Create mach fetch command

python/servo/devenv_commands.py

@@ -21,6 +21,12 @@
 
 from servo.command_base import CommandBase, cd, call
 
+CARGO_PATHS = [
+    path.join('components', 'servo'),
+    path.join('ports', 'cef'),
+    path.join('ports', 'geckolib'),
+]
+
 
 @CommandProvider
 class MachCommands(CommandBase):
@@ -81,11 +87,7 @@ def update_cargo(self, params=None, package=None, all_packages=None):
             print("flag or update all packages with --all-packages (-a) flag")
             sys.exit(1)
 
-        cargo_paths = [path.join('components', 'servo'),
-                       path.join('ports', 'cef'),
-                       path.join('ports', 'geckolib')]
-
-        for cargo_path in cargo_paths:
+        for cargo_path in CARGO_PATHS:
             with cd(cargo_path):
                 print(cargo_path)
                 call(["cargo", "update"] + params,
@@ -153,6 +155,19 @@ def grep(self, params):
             ["git"] + ["grep"] + params + ['--'] + grep_paths + [':(exclude)*.min.js'],
             env=self.build_env())
 
+    @Command('fetch',
+             description='Fetch Rust, Cargo and Cargo dependencies',
+             category='devenv')
+    def fetch(self):
+        # Fetch Rust and Cargo
+        self.ensure_bootstrapped()
+
+        # Fetch Cargo dependencies
+        for cargo_path in CARGO_PATHS:
+            with cd(cargo_path):
+                print(cargo_path)
+                call(["cargo", "fetch"], env=self.build_env())
+
     @Command('wpt-upgrade',
              description='upgrade wptrunner.',
              category='devenv')