Update which() to use os.environ['PATH']

Update to saltstack's latest `salt.util.which`.

See also: https://redd.it/4laeut

Author: tony

libtmux/common.py

@@ -11,6 +11,7 @@
 import re
 import subprocess
 from distutils.version import StrictVersion
+from functools import wraps
 
 from . import exc
 from ._compat import console_to_str
@@ -312,6 +313,21 @@ def get_by_id(self, id):
         return None
 
 
+def real_memoize(func):
+    '''
+    Memoize aka cache the return output of a function
+    given a specific set of arguments
+    '''
+    cache = {}
+
+    @wraps(func)
+    def _memoize(*args):
+        if args not in cache:
+            cache[args] = func(*args)
+        return cache[args]
+    return _memoize
+
+
 def which(exe=None):
     """Return path of bin. Python clone of /usr/bin/which.
 
@@ -322,24 +338,51 @@ def which(exe=None):
     :rtype: string
 
     """
-    if exe:
-        if os.access(exe, os.X_OK):
-            return exe
-
-        # default path based on busybox's default
-        search_path = '/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin'
+    def _is_executable_file_or_link(exe):
+        # check for os.X_OK doesn't suffice because directory may executable
+        return (os.access(exe, os.X_OK) and
+                (os.path.isfile(exe) or os.path.islink(exe)))
+
+    if _is_executable_file_or_link(exe):
+        # executable in cwd or fullpath
+        return exe
+
+    ext_list = os.environ.get('PATHEXT', '.EXE').split(';')
+
+    @real_memoize
+    def _exe_has_ext():
+        '''
+        Do a case insensitive test if exe has a file extension match in
+        PATHEXT
+        '''
+        for ext in ext_list:
+            try:
+                pattern = r'.*\.' + ext.lstrip('.') + r'$'
+                re.match(pattern, exe, re.I).groups()
+                return True
+            except AttributeError:
+                continue
+        return False
+
+    # Enhance POSIX path for the reliability at some environments, when
+    # $PATH is changing. This also keeps order, where 'first came, first
+    # win' for cases to find optional alternatives
+    search_path = os.environ.get('PATH') and \
+        os.environ['PATH'].split(os.pathsep) or list()
+    for default_path in [
+        '/bin', '/sbin', '/usr/bin', '/usr/sbin', '/usr/local/bin'
+    ]:
+        if default_path not in search_path:
+            search_path.append(default_path)
+    os.environ['PATH'] = os.pathsep.join(search_path)
+    for path in search_path:
+        full_path = os.path.join(path, exe)
+        if _is_executable_file_or_link(full_path):
+            return full_path
+    logger.trace(
+        '\'{0}\' could not be found in the following search path: '
+        '\'{1}\''.format(exe, search_path))
 
-        for path in search_path.split(os.pathsep):
-            full_path = os.path.join(path, exe)
-            if os.access(full_path, os.X_OK):
-                return full_path
-        raise exc.LibTmuxException(
-            '{0!r} could not be found in the following search '
-            'path: {1!r}'.format(
-                exe, search_path
-            )
-        )
-    logger.error('No executable was passed to be searched by which')
     return None