MM-65815: Fix search results causing blank page when leaving channel (mattermost#33962)

* getSearchResults: handle posts removed from the store

* remove unused posts caching

* add unit tests for getSearchResults selector

Tests verify that the selector properly filters out posts that
don't exist in the posts state when referenced in search results.

Author: lieut-data

webapp/channels/src/components/search_results/index.tsx

@@ -30,25 +30,15 @@ function makeMapStateToProps() {
     let results: Post[];
     let fileResults: FileSearchResultItem[];
     let files: FileSearchResultItem[] = [];
-    let posts: Post[];
     const addDateSeparatorsForSearchResults = makeAddDateSeparatorsForSearchResults();
 
     return function mapStateToProps(state: GlobalState, ownProps: OwnProps) {
         const newResults = getSearchResults(state);
 
-        // Cache posts and channels
+        // Cache results
         if (newResults && newResults !== results) {
             results = newResults;
 
-            posts = [];
-            results.forEach((post) => {
-                if (!post) {
-                    return;
-                }
-
-                posts.push(post);
-            });
-
             if (ownProps.isPinnedPosts) {
                 results = results.sort((postA: Post | FileSearchResultItem, postB: Post | FileSearchResultItem) => postB.create_at - postA.create_at);
             }

webapp/channels/src/packages/mattermost-redux/src/selectors/entities/posts.test.ts

@@ -1438,3 +1438,80 @@ describe('makeGetProfilesForThread', () => {
         expect(getProfilesForThread(state, '1001')).toEqual([]);
     });
 });
+
+describe('getSearchResults', () => {
+    it('should return empty array when no search results', () => {
+        const state = {
+            entities: {
+                posts: {
+                    posts: {},
+                },
+                search: {
+                    results: [],
+                },
+            },
+        } as unknown as GlobalState;
+
+        const results = Selectors.getSearchResults(state);
+        expect(results).toEqual([]);
+    });
+
+    it('should return posts for valid search result IDs', () => {
+        const post1 = p({id: 'post1', message: 'Hello'});
+        const post2 = p({id: 'post2', message: 'World'});
+
+        const state = {
+            entities: {
+                posts: {
+                    posts: {
+                        post1,
+                        post2,
+                    },
+                },
+                search: {
+                    results: ['post1', 'post2'],
+                },
+            },
+        } as unknown as GlobalState;
+
+        const results = Selectors.getSearchResults(state);
+        expect(results).toEqual([post1, post2]);
+    });
+
+    it('should filter out non-existent posts from search results', () => {
+        const post1 = p({id: 'post1', message: 'Hello'});
+
+        const state = {
+            entities: {
+                posts: {
+                    posts: {
+                        post1,
+                    },
+                },
+                search: {
+                    results: ['post1', 'non_existent_post', 'another_missing_post'],
+                },
+            },
+        } as unknown as GlobalState;
+
+        const results = Selectors.getSearchResults(state);
+        expect(results).toEqual([post1]);
+        expect(results).toHaveLength(1);
+    });
+
+    it('should return empty array when all search result posts are non-existent', () => {
+        const state = {
+            entities: {
+                posts: {
+                    posts: {},
+                },
+                search: {
+                    results: ['non_existent_post1', 'non_existent_post2'],
+                },
+            },
+        } as unknown as GlobalState;
+
+        const results = Selectors.getSearchResults(state);
+        expect(results).toEqual([]);
+    });
+});

webapp/channels/src/packages/mattermost-redux/src/selectors/entities/posts.ts

@@ -336,7 +336,8 @@ export const getSearchResults: (state: GlobalState) => Post[] = createSelector(
             return [];
         }
 
-        return postIds.map((id) => posts[id]);
+        // Filter out posts that may no longer exist
+        return postIds.map((id) => posts[id]).filter((post) => post);
     },
 );