Exclude a source file from the build

[ncoghlan]

I have a header file that I want to include to get access to some constants and enums exported by a library, but ct-cake is interpreting that as a request to build and statically link another copy of that library, which then fails at link time.

The SOURCE flag in https://github.com/Zomojo/compiletools/blob/master/README.ct-magicflags.rst offers a way to add extra files to the build, but is there a way to exclude particular headers from the process of finding source files?

[Zomojo-Geoff]

The very short answer is that as of 20190617 there is no exclude option.

Would it be possible to add in an EXCLUDE magicflag, the answer is yes, and patches will be happily accepted. :)

If you are looking for a quick workaround, then what we need to do is think up a way of putting the header in question into a directory separate from the cpp.

<#untested air coding>
Perhaps something like

|_ myinc\
|_______\awesome.hpp
|_ mylib\
| ______\awesome.cpp
|_myexe
|_______\main.cpp

then awesome.cpp will

#include "../myinc/awesome.hpp"

and it will naturally build into libawesome

main.cpp would be something like

#include "../myinc/awesome.hpp"
//#LDFLAGS=-lawesome

but when ct-cake goes hunting in myinc/ for the .cpp it wont find one and just move along, and the linker will be happy because it finds the required symbols inside libawesome.

</untested air coding>

[ncoghlan]

In this case, there's just the one numeric constant that I need from the header (an error code), so my workaround has been to redefine that constant in the cpp that needs it, with a link here to explain what we need to implement to get rid of the workaround.

I did try symlinking the header (and only the header) from a different directory first, but I think compiletools must be resolving the symlink before looking for adjacent cpp files. (It's a third party library, so we don't want to go changing its internal file layout or include statements).

If a new magic flag would be acceptable, how would you feel about NOSOURCE as the name?

EXCLUDES doesn't feel clear enough (What's being excluded from where?), but the idea behind NOSOURCE would be that where SOURCE means "add these extra files to the source list", "NOSOURCE" would mean "Don't infer any source files from the named header files".

[Zomojo-Geoff]

I like NOSOURCE. I agree with your reasoning that it is clear and matches SOURCE

[Zomojo-Geoff]

As for implementation, note that the MagicFlagsBase just does a regex and declares anything matching "//#key=value1 value2"
is a magicflag. From memory. all that needs to be added is the code into Hunter that will pay attention to NOSOURCE