Add script to list stable features in RuntimeEnabledFeatures, with th…

…eir ages.

This script lists the features in RuntimeEnabledFeatures that are
status: stable, with the first Chrome milestone in which they were
status: stable.  This is useful for finding feature flags that we might
be able to remove.

Change-Id: Ic80306bcc50b45c7cdd10b70897c5ce31da6a7f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5001788
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: David Baron <dbaron@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1222541}

third_party/blink/tools/list_stable_features.py

@@ -0,0 +1,99 @@
+#!/usr/bin/env vpython3
+
+# Copyright 2023 The Chromium Authors
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# This script lists the features in RuntimeEnabledFeatures that are
+# status: stable, with the first Chrome milestone in which they were
+# status: stable.  This is useful for finding feature flags that we
+# might be able to remove.
+
+import os.path
+import re
+import sys
+
+from blinkpy.common import path_finder
+from blinkpy.common.system.filesystem import FileSystem
+from blinkpy.common.checkout.git import Git
+
+finder = path_finder.PathFinder(FileSystem())
+sys.path.append(finder.path_from_chromium_base('third_party', 'pyjson5',
+                                               'src'))
+import json5
+
+
+def version_to_ints(version):
+    return list(map(int, version.split(".")))
+
+
+def list_milestone_tags(git):
+    """Return the latest (by numeric sort) tag for each Chrome milestone."""
+    version_re = re.compile(r'^\d+\.\d+\.\d+\.\d+$')
+    milestones = dict()
+    for line in git.run(["tag", "-l"]).splitlines():
+        line = line.strip()
+        if version_re.match(line):
+            version = version_to_ints(line)
+            major = version[0]
+            if not major in milestones or version_to_ints(
+                    milestones[major]) < version:
+                milestones[major] = line
+    result = []
+    for major in sorted(milestones.keys()):
+        result.append(milestones[major])
+    return result
+
+
+def features_file(milestone=None):
+    # These paths use / rather than os.path.join() because we (mostly)
+    # want to pass them to git show.
+    if (milestone is None or milestone >= 67):
+        return "third_party/blink/renderer/platform/runtime_enabled_features.json5"
+
+    # Moved in 0aee4434a4dba42a42abaea9bfbc0cd196a63bc1 (M67)
+
+    if (milestone >= 63):
+        return "third_party/WebKit/Source/platform/runtime_enabled_features.json5"
+
+    # Moved in a9b51b33da012d575b69c1d535c85dd68a76c8ad (M63)
+
+    if (milestone >= 58):
+        return "third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5"
+
+    # Converted to json5 in 5821741047894731b6527b607edfb8ddef33fd1b (M58)
+    # return "third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in"
+    return None  # We can't parse it
+
+
+def main():
+    git = Git()
+    with open(
+            os.path.join(os.path.normpath(git.checkout_root),
+                         os.path.normpath(features_file()))) as features_io:
+        current_features_data = json5.load(features_io)["data"]
+    stable_features = dict()
+    for feature in current_features_data:
+        if feature.get("status", "") == "stable":
+            stable_features[feature["name"]] = "current"
+    for version in reversed(list_milestone_tags(git)):
+        major = version_to_ints(version)[0]
+        features_filepath = features_file(major)
+        if features_filepath is not None:
+            old_file = git.run(
+                ["show", "{}:{}".format(version, features_filepath)])
+            old_data = json5.loads(old_file)["data"]
+            for feature in old_data:
+                name = feature["name"]
+                if feature.get("status",
+                               "") == "stable" and name in stable_features:
+                    stable_features[name] = version
+    for (feature, version) in sorted(
+            stable_features.items(),
+            key=lambda t: [1000000, 0, 0, 0, t[0]]
+            if t[1] == "current" else version_to_ints(t[1]) + [t[0]]):
+        print(version, feature)
+
+
+if __name__ == "__main__":
+    sys.exit(main())