Prevent resizing terminal to a lower-than-minimum width (#8066)

Until now, we relied on WM_SIZING to ensure that the island is not
downsized below minimal allowed dimensions. However, on some occasions
WM_WINDOWPOSCHANGED, e.g. when anchoring a window to the top/bottom of
the screen. This message will use dimensions obtained from
WM_GETMINMAXINFO. Until now we didn't override this value, falling back
to the defaults. As a result we got an inconsistent behavior (at least
when attaching the anchor).

I added logic very similar to the one we use in IslandWindow::_OnSizing
to the MINMAXINFO handler: snap the client area, add non client
exclusive are, consider DPI along the computation.

* Manual testing of minimizing, maximizing, resizing, attaching
  different anchors, etc.

Closes #8026

(cherry picked from commit e3fcfcc)

.github/actions/spell-check/expect/expect.txt

@@ -2828,4 +2828,6 @@ zy
 AAAAABBBBBBCCC
 AAAAA
 BBBBBCCC
-abcd
+abcd
+LPMINMAXINFO
+MINMAXINFO

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -1749,7 +1749,7 @@ namespace winrt::TerminalApp::implementation
     // - See Pane::CalcSnappedDimension
     float TerminalPage::CalcSnappedDimension(const bool widthOrHeight, const float dimension) const
     {
-        if (_settings.GlobalSettings().SnapToGridOnResize())
+        if (_settings && _settings.GlobalSettings().SnapToGridOnResize())
         {
             if (auto index{ _GetFocusedTabIndex() })
             {

src/cascadia/WindowsTerminal/IslandWindow.cpp

@@ -276,10 +276,77 @@ void IslandWindow::OnSize(const UINT width, const UINT height)
     }
 }
 
+// Method Description:
+// - Handles a WM_GETMINMAXINFO message, issued before the window sizing starts.
+//   This message allows to modify the minimal and maximal dimensions of the window.
+//   We focus on minimal dimensions here
+//   (the maximal dimension will be calculate upon maximizing)
+//   Our goal is to protect against to downsizing to less than minimal allowed dimensions,
+//   that might occur in the scenarios where _OnSizing is bypassed.
+//   An example of such scenario is anchoring the window to the top/bottom screen border
+//   in order to maximize window height (GH# 8026).
+//   The computation is similar to what we do in _OnSizing:
+//   we need to consider both the client area and non-client exclusive area sizes,
+//   while taking DPI into account as well.
+// Arguments:
+// - lParam: Pointer to the requested MINMAXINFO struct,
+//   a ptMinTrackSize field of which we want to update with the computed dimensions.
+//   It also acts as the return value (it's a ref parameter).
+// Return Value:
+// - <none>
+
+void IslandWindow::_OnGetMinMaxInfo(const WPARAM /*wParam*/, const LPARAM lParam)
+{
+    // Without a callback we don't know to snap the dimensions of the client area.
+    // Should not be a problem, the callback is not set early in the startup
+    // The initial dimensions will be set later on
+    if (!_pfnSnapDimensionCallback)
+    {
+        return;
+    }
+
+    HMONITOR hmon = MonitorFromWindow(GetHandle(), MONITOR_DEFAULTTONEAREST);
+    if (hmon == NULL)
+    {
+        return;
+    }
+
+    UINT dpix = USER_DEFAULT_SCREEN_DPI;
+    UINT dpiy = USER_DEFAULT_SCREEN_DPI;
+    GetDpiForMonitor(hmon, MDT_EFFECTIVE_DPI, &dpix, &dpiy);
+
+    // From now we use dpix for all computations (same as in _OnSizing).
+    const auto nonClientSizeScaled = GetTotalNonClientExclusiveSize(dpix);
+    const auto scale = base::ClampedNumeric<float>(dpix) / USER_DEFAULT_SCREEN_DPI;
+
+    auto lpMinMaxInfo = reinterpret_cast<LPMINMAXINFO>(lParam);
+    lpMinMaxInfo->ptMinTrackSize.x = _calculateTotalSize(true, minimumWidth * scale, nonClientSizeScaled.cx);
+    lpMinMaxInfo->ptMinTrackSize.y = _calculateTotalSize(false, minimumHeight * scale, nonClientSizeScaled.cy);
+}
+
+// Method Description:
+// - Helper function that calculates a singe dimension value, given initialWindow and nonClientSizes
+// Arguments:
+// - isWidth: parameter to pass to SnapDimensionCallback.
+//   True if the method is invoked for width computation, false if for height.
+// - clientSize: the size of the client area (already)
+// - nonClientSizeScaled: the exclusive non-client size (already scaled)
+// Return Value:
+// - The total dimension
+long IslandWindow::_calculateTotalSize(const bool isWidth, const long clientSize, const long nonClientSize)
+{
+    return gsl::narrow_cast<int>(_pfnSnapDimensionCallback(isWidth, gsl::narrow_cast<float>(clientSize)) + nonClientSize);
+}
+
 [[nodiscard]] LRESULT IslandWindow::MessageHandler(UINT const message, WPARAM const wparam, LPARAM const lparam) noexcept
 {
     switch (message)
     {
+    case WM_GETMINMAXINFO:
+    {
+        _OnGetMinMaxInfo(wparam, lparam);
+        return 0;
+    }
     case WM_CREATE:
     {
         _HandleCreateWindow(wparam, lparam);

src/cascadia/WindowsTerminal/IslandWindow.h

@@ -74,7 +74,15 @@ class IslandWindow :
 
     LONG _getDesiredWindowStyle() const;
 
+    void _OnGetMinMaxInfo(const WPARAM wParam, const LPARAM lParam);
+    long _calculateTotalSize(const bool isWidth, const long clientSize, const long nonClientSize);
+
 private:
     // This minimum width allows for width the tabs fit
     static constexpr long minimumWidth = 460L;
+
+    // We run with no height requirement for client area,
+    // though the total height will take into account the non-client area
+    // and the requirements of components hosted in the client area
+    static constexpr long minimumHeight = 0L;
 };

src/cascadia/WindowsTerminal/pch.h

@@ -69,5 +69,5 @@ TRACELOGGING_DECLARE_PROVIDER(g_hWindowsTerminalProvider);
 // For commandline argument processing
 #include <shellapi.h>
 #include <processenv.h>
-
+#include <WinUser.h>
 #include "til.h"