How to make a syntax region stop on empty lines?

Question

I would like to adapt this syntax file so that the formatting in VIM matches more closely what this online Markdown editor (GitLab-flavor) displays (the output on the right is relevant, this is how I want the text to look in VIM). In particular, I am looking at the detection of italics triggered by framing text with asterisks.

I made some progress by simplifying the start and end patterns and by adding "oneline". But actually I would like the region to extend beyond a single line to an entire paragraph. In other words, the region should include subsequent lines until an empty line is encountered. If I omit the "oneline" attribute, the region just goes on and does not stop on an empty line. How can I make this region include subsequent non-empty lines but stop at the first empty line (or, obviously, the end pattern, whatever comes first)?

Note that a piece of text that contains the start pattern, but no end pattern and that is terminated by an empty line should NOT be detected as a region. The empty line is not an alternative end, it should just be interpreted as "stop looking here for the end pattern".

exe 'syn region markdownItalic matchgroup=markdownItalicDelimiter start="\*\S\@=" end="\S\@<=\*" keepend oneline contains=markdownLineStart' . s:concealends

Answer 1

An empty line can be recognized by two consecutive newlines. You can match everything that is not two newlines with the following pattern:

\([^\n]\|\n[^\n]\)*

Place this between the "start" and "end" patterns to match the whole italicized region at once. It will require that your syntax item is a match rather than a region:

syn match markdownItalic "\*\S\@=\([^\n]\|\n[^\n]\)\{-}\S\@<=\*"

The \{-} ensures that the match ends at the first possible end-marker. Alternatively, you could include * in the negated character list.