly a better solution would be for the .o files to be  
named .c.o, .m.o, .cpp.o and so on, and the dependency rules  
constructed to match.  The two hundred layers of indirection in GS  
Make hurt my brain though, so I have no idea how easy this is.

The only work around I've found is to ensure that the prefix for  
every file is different and delete all of the .d files periodically.

> I suggest when you try to switch to Objective-C, create a new empty  
> directory,
> and put only test.m and your GNUmakefile in there.  Make sure to do  
> all changes
> to the GNUmakefile, then try again.

Removing the .d files and the .c file should be enough.

David