Improve typing of normalizeRecipients

src/chat/__tests__/narrowsReducer-test.js

@@ -175,6 +175,7 @@ describe('narrowsReducer', () => {
 
     const message = {
       id: 1,
+      type: 'private',
       display_recipient: [{ email: '[email protected]' }],
       flags: [],
     };

src/utils/__tests__/recipient-test.js

@@ -20,15 +20,6 @@ describe('normalizeRecipients', () => {
 
     expect(normalized).toEqual(expectedResult);
   });
-
-  test('on a string input, returns same string', () => {
-    const recipients = '[email protected]';
-    const expectedResult = '[email protected]';
-
-    const normalized = normalizeRecipients(recipients);
-
-    expect(normalized).toEqual(expectedResult);
-  });
 });
 
 describe('normalizeRecipientsSansMe', () => {

src/utils/narrow.js

@@ -211,6 +211,9 @@ export const isSearchNarrow = (narrow?: Narrow): boolean =>
 /** (For search narrows, just returns false.) */
 export const isMessageInNarrow = (message: Message, narrow: Narrow, ownEmail: string): boolean => {
   const matchRecipients = (emails: string[]) => {
+    if (message.type !== 'private') {
+      return false;
+    }
     const normalizedRecipients = normalizeRecipients(message.display_recipient);
     const normalizedNarrow = [...emails, ownEmail].sort().join(',');
     return normalizedRecipients === ownEmail || normalizedRecipients === normalizedNarrow;

src/utils/recipient.js

@@ -12,15 +12,26 @@ import type { PmRecipientUser, Message, Outbox, User } from '../types';
 const filterRecipients = (recipients: PmRecipientUser[], ownUserId: number): PmRecipientUser[] =>
   recipients.length === 1 ? recipients : recipients.filter(r => r.id !== ownUserId);
 
-// TODO types: this union is confusing
-export const normalizeRecipients = (recipients: $ReadOnlyArray<{ email: string, ... }> | string) =>
-  !Array.isArray(recipients)
-    ? recipients
-    : recipients
-        .map(s => s.email.trim())
-        .filter(x => x.length > 0)
-        .sort()
-        .join(',');
+/**
+ * "Hash" a set of recipients, represented as an unsorted list, into a string.
+ * (A "recipient" is usually either a `User` or a `PmRecipientUser`.)
+ *
+ * Considered as a map from sets of users to strings, this function is
+ * injective. Do not rely on any other property of its output.
+ */
+// Unfortunately we do exactly that in a lot of places.
+//
+// TODO: fix that. Then, possibly, make this function nontrivial to invert, so
+// that we can't accidentally do that again.
+export const normalizeRecipients = (recipients: $ReadOnlyArray<{ email: string, ... }>): string =>
+  recipients
+    // The purpose of the `trim` and `filter` below are obscure; they've been
+    // present without explanation since antiquity (commit a2419662d4,
+    // 0.7.1~251). As of 2020-05, they're believed to be superfluous.
+    .map(s => s.email.trim())
+    .filter(x => x.length > 0)
+    .sort()
+    .join(',');
 
 export const normalizeRecipientsSansMe = (
   recipients: $ReadOnlyArray<{ email: string, ... }>,