How can attributes of a dependency (includes, compiler flags, etc.) be printed?

[wbthomason]

I'm building a C++ project with Meson and have an unexpected include directory added to my compiler args that's causing some problems. I'd like to be able to print the include directories and compiler args added by my external dependencies to debug this, but I haven't been able to figure out how to do so with Meson.

I'm aware of get_pkgconfig_variable, but (a) not all of my external dependencies are pkg-config dependencies and (b) I seem to be using this method incorrectly, e.g. some_dep.get_pkgconfig_variable('Cflags') tells me that the Cflags variable isn't defined for some_dep (Where some_dep.pc does have a Cflags variable defined, and I've tried all of CFlags, Cflags, and cflags in case capitalization is odd).

It seems like there should be some include_directories or includes attribute accessible for a dependency object, but I haven't been able to find anything like this. Is this possible with Meson, or am I out of luck?

Thanks!

[wbthomason]

As an additional note, I've tried printing the attributes defined in the base class (e.g. https://github.com/mesonbuild/meson/blob/master/mesonbuild/dependencies/base.py#L109), but I get an error "expecting lparen got rparen" indicating that the parser isn't happy. Specifically, I'm using warning(some_dep.compile_args), but get this error. Attempting to use the get_compile_args method instead fixes the parse error but complains that get_compile_args is an unknown method (though it seems to be defined here: https://github.com/mesonbuild/meson/blob/master/mesonbuild/dependencies/base.py#L121)

I'm using meson version 0.48.2 - is this method perhaps unreleased?

[jon-turney]

I agree some better way of inspecting the dependency is needed.

some_dep.get_pkgconfig_variable('Cflags') tells me that the Cflags variable isn't defined for some_dep (Where some_dep.pc does have a Cflags variable defined,

This detail is because cflags is a pkg-config keyword, not a variable. (See the metadata file syntax section in the pkg-config man-page). pkg-config --cflags is not the same as pkg-config --variable=cflags.

[dankegel]

This affects me, too. I desperately need a way to diagnose dependency problems.
It would be cool if message(dep) worked, at least.

[nirbheek]

It would be cool if message(dep) worked, at least.

Sounds like a useful feature to have, would you like to whip up a patch? Just implementing __repr__ should suffice.

[dankegel]

Like this? https://github.com/mesonbuild/meson/blob/master/mesonbuild/dependencies/base.py#L120

Lessee:

$ cat meson.build 
project('demo', 'c', version : '1.0', license : 'GPL')
zdep = dependency('zlib')
if zdep.found()
  message('blah @0@'.format(zdep))
  message(zdep)
endif

$ meson . foo
The Meson build system
Version: 0.50.0
...
Found pkg-config: /usr/bin/pkg-config (0.29.1)
Dependency zlib found: YES 1.2.11
Message: blah <Holder: <PkgConfigDependency zlib: True None>>

meson.build:5:2: ERROR: Function accepts only strings, integers, lists and lists thereof.

So it's there, but not very useful yet, and has to be accessed indirectly.

Changing base.py as follows:

--- a/mesonbuild/dependencies/base.py
+++ b/mesonbuild/dependencies/base.py
@@ -602,9 +602,10 @@ class PkgConfigDependency(ExternalDependency):
         self.is_found = True
 
     def __repr__(self):
-        s = '<{0} {1}: {2} {3}>'
+        s = '<{0} {1}: {2} {3} compile_args: {4} link_args {5}>'
         return s.format(self.__class__.__name__, self.name, self.is_found,
-                        self.version_reqs)
+                        self.version_reqs,
+                        self.compile_args, self.link_args)

makes the demo output

Message: blah <Holder: <PkgConfigDependency zlib: True None compile_args: [] link_args ['/usr/lib/x86_64-linux-gnu/libz.so']>>

and I guess that's useful enough for the moment. What would a real solution look like?

[pevik]

People just print it manually (which is horrible, upstream support would be nice):
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/blob/master/meson.build#L894

output = '\nSystem paths:\n'
output += '  prefix: ' + nm_prefix + '\n'
output += '  exec_prefix: ' + nm_prefix + '\n'
output += '  systemdunitdir: ' + systemd_systemdsystemunitdir + '\n'
...
output += '\nFeatures:\n'
output += '  wext: ' + enable_wext.to_string() + '\n'
output += '  wifi: ' + enable_wifi.to_string() + '\n'
output += '  iwd:  ' + enable_iwd.to_string() + '\n'
output += '  pppd: ' + enable_ppp.to_string()
if enable_ppp
  output += ' ' + pppd_path + ' plugins:' + pppd_plugin_dir
endif
output += '\n'
...
output += '  ebpf: ' + enable_ebpf.to_string() + '\n'
message(output)

[Makogan]

I would find this useful too!

[eli-schwartz]

@pevik Manually printing lots of strings could be a lot less ugly, simply by using summary() instead of manual string formatted message(). This does require meson 0.53

That being said, I don't see how this at all helps people seeking to print out the compile/link args.

@Makogan @wbthomason

in builddir/meson-logs/meson-log.txt you will find a lot of debug info about how meson resolved the build definition. For example, you will see log lines like this:

Determining dependency 'libcurl' with pkg-config executable '/usr/bin/pkg-config'
env[PKG_CONFIG_PATH]: 
Called `/usr/bin/pkg-config --modversion libcurl` -> 0
7.79.1
env[PKG_CONFIG_PATH]: 
Called `/usr/bin/pkg-config --cflags libcurl` -> 0

env[PKG_CONFIG_ALLOW_SYSTEM_LIBS]: 1
env[PKG_CONFIG_PATH]: 
Called `/usr/bin/pkg-config --libs libcurl` -> 0
-L/usr/lib -lcurl
env[PKG_CONFIG_PATH]: 
Called `/usr/bin/pkg-config --libs libcurl` -> 0
-lcurl
Run-time dependency libcurl found: YES 7.79.1

Is this sufficiently helpful for your needs?

[pevik]

@pevik Manually printing lots of strings could be a lot less ugly, simply by using summary() instead of manual string formatted message(). This does require meson 0.53

@eli-schwartz Thanks a lot. 0.53 might be still quite new for projects which want to support LTS distros, but that's just a question of time.

[eli-schwartz]

https://repology.org/project/meson/versions
Debian stable and the latest Ubuntu LTS do have it. Debian oldstable does not have it unless you enable backports. Ubuntu 18.04 doesn't have it at all. Of course, make your own cost-benefit analysis.

[robUx4]

Almost 4 years and there's still no way to print compiler flags / link libraries for a dependency ?

[germandiagogomez]

Same problem here.

[CarloWood]

6 years