cerbero: Refactor variant handling in platform config files

While parsing config files such as the platform config files, we were
exposing variants as an unresolved `list` of "operations" that will
enable or disable the variant once they've all been resolved

This is buggy because it means that platform config files have no way
to know whether a variant has actually been disabled or enabled by the
user.

Now we always parse variants into the `Variants` object before parsing
all configuration files.

Part-of: <https://gitlab.freedesktop.org/gstreamer/cerbero/-/merge_requests/480>

12 files changed, 24 insertions, 43 deletions

diff --git a/config/android.config b/config/android.config
index c3c170f1..199c8e27 100644
--- a/config/android.config
+++ b/config/android.config
@@ -26,7 +26,7 @@ import cerbero.utils.messages as m
 # sysroot: location of the API-level libraries (no headers)
 # isysroot: location of the headers
 
-variants += ['nopython', 'notestspackage']
+variants.override(['nopython', 'notestspackage'])
 
 # We don't want anything from linux system to be used on android :)
 allow_system_libs=False
@@ -116,7 +116,7 @@ env['ANDROID_NDK'] = toolchain_prefix
 # so that we can construct different paths to include/lib directories to where
 # they actually are.  Without this we don't know where the headers/libs will
 # actually end up
-if 'universal' in variants:
+if universal_archs:
     incl_dir = os.path.join(prefix, _cerbero_arch, 'include')
     lib_dir = os.path.join(prefix, _cerbero_arch, 'lib')
 else:
diff --git a/config/cross-android-arm64.cbc b/config/cross-android-arm64.cbc
index ab90259b..fc495db2 100644
--- a/config/cross-android-arm64.cbc
+++ b/config/cross-android-arm64.cbc
@@ -6,4 +6,4 @@ target_distro = Distro.ANDROID
 target_distro_version = DistroVersion.ANDROID_LOLLIPOP
 target_arch = Architecture.ARM64
 
-#variants = ['nodebug']
+#variants.override('nodebug')
diff --git a/config/cross-android-armv7.cbc b/config/cross-android-armv7.cbc
index 9f0eb2f2..1b30fb26 100644
--- a/config/cross-android-armv7.cbc
+++ b/config/cross-android-armv7.cbc
@@ -6,4 +6,4 @@ target_distro = Distro.ANDROID
 target_distro_version = DistroVersion.ANDROID_JELLY_BEAN
 target_arch = Architecture.ARMv7
 
-#variants = ['nodebug']
+variants.override('nodebug')
diff --git a/config/cross-android-universal.cbc b/config/cross-android-universal.cbc
index 81a3f3a7..9f204a3e 100644
--- a/config/cross-android-universal.cbc
+++ b/config/cross-android-universal.cbc
@@ -15,5 +15,5 @@ universal_archs = {
             Architecture.X86_64: "cross-android-x86-64.cbc",
         }
 
-#variants = ['nodebug']
+#variants.override('nodebug')
 allow_parallel_build = True
diff --git a/config/cross-android-x86-64.cbc b/config/cross-android-x86-64.cbc
index 43f77af1..d17af197 100644
--- a/config/cross-android-x86-64.cbc
+++ b/config/cross-android-x86-64.cbc
@@ -6,4 +6,4 @@ target_distro = Distro.ANDROID
 target_distro_version = DistroVersion.ANDROID_LOLLIPOP
 target_arch = Architecture.X86_64
 
-#variants = ['nodebug']
+#variants.override('nodebug')
diff --git a/config/cross-android-x86.cbc b/config/cross-android-x86.cbc
index 1ed47611..fa551bcb 100644
--- a/config/cross-android-x86.cbc
+++ b/config/cross-android-x86.cbc
@@ -6,4 +6,4 @@ target_distro = Distro.ANDROID
 target_distro_version = DistroVersion.ANDROID_JELLY_BEAN
 target_arch = Architecture.X86
 
