blueslip: Replace fatal with throw new Error(…).

This makes it clear to humans and ESLint that execution will not
continue.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

docs/subsystems/logging.md

@@ -130,10 +130,9 @@ new feature hard to miss.
   this log from the browser console using `blueslip.get_log()`.
 
 Blueslip supports several error levels:
-* `blueslip.fatal`: For fatal errors that cannot be easily recovered
-  from.  We try to avoid using it, since it kills the current JS
-  thread, rather than returning execution to the caller.  Unhandled
-  exceptions in our JS code are treated like `blueslip.fatal`.
+* `throw new Error(…)`: For fatal errors that cannot be easily
+  recovered from.  We try to avoid using it, since it kills the
+  current JS thread, rather than returning execution to the caller.
 * `blueslip.error`: For logging of events that are definitely caused
   by a bug and thus sufficiently important to be reported, but where
   we can handle the error without creating major user-facing problems

static/js/blueslip.js

@@ -246,11 +246,9 @@ exports.error = function blueslip_error(msg, more_info, stack) {
     if (page_params.debug_mode) {
         throw new BlueslipError(msg, more_info);
     }
-};
 
-exports.fatal = function blueslip_fatal(msg, more_info) {
-    report_error(msg, Error().stack, {more_info});
-    throw new BlueslipError(msg, more_info);
+    // This function returns to its caller in production!  To raise a
+    // fatal error even in production, use throw new Error(…) instead.
 };
 
 exports.timings = new Map();

static/js/message_fetch.js

@@ -275,8 +275,7 @@ exports.get_backfill_anchor = function (msg_list) {
 
     // msg_list is empty, which is an impossible
     // case, raise a fatal error.
-    blueslip.fatal("There are no message available to backfill.");
-    return;
+    throw new Error("There are no message available to backfill.");
 };
 
 exports.get_frontfill_anchor = function (msg_list) {
@@ -295,8 +294,7 @@ exports.get_frontfill_anchor = function (msg_list) {
     // and user cannot be scrolling down on an empty message_list to
     // fetch more data, and if user is, then the available data is wrong
     // and we raise a fatal error.
-    blueslip.fatal("There are no message available to frontfill.");
-    return;
+    throw new Error("There are no message available to frontfill.");
 };
 
 exports.maybe_load_older_messages = function (opts) {

static/js/message_list.js

@@ -152,7 +152,7 @@ class MessageList {
         const convert_id = (str_id) => {
             const id = parseFloat(str_id);
             if (isNaN(id)) {
-                blueslip.fatal("Bad message id " + str_id);
+                throw new Error("Bad message id " + str_id);
             }
             return id;
         };
@@ -184,7 +184,7 @@ class MessageList {
                 id,
                 items_length: this.data.num_items(),
             };
-            blueslip.fatal("Cannot select id -1", error_data);
+            throw new Error("Cannot select id -1", error_data);
         }
 
         id = closest_id;

static/js/message_list_data.js

@@ -442,7 +442,7 @@ class MessageListData {
         messages.forEach((elem) => {
             const id = parseFloat(elem.id);
             if (isNaN(id)) {
-                blueslip.fatal("Bad message id");
+                throw new Error("Bad message id");
             }
             if (this._is_localonly_id(id)) {
                 this._local_only.add(id);

static/js/settings_users.js

@@ -130,7 +130,7 @@ function get_status_field() {
         case "bot-list-admin":
             return $("#bot-field-status").expectOne();
         default:
-            blueslip.fatal("Invalid admin settings page");
+            throw new Error("Invalid admin settings page");
     }
 }
 

static/js/stream_data.js

@@ -761,8 +761,8 @@ exports.create_streams = function (streams) {
 
 exports.create_sub_from_server_data = function (attrs) {
     if (!attrs.stream_id) {
-        // fail fast (blueslip.fatal will throw an error on our behalf)
-        blueslip.fatal("We cannot create a sub without a stream_id");
+        // fail fast
+        throw new Error("We cannot create a sub without a stream_id");
     }
 
     let sub = exports.get_sub_by_id(attrs.stream_id);