prepare-commit-msg hook doesn't generate a changed file list with Win…

…dows Git

https://bugs.webkit.org/show_bug.cgi?id=261097

Reviewed by Jonathan Bedard.

prepare-ChangeLog reproted "Can't locate VCSUtils.pm in @inc" error if
it was executed from prepare-commit-msg hook of Windows Git. It failed
to set a library path to 'Tools/Scripts' directory.

Windows Git includes msys perl. prepare-commit-msg hook unexpectedly
executed it. It should execute Windows Perl.

Use shutil.which to get perl's absolute path. But, it's available for
Python 3.3 or newer. Windows port developers have been switched to
Python 3. Use the original relative command name 'perl' for older
Python.

* Tools/Scripts/hooks/prepare-commit-msg:
* Tools/Scripts/libraries/webkitscmpy/webkitscmpy/program/install_hooks.py:
* (InstallHooks.main): Added a new template variable 'perl' to set
perl's absolute path.

Canonical link: https://commits.webkit.org/267649@main

Tools/Scripts/hooks/prepare-commit-msg

@@ -106,7 +106,7 @@ def parseChanges(command, commit_message):
 
 def message(source=None, sha=None):
     commit_message = []
-    command = ['perl', os.path.join(SCRIPTS, 'prepare-ChangeLog'), '--no-write', '--only-files', '--delimiters', '--git-index']
+    command = [{{ perl }}, os.path.join(SCRIPTS, 'prepare-ChangeLog'), '--no-write', '--only-files', '--delimiters', '--git-index']
 
     if sha:
         commit_message.append('Amend changes:')

Tools/Scripts/libraries/webkitscmpy/webkitscmpy/program/install_hooks.py

@@ -23,6 +23,7 @@
 import os
 import re
 import sys
+import shutil
 
 from .command import Command
 from webkitbugspy import radar
@@ -181,6 +182,9 @@ def main(cls, args, repository, hooks=None, identifier_template=None, **kwargs):
 
         trailers_to_strip = ['Identifier'] + ([identifier_template.split(':', 1)[0]] if identifier_template else [])
         source_remotes = repository.source_remotes() or ['origin']
+        perl = 'perl'
+        if sys.version_info >= (3, 3):
+            perl = shutil.which('perl')
 
         installed_hooks = 0
         for hook in hook_names:
@@ -197,6 +201,7 @@ def main(cls, args, repository, hooks=None, identifier_template=None, **kwargs):
                 from jinja2 import Template
                 contents = Template(f.read()).render(
                     location=os.path.relpath(source_path, repository.root_path),
+                    perl=repr(perl),
                     python=os.path.basename(sys.executable),
                     prefer_radar=bool(radar.Tracker.radarclient()),
                     default_pre_push_mode="'{}'".format(getattr(args, 'mode', cls.MODES[0])),