commands: allow extension commands with arbitrary names

The restriction that extension commands have names which are valid
Python identifiers is arbitrary and unnecessarily restrictive.

For example, it should be possible to have a command with a dash (-)
in its name to separate words, like "submit-pr". This is currently not
possible.

Resolve that by generating module names from an infinite iterator of
fresh per-file values instead of relying on the command name. We don't
actually need the name! Just the canonical path of the file which
defines it is important to avoid double imports.

Signed-off-by: Marti Bolivar <marti@foundries.io>

src/west/commands/command.py

@@ -6,7 +6,7 @@
 from abc import ABC, abstractmethod
 from collections import OrderedDict
 import importlib
-from keyword import iskeyword
+import itertools
 import os
 import sys
 
@@ -230,43 +230,25 @@ def _ext_specs_from_desc(project, commands_desc):
     return thunks
 
 
-def _commands_module_from_file(command_name, file):
+def _commands_module_from_file(file):
     # Python magic for importing a module containing west extension
     # commands. To avoid polluting the sys.modules key space, we put
     # these modules in an (otherwise unpopulated) west.commands.ext
     # package.
     #
     # The file is imported as a module named
-    # west.commands.ext.<command_name>, so the name must be a
-    # non-keyword identifier. This module object is returned from a
-    # cache if the same file is ever imported again, to avoid a double
-    # import in case the file maintains module-level state or defines
-    # multiple commands.
-    #
-    # (This shouldn't be a problem for west itself since main.py
-    # executes at most one WestCommand -- and creates at most one
-    # external command -- per process, but better safe than sorry in
-    # case this code gets called from elsewhere.)
-    #
-    # If we ever try to re-use a command_name, a ValueError() is
-    # raised; this prevents the import machinery from returning a
-    # previously cached module from sys.modules for an unrelated file,
-    # and is a decent sanity check against two providers of the same
-    # command.
+    # west.commands.ext.A_FRESH_IDENTIFIER. This module object is
+    # returned from a cache if the same file is ever imported again,
+    # to avoid a double import in case the file maintains module-level
+    # state or defines multiple commands.
     global _EXT_MODULES_CACHE
-    mod_name = 'west.commands.ext.{}'.format(command_name)
-
-    if not command_name.isidentifier() or iskeyword(command_name):
-        raise ValueError('bad command name "{}"'.format(command_name))
-    elif mod_name in sys.modules:
-        raise ValueError('command {} is already defined'.format(
-            mod_name.rsplit('.', 1)[-1]))
+    global _EXT_MODULES_NAME_IT
 
     file = os.path.normcase(os.path.realpath(file))
-
     if file in _EXT_MODULES_CACHE:
         return _EXT_MODULES_CACHE[file]
 
+    mod_name = next(_EXT_MODULES_NAME_IT)
     # The Python 3.4 way to import a module given its file got deprecated
     # later on, but we still need to support 3.4. If that requirement ever
     # gets dropped, this code can be simplified.
@@ -290,8 +272,12 @@ def _commands_module_from_file(command_name, file):
 _EXT_SCHEMA_PATH = os.path.join(os.path.dirname(__file__),
                                 'west-commands-schema.yml')
 
-
+# Cache which maps files implementing extension commands their
+# imported modules.
 _EXT_MODULES_CACHE = {}
+# Infinite iterator of "fresh" extension command module names.
+_EXT_MODULES_NAME_IT = ('west.commands.ext.cmd_{}'.format(i)
+                        for i in itertools.count(1))
 
 
 class _ExtFactory:
@@ -310,9 +296,7 @@ class _ExtFactory:
         # Load the module containing the command. Convert only
         # expected exceptions to BadExternalCommand.
         try:
-            mod = _commands_module_from_file(self.name, self.py_file)
-        except ValueError as ve:
-            raise BadExternalCommand from ve
+            mod = _commands_module_from_file(self.py_file)
         except ImportError as ie:
             raise BadExternalCommand from ie