Restyle a paragraph up to the end throws indexes off

[Symeon94]

I was working on refactoring the Paragraph class after having added tests and I looked at the bugs I highlighted in the PR adding the tests. I think it deserves its own issue, that's why I'm creating it here.

I'm refactoring the method, but I'm not modifying its behaviour for now, I will do that on a separate PR.

I have yet to figure out what is happening.

If you restyle a Paragraph up to len - 1 you don't have any issue, but you do if you restyle up to len. As you can see in below test, the indexes in that cases are way off.

checkStyle(p3, 18, new String[] {"text", "unknown", "keyword", "text"},
	0, 3, // text
	3, 10, // unknown
	10, 12, // keyword
	12, 18); // text

// Restyle up to the end
checkStyle(p3.restyle(11, 17, "out"), 18, new String[] {"text", "unknown", "keyword", "out", "text"},
	0, 3,
	3, 10,
	10, 11,
	11, 17,
	17, 18);

// Restyle up to the end - Bug: indexes are totally of
checkStyle(p3.restyle(11, 18, "out"), 18, new String[] {"text", "unknown", "keyword", "out"},
	0, 3,
	3, 10,
	0, 1,
	0, 7);

[Symeon94]

Ok, the issue is that the append is actually creating a new object of type AppendedSpans which is keeping the current StyleSpans and putting a new one next to it.
When you are getting the last StyleSpan it returns that appended value and it has the indexes it had.

It could be that the code does not has an issue with that, but it creates a flaw in the logic. I would be in favor of modifying the appended value to properly match the indexes.

[Symeon94]

The problem with fixing that one is that it is likely that the styling use only the length, so it is likely that I will not be able to find an actual user facing bug. But it is a bomb waiting to explode the day anybody writes code expecting the start position to work.
So either;

• We fix it and hope it doesn't blow somewhere because some code used the bug as an assumption
• We remove start position fully (or only keep the first style position)
• We keep the bug and hope for the best

I prefer solution 1.