Fix the build on Ubuntu 20.04 (servo#31019)

Ubuntu 20.04 doesn't have a new enough version of GStreamer, so
automatically disable media when running on that platform.

This also cleans up the media detection a bit, putting the result in a
`enable-media` variable and moving some of the logic into the build
scripts themselves rather than the platform module.

python/servo/build_commands.py

@@ -58,7 +58,6 @@ class MachCommands(CommandBase):
     def build(self, build_type: BuildType, jobs=None, params=None, no_package=False,
               verbose=False, very_verbose=False, libsimpleservo=False, **kwargs):
         opts = params or []
-        has_media_stack = "media-gstreamer" in self.features
 
         if build_type.is_release():
             opts += ["--release"]
@@ -74,7 +73,7 @@ def build(self, build_type: BuildType, jobs=None, params=None, no_package=False,
         if very_verbose:
             opts += ["-vv"]
 
-        env = self.build_env(is_build=True)
+        env = self.build_env()
         self.ensure_bootstrapped()
         self.ensure_clobbered()
 
@@ -173,7 +172,7 @@ def package_generated_shared_libraries(libs, build_path, servo_exe_dir):
                     status = 1
 
                 # copy needed gstreamer DLLs in to servo.exe dir
-                if has_media_stack:
+                if self.enable_media:
                     print("Packaging gstreamer DLLs")
                     if not package_gstreamer_dlls(env, servo_exe_dir, target_triple):
                         status = 1
@@ -189,7 +188,7 @@ def package_generated_shared_libraries(libs, build_path, servo_exe_dir):
                 servo_bin_dir = os.path.dirname(servo_path)
                 assert os.path.exists(servo_bin_dir)
 
-                if has_media_stack:
+                if self.enable_media:
                     print("Packaging gstreamer dylibs")
                     if not package_gstreamer_dylibs(self.cross_compile_target, servo_path):
                         return 1

python/servo/command_base.py

@@ -250,6 +250,7 @@ class CommandBase(object):
 
     def __init__(self, context):
         self.context = context
+        self.enable_media = False
         self.features = []
         self.cross_compile_target = None
         self.is_android_build = False
@@ -493,13 +494,13 @@ def vs_dirs(self):
             'vcdir': vcinstalldir,
         }
 
-    def build_env(self, is_build=False):
+    def build_env(self):
         """Return an extended environment dictionary."""
         env = os.environ.copy()
 
-        servo.platform.get().set_gstreamer_environment_variables_if_necessary(
-            env, cross_compilation_target=self.cross_compile_target,
-            check_installation=is_build)
+        if self.enable_media and not self.is_android_build:
+            servo.platform.get().set_gstreamer_environment_variables_if_necessary(
+                env, cross_compilation_target=self.cross_compile_target)
 
         effective_target = self.cross_compile_target or servo.platform.host_triple()
         if "msvc" in effective_target:
@@ -806,7 +807,7 @@ def configuration_decorator(self, *args, **kwargs):
                 if build_configuration:
                     self.configure_cross_compilation(kwargs['target'], kwargs['android'], kwargs['win_arm64'])
                     self.features = kwargs.get("features", None) or []
-                    self.configure_media_stack(kwargs['media_stack'])
+                    self.enable_media = self.is_media_enabled(kwargs['media_stack'])
 
                 return original_function(self, *args, **kwargs)
 
@@ -874,10 +875,10 @@ def configure_cross_compilation(
         if self.cross_compile_target:
             print(f"Targeting '{self.cross_compile_target}' for cross-compilation")
 
-    def configure_media_stack(self, media_stack: Optional[str]):
-        """Determine what media stack to use based on the value of the build target
+    def is_media_enabled(self, media_stack: Optional[str]):
+        """Determine whether media is enabled based on the value of the build target
            platform and the value of the '--media-stack' command-line argument.
-           The chosen media stack is written into the `features` instance variable."""
+           Returns true if media is enabled."""
         if not media_stack:
             if self.config["build"]["media-stack"] != "auto":
                 media_stack = self.config["build"]["media-stack"]
@@ -890,8 +891,16 @@ def configure_media_stack(self, media_stack: Optional[str]):
                 media_stack = "gstreamer"
             else:
                 media_stack = "dummy"
-        if media_stack != "dummy":
-            self.features += ["media-" + media_stack]
+
+        # This is a workaround for Ubuntu 20.04, which doesn't support a new enough GStreamer.
+        # Once we drop support for this platform (it's currently needed for wpt.fyi runners),
+        # we can remove this workaround and officially only support Ubuntu 22.04 and up.
+        platform = servo.platform.get()
+        if not self.cross_compile_target and platform.is_linux and \
+                not platform.is_gstreamer_installed(self.cross_compile_target):
+            return False
+
+        return media_stack != "dummy"
 
     def run_cargo_build_like_command(
         self, command: str, cargo_args: List[str],
@@ -903,6 +912,17 @@ def run_cargo_build_like_command(
     ):
         env = env or self.build_env()
 
