wip internal_link [nfc]: Propagate InternalLink up to caller; TODO test?

Author: gnprice

lib/model/internal_link.dart

@@ -125,29 +125,33 @@ class NarrowLink extends InternalLink {
   final Narrow narrow;
 }
 
-/// A [Narrow] from a given URL, on `store`'s realm.
+/// Try to parse the given URL as a page in this app, on `store`'s realm.
 ///
 /// `url` must already be a result from [PerAccountStore.tryResolveUrl]
 /// on `store`.
 ///
-/// Returns `null` if any of the operator/operand pairs are invalid.
+/// Returns null if the URL isn't on this realm,
+/// or isn't a valid Zulip URL,
+/// or isn't currently supported as leading to a page in this app.
 ///
+/// In particular this will return null if `url` is a `/#narrow/…` URL
+/// and any of the operator/operand pairs are invalid.
 /// Since narrow links can combine operators in ways our [Narrow] type can't
 /// represent, this can also return null for valid narrow links.
 ///
 /// This can also return null for some valid narrow links that our Narrow
 /// type *could* accurately represent. We should try to understand these
-/// better, but some kinds will be rare, even unheard-of:
+/// better, but some kinds will be rare, even unheard-of.  For example:
 ///   #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

@@ -1536,15 +1536,17 @@ 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');
+}