Subject: bug#20481: 24.5;, Newlines in message-box output don't work on Windows

From: Cecilio Pardo <[email-masked]>
Date: Mon, 19 Aug 2024 18:13:31 +0200

This patch adds support on Windows Vista an later for dialog boxes using 
TaskDialog.

diff --git a/src/w32menu.c b/src/w32menu.c
index cea4f4892a4..029e4bbf805 100644
--- a/src/w32menu.c
+++ b/src/w32menu.c
@@ -52,6 +52,9 @@
 
 #include "w32common.h"	/* for osinfo_cache */
 
+#include "commctrl.h"
+
+/* This only applies to OS versions prior to Vista. */
 #undef HAVE_DIALOGS /* TODO: Implement native dialogs.  */
 
 #ifndef TRUE
@@ -101,14 +104,148 @@ #define FALSE 0
 
 void w32_free_menu_strings (HWND);
 
+
+#define TASK_DIALOG_MAX_BUTTONS = 10;
+
+static HRESULT
+task_dialog_callback(HWND hwnd, UINT msg, WPARAM wParam,
+		     LPARAM lParam, LONG_PTR callback_data)
+{
+  switch (msg)
+    {
+    case TDN_CREATED:
+      /* Disable all buttons with ID >= 2000 */
+      for (int i = 0; i < TASK_DIALOG_MAX_BUTTONS; i++)
+	SendMessage( hwnd, TDM_ENABLE_BUTTON, 2000 + i, FALSE );
+      break;
+    }
+  return S_OK;
+}
+
 Lisp_Object
 w32_popup_dialog (struct frame *f, Lisp_Object header, Lisp_Object contents)
 {
-
   check_window_system (f);
 
-#ifndef HAVE_DIALOGS
+  void *task_dialog_indirect =
+    get_proc_addr (GetModuleHandle ("comctl32.dll"), "TaskDialogIndirect");
+
+  if (task_dialog_indirect)
+    {
+      /* Get the title as a UTF-16 string. */
+      CHECK_STRING (XCAR (contents));
+      char *title =  SSDATA (XCAR (contents));
+      int wide_length = sizeof(WCHAR) *
+	pMultiByteToWideChar (CP_UTF8, 0, title, -1, NULL, 0);
+      WCHAR *title_text_wide = alloca (wide_length);
+      pMultiByteToWideChar (CP_UTF8, 0, title, -1,
+			    title_text_wide, wide_length);
+
+      /* Prepare the struct with the dialog's buttons. */
+      TASKDIALOG_BUTTON buttons[TASK_DIALOG_MAX_BUTTONS];
+      Lisp_Object button_values[TASK_DIALOG_MAX_BUTTONS];
+      int button_count = 0;
+      Lisp_Object b = XCDR (contents);
+
+      while ( !NILP (b) ) {
+	if ( button_count >= TASK_DIALOG_MAX_BUTTONS )
+	  {
+	    /* We have too many buttons. We ignore the rest. */
+	    break;
+	  }
+
+	Lisp_Object item = XCAR(b);
+
+	if (Fconsp (item))
+	  {
+	    /* A normal item (text . value) */
+	    Lisp_Object item_name = XCAR (item);
+	    Lisp_Object item_value = XCDR (item);
+
+	    CHECK_STRING (item_name);
+
+	    int wide_length = sizeof(WCHAR) *
+	      pMultiByteToWideChar (CP_UTF8, 0, SSDATA (item_name), -1,
+				    NULL, 0);
+	    buttons[button_count].pszButtonText = alloca (wide_length);
+	    pMultiByteToWideChar (CP_UTF8, 0, SSDATA (item_name), -1,
+				  (LPWSTR)
+				  buttons[button_count].pszButtonText,
+				  wide_length);
+	    buttons[button_count].nButtonID = 1000 + button_count;
+	    button_values[button_count++] = item_value;
+	  }
+	else if (NILP (item))
+	  {
+	    /* A nil item means to put all following items on the
+	       right. We ignore this. */
+	  }
+	else if (STRINGP(item))
+	  {
+	    /* A string item means an unselectable button. We add a
+	       button, an then need to disable it on the callback.
+	       We use ids based on 2000 to mark these buttons */
+	    int wide_length = sizeof(WCHAR) *
+	      pMultiByteToWideChar (CP_UTF8, 0, SSDATA (item), -1, NULL, 0);
+	    buttons[button_count].pszButtonText = alloca (wide_length);
+	    pMultiByteToWideChar (CP_UTF8, 0, SSDATA (item), -1,
+				  (LPWSTR)
+				  buttons[button_count].pszButtonText,
+				  wide_length);
+	    buttons[button_count].nButtonID = 2000 + button_count;
+	    button_values[button_count++] = Qnil;
+	  }
+
+	b = XCDR (b);
+      }
+
+      int pressed_button = 0;
+
+      TASKDIALOGCONFIG config = { };
+      config.hwndParent = FRAME_W32_WINDOW (f);
+      config.cbSize = sizeof(config);
+      config.hInstance = hinst;
+      config.dwFlags = TDF_ALLOW_DIALOG_CANCELLATION;
+      config.pfCallback = task_dialog_callback;
+
+      config.pszWindowTitle = L"Question";
+      if (!NILP (header))
+	{
+	  config.pszWindowTitle = L"Information";
+	  config.pszMainIcon = TD_INFORMATION_ICON;
+	}
 
+      config.pszMainInstruction = title_text_wide;
+      config.pButtons = buttons;
+      config.cButtons = button_count;
+
+      if (!SUCCEEDED (TaskDialogIndirect (&config, &pressed_button,
+					  NULL, NULL)))
+	return quit ();
+
+
+      switch (pressed_button)
+	{
+	case IDOK:
+	  /* This can only happen if no buttons where
+	     provided. An OK button is automatically added. */
+	  return Qt;
+	case IDCANCEL:
+	  /* The user closed the dialog without using the buttons */
+	  return quit();
+	default:
+	  /* One of the specified buttons. */
+	  int button_index = pressed_button - 1000;
+	  if ( button_index >= 0 && button_index < button_count )
+	    return button_values[button_index];
+	  return quit();
+	}
+    }
+
+  /* If we get here, TaskDialog is not supported. Use MessageBox/Menu. */
+
+
+#ifndef HAVE_DIALOGS
   /* Handle simple Yes/No choices as MessageBox popups.  */
   if (is_simple_dialog (contents))
     return simple_dialog_show (f, contents, header);