fix: shared indices for first row of data and headers (StyleFunc bug)

[bashbunni]

While migrating the table bubble to use Lip Gloss, I noticed some rendering issues where the cursor was constantly off by one. After fixing the off by one error, I was still having some range issues where the first element was never showing the selected style. Turns out, both the first element in the list and the header are the same index, so whatever style was returned first would be rendered by both the header and first element in the list.

Despite the cursor being in the right position, it was rendering the next element in the list with the declared styles.

Note

This is a bit of a breaking change, though necessary for the first element to ever render correctly when there are also styles set on the headers. This would require table users to update their StyleFunc implementations to use HeaderRow instead of 0.

Before:

After:

(it's failing intentionally so I could see the outputs)

This PR introduces a test to Lip Gloss that adds unique styles to both the header and first row of data to showcase the issue. When running the test against master, you'd need to comment out the HeaderRow stuff and you'll see that both the first row and header use the same style.

[bashbunni]

This is the test that reproduces the behaviour I was seeing in the bubble (in the screenshots above) https://github.com/charmbracelet/lipgloss/blob/fix-stylefunc/table/table_test.go#L1144-L1169

[meowgorithm]

Does this need to be exported?

[bashbunni]

Yeah this is the value they would be using in StyleFunc to style the header instead of 0. I figured better to export a const than have them check for -1

[meowgorithm]

Thanks, @bashbunni! If it's not too much trouble, can you plop down some source code for a quick program to reproduce this (even if it's based on the tests)? It's helpful to see the before/after interactively to understand what we're lookin' for.

Ah, wait, this is Lip Gloss. Okay, will poke around on this one.

[bashbunni]

@meowgorithm the tests are probably the best place to see the changes!

[meowgorithm]

Nicely done 👌