flow: Mark message- and realm-emoji-related types read-only and exact.

We basically make the assumption throughout our codebase that we don't
mutate data like these; this lets us propagate that assumption through
and have it checked by machine.

Author: gnprice

src/api/apiTypes.js

@@ -28,12 +28,12 @@ export type DevUser = {
 export type ReactionType = 'unicode_emoji' | 'realm_emoji' | 'zulip_extra_emoji';
 
 /** An emoji reaction to a message. */
-export type Reaction = {
-  user: {
+export type Reaction = $ReadOnly<{|
+  user: $ReadOnly<{|
     email: string,
     full_name: string,
     user_id: number,
-  },
+  |}>,
   emoji_name: string,
   reaction_type: ReactionType,
 
@@ -45,16 +45,16 @@ export type Reaction = {
    *   https://github.com/zulip/zulip/blob/master/zerver/models.py
    */
   emoji_code: string,
-};
+|}>;
 
-export type MessageEdit = {
+export type MessageEdit = $ReadOnly<{|
   prev_content?: string,
   prev_rendered_content?: string,
   prev_rendered_content_version?: number,
   prev_subject?: string,
   timestamp: number,
   user_id: number,
-};
+|}>;
 
 /**
  * A Zulip message.
@@ -91,7 +91,7 @@ export type MessageEdit = {
  *
  * See also `Outbox`.
  */
-export type Message = {
+export type Message = $ReadOnly<{
   /** Our own flag; if true, really type `Outbox`. */
   isOutbox: false,
 
@@ -115,20 +115,20 @@ export type Message = {
    *  * Absent in the Redux `state.messages`; we move the information to a
    *    separate subtree `state.flags`.
    */
-  flags?: string[],
+  flags?: $ReadOnlyArray<string>,
 
   /** The rest are believed to really appear in `message` events. */
   avatar_url: ?string,
   client: string,
   content: string,
   content_type: 'text/html' | 'text/markdown',
   display_recipient: $FlowFixMe, // `string` for type stream, else PmRecipientUser[].
-  edit_history: MessageEdit[],
+  edit_history: $ReadOnlyArray<MessageEdit>,
   gravatar_hash: string,
   id: number,
   is_me_message: boolean,
   last_edit_timestamp?: number,
-  reactions: Reaction[],
+  reactions: $ReadOnlyArray<Reaction>,
   recipient_id: number,
   sender_email: string,
   sender_full_name: string,
@@ -137,11 +137,11 @@ export type Message = {
   sender_short_name: string,
   stream_id: number, // FixMe: actually only for type `stream`, else absent.
   subject: string,
-  subject_links: string[],
-  submessages: Message[],
+  subject_links: $ReadOnlyArray<string>,
+  submessages: $ReadOnlyArray<Message>,
   timestamp: number,
   type: 'stream' | 'private',
-};
+}>;
 
 export type NarrowOperator =
   | 'is'
@@ -154,31 +154,31 @@ export type NarrowOperator =
   | 'pm-with'
   | 'search';
 
-export type NarrowElement = {
+export type NarrowElement = $ReadOnly<{|
   operand: string,
   operator?: NarrowOperator, // TODO type: this shouldn't be absent.
-};
+|}>;
 
-export type Narrow = NarrowElement[];
+export type Narrow = $ReadOnlyArray<NarrowElement>;
 
-export type RealmEmojiType = {
-  author: {
+export type RealmEmojiType = $ReadOnly<{|
+  author: $ReadOnly<{|
     email: string,
     full_name: string,
     id: number,
-  },
+  |}>,
   deactivated: boolean,
   id: number,
   name: string,
   source_url: string,
   // This prevents accidentally using this type as a map.
   // See https://github.com/facebook/flow/issues/4257#issuecomment-321951793
   [empty]: mixed,
-};
+|}>;
 
-export type RealmEmojiState = {
+export type RealmEmojiState = $ReadOnly<{
   [id: string]: RealmEmojiType,
-};
+}>;
 
 export type RealmFilter = [string, string, number];
 

src/chat/flagsReducers.js

@@ -35,8 +35,8 @@ const initialState = {
 
 const addFlagsForMessages = (
   state: FlagsState,
-  messages: number[],
-  flags?: string[],
+  messages: $ReadOnlyArray<number>,
+  flags?: $ReadOnlyArray<string>,
 ): FlagsState => {
   if (!messages || messages.length === 0 || !flags || flags.length === 0) {
     return state;

src/emoji/data.js

@@ -26,7 +26,7 @@ export const codeToEmojiMap = unicodeEmojiNames.reduce((obj, name) => {
 
 export const getFilteredEmojiNames = (
   query: string,
-  activeRealmEmojiByName: { [string]: RealmEmojiType },
+  activeRealmEmojiByName: $ReadOnly<{ [string]: RealmEmojiType }>,
 ): string[] => {
   const names = [...unicodeEmojiNames, ...Object.keys(activeRealmEmojiByName)];
   return Array.from(new Set([...names.filter(x => x.indexOf(query) === 0).sort()]));

src/message/messageUpdates.js

@@ -4,7 +4,7 @@ import type { Narrow } from '../types';
 
 type Props = $ReadOnly<{
   narrow: Narrow,
-  messages: $ReadOnlyArray<{ id: number }>,
+  messages: $ReadOnlyArray<$ReadOnly<{ id: number }>>,
 }>;
 
 type TransitionProps = {

src/reactions/aggregateReactions.js

@@ -1,7 +1,10 @@
 /* @flow strict-local */
 import type { Reaction, AggregatedReaction } from '../types';
 
-export default (reactions: Reaction[], ownEmail: string): AggregatedReaction[] =>
+export default (
+  reactions: $ReadOnlyArray<Reaction>,
+  ownEmail: string,
+): $ReadOnlyArray<AggregatedReaction> =>
   Array.from(
     reactions
       .reduce((reactionMap, x) => {

src/webview/MessageList.js

@@ -64,7 +64,7 @@ export type BackgroundData = $ReadOnly<{
   flags: FlagsState,
   mute: MuteState,
   ownEmail: string,
-  allRealmEmojiById: { [id: string]: RealmEmojiType },
+  allRealmEmojiById: $ReadOnly<{ [id: string]: RealmEmojiType }>,
   twentyFourHourTime: boolean,
   subscriptions: Subscription[],
 }>;

src/webview/html/messageAsHtml.js

@@ -30,7 +30,7 @@ const messageTagsAsHtml = (isStarred: boolean, timeEdited: number | void): strin
 
 const messageReactionAsHtml = (
   reaction: AggregatedReaction,
-  allRealmEmojiById: { [id: string]: RealmEmojiType },
+  allRealmEmojiById: $ReadOnly<{ [id: string]: RealmEmojiType }>,
 ): string =>
   template`<span onClick="" class="reaction${reaction.selfReacted ? ' self-voted' : ''}"
         data-name="${reaction.name}"
@@ -42,9 +42,9 @@ const messageReactionAsHtml = (
   }&nbsp;${reaction.count}</span>`;
 
 const messageReactionListAsHtml = (
-  reactions: Reaction[],
+  reactions: $ReadOnlyArray<Reaction>,
   ownEmail: string,
-  allRealmEmojiById: { [id: string]: RealmEmojiType },
+  allRealmEmojiById: $ReadOnly<{ [id: string]: RealmEmojiType }>,
 ): string => {
   if (reactions.length === 0) {
     return '';