[Bug]: DLIB_IN_PROJECT_BUILD incorrectly puts -llapack into `Libs` of `dlib-1.pc`

[nh2]

What Operating System(s) are you seeing this problem on?

Linux (x86-64)

dlib version

19.24.4

Python version

No response

Compiler

GCC 13

Expected Behavior

No response

Current Behavior

With -DDLIB_IN_PROJECT_BUILD=on, dlib generates this .pc file:

Libs: -L${libdir} -ldlib -L/path/to/lapack-3/lib -llapack

This is wrong, because as far as I can tell, lapack is a private library to dlib (its types are not used in dlib's header files).

If shared linking is requested, it is enough that that the libdlib.so dynamically links against liblapack.so; a downstream compiler using -ldlib should only pass that flag, not -llapack.

-L/path/to/lapack-3/lib -llapack is only required for static linking, so these flags should be in Libs.private instead of Libs, see https://people.freedesktop.org/~dbn/pkg-config-guide.html#faq

My library z uses libx internally, but does not expose libx data types in its public API. What do I put in my z.pc file?

[...] If libx does not support pkg-config, add the necessary linker flags to Libs.private.

This was recently slightly incorrectly implemented in:

• https://github.com/davisking/dlib/pull/2923

---

As an aside, the .pc file should probably instead generate Requires / Requires.private listead of Libs* when blas/lapack were found via pkg-config in

https://github.com/davisking/dlib/blob/51c7a3597935ed2cb969521a0ada0b7209f78ec2/dlib/cmake_utils/find_blas.cmake#L67-L70

(explanation in the same pkg-config explanations section I linked above.

Steps to Reproduce

cmake with DDLIB_IN_PROJECT_BUILD=on.

Anything else?

No response

[nh2]

Hm, I might be wrong here.

Is e.g. https://github.com/davisking/dlib/blob/51c7a3597935ed2cb969521a0ada0b7209f78ec2/dlib/matrix/lapack/gesvd.h a header for public consumption?

I suspect that because it declares inline functions such as

https://github.com/davisking/dlib/blob/51c7a3597935ed2cb969521a0ada0b7209f78ec2/dlib/matrix/lapack/gesvd.h#L42-L51

-llapack actually has to be given even in the downstream project.

Let me know what's right!

[davisking]

Right, all the linear algebra stuff in dlib is templated and in headers. You don't even have to compile any of the .cpp files in dlib to use that stuff, so the client has to link to lapack.

[nh2]

All clear, then there is no bug here. Closing!