Old-style [provides] depname=variable in wrap file overrides both cross and native dependencies

[Akaricchi]

Describe the bug

Suppose you have a project that contains both host-machine (i.e. 'cross') and build-machine (i.e. 'native') build targets. Both of them depend on libfoo. You are ok with using the system-provided libfoo for the native targets, and you also bundle a libfoo subproject for the cross targets.

The libfoo subproject does not call meson.override_dependency. You want to use the implicit dependency fallback, so you add the following to the wrap file:

[provide]
libfoo=libfoo_dep

In the main project you have:

libfoo = dependency('libfoo')
libfoo_native = dependency('libfoo', native : true)

exe = executable('mwtf', 'mwtf.c',
  dependencies : libfoo)

exe_native = executable('mwtf-native', 'mwtf.c',
  native : true,
  dependencies : libfoo_native)

Then you try to set up a cross build and get:

meson.build:12:0: ERROR: Tried to mix libraries for machines 0 and 1 in target 'mwtf-native' This is not possible in a cross build.

Line 12 here is where exe_native is defined. This happens because apparently both dependency() calls returned the same object, the cross version of libfoo.

To Reproduce

Download mwtf.tar.gz and try to build it in any cross environment.

Expected behavior

Removing the provides section and adding an explicit fallback to the first dependency call makes this example work as expected:

meson.build:7:0: ERROR: Dependency 'libfoo' is required but not found.

The first dependency() call returns the cross-libfoo from the subproject, while the second errors out because I obviously do not have a libfoo actually installed on my system.

I don't think it's ever reasonable to override both cross and native dependencies with the same object; that will just never work. Sadly it's not possible to specify which type of dependency to override inside the wrap file. Most of the time, you probably want the cross dependency overriden, although theoretically it is possible that some weird project expects to override native dependencies there. It is probably possible (although not trivial) to inspect the dependency object and figure out whether a cross or a native override was intended, but I don't know if we want to go that far.

system parameters

• Cross build
• openSUSE Tumbleweed
• Python 3.10.8
• Meson 1.0.0.rc1 (git dd25b88)
• Ninja 1.11.1

[Akaricchi]

It should be noted that calling meson.override_dependency() from libfoo does not support this use-case either, sadly. It doesn't override the native dependency, but it does not allow a system fallback, either:

Dependency libfoo found: YES 0.1 (overridden)
WARNING: Subproject 'libfoo' did not override 'libfoo' dependency and no variable name specified
Dependency libfoo from subproject subprojects/libfoo found: NO

meson.build:7:0: ERROR: Dependency 'libfoo' is required but not found.

[dcbaker]

This is probably related to #11121, but this should be fixable before that.