buddy list: Relax count limit when doing searches.

A recent change filtered out offline users from the buddy list
whenever the list size would otherwise exceed 600.

This commit reverts half that change--we can now show 600+ users
again, but only when searching.

frontend_tests/node_tests/buddy_data.js

@@ -14,7 +14,7 @@ set_global('page_params', {});
     _.each(_.range(1000, 2000), (i) => {
         const person = {
             user_id: i,
-            full_name: `Person ${i}`,
+            full_name: `Human ${i}`,
             email: `person${i}@example.com`,
         };
         people.add_in_realm(person);
@@ -42,9 +42,35 @@ set_global('page_params', {});
 }());
 
 (function test_user_ids() {
-    const user_ids = buddy_data.get_filtered_and_sorted_user_ids();
+    var user_ids;
 
-    // Even though we have 900 users, we only get the 400 active
+    // Even though we have 1000 users, we only get the 400 active
     // users.  This is a consequence of buddy_data.maybe_shrink_list.
+    user_ids = buddy_data.get_filtered_and_sorted_user_ids();
     assert.equal(user_ids.length, 400);
+
+    user_ids = buddy_data.get_filtered_and_sorted_user_ids('');
+    assert.equal(user_ids.length, 400);
+
+    // We don't match on "s", because it's not at the start of a
+    // word in the name/email.
+    user_ids = buddy_data.get_filtered_and_sorted_user_ids('s');
+    assert.equal(user_ids.length, 0);
+
+    // We match on "h" for the first name, and the result limit
+    // is relaxed for searches.
+    user_ids = buddy_data.get_filtered_and_sorted_user_ids('h');
+    assert.equal(user_ids.length, 1000);
+
+    // We match on "p" for the email.
+    user_ids = buddy_data.get_filtered_and_sorted_user_ids('p');
+    assert.equal(user_ids.length, 1000);
+
+
+    // Make our shrink limit higher, and go back to an empty search.
+    // We won't get all 1000 users, just the present ones.
+    buddy_data.max_size_before_shrinking = 50000;
+
+    user_ids = buddy_data.get_filtered_and_sorted_user_ids('');
+    assert.equal(user_ids.length, 700);
 }());

static/js/buddy_data.js

@@ -11,7 +11,7 @@ var exports = {};
 
 */
 
-var max_size_before_shrinking = 600;
+exports.max_size_before_shrinking = 600;
 
 var presence_descriptions = {
     active: 'is active',
@@ -108,8 +108,18 @@ function user_is_recently_active(user_id) {
     return level(presence.get_status(user_id)) <= 2;
 }
 
-function maybe_shrink_list(user_ids) {
+function maybe_shrink_list(user_ids, filter_text) {
-    if (user_ids.length <= max_size_before_shrinking) {
+    if (user_ids.length <= exports.max_size_before_shrinking) {
+        return user_ids;
+    }
+
+    if (filter_text) {
+        // If the user types something, we want to show all
+        // users matching the text, even if they have not been
+        // online recently.
+        // For super common letters like "s", we may
+        // eventually want to filter down to only users that
+        // are in presence.get_user_ids().
         return user_ids;
     }
 
@@ -132,7 +142,7 @@ exports.get_filtered_and_sorted_user_ids = function (filter_text) {
         user_ids = presence.get_user_ids();
     }
 
-    user_ids = maybe_shrink_list(user_ids);
+    user_ids = maybe_shrink_list(user_ids, filter_text);
 
     return exports.sort_users(user_ids);
 };