Bug 1577501 - [mach] Make sure ./mach help <command> uses the correct Python, r=glandium

Some commands use external argument parsers, so invoking |mach help <command>| will import
external modules (which may only be Python 2 compatible).

This makes sure that we detect the actual subcommand we're generating help for
and use the proper Python.

A much simpler solution would have been to run |mach help| with Python 2 all
the time. However, as we convert things to Python 3 this would have meant that
Python 3 only code would blow up. This would have forced us to continue
supporting Python 2, even for Python 3-only commands.

Differential Revision: https://phabricator.services.mozilla.com/D43989

--HG--
extra : moz-landing-system : lando

mach

@@ -138,8 +138,15 @@ run_py() {
 }
 
 first_arg=$1
+if [ "$first_arg" = "help" ]; then
+    # When running `./mach help <command>`, the correct Python for <command>
+    # needs to be used.
+    first_arg=$2
+fi
+
 if [ -z "$first_arg" ]; then
-    run_py python3
+    # User ran `./mach` or `./mach help`, use Python 3.
+    run_py python3 "$@"
 fi
 
 case "${first_arg}" in

python/mach/mach/dispatcher.py

@@ -108,7 +108,7 @@ class CommandAction(argparse.Action):
             if command == 'help':
                 if args and args[0] not in ['-h', '--help']:
                     # Make sure args[0] is indeed a command.
-                    self._handle_command_help(parser, args[0], args)
+                    self._handle_command_help(parser, args[0], args, namespace.print_command)
                 else:
                     self._handle_main_help(parser, namespace.verbose)
                 sys.exit(0)
@@ -118,10 +118,10 @@ class CommandAction(argparse.Action):
                     # -- is in command arguments
                     if '-h' in args[:args.index('--')] or '--help' in args[:args.index('--')]:
                         # Honor -h or --help only if it appears before --
-                        self._handle_command_help(parser, command, args)
+                        self._handle_command_help(parser, command, args, namespace.print_command)
                         sys.exit(0)
                 else:
-                    self._handle_command_help(parser, command, args)
+                    self._handle_command_help(parser, command, args, namespace.print_command)
                     sys.exit(0)
         else:
             raise NoCommandError()
@@ -137,6 +137,12 @@ class CommandAction(argparse.Action):
             # Try to find similar commands, may raise UnknownCommandError.
             command = self._suggest_command(command)
 
+        # This is used by the `mach` driver to find the command name amidst
+        # global arguments.
+        if namespace.print_command:
+            print(command)
+            sys.exit(0)
+
         handler = self._mach_registrar.command_handlers.get(command)
 
         usage = '%(prog)s [global arguments] ' + command + \
@@ -304,12 +310,16 @@ class CommandAction(argparse.Action):
                 group = extra_groups[group_name]
             group.add_argument(*arg[0], **arg[1])
 
-    def _handle_command_help(self, parser, command, args):
+    def _handle_command_help(self, parser, command, args, print_command):
         handler = self._mach_registrar.command_handlers.get(command)
 
         if not handler:
             raise UnknownCommandError(command, 'query')
 
+        if print_command:
+            print(command)
+            sys.exit(0)
+
         if handler.subcommand_handlers:
             self._handle_subcommand_help(parser, handler, args)
             return

python/mach/mach/main.py

@@ -434,12 +434,6 @@ To see more help for a specific command, run:
 
         handler = getattr(args, 'mach_handler')
 
-        # This is used by the `mach` driver to find the command name amidst
-        # global arguments.
-        if args.print_command:
-            print(handler.name)
-            sys.exit(0)
-
         # Add JSON logging to a file if requested.
         if args.logfile:
             self.log_manager.add_json_handler(args.logfile)