In TPC in Glasgow I released App::ccdiff, which - in short - will more clearly shows horizontal diff as well as vertical diff.

That might look like (with all verbosity on) like this screenshot

$ ccdiff -u0m --ascii termc*
5,5c5,5
-
+
+ ^
40,41c40,41
-       :Va=\E[0m:Vc=\E[0;33m:Ve=\E[0;4m:Vg=\E[0;4;36m:\
-                          ^
-       :Vi=\E[0;37;41m:Vk=\E[0;1;33;41m:Vo=\E[0;1;36;41;4m:cQ=\E?25I:
-                    ^             ^  ^                ^
+       :Va=\E[0m:Vc=\E[0;36m:Ve=\E[0;4m:Vg=\E[0;4;36m:\
+                          ^
+       :Vi=\E[0;37;44m:Vk=\E[0;1;37;44m:Vo=\E[0;1;36;44;4m:cQ=\E?25I:
+                    ^             ^  ^                ^
[download]

This works fine for the purpose it is written for: find tiny changes with more ease.

It however makes no sense if chunk shows a change of 4 lines to 24 lines with a completely different content, in which case you just want to see the chunk as lines-deleted + lines-added, with no markers to the changed characters in there, as that would mean that almost every character will be marked.

As I currently see it, there are multiple approaches to the fallback of the current behavior to a normal diff report:

• If the number of lines mismatch
  If the removed chunk has n lines and the added chunk has n ± x lines and the user can define x, the horizontal diff is invoked, otherwise it will fallback to normal diff-like behavior. A default of 2 seems reasonable.
• If the percentage of changed characters is over x%, where the user can specify x
  If the percentage of changed characters in a chunk (all characters marked as removed or added compared to those that did not change) is over x%, fallback to normal diff-like behavior. A default of 40% seems reasonable.

It is possible to implement both and allow both at the same time.

1. Did I state the problem well enough?
2. Do these options make sense?
3. Do the defaults make sense?
4. Do you envision other options (that you would use)?

Before I start coding/changing, I'd like opinions on how you would use it and/or expect it to use, in order to raise DWIM behavior