Adds --debug and --debugger flags to ./mach run

python/servo/post_build_commands.py

@@ -1,10 +1,12 @@
 from __future__ import print_function, unicode_literals
 
+import argparse
 import os.path as path
 from os import chdir
 import subprocess
 import SimpleHTTPServer
 import SocketServer
+import mozdebug
 from shutil import copytree, rmtree, ignore_patterns
 
 from mach.decorators import (
@@ -21,14 +23,44 @@ class MachCommands(CommandBase):
     @Command('run',
              description='Run Servo',
              category='post-build')
+    @CommandArgument('--debug', action='store_true',
+                     help='Enable the debugger. Not specifying a '
+                          '--debugger option will result in the default '
+                          'debugger being used. The following arguments '
+                          'have no effect without this.')
+    @CommandArgument('--debugger', default=None, type=str,
+        help='Name of debugger to use.')
     @CommandArgument(
         'params', nargs='...',
         help="Command-line arguments to be passed through to Servo")
-    def run(self, params):
+    def run(self, params, debug=False, debugger=None):
         env = self.build_env()
         env["RUST_BACKTRACE"] = "1"
-        subprocess.check_call([path.join("target", "servo")] + params,
-                              env=env)
+
+        args = [path.join("target", "servo")]
+
+        # Borrowed and modified from:
+        # http://hg.mozilla.org/mozilla-central/file/c9cfa9b91dea/python/mozbuild/mozbuild/mach_commands.py#l883
+        if debug:
+            import mozdebug
+            if not debugger:
+                # No debugger name was provided. Look for the default ones on
+                # current OS.
+                debugger = mozdebug.get_default_debugger_name(
+                    mozdebug.DebuggerSearch.KeepLooking)
+
+            self.debuggerInfo = mozdebug.get_debugger_info(debugger)
+            if not self.debuggerInfo:
+                print("Could not find a suitable debugger in your PATH.")
+                return 1
+
+            # Prepend the debugger args.
+            args = ([self.debuggerInfo.path] + self.debuggerInfo.args
+                    + args + params)
+        else:
+            args = args + params
+
+        subprocess.check_call(args, env=env)
 
     @Command('doc',
              description='Generate documentation',