Bug 1820654 - Migrate string after changing markup in string. r=flod

Differential Revision: https://phabricator.services.mozilla.com/D175525

python/l10n/fluent_migrations/bug_1820654_update_manual.py

@@ -0,0 +1,30 @@
+# Any copyright is dedicated to the Public Domain.
+# http://creativecommons.org/publicdomain/zero/1.0/
+
+import fluent.syntax.ast as FTL
+
+from fluent.migrate.transforms import TransformPattern
+
+
+class REPLACE_LABEL(TransformPattern):
+    # Used to replace `<label data-l10n-name="manual-link"/>`
+    def visit_TextElement(self, node):
+        node.value = node.value.replace("<label", "<a")
+
+        return node
+
+
+def migrate(ctx):
+    """Bug 1820654 - Use html:a in manualUpdate box, part {index}."""
+
+    aboutDialog_ftl = "browser/browser/aboutDialog.ftl"
+    ctx.add_transforms(
+        aboutDialog_ftl,
+        aboutDialog_ftl,
+        [
+            FTL.Message(
+                id=FTL.Identifier("aboutdialog-update-manual"),
+                value=REPLACE_LABEL(aboutDialog_ftl, "update-manual"),
+            ),
+        ],
+    )