"diff" should produce a diff with similar lines grouped together if
possible, so that it can be more easily readable and be word-diff
friendly.

Issues can occur on text files with paragraphs separated by a blank
line (like in wiki source files and LaTeX files), where a modification
consists in
  * some paragraph being split, and
  * some of the following paragraphs being slightly modified.

In such a case, a shift of the slightly modified lines can occur,
which makes the diff hardly readable and breaks word-diff (e.g.
when one opens the diff file with GNU Emacs).

I've attached an example:
  * file1 and file2: the files to be diff'ed (file2 is similar to
    file1, with the first paragraph split).
  * file-bad.diff: the diff produced by diff 3.10.
  * file-ok.diff: the diff I would expect.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / Pascaline project (LIP, ENS-Lyon)