wip nfc propagate InternalLink up; TODO update doc; test?

Author: gnprice

lib/model/internal_link.dart

@@ -140,14 +140,14 @@ class NarrowLink extends InternalLink {
 /// better, but some kinds will be rare, even unheard-of:
 ///   #narrow/stream/1-announce/stream/1-announce (duplicated operator)
 // TODO(#252): handle all valid narrow links, returning a search narrow
-Narrow? parseInternalLink(Uri url, PerAccountStore store) {
+InternalLink? parseInternalLink(Uri url, PerAccountStore store) {
   if (!_isInternalLink(url, store.realmUrl)) return null;
 
   final (category, segments) = _getCategoryAndSegmentsFromFragment(url.fragment);
   switch (category) {
     case 'narrow':
       if (segments.isEmpty || !segments.length.isEven) return null;
-      return _interpretNarrowSegments(segments, store)?.narrow;
+      return _interpretNarrowSegments(segments, store);
   }
   return null;
 }

lib/widgets/content.dart

@@ -1535,15 +1535,17 @@ void _launchUrl(BuildContext context, String urlString) async {
     return;
   }
 
-  final internalNarrow = parseInternalLink(url, store);
-  if (internalNarrow != null) {
-    unawaited(Navigator.push(context,
-      MessageListPage.buildRoute(context: context,
-        narrow: internalNarrow)));
-    return;
+  final internalLink = parseInternalLink(url, store);
+  assert(internalLink == null || internalLink.realmUrl == store.realmUrl);
+  switch (internalLink) {
+    case NarrowLink():
+      unawaited(Navigator.push(context,
+        MessageListPage.buildRoute(context: context,
+          narrow: internalLink.narrow)));
+
+    case null:
+      await PlatformActions.launchUrl(context, url);
   }
-
-  await PlatformActions.launchUrl(context, url);
 }
 
 /// Like [Image.network], but includes [authHeader] if [src] is on-realm.

test/model/internal_link_test.dart

@@ -160,7 +160,12 @@ void main() {
         test(urlString, () async {
           final store = await setupStore(realmUrl: realmUrl, streams: streams, users: users);
           final url = store.tryResolveUrl(urlString)!;
-          check(parseInternalLink(url, store)).equals(expected);
+          final result = parseInternalLink(url, store);
+          if (expected == null) {
+            check(result).isNull();
+          } else {
+            check(result).isA<NarrowLink>().narrow.equals(expected);
+          }
         });
       }
     }
@@ -564,3 +569,7 @@ void main() {
     });
   });
 }
+
+extension NarrowLinkChecks on Subject<NarrowLink> {
+  Subject<Narrow> get narrow => has((x) => x.narrow, 'narrow');
+}