build(mach): generate webrender revision via cargo lockfile

.gitignore

@@ -23,6 +23,7 @@ Servo.app
 .config.mk.last
 /glfw
 capture_webrender/
+/components/compositing/webrender_revision.rs
 
 # Editors
 

python/servo/command_base.py

@@ -213,6 +213,36 @@ def set_osmesa_env(bin_path, env):
     return env
 
 
+def generate_webrender_revision():
+    """Read current package id of web render to generate revision"""
+
+    lockfile_path = path.join(os.getcwd(), "Cargo.lock")
+    if not os.path.isfile(lockfile_path):
+        return
+
+    with open(lockfile_path) as f:
+        lockfile = toml.loads(f.read())
+
+    webrender_revision = ""
+    for package in lockfile.get("package", []):
+        pkgName = package.get("name")
+        if ("webrender" == pkgName):
+            webrender_revision = package.get("source")
+
+    revision = '''/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/// auto-generated by mach. do not manually modify.
+pub const REVISION: &'static str = \"%s\";''' % webrender_revision
+
+    compositor_path = os.path.join(os.getcwd(), "components", "compositing", "webrender_revision.rs")
+
+    revision_file = open(compositor_path, "w")
+    revision_file.write(revision)
+    revision_file.close()
+
+
 class BuildNotFound(Exception):
     def __init__(self, message):
         self.message = message
@@ -660,6 +690,8 @@ def ensure_bootstrapped(self, target=None):
         if "msvc" in target_platform:
             Registrar.dispatch("bootstrap", context=self.context)
 
+        generate_webrender_revision()
+
         self.context.bootstrapped = True
 
     def ensure_clobbered(self, target_dir=None):