feat(scripts): add flag inventory

package.json

@@ -112,6 +112,7 @@
     "lint:fix": "node lint/fix.js",
     "fix": "npm run format:fix && npm run lint:fix",
     "stats": "node scripts/statistics.js",
+    "flag-inventory": "node scripts/flag-inventory.js",
     "build": "node scripts/build/index.js",
     "gentypes": "node scripts/generate-types.js",
     "release": "node scripts/release/index.js",

scripts/flag-inventory.js

@@ -0,0 +1,66 @@
+/* This file is a part of @mdn/browser-compat-data
+ * See LICENSE file for more information. */
+
+import esMain from 'es-main';
+
+import walk from '../utils/walk.js';
+
+/** @import {InternalDataType} from '../types/index.js' */
+
+/**
+ * Compare map entries by key using locale-independent alphabetical order.
+ * @template T
+ * @param {[string, T]} a First entry
+ * @param {[string, T]} b Second entry
+ * @returns {number} Sort order
+ */
+const compareKeys = ([a], [b]) => (a < b ? -1 : a > b ? 1 : 0);
+
+/**
+ * List explicit flag occurrences by type, browser, and name, alphabetically.
+ * Each flags entry counts once, regardless of value or support version.
+ * @param {InternalDataType} [data] Source compatibility data
+ * @returns {string} The indented flag inventory
+ */
+const flagInventory = (data) => {
+  /** @type {Map<string, Map<string, Map<string, number>>>} */
+  const inventory = new Map();
+
+  for (const { compat } of walk(undefined, data)) {
+    for (const [browser, support] of Object.entries(compat.support)) {
+      if (support === 'mirror') {
+        continue;
+      }
+      for (const statement of Array.isArray(support) ? support : [support]) {
+        for (const { type, name } of statement.flags ?? []) {
+          const browsers = inventory.get(type) ?? new Map();
+          inventory.set(type, browsers);
+          const flags = browsers.get(browser) ?? new Map();
+          browsers.set(browser, flags);
+          flags.set(name, (flags.get(name) ?? 0) + 1);
+        }
+      }
+    }
+  }
+
+  const lines = [];
+  for (const [type, browsers] of [...inventory].sort(compareKeys)) {
+    lines.push(type);
+    for (const [browser, flags] of [...browsers].sort(compareKeys)) {
+      lines.push(`  ${browser}`);
+      for (const [name, count] of [...flags].sort(compareKeys)) {
+        lines.push(`    ${name}: ${count}`);
+      }
+    }
+  }
+  return lines.join('\n');
+};
+
+if (esMain(import.meta)) {
+  const output = flagInventory();
+  if (output) {
+    console.log(output);
+  }
+}
+
+export default flagInventory;

scripts/flag-inventory.test.js

@@ -0,0 +1,89 @@
+/* This file is a part of @mdn/browser-compat-data
+ * See LICENSE file for more information. */
+
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+
+import flagInventory from './flag-inventory.js';
+
+describe('flagInventory', () => {
+  it('counts all explicit occurrences and sorts each grouping', () => {
+    // The recursive InternalIdentifier index signature cannot type this fixture.
+    // eslint-disable-next-line jsdoc/reject-any-type
+    /** @type {*} */
+    const data = {
+      api: {
+        Example: {
+          __compat: {
+            support: {
+              firefox: [
+                {
+                  version_added: '2',
+                  flags: [
+                    { type: 'runtime_flag', name: 'z-flag' },
+                    { type: 'preference', name: 'z-pref' },
+                    {
+                      type: 'preference',
+                      name: 'a-pref',
+                      value_to_set: 'true',
+                    },
+                  ],
+                },
+                {
+                  version_added: '1',
+                  version_removed: '2',
+                  flags: [
+                    {
+                      type: 'preference',
+                      name: 'a-pref',
+                      value_to_set: 'false',
+                    },
+                  ],
+                },
+              ],
+              firefox_android: 'mirror',
+              chrome: {
+                version_added: '1',
+                flags: [{ type: 'preference', name: 'a-pref' }],
+              },
+              safari: { version_added: false },
+            },
+          },
+          nested: {
+            __compat: {
+              support: {
+                firefox: {
+                  version_added: '1',
+                  flags: [
+                    { type: 'preference', name: 'a-pref' },
+                    { type: 'runtime_flag', name: 'a-pref' },
+                  ],
+                },
+              },
+            },
+          },
+        },
+      },
+    };
+
+    assert.equal(
+      flagInventory(data),
+      [
+        'preference',
+        '  chrome',
+        '    a-pref: 1',
+        '  firefox',
+        '    a-pref: 3',
+        '    z-pref: 1',
+        'runtime_flag',
+        '  firefox',
+        '    a-pref: 1',
+        '    z-flag: 1',
+      ].join('\n'),
+    );
+  });
+
+  it('returns empty output when there are no flags', () => {
+    assert.equal(flagInventory({}), '');
+  });
+});