Find viable bash.exe for running hooks on Windows

When running hooks on Windows, bash.exe must be supplied on the command
line to run the hook script. This change tries to find a viable bash.exe
from the user's PATH, while avoiding the bash.exe stub in the OS's System32
directory.

This change is adapted from Michael Wild's PR #103.

Signed-off-by: Peter Grayson <[email protected]>

Author: jpgrayson

stgit/utils.py

@@ -2,6 +2,8 @@
 
 import os
 import re
+import shutil
+import sys
 import tempfile
 from io import open
 
@@ -90,16 +92,43 @@ def get_hook(repository, hook_name, extra_env=None):
     extra_env = add_dict(extra_env, {'GIT_PREFIX': prefix})
 
     def hook(*parameters):
-        argv = [hook_path]
-        argv.extend(parameters)
+        if sys.platform == 'win32':
+            # On Windows, run the hook using "bash" explicitly.
+            # Try to locate bash.exe in user's PATH, but avoid the WSL
+            # shim/bootstrapper %SYSTEMROOT%/System32/bash.exe
+            systemroot = os.environ.get('SYSTEMROOT')
+            if systemroot:
+                system32 = os.path.normcase(os.path.join(systemroot, 'system32'))
+                path = os.pathsep.join(
+                    p
+                    for p in os.environ.get('PATH', '').split(os.pathsep)
+                    if os.path.normcase(p) != system32
+                )
+            else:
+                path = None
+
+            # Find bash with user's path (sans System32).
+            bash_exe = shutil.which('bash.exe', path=path)
+            if not bash_exe:
+                # Next try finding the bash.exe that came with Git for Windows.
+                git_exe = shutil.which('git.exe', path=path)
+                if not git_exe:
+                    raise StgException('Failed to locate either bash.exe or git.exe')
+                bash_exe = os.path.join(
+                    os.path.dirname(os.path.dirname(git_exe)),
+                    'bin',
+                    'bash.exe',
+                )
+
+            argv = [bash_exe, hook_path]
+        else:
+            argv = [hook_path]
 
-        # On Windows, run the hook using "bash" explicitly
-        if os.name != 'posix':
-            argv.insert(0, 'bash')
+        argv.extend(parameters)
 
         repository.default_iw.run(argv, extra_env).run()
 
-    hook.__name__ = str(hook_name)
+    hook.__name__ = hook_name
     return hook