cc.find_library(...).as_system() throws "Unknown method" error

[kusma]

Calling compler.find_library(...).as_system() fails with the following error:

meson.build:3:42: ERROR: Unknown method "as_system" in object <[ExternalLibraryHolder] holds [ExternalLibrary]: <ExternalLibrary m: True>> of type ExternalLibraryHolder.

However, according to the dep documentation, compiler.find_library() is supposed to return a dep object, that has the as_system() method.

The more complete use-case I have, is to allow specifying the path to a mingw-build of GLUT when cross-compiling, while converting the include path to a system include (-isystem) so the code still can include <GL/glut.h>. The build of GLUT I have ships without .pc files, so I can't really use a dependecy() here...

glut_libdir = []
glut_incdir = []
with_glut = get_option('with-glut')
if with_glut != ''
  glut_libdir = with_glut / 'lib'
  glut_incdir = with_glut / 'include'
endif

dep_glut = cc.find_library(
  'glut',
  dirs: glut_libdir,
  has_headers: 'GL/glut.h',
  header_include_directories: include_directories(glut_incdir)).as_system()

To Reproduce

Try compiling this project

project('meson-repro', 'c')
meson.get_compiler('c').find_library('m').as_system()

Expected behavior

I expect the as_system() function to work, as the documentation suggests

system parameters

• Happens for both when cross-compiling and when building native
• Debian Sid
• Python 3.10.4
• Meson 0.62.0
• Ninja 1.10.1

[kusma]

Just to be clear, I'm aware that I can do include_directories(glut_incdir, is_system: true) instead, I just wanted to report this issue!

[eli-schwartz]

find_library() doesn't produce a dep object that has an include_directories() object as part of its interface. The as_system() method mutates the include_directories aspect of a dependency.

No, using header_include_directories does NOT make the returned ExternalLibrary object have an include_directories interface to mutate.

Since ExternalLibrary doesn't have anything for as_system to modify it makes no sense for it to allow such a method. The documentation is at fault for implying that a dependency() and a find_library() are identical -- they are not, even if the latter can generally be passed to any kwarg that accepts the former.

[kusma]

Yeah, I guess it's fair to say that this is a documentation bug, then.

[sla89]

I am new to meson and also came accross this issue since the documentation is still wrong about this topic. :(

So the solution is to use cc.find_library like this:

glut_incdir = 'some/path/to/headers'
dep_glut = cc.find_library(
  'glut',
  dirs: glut_libdir,
  has_headers: 'GL/glut.h',
  header_include_directories: include_directories(glut_incdir, is_system: true))

That does not work in all cases, see https://github.com/mesonbuild/meson/issues/13611 Thank you for your support!