Re: how to highlight fine differences in Diff mode?

[David Combs]

In article <mailman.18320.1133972403.20277.help-gnu-emacs@gnu.org>,
Drew Adams <drew.adams@oracle.com> wrote:
>    But sometimes I have to compare extremely large files, larger than Emacs
>    maximum buffer size.  So I simply run diff and redirect its output to a
>    .diff file, which is easily small enought to visit and navigate in Diff
>    mode.  What I'd like at that point is a command to highlight the changed
>    text within the current hunk, just like "*" does in Ediff:
>
>    ,----[ C-h k * ]
>    | * runs the command ediff-make-or-kill-fine-diffs
>    |    which is an interactive compiled Lisp function in `ediff-util'.
>    | (ediff-make-or-kill-fine-diffs ARG)
>    |
>    | Compute fine diffs.  With negative prefix arg, kill fine diffs.
>    | In both cases, operates on the current difference region.
>    `----
>
>    Is there any way to take advantage of the Ediff machinery inside
>    Diff mode?
>
>I don't have an answer for you, unfortunately. I do have some code that
>improves the highlighting of regular `diff' output slightly:
>http://www.emacswiki.org/cgi-bin/wiki/diff-mode-.el, but it doesn't do what
>you're asking.
>
>
>

1: "diff-mode": never heard of it.  Yes, there is one in the lisp
   subdirectory, at least of 22.0.50.1 (old) cvs.

2: So, I suppose the diff-mode.el in the wiki, vs the one that
   comes "in the box", have no relation to each other.  (Well,
   at least the on in the lisp dir says nothing about "drew adams".)

3: not seeing much doc in the built-in one (or in info, either),
   what does diff-mode enable me to do (easily) that ediff-mode
   doesn't?

4: In fact, are the two packages (for lack of better word)
   based on different concepts of what a "diff in emacs"
   should do?

5: Here's the tail end of the info-node "comparing files":


   Differences between versions of files are often distributed as
"patches", which are the output from `diff' or a version control system
that uses `diff'.  `M-x diff-mode' turns on Diff mode, a major mode for
viewing and editing patches, either as "unified diffs" or "context
diffs."

   You can use `M-x smerge-mode' to turn on Smerge mode, a minor mode
for editing output from the `diff3' program.  This is typically the
result of a failed merge from a version control system "update" outside
VC, due to conflicting changes to a file.  Smerge mode provides
commands to resolve conflicts by selecting specific changes.

   See also *Note Emerge::, and *Note Top: (ediff)Top, for convenient
facilities for merging two similar files.



Sure doesn't say much about diff-mode -- and suggests looking
at ediff ONLY IF YOU NEED TO *MERGE* FILES.

Methinks ediff has more uses than that????   

David