glx: provide the virtual GLX package

var/spack/repos/builtin/packages/mesa-glu/package.py

@@ -14,9 +14,7 @@ class MesaGlu(AutotoolsPackage):
 
     version('9.0.0', 'bbc57d4fe3bd3fb095bdbef6fcb977c4')
 
-    variant('mesa', default=True,
-       description='Usually depends on mesa, disable for accelerated OpenGL')
-    depends_on('mesa', when='+mesa')
+    depends_on('gl@3:')
 
     provides('glu@1.3')
 

var/spack/repos/builtin/packages/mesa/package.py

@@ -54,8 +54,8 @@ class Mesa(MesonPackage):
     variant('opengles', default=False, description="Enable OpenGL ES support.")
 
     # Provides
-    provides('gl@:4.5', when='+opengl')
-    provides('glx', when='+glx')
+    provides('gl@4.5', when='+opengl')
+    provides('glx@1.4', when='+glx')
     provides('egl', when='+egl')
 
     # Variant dependencies

var/spack/repos/builtin/packages/opengl/package.py

@@ -3,6 +3,8 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import sys
+
 from spack import *
 
 
@@ -18,6 +20,9 @@ class Opengl(Package):
     provides('gl@:4.1', when='@4.1:')
     provides('gl@:3.3', when='@3.3:')
 
+    if sys.platform != 'darwin':
+        provides('glx@1.4')
+
     # Override the fetcher method to throw a useful error message;
     # fixes GitHub issue (#7061) in which this package threw a
     # generic, uninformative error during the `fetch` step,