narrow: Add condition whether to show unread message first in narrow.

All narrows that have is: query or can mark unread message as read
will show unread message first.

frontend_tests/node_tests/filter.js

@@ -69,6 +69,7 @@ run_test('basics', () => {
 
     assert(!filter.is_search());
     assert(filter.can_mark_messages_read());
+    assert(filter.allow_use_first_unread_when_narrowing());
     assert(filter.can_apply_locally());
 
     operators = [
@@ -80,6 +81,7 @@ run_test('basics', () => {
 
     assert(filter.is_search());
     assert(!filter.can_mark_messages_read());
+    assert(!filter.allow_use_first_unread_when_narrowing());
     assert(!filter.can_apply_locally());
     assert(!filter.is_exactly('stream'));
 
@@ -110,7 +112,32 @@ run_test('basics', () => {
     assert(filter.has_operator('has'));
     assert(!filter.can_apply_locally());
 });
+run_test('show_first_unread', () => {
+    var operators = [
+        {operator: 'is', operand: 'any'},
+    ];
+    var filter = new Filter(operators);
+    assert(filter.allow_use_first_unread_when_narrowing());
 
+    operators = [
+        {operator: 'search', operand: 'query to search'},
+    ];
+    filter = new Filter(operators);
+    assert(!filter.allow_use_first_unread_when_narrowing());
+
+    filter = new Filter();
+    filter.can_mark_messages_read = () => true;
+    assert(filter.allow_use_first_unread_when_narrowing());
+
+    // Side case
+    operators = [
+        {operator: 'is', operand: 'any'},
+    ];
+    filter = new Filter(operators);
+    filter.can_mark_messages_read = () => false;
+    assert(filter.allow_use_first_unread_when_narrowing());
+
+});
 run_test('topic_stuff', () => {
     var operators = [
         {operator: 'stream', operand: 'foo'},

static/js/filter.js

@@ -378,7 +378,9 @@ Filter.prototype = {
     can_mark_messages_read: function () {
         return !this.has_operator('search');
     },
-
+    allow_use_first_unread_when_narrowing: function () {
+        return this.can_mark_messages_read() || this.has_operator('is');
+    },
     can_apply_locally: function () {
         if (this.is_search()) {
             // The semantics for matching keywords are implemented

static/js/narrow.js

@@ -226,9 +226,12 @@ exports.activate = function (raw_operators, opts) {
         if (id_info.final_select_id !== undefined) {
             anchor = id_info.final_select_id;
             use_first_unread = false;
-        } else {
+        } else if (narrow_state.filter().allow_use_first_unread_when_narrowing()) {
             anchor = -1;
             use_first_unread = true;
+        } else {
+            anchor = 10000000000000000;
+            use_first_unread = false;
         }
 
         message_fetch.load_messages_for_narrow({