Recognizing the right expression to complete in insert mode

Question

When one triggers a completion, vim guesses what was the expression (behind the cursor) that you want to complete. I don't fully understand the logic, but it seems that it assumes that the expression is a sequence of alphabetic chars+some additional.

Suppose I have a graph named "G_{walk}" (I do have - latex). I want to refer to it.

I can trigger a completion that would recognize it when I type G_<c-x><c-n>. But if I type G_{<c-x><c-n>, it regards whatever that follows { as a completely different expression and it won't find "G_{walk}".

So, how can I control the expression? Sometimes I just want it to ignore all its stupid rules, and complete from the moment I press a key and until I tell it to stop. Can it be done?

Thanks.

PS I did read about ins-completion. I don't understand how what I see in syntax list or how omnifunction related to the question I asked about <c-x><c-n> as main example.

Answer 1

Most of auto-completion works with keywords, so the set of characters that make up possible completion prefixes and candidates is controlled by the 'iskeyword' setting.

For instance, under :help compl-current you'll find:

If there is a keyword in front of the cursor (a name made out of alphabetic characters and characters in 'iskeyword'), it is used as the search pattern, with "\<" prepended (meaning: start of a word). [...]

Most other types of completion will typically follow the same definition of keywords.

In your particular case, in order to be able to complete G_{walk}, you might want to consider including the curly brace characters in the set of valid keyword characters, which you can do with:

:set iskeyword+={,}

Note that this might affect keyword splitting elsewhere, since { and } are used in TeX/LaTeX for parameters, some words that were previously considered keywords on their own will cease to do so. You should consider this trade-off if you decide to touch the 'iskeyword' setting.