Bug 1645196: Tune git settings to improve performance r=rstewart

Also adds a warning if a user's git version is older than 2.24

Differential Revision: https://phabricator.services.mozilla.com/D82128

python/mozboot/mozboot/bootstrap.py

@@ -11,6 +11,7 @@ import platform
 import sys
 import subprocess
 import time
+from distutils.version import LooseVersion
 
 # NOTE: This script is intended to be run with a vanilla Python install.  We
 # have to rely on the standard library instead of Python 2+3 helpers like
@@ -43,9 +44,7 @@ from mozboot.void import VoidBootstrapper
 from mozboot.windows import WindowsBootstrapper
 from mozboot.mozillabuild import MozillaBuildBootstrapper
 from mozboot.mozconfig import find_mozconfig
-from mozboot.util import (
-    get_state_dir,
-)
+from mozboot.util import get_state_dir
 
 # Use distro package to retrieve linux platform information
 import distro
@@ -233,6 +232,15 @@ Proceed at your own peril.
 '''
 
 
+# Version 2.24 changes the "core.commitGraph" setting to be "True" by default.
+MINIMUM_RECOMMENDED_GIT_VERSION = LooseVersion('2.24')
+OLD_GIT_WARNING = '''
+You are running an older version of git ("{old_version}").
+We recommend upgrading to at least version "{minimum_recommended_version}" to improve
+performance.
+'''.strip()
+
+
 def update_or_create_build_telemetry_config(path):
     """Write a mach config file enabling build telemetry to `path`. If the file does not exist,
     create it. If it exists, add the new setting to the existing data.
@@ -802,6 +810,20 @@ def update_git_repo(git, url, dest):
 
 def configure_git(git, cinnabar, root_state_dir, top_src_dir):
     """Run the Git configuration steps."""
+    from mozversioncontrol import GitRepository
+
+    repository = GitRepository(top_src_dir)
+    git_version = LooseVersion(repository.tool_version)
+
+    if git_version < MINIMUM_RECOMMENDED_GIT_VERSION:
+        print(OLD_GIT_WARNING.format(
+            old_version=git_version,
+            minimum_recommended_version=MINIMUM_RECOMMENDED_GIT_VERSION))
+
+    if git_version >= LooseVersion('2.17'):
+        # "core.untrackedCache" has a bug before 2.17
+        repository.set_config('core.untrackedCache', 'true')
+
     cinnabar_dir = update_git_tools(git, root_state_dir, top_src_dir)
 
     if not cinnabar:

python/mozversioncontrol/mozversioncontrol/__init__.py

@@ -585,6 +585,9 @@ class GitRepository(Repository):
         finally:
             self._run('reset', 'HEAD~')
 
+    def set_config(self, name, value):
+        self._run('config', name, value)
+
 
 def get_repository_object(path, hg='hg', git='git'):
     '''Get a repository object for the repository at `path`.