Add clobber mechanism

CLOBBER

@@ -0,0 +1,8 @@
+# To trigger a clobber replace ALL of the textual description below,
+# giving a pull request number and a one line description of why a clobber is
+# required.
+#
+# Modifying this file will now automatically clobber the buildbot machines \o/
+#
+
+Pull 16722 - Added CLOBBER file

python/servo/build_commands.py

@@ -24,7 +24,7 @@ from mach.decorators import (
     Command,
 )
 
-from servo.command_base import CommandBase, cd, call, BIN_SUFFIX
+from servo.command_base import CommandBase, cd, call, check_call, BIN_SUFFIX
 from servo.util import host_triple
 
 
@@ -228,6 +228,7 @@ class MachCommands(CommandBase):
             opts += ["--target", target]
 
         self.ensure_bootstrapped(target=target)
+        self.ensure_clobbered()
 
         if debug_mozjs:
             features += ["debugmozjs"]
@@ -360,6 +361,7 @@ class MachCommands(CommandBase):
     def build_cef(self, jobs=None, verbose=False, release=False,
                   with_debug_assertions=False):
         self.ensure_bootstrapped()
+        self.ensure_clobbered()
 
         ret = None
         opts = []
@@ -411,6 +413,7 @@ class MachCommands(CommandBase):
     def build_geckolib(self, with_gecko=None, jobs=None, verbose=False, release=False):
         self.set_use_stable_rust()
         self.ensure_bootstrapped()
+        self.ensure_clobbered()
 
         env = self.build_env(is_build=True, geckolib=True)
 
@@ -455,7 +458,7 @@ class MachCommands(CommandBase):
                      help='Print verbose output')
     @CommandArgument('params', nargs='...',
                      help="Command-line arguments to be passed through to Cargo")
-    def clean(self, manifest_path, params, verbose=False):
+    def clean(self, manifest_path=None, params=[], verbose=False):
         self.ensure_bootstrapped()
 
         opts = []
@@ -464,5 +467,5 @@ class MachCommands(CommandBase):
         if verbose:
             opts += ["-v"]
         opts += params
-        return call(["cargo", "clean"] + opts,
-                    env=self.build_env(), cwd=self.servo_crate(), verbose=verbose)
+        return check_call(["cargo", "clean"] + opts,
+                          env=self.build_env(), cwd=self.servo_crate(), verbose=verbose)

python/servo/command_base.py

@@ -574,3 +574,30 @@ class CommandBase(object):
             Registrar.dispatch("bootstrap-cargo", context=self.context)
 
         self.context.bootstrapped = True
+
+    def ensure_clobbered(self, target_dir=None):
+        if target_dir is None:
+            target_dir = self.get_target_dir()
+        auto = True if os.environ.get('AUTOCLOBBER', False) else False
+        src_clobber = os.path.join(self.context.topdir, 'CLOBBER')
+        target_clobber = os.path.join(target_dir, 'CLOBBER')
+
+        if not os.path.exists(target_dir):
+            os.makedirs(target_dir)
+
+        if not os.path.exists(target_clobber):
+            # Simply touch the file.
+            with open(target_clobber, 'a'):
+                pass
+
+        if auto:
+            if os.path.getmtime(src_clobber) > os.path.getmtime(target_clobber):
+                print('Automatically clobbering target directory: {}'.format(target_dir))
+
+                try:
+                    Registrar.dispatch("clean", context=self.context, verbose=True)
+                    print('Successfully completed auto clobber.')
+                except subprocess.CalledProcessError as error:
+                    sys.exit(error)
+            else:
+                print("Clobber not needed.")