Pressing Alt on a form without a menu causes the application MainForm to come forward

[JackTrapper]

Tested

Delphi XE6: Fails Delphi 10.3: Fails Delphi 10.4: Fails

Picture the scenario where the user just taps the Alt key.

Normal Windows apps highlight the menu on the current form, or do nothing if they don't have a menu. The code that handles CMAppSysCommand propagates CM_APPSYSCOMMAND to the Application, which gets handled by the MainForm.

I cannot see any reason for doing this.

• It doesn't do anything if the main form is disabled (which is the case if something is shown modally from it)
• If the main form is enabled: it pops the main form forward and highlights the menu.

This is awkward, and I can't imagine that can ever be an intended behavior.

The fix

Stop doing that.

procedure TCustomForm.CMAppSysCommand(var Message: TMessage);
{$IF NOT DEFINED(CLR)}
type
  PWMSysCommand = ^TWMSysCommand;
{$ENDIF}
begin
  Message.Result := 0;
  if (csDesigning in ComponentState) or (FormStyle = fsMDIChild) or
   (Menu = nil) or Menu.AutoMerge then
{$IF DEFINED(CLR)}
    with TWMSysCommand.Create(Message) do
{$ELSE}
    with PWMSysCommand(Message.lParam)^ do
{$ENDIF}
    begin
      {
        Picture the scenario where the user just taps the Alt key. 

        Normal Windows apps highlight the menu on the current form, or do nothing if they don't have a menu. 
        The code that handles **CMAppSysCommand** propagates `CM_APPSYSCOMMAND` to the **Application**, which gets handled by the **MainForm**.

        I cannot see any reason for doing this. 

        - It doesn't do anything if the main form is disabled (which is the case if something is shown modally from it)
        - If the main form is enabled: it pops the main form forward and highlights the menu. 

        This is awkward, and I can't imagine that can ever be an intended behavior. 

        Comment out the the propagation to the main form, and act as though we handled the message ourselves
    }
//      SendCancelMode(nil);
//      if SendAppMessage(CM_APPSYSCOMMAND, CmdType, Key) <> 0 then
        Message.Result := 1;
    end;
end;