mach: switch to `uv` for managing python venv (#34504)

This patch switches servo to use `uv` for both installing a pinned
Python version as well as installing the dependency packages using
`uv`'s pip compatible interface. It also introduces a new 'composite'
GitHub action to setup python in the different CI workflows.

There is no support for externally managed python installations and
virtual environments. These could be added in the future.

Fixes #34095

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

1 files changed, 15 insertions, 19 deletions

diff --git a/python/mach_bootstrap.py b/python/mach_bootstrap.py
index 43690c3d951..fc6e916ff80 100644
--- a/python/mach_bootstrap.py
+++ b/python/mach_bootstrap.py
@@ -4,7 +4,6 @@
 
 import hashlib
 import os
-import platform
 import site
 import subprocess
 import sys
@@ -93,11 +92,13 @@ def _get_virtualenv_script_dir():
 def _get_virtualenv_lib_dir():
     if os.name == "nt" and os.sep != "/":
         return os.path.join("Lib", "site-packages")
-    return os.path.join(
-        "lib",
-        f"python{sys.version_info[0]}.{sys.version_info[1]}",
-        "site-packages"
-    )
+    with open(".python-version", "r") as python_version_file:
+        python_version = python_version_file.read().strip()
+        return os.path.join(
+            "lib",
+            f"python{python_version}",
+            "site-packages"
+        )
 
 
 def _process_exec(args):
@@ -131,11 +132,8 @@ def install_virtual_env_requirements(project_path: str, python: str, virtualenv_
     requirements_hash = requirements_hasher.hexdigest()
 
     if marker_hash != requirements_hash:
-        print(" * Upgrading pip...")
-        _process_exec([python, "-m", "pip", "install", "--upgrade", "pip"])
-
         print(" * Installing Python requirements...")
-        _process_exec([python, "-m", "pip", "install", "-I",
+        _process_exec(["uv", "pip", "install",
                        "-r", requirements_paths[0],
                        "-r", requirements_paths[1],
                        "-r", requirements_paths[2]])
@@ -144,14 +142,14 @@ def install_virtual_env_requirements(project_path: str, python: str, virtualenv_
 
 
 def _activate_virtualenv(topdir):
-    virtualenv_path = os.path.join(topdir, "python", "_venv%d.%d" % (sys.version_info[0], sys.version_info[1]))
+    virtualenv_path = os.path.join(topdir, ".venv")
     python = sys.executable
 
     if os.environ.get("VIRTUAL_ENV") != virtualenv_path:
         venv_script_path = os.path.join(virtualenv_path, _get_virtualenv_script_dir())
         if not os.path.exists(virtualenv_path):
             print(" * Setting up virtual environment...")
-            _process_exec([python, "-m", "venv", "--system-site-packages", virtualenv_path])
+            _process_exec(["uv", "venv"])
 
         # This general approach is taken from virtualenv's `activate_this.py`.
         os.environ["PATH"] = os.pathsep.join([venv_script_path, *os.environ.get("PATH", "").split(os.pathsep)])
@@ -171,6 +169,11 @@ def _activate_virtualenv(topdir):
 
     install_virtual_env_requirements(topdir, python, virtualenv_path)
 
+    # Turn off warnings about deprecated syntax in our indirect dependencies.
+    # TODO: Find a better approach for doing this.
+    import warnings
+    warnings.filterwarnings('ignore', category=SyntaxWarning, module=r'.*.venv')
+
 
 def _ensure_case_insensitive_if_windows():
     # The folder is called 'python'. By deliberately checking for it with the wrong case, we determine if the file
@@ -221,13 +224,6 @@ def bootstrap(topdir):
         print('Current path:', topdir)
         sys.exit(1)
 
-    # Ensure we are running Python 3.10+. We put this check here so we generate a
-    # user-friendly error message rather than a cryptic stack trace on module import.
-    if sys.version_info < (3, 10):
-        print('Python3 (>=3.10) is required to run mach.')
-        print('You are running Python', platform.python_version())
-        sys.exit(1)
-
     _activate_virtualenv(topdir)
 
     def populate_context(context, key=None):