Add pm_perma_link helper.

frontend_tests/node_tests/people.js

@@ -403,6 +403,7 @@ run_test('message_methods', () => {
         sender_id: charles.user_id,
     };
     assert.equal(people.pm_with_url(message), '#narrow/pm-with/451,452-group');
+    assert.equal(people.pm_perma_link(message), '#narrow/pm-with/30,451,452-group');
     assert.equal(people.pm_reply_to(message),
                  'Athens@example.com,charles@example.com');
     assert.equal(people.small_avatar_url(message),
@@ -417,6 +418,7 @@ run_test('message_methods', () => {
         avatar_url: 'legacy.png',
     };
     assert.equal(people.pm_with_url(message), '#narrow/pm-with/452-athens');
+    assert.equal(people.pm_perma_link(message), '#narrow/pm-with/30,452-pm');
     assert.equal(people.pm_reply_to(message),
                  'Athens@example.com');
     assert.equal(people.small_avatar_url(message),
@@ -446,9 +448,11 @@ run_test('message_methods', () => {
         ],
     };
     assert.equal(people.pm_with_url(message), '#narrow/pm-with/30-me');
+    assert.equal(people.pm_perma_link(message), '#narrow/pm-with/30-pm');
 
     message = { type: 'stream' };
     assert.equal(people.pm_with_user_ids(message), undefined);
+    assert.equal(people.all_user_ids_in_pm(message), undefined);
 
     // Test undefined user_ids
     assert.equal(people.pm_reply_to(message), undefined);

frontend_tests/node_tests/people_errors.js

@@ -82,7 +82,9 @@ run_test('blueslip', () => {
     blueslip.set_test_data('error', 'Empty recipient list in message');
     people.pm_with_user_ids(message);
     people.group_pm_with_user_ids(message);
-    assert.equal(blueslip.get_test_logs('error').length, 2);
+    people.all_user_ids_in_pm(message);
+    assert.equal(people.pm_perma_link(message), undefined);
+    assert.equal(blueslip.get_test_logs('error').length, 4);
     blueslip.clear_test_data();
 
     var charles = {

static/js/people.js

@@ -341,6 +341,24 @@ exports.pm_lookup_key = function (user_ids_string) {
     return user_ids.join(',');
 };
 
+exports.all_user_ids_in_pm = function (message) {
+    if (message.type !== 'private') {
+        return;
+    }
+
+    if (message.display_recipient.length === 0) {
+        blueslip.error('Empty recipient list in message');
+        return;
+    }
+
+    var user_ids = _.map(message.display_recipient, function (elem) {
+        return elem.user_id || elem.id;
+    });
+
+    user_ids = sort_numerically(user_ids);
+    return user_ids;
+};
+
 exports.pm_with_user_ids = function (message) {
     if (message.type !== 'private') {
         return;
@@ -382,6 +400,26 @@ exports.group_pm_with_user_ids = function (message) {
     return false;
 };
 
+exports.pm_perma_link = function (message) {
+    var user_ids = exports.all_user_ids_in_pm(message);
+
+    if (!user_ids) {
+        return;
+    }
+
+    var suffix;
+
+    if (user_ids.length >= 3) {
+        suffix = 'group';
+    } else {
+        suffix = 'pm';
+    }
+
+    var slug = user_ids.join(',') + '-' + suffix;
+    var uri = "#narrow/pm-with/" + slug;
+    return uri;
+};
+
 exports.pm_with_url = function (message) {
     var user_ids = exports.pm_with_user_ids(message);