Need better long string diff

[yaitskov]

The library does just what I was looking for, but it is to complicated to use it in existing project for app config type, because it contains dozens of types spread across submodules and 3rd packages. To much work to make 1 test failure more readable. I would like to use ediffEq for Showable types. ediffEq doesn't look inside strings and it is not obvious what is different when long strings are compared.

[phadej]

Patches are welcome

[phadej]

Sorry, now as I read properly, you want tree-diff to work with just Show? I don't see how it is possible (maybe via https://hackage.haskell.org/package/pretty-simple?) but I wont work on that myself (it probably better to be prototyped in separate).

[yaitskov]

After some search on hackage, google doesn't get what I want by "diff", I found "Diff" package. There is getGroupedDiff function taking 2 equable lists and returns list of same/left/right chunks. I think it would help tree-diff too to deal with long text.

[phadej]

There is already list diffing algorithm in tree-diff. it's just not used on String types. Partly because we need to think how to represent these diffs. Currently the diff (and representation) is line based:

*Data.TreeDiff> ansiWlEditExprCompact $ ediff (unlines ["first", "second", "third"]) (unlines ["first", "third"])
concat
  [
    "first\n",
    -"second\n",
    "third\n"]

And I'm not convinced that complicating that further to make cases like

*Data.TreeDiff> ansiWlEditExprCompact $ ediff (unlines ["first", "second", "third"]) (unlines ["first", "sec", "third"])
concat
  [
    "first\n",
    -"second\n",
    +"sec\n",
    "third\n"]

shown like on GitHub (e.g. highlighted what the difference between these two) is worth the trouble if there isn't some elegant solution.

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Ideas and patches welcome.