Restore the ability for alt+tab to restore the Terminal after minimiz…

…ing with taskbar (microsoft#13624)

Curiously, at least on Windows 10 (and rarely on Windows 11), if you minimize the Terminal by clicking on the taskbar, then alt-tab to try and restore the window, the Taskbar will decide to call `SwitchToWindow` on the invisible, owned ConPTY window instead of the main window. When that happens, ConPTY'll get a `WM_SIZE(SIZE_RESTORED, lParam=0)`. The main window will NOT get a `SwitchToWindow` called. If ConPTY doesn't actually inform the hosting process about this, then the main HWND might stay hidden.

* Refer to microsoft#13158 where we disabled this.
* Closes microsoft#13589
* Closes microsoft#13248
* Tested manually on a Windows 10 VM.
* Confirmed that opening tabs while maximized/snapped doesn't restore down.
* `[Native]::ShowWindow([Native]::GetConsoleWindow(), 6)` still works

(cherry picked from commit d1fc112)
Service-Card-Id: 84673887
Service-Version: 1.15

src/cascadia/WindowsTerminal/IslandWindow.cpp

@@ -834,10 +834,20 @@ void IslandWindow::SetAlwaysOnTop(const bool alwaysOnTop)
 // - <none>
 void IslandWindow::ShowWindowChanged(const bool showOrHide)
 {
-    const auto hwnd = GetHandle();
-    if (hwnd)
+    if (const auto hwnd = GetHandle())
     {
-        PostMessage(hwnd, WM_SYSCOMMAND, showOrHide ? SC_RESTORE : SC_MINIMIZE, 0);
+        // IMPORTANT!
+        //
+        // ONLY "restore" if already minimized. If the window is maximized or
+        // snapped, a restore will restore-down the window instead.
+        if (showOrHide == true && ::IsIconic(hwnd))
+        {
+            ::PostMessage(hwnd, WM_SYSCOMMAND, SC_RESTORE, 0);
+        }
+        else if (showOrHide == false)
+        {
+            ::PostMessage(hwnd, WM_SYSCOMMAND, SC_MINIMIZE, 0);
+        }
     }
 }
 

src/interactivity/base/InteractivityFactory.cpp

@@ -436,6 +436,15 @@ void InteractivityFactory::SetPseudoWindowCallback(std::function<void(bool)> fun
     // It can be fun to toggle WM_QUERYOPEN but DefWindowProc returns TRUE.
     case WM_SIZE:
     {
+        // Curiously, at least on Windows 10 (and rarely on Windows 11), if you
+        // minimize the Terminal by clicking on the taskbar, then alt-tab to try
+        // and restore the window, the Taskbar will decide to call
+        // SwitchToWindow on us, the invisible, owned window of the main window.
+        // When that happens, we'll get a WM_SIZE(SIZE_RESTORED, lParam=0). The
+        // main window will NOT get a SwitchToWindow called. If we don't
+        // actually inform the hosting process about this, then the main HWND
+        // might stay hidden. Refer to GH#13589
+
         if (wParam == SIZE_RESTORED)
         {
             _WritePseudoWindowCallback(true);
@@ -447,23 +456,23 @@ void InteractivityFactory::SetPseudoWindowCallback(std::function<void(bool)> fun
         }
         break;
     }
-        // case WM_WINDOWPOSCHANGING:
-        // As long as user32 didn't eat the `ShowWindow` call because the window state requested
-        // matches the existing WS_VISIBLE state of the HWND... we should hear from it in WM_WINDOWPOSCHANGING.
-        // WM_WINDOWPOSCHANGING can tell us a bunch through the flags fields.
-        // We can also check IsIconic/IsZoomed on the HWND during the message
-        // and we could suppress the change to prevent things from happening.
+    // case WM_WINDOWPOSCHANGING:
+    //     As long as user32 didn't eat the `ShowWindow` call because the window state requested
+    //     matches the existing WS_VISIBLE state of the HWND... we should hear from it in WM_WINDOWPOSCHANGING.
+    //     WM_WINDOWPOSCHANGING can tell us a bunch through the flags fields.
+    //     We can also check IsIconic/IsZoomed on the HWND during the message
+    //     and we could suppress the change to prevent things from happening.
     // case WM_SYSCOMMAND:
-    // WM_SYSCOMMAND will not come through. Don't try.
+    //   WM_SYSCOMMAND will not come through. Don't try.
+    // WM_SHOWWINDOW does come through on some of the messages.
     case WM_SHOWWINDOW:
-        // WM_SHOWWINDOW comes through on some of the messages.
+    {
+        if (0 == lParam) // Someone explicitly called ShowWindow on us.
         {
-            if (0 == lParam) // Someone explicitly called ShowWindow on us.
-            {
-                _WritePseudoWindowCallback((bool)wParam);
-            }
+            _WritePseudoWindowCallback((bool)wParam);
         }
     }
+    }
     // If we get this far, call the default window proc
     return DefWindowProcW(hWnd, Message, wParam, lParam);
 }
@@ -478,18 +487,12 @@ void InteractivityFactory::SetPseudoWindowCallback(std::function<void(bool)> fun
 // - <none>
 void InteractivityFactory::_WritePseudoWindowCallback(bool showOrHide)
 {
-    // BODGY
-    //
-    // GH#13158 - At least temporarily, only allow the PTY to HIDE the terminal
-    // window. There seem to be many issues with this so far, and the quickest
-    // route to mitigate them seems to be limiting the interaction here to
-    // allowing ConPTY to minimize the terminal only. This will still allow
-    // applications to hide the Terminal via GetConsoleWindow(), but should
-    // broadly prevent any other impact of this feature.
+    // IMPORTANT!
     //
-    // Should we need to restore this functionality in the future, we should
-    // only do so with great caution.
-    if (_pseudoWindowMessageCallback && showOrHide == false)
+    // A hosting terminal window should only "restore" itself in response to
+    // this message, if it's already minimized. If the window is maximized a
+    // restore will restore-down the window instead.
+    if (_pseudoWindowMessageCallback)
     {
         _pseudoWindowMessageCallback(showOrHide);
     }