Use local messages for more narrow searches.

We now try harder to find the first unread message in an
upcoming narrow, which has the user-visible effect that we
select the unread message before waiting for search results.

Before this change, we only applied this logic to searches
that were things like exactly stream/topic or exactly is-private.

Now we will also handle things like stream/topic/sender.  For
the stream/topic piece we look up candidate unread ids using
the steam/topic buckets in unread.js, but then we still filter
those messages by stream/topic/sender as we look for the first
unread id.

frontend_tests/node_tests/narrow_unread.js

@@ -5,6 +5,9 @@ zrequire('unread');
 zrequire('util');
 set_global('blueslip', global.make_zblueslip());
 
+set_global('message_store', {});
+set_global('page_params', {});
+
 set_global('muting', {
     is_topic_muted: () => false,
 });
@@ -91,6 +94,10 @@ function candidate_ids() {
     assert_unread_info({flavor: 'not_found'});
 
     unread.process_loaded_messages([stream_msg]);
+    message_store.get = (msg_id) => {
+        assert.equal(msg_id, stream_msg.id);
+        return stream_msg;
+    };
 
     unread_ids = candidate_ids();
     assert.deepEqual(unread_ids, [stream_msg.id]);
@@ -131,9 +138,19 @@ function candidate_ids() {
 
     unread.process_loaded_messages([private_msg]);
 
+    message_store.get = (msg_id) => {
+        assert.equal(msg_id, private_msg.id);
+        return private_msg;
+    };
+
     unread_ids = candidate_ids();
     assert.deepEqual(unread_ids, [private_msg.id]);
 
+    assert_unread_info({
+        flavor: 'found',
+        msg_id: private_msg.id,
+    });
+
     terms = [
         {operator: 'is', operand: 'private'},
     ];
@@ -156,4 +173,14 @@ function candidate_ids() {
     set_filter(terms);
     unread_ids = candidate_ids();
     assert.deepEqual(unread_ids, []);
+
+    terms = [
+        {operator: 'search', operand: 'needle'},
+    ];
+    set_filter(terms);
+
+    blueslip.set_test_data('error', 'unexpected call to get_first_unread_info');
+    assert_unread_info({
+        flavor: 'cannot_compute',
+    });
 }());

static/js/narrow_state.js

@@ -170,6 +170,15 @@ exports.pm_string = function () {
 };
 
 exports.get_first_unread_info = function () {
+    if ((current_filter === undefined) || !current_filter.can_apply_locally()) {
+        // we expect our callers to make sure a "local" narrow
+        // makes sense (and we don't yet support the all-messages view)
+        blueslip.error('unexpected call to get_first_unread_info');
+        return {
+            flavor: 'cannot_compute',
+        };
+    }
+
     var unread_ids = exports._possible_unread_message_ids();
 
     if (unread_ids === undefined) {
@@ -179,12 +188,15 @@ exports.get_first_unread_info = function () {
         };
     }
 
-    if (unread_ids.length === 0) {
+    var msg_id = current_filter.first_valid_id_from(unread_ids);
+
+    if (msg_id === undefined) {
         return {
             flavor: 'not_found',
         };
     }
 
+
     return {
         flavor: 'found',
         msg_id: unread_ids[0],
@@ -207,7 +219,7 @@ exports._possible_unread_message_ids = function () {
     var topic_name;
     var pm_string;
 
-    if (current_filter.is_exactly('stream', 'topic')) {
+    if (current_filter.can_bucket_by('stream', 'topic')) {
         stream_id = exports.stream_id();
         if (stream_id === undefined) {
             return [];
@@ -216,7 +228,7 @@ exports._possible_unread_message_ids = function () {
         return unread.get_msg_ids_for_topic(stream_id, topic_name);
     }
 
-    if (current_filter.is_exactly('stream')) {
+    if (current_filter.can_bucket_by('stream')) {
         stream_id = exports.stream_id();
         if (stream_id === undefined) {
             return [];
@@ -224,7 +236,7 @@ exports._possible_unread_message_ids = function () {
         return unread.get_msg_ids_for_stream(stream_id);
     }
 
-    if (current_filter.is_exactly('pm-with')) {
+    if (current_filter.can_bucket_by('pm-with')) {
         pm_string = exports.pm_string();
         if (pm_string === undefined) {
             return [];
@@ -232,15 +244,15 @@ exports._possible_unread_message_ids = function () {
         return unread.get_msg_ids_for_person(pm_string);
     }
 
-    if (current_filter.is_exactly('is-private')) {
+    if (current_filter.can_bucket_by('is-private')) {
         return unread.get_msg_ids_for_private();
     }
 
-    if (current_filter.is_exactly('is-mentioned')) {
+    if (current_filter.can_bucket_by('is-mentioned')) {
         return unread.get_msg_ids_for_mentions();
     }
 
-    if (current_filter.is_exactly('is-starred')) {
+    if (current_filter.can_bucket_by('is-starred')) {
         return unread.get_msg_ids_for_starred();
     }