-#variants = ['nodebug']
+#variants.override('nodebug')
diff --git a/config/cross-lin-arm.cbc b/config/cross-lin-arm.cbc
index fc5c8331..03765ed8 100644
--- a/config/cross-lin-arm.cbc
+++ b/config/cross-lin-arm.cbc
@@ -4,5 +4,5 @@ from cerbero.config import Platform, Architecture, Distro, DistroVersion
 target_platform = Platform.LINUX
 target_distro = Distro.DEBIAN
 target_arch = Architecture.ARMv7
-variants = ['noalsa', 'nox11', 'nopulse', 'nocdparanoia', 'nosdl',
-            'nov4l2', 'notestspackage', 'nopython']
+variants.override(['noalsa', 'nox11', 'nopulse', 'nocdparanoia', 'nosdl',
+                   'nov4l2', 'notestspackage', 'nopython'])
diff --git a/config/cross-lin-arm64.cbc b/config/cross-lin-arm64.cbc
index cec3a4dd..fedef53d 100644
--- a/config/cross-lin-arm64.cbc
+++ b/config/cross-lin-arm64.cbc
@@ -4,8 +4,8 @@ from cerbero.config import Platform, Architecture, Distro, DistroVersion
 target_platform = Platform.LINUX
 target_distro = Distro.DEBIAN
 target_arch = Architecture.ARM64
-variants = ['noalsa', 'nox11', 'nopulse', 'nocdparanoia', 'nosdl',
-            'nov4l2', 'notestspackage', 'nopython']
+variants.override(['noalsa', 'nox11', 'nopulse', 'nocdparanoia', 'nosdl',
+                   'nov4l2', 'notestspackage', 'nopython'])
 
 extra_bootstrap_packages = {
     Platform.LINUX : {
diff --git a/config/darwin.config b/config/darwin.config
index 22b6af3a..a4dcf4dc 100644
--- a/config/darwin.config
+++ b/config/darwin.config
@@ -12,8 +12,8 @@ from cerbero.errors import FatalError
 # used later. System libs are passed through the -isysroot option
 allow_system_libs=False
 
-if 'nogi' not in variants:
-    variants.append('gi')
+# Enable introspection by default
+variants.override('gi')
 
 if target_arch == Architecture.X86_64:
     build='x86_64-apple-darwin12'
diff --git a/config/ios.config b/config/ios.config
index dd212b23..4f4bb0dc 100644
--- a/config/ios.config
+++ b/config/ios.config
@@ -9,7 +9,7 @@ from cerbero.utils import shell
 from cerbero.config import Architecture, DistroVersion
 from cerbero.errors import FatalError
 
-variants += ['nopython', 'notestspackage']
+variants.override(['nopython', 'notestspackage'])
 
 # We don't want anything from macports detected in configure and
 # used later. System libs are passed through the -isysroot option
@@ -95,7 +95,7 @@ else:
   raise FatalError("Arch %s not supported" % target_arch)
 
 includedir = os.path.join(prefix, 'include')
-if 'universal' in variants:
+if universal_archs:
     lib_dir = os.path.join(prefix, target_arch, 'lib')
 else:
     lib_dir = os.path.join(prefix, 'lib')
diff --git a/config/linux.config b/config/linux.config
index 370c1e7d..77ef1f91 100644
--- a/config/linux.config
+++ b/config/linux.config
@@ -6,20 +6,8 @@
 import os
 from cerbero.config import Architecture, Distro
 
-if 'noalsa' not in variants:
-    variants.append('alsa')
-if 'nox11' not in variants:
-    variants.append('x11')
-if 'nopulse' not in variants:
-    variants.append('pulse')
-if 'nocdparanoia' not in variants:
-    variants.append('cdparanoia')
-if 'nov4l2' not in variants:
-    variants.append('v4l2')
-if 'nogi' not in variants:
-    variants.append('gi')
-if 'nounwind' not in variants:
-    variants.append('unwind')
+# Set default values for some optional variants
+variants.override(['alsa', 'x11', 'pulse', 'cdparanoia', 'v4l2', 'gi', 'unwind'])
 
