meson: fix warnings about comparing unlike types

In the old days (0.42.x), when mesa's meson system was written the
recommendation for handling conditional dependencies was to define them
as empty lists. When meson would evaluate the dependencies of a target
it would recursively flatten all of the arguments, and empty lists would
be removed. There are some problems with this, among them that lists and
dependencies have different methods (namely .found()), so the
recommendation changed to use `dependency('', required : false)` for
such cases.  This has the advantage of providing a .found() method, so
there is no need to do things like `dep_foo != [] and dep_foo.found()`,
such a dependency should never exist.

I've tested this with 0.42 (the minimum we claim to support) and 0.45.
On 0.45 this removes warnings about comparing unlike types, such as:

meson.build:1337: WARNING: Trying to compare values of different types
(DependencyHolder, list) using !=.

v2: - Use dependency('', required : false) instead of
      declare_dependency(), the later will always report that it is
      found, which is not what we want.

Signed-off-by: Dylan Baker <[email protected]>
Reviewed-by: Caio Marcelo de Oliveira Filho <[email protected]>

2 files changed, 2 insertions, 2 deletions

diff --git a/src/glx/apple/meson.build b/src/glx/apple/meson.build
index 2d1014da0f8..c6b1d617c4f 100644
--- a/src/glx/apple/meson.build
+++ b/src/glx/apple/meson.build
@@ -46,7 +46,7 @@ files_libappleglx = files(
   'glx_empty.c',
 )
 
-dep_xplugin = []
+dep_xplugin = null_dep
 if with_dri_platform == 'apple'
   dep_xplugin = meson.get_compiler('c').find_library('Xplugin')
 endif
diff --git a/src/glx/meson.build b/src/glx/meson.build
index 7ac46ac0662..90ab552ac4d 100644
--- a/src/glx/meson.build
+++ b/src/glx/meson.build
@@ -137,7 +137,7 @@ gl_lib_cargs = [
   '-DDEFAULT_DRIVER_DIR="@0@"'.format(dri_search_path),
 ]
 
-if dep_xxf86vm != [] and dep_xxf86vm.found()
+if dep_xxf86vm.found()
   gl_lib_cargs += '-DHAVE_XF86VIDMODE'
 endif