From fb4885d79df649bc6a6741f8537824b39f0fa554 Mon Sep 17 00:00:00 2001
From: Claas Augner <caugner@mozilla.com>
Date: Tue, 7 Apr 2026 13:33:20 +0200
Subject: [PATCH] fix(build): filter unmirrorable notes

---
 scripts/build/mirror.js      | 34 ++++++++++++++---
 scripts/build/mirror.test.js | 71 +++++++++++++++++++++++++++++++++++-
 2 files changed, 98 insertions(+), 7 deletions(-)

diff --git a/scripts/build/mirror.js b/scripts/build/mirror.js
index c8188a893cd067..45553e16fdbd2c 100644
--- a/scripts/build/mirror.js
+++ b/scripts/build/mirror.js
@@ -156,23 +156,43 @@ export const getMatchingBrowserVersion = (targetBrowser, sourceVersion) => {
  * @param {(string) => (string | false)} versionMapper - Receives the source browser version and returns the target browser version.
  * @returns {Notes | null} The notes with replacement performed
  */
-const updateNotes = (notes, regex, replace, versionMapper) => {
+export const updateNotes = (notes, regex, replace, versionMapper) => {
   if (!notes) {
     return null;
   }
 
   if (Array.isArray(notes)) {
-    return /** @type {Notes} */ (
-      notes.map((note) => updateNotes(note, regex, replace, versionMapper))
-    );
+    const mapped = notes
+      .map((note) => updateNotes(note, regex, replace, versionMapper))
+      .filter(Boolean);
+
+    if (mapped.length === 0) {
+      return null;
+    }
+
+    if (mapped.length === 1) {
+      return /** @type {Notes} */ (mapped[0]);
+    }
+
+    return /** @type {Notes} */ (mapped);
   }
 
-  return notes
+  let hasUnmappedVersion = false;
+  const result = notes
     .replace(regex, replace)
     .replace(
       new RegExp(`(${replace}|version)\\s(\\d+)`, 'g'),
-      (match, p1, p2) => p1 + ' ' + versionMapper(p2),
+      (match, p1, p2) => {
+        const mapped = versionMapper(p2);
+        if (mapped === false) {
+          hasUnmappedVersion = true;
+          return match;
+        }
+        return p1 + ' ' + mapped;
+      },
     );
+
+  return hasUnmappedVersion ? null : result;
 };
 
 /**
@@ -306,6 +326,8 @@ export const bumpSupport = (sourceData, sourceBrowser, destination) => {
     );
     if (newNotes) {
       newData.notes = newNotes;
+    } else {
+      delete newData.notes;
     }
   }
 
diff --git a/scripts/build/mirror.test.js b/scripts/build/mirror.test.js
index 30468fe4bda99e..41c7d21e81037c 100644
--- a/scripts/build/mirror.test.js
+++ b/scripts/build/mirror.test.js
@@ -10,7 +10,7 @@ import assert from 'node:assert/strict';
 
 import bcd from '../../index.js';
 
-import mirrorSupport, { isOSLimitation } from './mirror.js';
+import mirrorSupport, { isOSLimitation, updateNotes } from './mirror.js';
 
 describe('mirror', () => {
   describe('isOSLimitation', () => {
@@ -172,6 +172,75 @@ describe('mirror', () => {
       }
     });
 
+    describe('updateNotes', () => {
+      /** @type {(string) => (string | false)} */
+      const versionMapper = (v) => (v === '99' ? false : String(Number(v) + 1));
+      const regex = /\bChrome\b/g;
+
+      it('notes with unmapped versions are filtered out', () => {
+        assert.equal(
+          updateNotes(
+            'Supported since Chrome 99.',
+            regex,
+            'Opera',
+            versionMapper,
+          ),
+          null,
+        );
+      });
+
+      it('notes without version references are kept unchanged', () => {
+        assert.equal(
+          updateNotes(
+            'Supported on ChromeOS, macOS, and Windows.',
+            regex,
+            'Opera',
+            versionMapper,
+          ),
+          'Supported on ChromeOS, macOS, and Windows.',
+        );
+      });
+
+      it('notes with mapped versions are updated', () => {
+        assert.equal(
+          updateNotes(
+            'Supported since Chrome 70.',
+            regex,
+            'Opera',
+            versionMapper,
+          ),
+          'Supported since Opera 71.',
+        );
+      });
+
+      it('in an array, only notes with unmapped versions are filtered out', () => {
+        assert.deepEqual(
+          updateNotes(
+            [
+              'Supported on ChromeOS, macOS, and Windows.',
+              'Supported since Chrome 99.',
+            ],
+            regex,
+            'Opera',
+            versionMapper,
+          ),
+          'Supported on ChromeOS, macOS, and Windows.',
+        );
+      });
+
+      it('returns null when all array notes are filtered out', () => {
+        assert.equal(
+          updateNotes(
+            ['Supported since Chrome 99.', 'Available since Chrome 99.'],
+            regex,
+            'Opera',
+            versionMapper,
+          ),
+          null,
+        );
+      });
+    });
+
     describe('Notes', () => {
       it('version numbers in notes are mapped', () => {
         /** @type {InternalSupportBlock} */