 for f in ['CPPFLAGS', 'CFLAGS', 'CCASFLAGS', 'CXXFLAGS', 'LDFLAGS',
           'OBJCFLAGS']:
@@ -89,8 +77,7 @@ if target_arch != arch:
     if distro == Distro.REDHAT:
         workaround_cflags += '-I/usr/arm-linux-gnu/include'
     # Disable gi if we are cross-compiling
-    if 'gi' in variants:
-        variants.remove('gi')
+    variants.gi = False
 
 env['CFLAGS'] += arch_flags + workaround_cflags
 env['CXXFLAGS'] += arch_flags + workaround_cflags
diff --git a/config/windows.config b/config/windows.config
index d6bf61e7..aac941bd 100644
--- a/config/windows.config
+++ b/config/windows.config
@@ -9,12 +9,6 @@ from cerbero.config import Architecture, Platform
 # used later.
 allow_system_libs = False
 
-# We currently don't use Visual Studio by default anywhere
-if 'visualstudio' not in variants:
-    variants.append('novisualstudio')
-if 'uwp' not in variants:
-    variants.append('nouwp')
-
 if platform == Platform.WINDOWS:
     separator = ';'
     if target_arch == Architecture.X86:
@@ -67,7 +61,7 @@ def cmd(command, args='', wrapper=''):
 target_winver = '0x0601'
 
 # Default GCC compiler flags
-if not for_shell or 'novisualstudio' in variants:
+if not for_shell or not variants.visualstudio:
     env['CFLAGS'] = arch_flags
     env['CPPFLAGS'] = arch_flags
     env['CASFLAGS'] = arch_flags
@@ -76,7 +70,7 @@ if not for_shell or 'novisualstudio' in variants:
 else:
     env['CFLAGS'] = ''
     env['CPPFLAGS'] = ''
-    if 'uwp' in variants:
+    if variants.uwp:
         # Target distro for UWP is Windows 10
         target_winver = '0x0A00'
         # Setting WINAPI_FAMILY to APP allows us to get link-time errors for
@@ -105,7 +99,7 @@ env['DLLTOOL'] = cmd('dlltool', dlltool_flags)
 # Ensure that we never accidentally use MSYS/MinGW objc/c++ compilers
 env['OBJC'] = 'false'
 env['OBJCXX'] = 'false'
-if not for_shell or 'novisualstudio' in variants:
+if not for_shell or not variants.visualstudio:
     env['LIBRARY_PATH'] = "{0}/lib{1}".format(prefix, lib_suffix)
     env['CC'] = cmd('gcc', arch_flags, ccache)
     env['CXX'] = cmd('g++', arch_flags, ccache)
@@ -139,13 +133,13 @@ if platform == Platform.WINDOWS:
     # Only use one process to make the build more reliable.
     allow_parallel_build = False
 
-if platform == Platform.WINDOWS and 'visualstudio' in variants:
+if platform == Platform.WINDOWS and variants.visualstudio:
     from cerbero.ide.vs.env import get_msvc_env, append_path
     # Contains only the env vars that MSVC needs, including any existing vars
     # that were appended/prepended and have new values
     # FIXME: Use EnvVarOp class from cerbero/build/build.py
     msvc_toolchain_env = {}
-    env, msvc_version = get_msvc_env(arch, target_arch, 'uwp' in variants,
+    env, msvc_version = get_msvc_env(arch, target_arch, variants.uwp,
                                      vs_install_version, vs_install_path)
     for key, value in env.items():
         if key in ('PATH', 'PATHEXT', 'INCLUDE', 'LIB'):
@@ -161,7 +155,7 @@ if platform == Platform.WINDOWS and 'visualstudio' in variants:
     msvc_toolchain_env['LIB'][0] = append_path(msvc_toolchain_env['LIB'][0],
                                                os.path.join(prefix, 'lib' + lib_suffix))
     msvc_toolchain_env['WINDRES'] = ['rc', '']
-    if 'uwp' in variants:
+    if variants.uwp:
         meson_cross_properties['needs_exe_wrapper'] = 'true'
 
     # If no BOM is found from source file, msvc assumes the file is encoded