+        # Android GStreamer integration is handled elsewhere.
+        # NB: On non-Linux platforms we cannot check whether GStreamer is installed until
+        # environment variables are set via `self.build_env()`.
+        platform = servo.platform.get()
+        if self.enable_media and not self.is_android_build and \
+                not platform.is_gstreamer_installed(self.cross_compile_target):
+            raise FileNotFoundError(
+                "GStreamer libraries not found (>= version 1.18)."
+                "Please see installation instructions in README.md"
+            )
+
         args = []
         if "--manifest-path" not in cargo_args:
             if libsimpleservo or self.is_android_build:
@@ -922,6 +942,8 @@ def run_cargo_build_like_command(
 
         if "-p" not in cargo_args:  # We're building specific package, that may not have features
             features = list(self.features)
+            if self.enable_media:
+                features.append("media-gstreamer")
             if self.config["build"]["debug-mozjs"] or debug_mozjs:
                 features.append("debugmozjs")
 

python/servo/platform/base.py

@@ -26,11 +26,6 @@ def __init__(self, triple: str):
     def set_gstreamer_environment_variables_if_necessary(
         self, env: Dict[str, str], cross_compilation_target: Optional[str], check_installation=True
     ):
-        # Environment variables are not needed when cross-compiling on any platform other
-        # than Windows. GStreamer for Android is handled elsewhere.
-        if cross_compilation_target and (not self.is_windows or "android" in cross_compilation_target):
-            return
-
         # We may not need to update environment variables if GStreamer is installed
         # for the system on Linux.
         gstreamer_root = self.gstreamer_root(cross_compilation_target)
@@ -52,14 +47,6 @@ def set_gstreamer_environment_variables_if_necessary(
             )
             env["GST_PLUGIN_SYSTEM_PATH"] = os.path.join(gstreamer_root, "lib", "gstreamer-1.0")
 
-        # If we are not cross-compiling GStreamer must be installed for the system. In
-        # the cross-compilation case, we might be picking it up from another directory.
-        if check_installation and not self.is_gstreamer_installed(cross_compilation_target):
-            raise FileNotFoundError(
-                "GStreamer libraries not found (>= version 1.18)."
-                "Please see installation instructions in README.md"
-            )
-
     def gstreamer_root(self, _cross_compilation_target: Optional[str]) -> Optional[str]:
         raise NotImplementedError("Do not know how to get GStreamer path for platform.")
 

python/servo/platform/linux.py

@@ -12,7 +12,6 @@
 from typing import Optional, Tuple
 
 import distro
-from .. import util
 from .base import Base
 
 # Please keep these in sync with the packages on the wiki, using the instructions below
@@ -75,8 +74,6 @@
 
 GSTREAMER_URL = \
     "https://github.com/servo/servo-build-deps/releases/download/linux/gstreamer-1.16-x86_64-linux-gnu.20190515.tar.gz"
-PREPACKAGED_GSTREAMER_ROOT = \
-    os.path.join(util.get_target_dir(), "dependencies", "gstreamer")
 
 
 class Linux(Base):
@@ -154,7 +151,6 @@ def _platform_bootstrap(self, force: bool) -> bool:
                                       f"{self.distro}, please file a bug")
 
         installed_something = self.install_non_gstreamer_dependencies(force)
-        installed_something |= self._platform_bootstrap_gstreamer(force)
         return installed_something
 
     def install_non_gstreamer_dependencies(self, force: bool) -> bool:
@@ -199,18 +195,9 @@ def run_as_root(command, force=False):
         return True
 
     def gstreamer_root(self, cross_compilation_target: Optional[str]) -> Optional[str]:
-        if cross_compilation_target:
-            return None
-        if os.path.exists(PREPACKAGED_GSTREAMER_ROOT):
-            return PREPACKAGED_GSTREAMER_ROOT
-        # GStreamer might be installed system-wide, but we do not return a root in this
-        # case because we don't have to update environment variables.
         return None
 
-    def _platform_bootstrap_gstreamer(self, force: bool) -> bool:
-        if not force and self.is_gstreamer_installed(cross_compilation_target=None):
-            return False
-
+    def _platform_bootstrap_gstreamer(self, _force: bool) -> bool:
         raise EnvironmentError(
             "Bootstrapping GStreamer on Linux is not supported. "
             + "Please install it using your distribution package manager.")

python/servo/post_build_commands.py

@@ -266,7 +266,7 @@ def doc(self, params: List[str], **kwargs):
                     else:
                         copy2(full_name, destination)
 
-        env = self.build_env(is_build=True)
+        env = self.build_env()
         returncode = self.run_cargo_build_like_command("doc", params, env=env, **kwargs)
         if returncode:
             return returncode

python/servo/testing_commands.py

@@ -258,9 +258,7 @@ def test_unit(self, build_type: BuildType, test_name=None, package=None, bench=F
         if nocapture:
             args += ["--", "--nocapture"]
 
-        # We are setting is_build here to true, because running `cargo test` can trigger builds.
-        env = self.build_env(is_build=True)
-
+        env = self.build_env()
         return self.run_cargo_build_like_command(
             "bench" if bench else "test",
             args,