Implement `bootstrap-gstreamer` for all platforms

This change makes it so that the Platform classes can now handle
installing GStreamer dependencies and properly setting up the
environment including when cross-compiling. For Windows and Linux
is now installed into `target/dependencies/gstreamer` when not installed
system-wide. In addition:

1. Creating and moving existing environment path append helpers to
   `util.py`.
2. Combining the `set_run_env` and `build_dev` functions and moving
   some outside code into them so that it can be shared. Now code that
   used to call `set_run_env` calls `build_dev` and then
   `os.environ.update(...)`.
3. Adding Python typing information in many places.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

1 files changed, 18 insertions, 8 deletions

diff --git a/python/servo/platform/__init__.py b/python/servo/platform/__init__.py
index 84968550d00..e06bebaf863 100644
--- a/python/servo/platform/__init__.py
+++ b/python/servo/platform/__init__.py
@@ -9,9 +9,10 @@
 
 import platform
 
-from .base import Base
 from .windows import Windows
 
+__platform__ = None
+
 
 def host_platform():
     os_type = platform.system().lower()
@@ -47,18 +48,27 @@ def host_triple():
 
 
 def get():
+    # pylint: disable=global-statement
+    global __platform__
+    if __platform__:
+        return __platform__
+
     # We import the concrete platforms in if-statements here, because
     # each one might have platform-specific imports which might not
     # resolve on all platforms.
     # TODO(mrobinson): We should do this for Windows too, once we
     # stop relying on platform-specific code outside of this module.
     # pylint: disable=import-outside-toplevel
-    if "windows-msvc" in host_triple():
-        return Windows()
-    if "linux-gnu" in host_triple():
+    triple = host_triple()
+    if "windows-msvc" in triple:
+        __platform__ = Windows(triple)
+    elif "linux-gnu" in triple:
         from .linux import Linux
-        return Linux()
-    if "apple-darwin" in host_triple():
+        __platform__ = Linux(triple)
+    elif "apple-darwin" in triple:
         from .macos import MacOS
-        return MacOS()
-    return Base()
+        __platform__ = MacOS(triple)
+    else:
+        from .base import Base
+        __platform__ = Base(triple)
+    return __platform__