Added test-tidy check for blocked packages.

python/tidy/servo_tidy/tidy.py

@@ -81,6 +81,27 @@
     " accessible to\n// web pages."
 ]
 
+# Packages which we avoid using in Servo.
+# For each blocked package, we can list the exceptions,
+# which are packages allowed to use the blocked package.
+BLOCKED_PACKAGES = {
+    "rand": [
+        "deque",
+        "gaol",
+        "ipc-channel",
+        "num-bigint",
+        "parking_lot_core",
+        "phf_generator",
+        "rayon",
+        "servo_rand",
+        "tempdir",
+        "tempfile",
+        "uuid",
+        "websocket",
+        "ws",
+    ],
+}
+
 
 def is_iter_empty(iterator):
     try:
@@ -338,6 +359,20 @@ def find_reverse_dependencies(name, content):
                     message += "\n\t\t" + name
         yield (1, message)
 
+    # Check to see if we are transitively using any blocked packages
+    for package in content.get("package", []):
+        package_name = package.get("name")
+        package_version = package.get("version")
+        for dependency in package.get("dependencies", []):
+            dependency = dependency.split()
+            dependency_name = dependency[0]
+            whitelist = BLOCKED_PACKAGES.get(dependency_name)
+            if whitelist is not None:
+                if package_name not in whitelist:
+                    fmt = "Package {} {} depends on blocked package {}."
+                    message = fmt.format(package_name, package_version, dependency_name)
+                    yield (1, message)
+
 
 def check_toml(file_name, lines):
     if not file_name.endswith("Cargo.toml"):