meson: turn `glvnd` option into a feature

Makes for nicer code, and allows the next commit.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26367>

.gitlab-ci/build/gitlab-ci.yml

@@ -265,7 +265,7 @@ alpine-build-testing:
       -D glx=disabled
       -D gbm=enabled
       -D egl=enabled
-      -D glvnd=false
+      -D glvnd=disabled
       -D platforms=wayland
     LLVM_VERSION: "16"
     GALLIUM_DRIVERS: "crocus,etnaviv,freedreno,iris,kmsro,lima,nouveau,panfrost,r300,r600,radeonsi,svga,swrast,tegra,v3d,vc4,virgl,zink"
@@ -305,7 +305,7 @@ fedora-release:
       -D glx=dri
       -D gbm=enabled
       -D egl=enabled
-      -D glvnd=true
+      -D glvnd=enabled
       -D platforms=x11,wayland
     EXTRA_OPTION: >
       -D b_lto=true
@@ -540,7 +540,7 @@ debian-clang:
       -D glx=dri
       -D gbm=enabled
       -D egl=enabled
-      -D glvnd=true
+      -D glvnd=enabled
       -D platforms=x11,wayland
     GALLIUM_ST: >
       -D dri3=enabled

docs/drivers/svga3d.rst

@@ -122,7 +122,7 @@ Building the Code
    ::
 
       cd $TOP/mesa
-      meson builddir -Dvulkan-drivers= -Dgallium-drivers=svga -Ddri-drivers= -Dglvnd=true -Dglvnd-vendor-name=mesa
+      meson builddir -Dvulkan-drivers= -Dgallium-drivers=svga -Ddri-drivers= -Dglvnd=enabled -Dglvnd-vendor-name=mesa
 
       meson compile -C builddir
       sudo meson install -C builddir

meson.build

@@ -543,20 +543,18 @@ if with_glx != 'disabled'
   endif
 endif
 
-dep_glvnd = null_dep
-with_glvnd = get_option('glvnd')
+_glvnd = get_option('glvnd') \
+  .require(not with_platform_windows,
+           error_message: 'glvnd cannot be used on Windows') \
+  .require(with_glx != 'xlib',
+           error_message: 'Cannot build glvnd support for GLX that is not DRI based.') \
+  .require(with_glx != 'disabled' or with_egl,
+           error_message: 'glvnd requires DRI based GLX and/or EGL') \
+  .require(get_option('egl-lib-suffix') == '',
+           error_message: '''EGL lib suffix can't be used with libglvnd''')
+dep_glvnd = dependency('libglvnd', version : '>= 1.3.2', required : _glvnd)
+with_glvnd = dep_glvnd.found()
 if with_glvnd
-  if with_platform_windows
-    error('glvnd cannot be used on Windows')
-  elif with_glx == 'xlib'
-    error('Cannot build glvnd support for GLX that is not DRI based.')
-  elif with_glx == 'disabled' and not with_egl
-    error('glvnd requires DRI based GLX and/or EGL')
-  endif
-  if get_option('egl-lib-suffix') != ''
-    error('''EGL lib suffix can't be used with libglvnd''')
-  endif
-  dep_glvnd = dependency('libglvnd', version : '>= 1.3.2')
   pre_args += '-DUSE_LIBGLVND=1'
 endif
 glvnd_vendor_name = get_option('glvnd-vendor-name')

meson_options.txt

@@ -361,8 +361,9 @@ option(
 
 option(
   'glvnd',
-  type : 'boolean',
-  value : false,
+  type : 'feature',
+  value : 'disabled',
+  deprecated: {'true': 'enabled', 'false': 'disabled'},
   description : 'Enable GLVND support.'
 )