Diff requires two newlines between diff-blocks to highlight properly

[johannesstricker]

Name of the lexer
diff

Code sample

// path/to/file.js

+ this is inserted
+ over multiple lines

- this is removed
- over multiple lines

This is how the output looks:

As you can see, it doesn't highlight the first line of a new diff block. It only works when I add an additional newline in between.
Also, why is the // at the beginning of the file wrapped in a <span class="err"> 🤔

[connection-reset]

I have the same issue and did some investigation. The diff lexer is correct, if strict.
In the unified diff format, there is always at least the prefix character + (plus), - (minus), or ␣ (space).
So apparently empty lines in a diff are not empty, they contain ␣\n (space)(newline).

The diff lexer does not understand empty lines, i.e. lines that only contain \n (newline). It prepends them to the next line and yields that as a text token, i.e. \n+some insert\n.

I am using AsciiDoctor to render AsciiDoc with embedded diffs to HTML.
AsciiDoctor strips whitespace of the whole document before passing code blocks to Rouge, resulting in this issue.
I believe this is a bug in AsciiDoctor.

[colinodell]

I encountered this exact same issue using Rouge within Jekyll. It turns out my IDE was stripping trailing whitespace which caused the single space on those "empty" lines to be removed, thus triggering this issue.

[stale]

This issue has been automatically marked as stale because it has not had any activity for more than a year. It will be closed if no additional activity occurs within the next 14 days.
If you would like this issue to remain open, please reply and let us know if the issue is still reproducible.

[tancnle]

@johannesstricker As part of #1854, the rule around empty lines has been relaxed, it no longer requires spaces. This issue can be marked as resolved.