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Using UltiSnips, I'm wondering if it's possible to do some lookahead assertion when detecting the trigger.

For example, this works:

snippet "dv" "derivative" ir
\dv{$1}{$2}$0
endsnippet

But this doesn't even get triggered:

snippet "dv(?=[ \n])" "derivative" ir
\dv{$1}{$2}$0
endsnippet

I've had similar issue with negative lookahead, except it always gets triggered regardless. I'd like to know if there is some possible workaround.

1 Answer 1

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Lookaheads are currently not supported by UltiSnips*, these include both positive and negative lookahead assertions.

You could use a context (see :h UltiSnips-custom-context-snippets) to inspect the text after the cursor. The cursor position is accessible with snip.cursor:

global !p

def text_after_cursor_matches(snip, string):
    (line, col) = snip.cursor
    text_after_cursor = snip.buffer[line][col:]
    # print(text_after_cursor)
    return re.match(string, text_after_cursor)

endglobal

context text_after_cursor_matches(snip, "[ \n]")
snippet dv "derivative" i
\dv{$1}{$2}
endsnippet

Above I used a custom function text_after_cursor_matches() to check if the characters that follow after the cursor matches a certain regex ("[ \n]" in this case). If True, the snippet is expanded.

*: as implied from the maintainer's response to this issue

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