Choose when to highlight more dynamically

[korreman]

I currently get unsupported language: <lang> errors specifically when I first open a supported file, then open an unsupported file in a new window with :new edit <file>. The same error as can be achieved by changing kts_lang to some nonsense.

Issue seems to be that a highlight-enable request is sent for the new client with the language of the previous window. A correct request is sent and denied right after, but by then highlighting has already been enabled. I think the more general issue is that we decide whether to highlight or not when a window is opened, and then never again.

A more reliable behavior might be to re-decide whether to highlight a buffer whenever its kts_lang is changed. For this to work, a hook would need to update kts_lang whenever filetype is changed. By removing this specific hook, you could then also get dynamic control over the highlighting though kts_lang.

[hadronized]

Indeed, I thought I had that hook lying around already. We can simply put this in it.

[hadronized]

I need to make a release of KTS but this is not going to be included because it’s a breaking change; I’m moving it to the next major.