report when blocked package exception is not needed

python/tidy/servo_tidy/tidy.py

@@ -402,18 +402,32 @@ def check_lock(file_name, contents):
         yield (1, message)
 
     # Check to see if we are transitively using any blocked packages
+    blocked_packages = config["blocked-packages"]
+    # Create map to keep track of visited exception packages
+    visited_whitelisted_packages = {package: {} for package in blocked_packages.keys()}
+
     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 = config['blocked-packages'].get(dependency_name)
+            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)
+                else:
+                    visited_whitelisted_packages[dependency_name][package_name] = True
+
+    # Check if all the exceptions to blocked packages actually depend on the blocked package
+    for dependency_name, package_names in blocked_packages.iteritems():
+        for package_name in package_names:
+            if not visited_whitelisted_packages[dependency_name].get(package_name):
+                fmt = "Package {} is not required to be an exception of blocked package {}."
+                message = fmt.format(package_name, dependency_name)
+                yield (1, message)
 
 
 def check_toml(file_name, lines):

python/tidy/servo_tidy_tests/blocked_package.lock

@@ -0,0 +1,26 @@
+[root]
+name = "servo"
+version = "0.0.1"
+
+[[package]]
+name = "test_blocked"
+version = "0.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+    "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "test_exception"
+version = "0.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+    "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "test_unneeded_exception"
+version = "0.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+]

python/tidy/servo_tidy_tests/test_tidy.py

@@ -229,6 +229,25 @@ class CheckTidiness(unittest.TestCase):
 
         self.assertNoMoreErrors(errors)
 
+    def test_lock_exceptions(self):
+        tidy.config["blocked-packages"]["rand"] = ["test_exception", "test_unneeded_exception"]
+        errors = tidy.collect_errors_for_files(iterFile('blocked_package.lock'), [tidy.check_lock], [], print_text=False)
+
+        msg = (
+            "Package test_blocked 0.0.2 depends on blocked package rand."
+        )
+
+        msg2 = (
+            "Package test_unneeded_exception is not required to be an exception of blocked package rand."
+        )
+
+        self.assertEqual(msg, errors.next()[2])
+        self.assertEqual(msg2, errors.next()[2])
+        self.assertNoMoreErrors(errors)
+
+        # needed to not raise errors in other test cases
+        tidy.config["blocked-packages"]["rand"] = []
+
     def test_lint_runner(self):
         test_path = base_path + 'lints/'
         runner = tidy.LintRunner(only_changed_files=False, progress=False)