Remove `autoExpandCollapsedDiffs` feature flag

app/assets/javascripts/diffs/components/diff_file.vue

@@ -94,11 +94,7 @@ export default {
     },
     'file.file_hash': {
       handler: function watchFileHash() {
-        if (
-          this.glFeatures.autoExpandCollapsedDiffs &&
-          this.viewDiffsFileByFile &&
-          this.file.viewer.collapsed
-        ) {
+        if (this.viewDiffsFileByFile && this.file.viewer.collapsed) {
           this.isCollapsed = false;
           this.handleLoadCollapsedDiff();
         } else {
@@ -108,7 +104,7 @@ export default {
       immediate: true,
     },
     'file.viewer.collapsed': function setIsCollapsed(newVal) {
-      if (!this.viewDiffsFileByFile && !this.glFeatures.autoExpandCollapsedDiffs) {
+      if (!this.viewDiffsFileByFile) {
         this.isCollapsed = newVal;
       }
     },

app/controllers/projects/merge_requests_controller.rb

@@ -34,7 +34,6 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     push_frontend_feature_flag(:multiline_comments, @project, default_enabled: true)
     push_frontend_feature_flag(:file_identifier_hash)
     push_frontend_feature_flag(:batch_suggestions, @project, default_enabled: true)
-    push_frontend_feature_flag(:auto_expand_collapsed_diffs, @project, default_enabled: true)
     push_frontend_feature_flag(:approvals_commented_by, @project, default_enabled: true)
     push_frontend_feature_flag(:hide_jump_to_next_unresolved_in_threads, default_enabled: true)
     push_frontend_feature_flag(:merge_request_widget_graphql, @project)

changelogs/unreleased/defect-expand-all-files-does-nothing.yml

+---
+title: Fix issue causing 'Expand All' button to not work in MR diffs view (Remove `autoExpandCollapsedDiffs` feature flag)
+merge_request: 40960
+author:
+type: fixed

spec/frontend/diffs/components/diff_file_spec.js

@@ -128,26 +128,6 @@ describe('DiffFile', () => {
         });
       });
 
-      it('should auto-expand collapsed files when viewDiffsFileByFile is true', done => {
-        vm.$destroy();
-        window.gon = {
-          features: { autoExpandCollapsedDiffs: true },
-        };
-        vm = createComponentWithStore(Vue.extend(DiffFileComponent), createStore(), {
-          file: JSON.parse(JSON.stringify(diffFileMockDataUnreadable)),
-          canCurrentUserFork: false,
-          viewDiffsFileByFile: true,
-        }).$mount();
-
-        vm.$nextTick(() => {
-          expect(vm.$el.innerText).not.toContain('This diff is collapsed');
-
-          window.gon = {};
-
-          done();
-        });
-      });
-
       it('should be collapsed for renamed files', done => {
         vm.renderIt = true;
         vm.isCollapsed = false;