View crashes when trying to get seleciton when last char is " "

How to reproduce: Set last char of TextField (or ComboBox or maybe other views) text to " " then double click at next position.

Reproduceable both on main and nuget version. PrepareSelection method passes invalid parameters to String.SubString resulting an exception.

As I’ve understood, selection tries to ignore whitespace but there are some quircks, for example:

" abc " 
 ^ - if double click is called on first char then full string is selected


" abc " 
     ^ - if double click is called on last char "abc " is selected

" abc " 
      ^ - if double click is called on next after last char position then exception is thrown

It is easily reproduceable when the only char is " ". The code below then has start = 1 and length = 2 which results in exception. So I guess start = 1 is ok, but length of 2 is not. Considering text itself has 1 char only.

[tznind]

Thanks for bringing this up. Here is a test that demonstrates it:

[Fact]
[InitShutdown]
public void TextField_SpaceHandling()
{
    var tf = new TextField(){
        Width = 10,
        Text = " "
    };

    MouseEvent ev = new MouseEvent()
    {
        X = 0,
        Y = 0,
        Flags = MouseFlags.Button1DoubleClicked,
    };

    tf.MouseEvent (ev);

    ev = new MouseEvent()
    {
        X = 1,
        Y = 0,
        Flags = MouseFlags.Button1DoubleClicked,
    };
    
    tf.MouseEvent (ev);
}

Exception:

dling [FAIL]
  Failed Terminal.Gui.Views.TextFieldTests.TextField_SpaceHandling [9 ms]
  Error Message:
   System.ArgumentOutOfRangeException : Index and length must refer to a location within the string. (Parameter 'length')
  Stack Trace:
     at System.String.Substring(Int32 startIndex, Int32 length)
   at Terminal.Gui.TextField.PrepareSelection(Int32 x, Int32 direction) in /home/thomas/gui.cs/Terminal.Gui/Views/TextField.cs:line 815
   at Terminal.Gui.TextField.MouseEvent(MouseEvent ev) in /home/thomas/gui.cs/Terminal.Gui/Views/TextField.cs:line 766
   at Terminal.Gui.Views.TextFieldTests.TextField_SpaceHandling() in /home/thomas/gui.cs/UnitTests/TextFieldTests.cs:line 815

[tig]

Damn, @tznind, you continue to set the bar for how to treat bug reports. I love how, by providing test cases, you are

a) teaching others how to fish b) ensuring the entire project is always getting better.

Huge kudos!