Bug 1057694 - Command suggestions in mach. r=gps

python/mach/mach/base.py

@@ -29,11 +29,12 @@ class NoCommandError(MachError):
 class UnknownCommandError(MachError):
     """Raised when we attempted to execute an unknown command."""
 
-    def __init__(self, command, verb):
+    def __init__(self, command, verb, suggested_commands=None):
         MachError.__init__(self)
 
         self.command = command
         self.verb = verb
+        self.suggested_commands = suggested_commands or []
 
 class UnrecognizedArgumentError(MachError):
     """Raised when an unknown argument is passed to mach."""

python/mach/mach/dispatcher.py

@@ -5,6 +5,7 @@
 from __future__ import unicode_literals
 
 import argparse
+import difflib
 import sys
 
 from operator import itemgetter
@@ -105,12 +106,21 @@ class CommandAction(argparse.Action):
         else:
             raise NoCommandError()
 
-        handler = self._mach_registrar.command_handlers.get(command)
+        # Command suggestion
+        if command not in self._mach_registrar.command_handlers:
+            # We first try to look for a valid command that is very similar to the given command.
+            suggested_commands = difflib.get_close_matches(command, self._mach_registrar.command_handlers.keys(), cutoff=0.8)
+            # If we find more than one matching command, or no command at all, we give command suggestions instead
+            # (with a lower matching threshold). All commands that start with the given command (for instance: 'mochitest-plain',
+            # 'mochitest-chrome', etc. for 'mochitest-') are also included.
+            if len(suggested_commands) != 1:
+                suggested_commands = set(difflib.get_close_matches(command, self._mach_registrar.command_handlers.keys(), cutoff=0.5))
+                suggested_commands |= {cmd for cmd in self._mach_registrar.command_handlers if cmd.startswith(command)}
+                raise UnknownCommandError(command, 'run', suggested_commands)
+            sys.stderr.write("We're assuming the '%s' command is '%s' and we're executing it for you.\n\n" % (command, suggested_commands[0]))
+            command = suggested_commands[0]
 
-        # FUTURE consider looking for commands with similar names and
-        # suggest or run them.
-        if not handler:
-            raise UnknownCommandError(command, 'run')
+        handler = self._mach_registrar.command_handlers.get(command)
 
         # FUTURE
         # If we wanted to conditionally enable commands based on whether

python/mach/mach/main.py

@@ -78,10 +78,14 @@ Run |mach help| to show a list of commands.
 
 UNKNOWN_COMMAND_ERROR = r'''
 It looks like you are trying to %s an unknown mach command: %s
-
+%s
 Run |mach help| to show a list of commands.
 '''.lstrip()
 
+SUGGESTED_COMMANDS_MESSAGE = r'''
+Did you want to %s any of these commands instead: %s?
+'''
+
 UNRECOGNIZED_ARGUMENT_ERROR = r'''
 It looks like you passed an unrecognized argument into mach.
 
@@ -388,7 +392,8 @@ To see more help for a specific command, run:
             print(NO_COMMAND_ERROR)
             return 1
         except UnknownCommandError as e:
-            print(UNKNOWN_COMMAND_ERROR % (e.verb, e.command))
+            suggestion_message = SUGGESTED_COMMANDS_MESSAGE % (e.verb, ', '.join(e.suggested_commands)) if e.suggested_commands else ''
+            print(UNKNOWN_COMMAND_ERROR % (e.verb, e.command, suggestion_message))
             return 1
         except UnrecognizedArgumentError as e:
             print(UNRECOGNIZED_ARGUMENT_ERROR % (e.command,