Outputs a log of updated features

.gitignore

@@ -9,3 +9,4 @@ secrets.json
 tests.json
 tests.old.json
 .testtmp
+feature-list.json

scripts/add-new-bcd.ts

@@ -235,6 +235,7 @@ const main = async (): Promise<void> => {
     {addNewFeatures: true},
     bcd.browsers,
     overrides,
+    "",
   );
 
   console.log("Injecting BCD...");

scripts/update-bcd.ts

@@ -350,6 +350,12 @@ interface UpdateLog {
   reason: Reason;
 }
 
+interface FeatureListLog {
+  browser: BrowserName;
+  path: string;
+  statements: SimpleSupportStatement[];
+}
+
 /** Values available in operations. */
 interface UpdateState extends UpdateLog {
   shared: UpdateShared;
@@ -1008,6 +1014,27 @@ const pickLog = <T extends UpdateLog>({
   };
 };
 
+/**
+ * Picks specific properties from an object of type T and returns a new object of type FeatureListLog.
+ * @template T - The type of the input object.
+ * @param obj - The input object.
+ * @param obj.browser - The browser property of the input object.
+ * @param obj.path - The path property of the input object.
+ * @param obj.statements - The statements property of the input object.
+ * @returns - The new object of type FeatureListLog.
+ */
+const pickFeatureList = <T extends UpdateLog>({
+  browser,
+  path,
+  statements,
+}: T): FeatureListLog => {
+  return {
+    browser,
+    path,
+    statements,
+  };
+};
+
 /**
  * Generates a sequence of key-value pairs representing the entries in an object tree.
  * The keys are generated by concatenating the prefix with each nested key.
@@ -1035,14 +1062,14 @@ export const walkEntries = function* (
  * @param bcd - The BCD identifier.
  * @param supportMatrix - The support matrix.
  * @param options - Additional options for the update.
- * @returns A boolean indicating whether any changes were made during the update.
+ * @returns An array of objects representing BCD paths that have been updated.
  */
 export const update = (
   bcd: Identifier,
   supportMatrix: SupportMatrix,
   options: any,
-): boolean => {
-  const changes: UpdateLog[] = [];
+): FeatureListLog[] => {
+  const results: UpdateLog[] = [];
   for (const state of compose(
     expand("entry", function* () {
       for (const [path, entry] of walkEntries("", bcd)) {
@@ -1136,7 +1163,7 @@ export const update = (
       }
     }),
   )()) {
-    changes.push(pickLog(state));
+    results.push(pickLog(state));
     if (state.statements) {
       state.shared.support[state.browser] =
         state.statements.length === 1 ? state.statements[0] : state.statements;
@@ -1145,8 +1172,11 @@ export const update = (
       logger.warn(state.reason.message);
     }
   }
-  // TODO: Serialize changes to a file
-  return changes.some(({statements}) => Boolean(statements));
+
+  const updates = results
+    .filter(({statements}) => Boolean(statements))
+    .map((result) => pickFeatureList(result));
+  return updates;
 };
 
 /* c8 ignore start */
@@ -1191,13 +1221,15 @@ export const loadJsonFiles = async (
  * @param filter - An object containing filter options.
  * @param browsers - An object representing the browsers to include in the update.
  * @param overrides - An object containing override options.
+ * @param outputPath - An string specifying filename and path for feature list output. Defaults to `feature-list.json`.
  * @returns A Promise that resolves when the update is complete.
  */
 export const main = async (
   reportPaths: string[],
   filter: any,
   browsers: Browsers,
   overrides: Overrides,
+  outputPath: string,
 ): Promise<void> => {
   // Replace filter.path with a minimatch object.
   if (filter.path && filter.path.includes("*")) {
@@ -1232,18 +1264,25 @@ export const main = async (
     browsers,
     overrides.filter(Array.isArray as (item: unknown) => item is OverrideTuple),
   );
+  let featureList: FeatureListLog[] = [];
 
   // Should match https://github.com/mdn/browser-compat-data/blob/f10bf2cc7d1b001a390e70b7854cab9435ffb443/test/linter/test-style.js#L63
   // TODO: https://github.com/mdn/browser-compat-data/issues/3617
   for (const [file, data] of Object.entries(bcdFiles)) {
-    const modified = update(data, supportMatrix, filter);
-    if (!modified) {
+    const updates = update(data, supportMatrix, filter);
+    if (!updates.length) {
       continue;
     }
+    featureList = featureList.concat(updates);
     logger.info(`Updating ${path.relative(BCD_DIR, file)}`);
     const json = JSON.stringify(data, null, "  ") + "\n";
     await fs.writeFile(file, json);
   }
+
+  if (featureList.length) {
+    const featureListJSON = JSON.stringify(featureList, null, "  ") + "\n";
+    await fs.writeFile(outputPath, featureListJSON);
+  }
 };
 
 if (esMain(import.meta)) {
@@ -1292,10 +1331,17 @@ if (esMain(import.meta)) {
             'Only update when versions are a specific number (or "false"), disallowing ranges',
           type: "boolean",
           default: false,
+        })
+        .option("output", {
+          alias: "o",
+          describe:
+            'Specify filename and output path for a json list of updated features. Defaults to "feature-list.json"',
+          type: "string",
+          default: "feature-list.json",
         });
     },
   );
 
-  await main(argv.reports, argv, browsers, overrides);
+  await main(argv.reports, argv, browsers, overrides, argv.output);
 }
 /* c8 ignore stop */