message_fetch: Use user IDs for supported operators.

The approach taken here is basically use user IDs in operator that
support it when sending the request for fetching the messages
(see comments in code for more details).

frontend_tests/node_tests/message_fetch.js

@@ -12,6 +12,7 @@ zrequire('Filter', 'js/filter');
 zrequire('MessageListData', 'js/message_list_data');
 zrequire('message_list');
 zrequire('util');
+zrequire('people');
 
 set_global('page_params', {
     have_initial_messages: true,
@@ -37,6 +38,13 @@ set_global('stream_list', {
     maybe_scroll_narrow_into_view: () => {},
 });
 
+var alice = {
+    email: 'alice@example.com',
+    user_id: 7,
+    full_name: 'Alice',
+};
+people.add(alice);
+
 muting.is_topic_muted = function () { return false; };
 resize.resize_bottom_whitespace = noop;
 server_events.home_view_loaded = noop;
@@ -273,7 +281,7 @@ function simulate_narrow() {
 
     narrow_state.active = function () { return true; };
     narrow_state.public_operators = function () {
-        return 'operators-stub';
+        return [{ operator: 'pm-with', operand: alice.email }];
     };
 
     var msg_list = new message_list.MessageList({
@@ -321,7 +329,7 @@ run_test('loading_newer', () => {
                 anchor: '444',
                 num_before: 0,
                 num_after: 100,
-                narrow: '"operators-stub"',
+                narrow: `[{"operator":"pm-with","operand":[${alice.user_id}]}]`,
                 client_gravatar: true,
             },
             resp: {

frontend_tests/node_tests/people.js

@@ -853,3 +853,29 @@ run_test('initialize', () => {
     assert.equal(global.page_params.cross_realm_bots, undefined);
     assert.equal(global.page_params.realm_non_active_users, undefined);
 });
+
+run_test('emails_strings_to_user_ids_array', function () {
+    const steven = {
+        email: 'steven@example.com',
+        user_id: 7,
+        full_name: 'Steven',
+    };
+
+    const maria = {
+        email: 'maria@example.com',
+        user_id: 728,
+        full_name: 'Maria',
+    };
+
+    people.add(steven);
+    people.add(maria);
+
+    let user_ids = people.emails_strings_to_user_ids_array(`${steven.email},${maria.email}`);
+    assert.deepEqual(user_ids, [steven.user_id, maria.user_id]);
+
+    blueslip.set_test_data('warn', 'Unknown emails: dummyuser@example.com');
+    user_ids = people.emails_strings_to_user_ids_array('dummyuser@example.com');
+    assert.equal(user_ids, undefined);
+    assert.equal(blueslip.get_test_logs('warn').length, 1);
+    blueslip.clear_test_data();
+});

static/js/message_fetch.js

@@ -104,6 +104,29 @@ function get_messages_success(data, opts) {
     resize.resize_bottom_whitespace();
 }
 
+// This function modifies the data.narrow filters to use user IDs
+// instead of emails string if it is supported. We currently don't set
+// or convert the emails string to user IDs directly into the Filter code
+// because doing so breaks the app in various modules that expect emails string.
+function handle_user_ids_supported_operators(data) {
+    var user_ids_supported_operators = ['pm-with'];
+
+    if (data.narrow === undefined) {
+        return data;
+    }
+
+    data.narrow = JSON.parse(data.narrow);
+    data.narrow = _.map(data.narrow, function (filter) {
+        if (user_ids_supported_operators.indexOf(filter.operator) !== -1) {
+            filter.operand = people.emails_strings_to_user_ids_array(filter.operand);
+        }
+
+        return filter;
+    });
+
+    data.narrow = JSON.stringify(data.narrow);
+    return data;
+}
 
 exports.load_messages = function (opts) {
     var data = {anchor: opts.anchor,
@@ -139,6 +162,7 @@ exports.load_messages = function (opts) {
     }
 
     data.client_gravatar = true;
+    data = handle_user_ids_supported_operators(data);
 
     channel.get({
         url: '/json/messages',

static/js/people.js

@@ -188,6 +188,16 @@ exports.user_ids_string_to_ids_array = function (user_ids_string) {
     return ids;
 };
 
+exports.emails_strings_to_user_ids_array = function (emails_string) {
+    var user_ids_string = exports.emails_strings_to_user_ids_string(emails_string);
+    if (user_ids_string === undefined) {
+        return;
+    }
+
+    var user_ids_array = exports.user_ids_string_to_ids_array(user_ids_string);
+    return user_ids_array;
+};
+
 exports.reply_to_to_user_ids_string = function (emails_string) {
     // This is basically emails_strings_to_user_ids_string
     // without blueslip warnings, since it can be called with

zerver/views/messages.py

@@ -510,6 +510,10 @@ def narrow_parameter(json: str) -> Optional[List[Dict[str, Any]]]:
             return dict(operator=elem[0], operand=elem[1])
 
         if isinstance(elem, dict):
+            # Make sure to sync this list to frontend also when adding a new operator.
+            # that supports user IDs. Relevant code is located in static/js/message_fetch.js
+            # in handle_user_ids_supported_operators function where you will need to update
+            # the user_ids_supported_operator.
             user_ids_supported_operators = ['pm-with']
             if elem.get('operator', '') in user_ids_supported_operators:
                 operand_validator = check_string_or_int_list