From 6b00466a851ec234d1580998d32395263b8eea0d Mon Sep 17 00:00:00 2001
From: R Midhun Suresh <hi@midhun.dev>
Date: Tue, 7 Apr 2026 17:35:36 +0530
Subject: [PATCH] Collapsible Left Panel - Clicking on separator should expand
 to 100% when no width is available in settings (#33053)

* Expand panel to full width

* Write tests
---
 .../viewmodels/structures/ResizerViewModel.ts |  2 +-
 .../structures/ResizerViewModel-test.ts       | 35 +++++++++++++------
 2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/apps/web/src/viewmodels/structures/ResizerViewModel.ts b/apps/web/src/viewmodels/structures/ResizerViewModel.ts
index 3eeefed245..724bb6fd6e 100644
--- a/apps/web/src/viewmodels/structures/ResizerViewModel.ts
+++ b/apps/web/src/viewmodels/structures/ResizerViewModel.ts
@@ -76,7 +76,7 @@ export class ResizerViewModel
     public onSeparatorClick = (): void => {
         if (this.panelHandle?.isCollapsed()) {
             const lastSize = SettingsStore.getValue("RoomList.panelSize");
-            this.panelHandle.resize(`${lastSize}%`);
+            this.panelHandle.resize(`${lastSize ?? 100}%`);
         }
     };
 
diff --git a/apps/web/test/viewmodels/structures/ResizerViewModel-test.ts b/apps/web/test/viewmodels/structures/ResizerViewModel-test.ts
index 706efa7524..ea514fdafb 100644
--- a/apps/web/test/viewmodels/structures/ResizerViewModel-test.ts
+++ b/apps/web/test/viewmodels/structures/ResizerViewModel-test.ts
@@ -68,18 +68,33 @@ describe("LeftPanelResizerViewModel", () => {
         expect(() => vm.onSeparatorClick()).not.toThrow();
     });
 
-    it("should expand panel on onSeparatorClick()", () => {
-        const vm = new ResizerViewModel();
-        SettingsStore.setValue("RoomList.panelSize", null, SettingLevel.DEVICE, 34);
-        const mockHandle = {
-            resize: jest.fn(),
-            isCollapsed: jest.fn().mockReturnValue(true),
-        } as unknown as PanelImperativeHandle;
-        vm.setPanelHandle(mockHandle);
+    describe("should expand panel on onSeparatorClick()", () => {
+        it("to last non-zero width that the user set", () => {
+            const vm = new ResizerViewModel();
+            SettingsStore.setValue("RoomList.panelSize", null, SettingLevel.DEVICE, 34);
+            const mockHandle = {
+                resize: jest.fn(),
+                isCollapsed: jest.fn().mockReturnValue(true),
+            } as unknown as PanelImperativeHandle;
+            vm.setPanelHandle(mockHandle);
 
-        vm.onSeparatorClick();
+            vm.onSeparatorClick();
 
-        expect(mockHandle.resize).toHaveBeenCalledWith("34%");
+            expect(mockHandle.resize).toHaveBeenCalledWith("34%");
+        });
+
+        it("to maximum size of the panel", () => {
+            const vm = new ResizerViewModel();
+            const mockHandle = {
+                resize: jest.fn(),
+                isCollapsed: jest.fn().mockReturnValue(true),
+            } as unknown as PanelImperativeHandle;
+            vm.setPanelHandle(mockHandle);
+
+            vm.onSeparatorClick();
+
+            expect(mockHandle.resize).toHaveBeenCalledWith("100%");
+        });
     });
 
     it("should set isFocusedViaKeyboard state correctly", () => {