Auto merge of #17702 - upsuper:python-addr-in-generated, r=emilio

Avoid random python address to be added to generated files

This would catch cases like #17691 and avoid regressing [bug 1380327](https://bugzilla.mozilla.org/show_bug.cgi?id=1380327) in this manner.

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components/style/properties/build.py

@@ -4,6 +4,7 @@
 
 import json
 import os.path
+import re
 import sys
 
 BASE = os.path.dirname(__file__.replace('\\', '/'))
@@ -16,6 +17,8 @@ from mako.template import Template
 
 import data
 
+RE_PYTHON_ADDR = re.compile(r'<.+? object at 0x[0-9a-fA-F]+>')
+
 
 def main():
     usage = "Usage: %s [ servo | gecko ] [ style-crate | html ] [ testing | regular ]" % sys.argv[0]
@@ -68,7 +71,12 @@ def render(filename, **context):
 def write(directory, filename, content):
     if not os.path.exists(directory):
         os.makedirs(directory)
-    open(os.path.join(directory, filename), "wb").write(content)
+    full_path = os.path.join(directory, filename)
+    open(full_path, "wb").write(content)
+
+    python_addr = RE_PYTHON_ADDR.search(content)
+    if python_addr:
+        abort("Found \"{}\" in {} ({})".format(python_addr.group(0), filename, full_path))
 
 
 def write_html(properties):