git log: why are --full-diff and --pickaxe-all separate options?

I just did this:

$ git log -p -- /some/path

And didn't get the full commit. I know about the --pickaxe-all option, so I optimistically tried:

$ git log -p --pickaxe-all -- /some/path

Which of course, does not do what I want. Eventually I found in the man page that I can do this:

$ git log -p --full-diff -- /some/path

But now I wonder why these are separate options. Is there any reason they shouldn't be unified?

Regardless, perhaps --pickaxe-all without -S and --full-diff without -p should be errors?

j.

On Wed, Mar 24, 2010 at 11:52:13AM -0400, Jay Soffian wrote:

I agree it is confusing, and the answer is "maybe". A long and gory explanation can be found here:

  http://article.gmane.org/gmane.comp.version-control.git/34909

Read the later messages in the thread from Junio, too, as he goes back and forth a bit. I don't remember if anything happened after that, or why not.

-Peff

Jay Soffian <jaysoffian@gmail.com> writes:

They do entirely different things, and It does not make any sense to "unify" them.

But it would be an improvement to make them work better together.

 - Erroring out when --pickaxe-all is given without -S would make sense;

 - Making --full-diff to imply --pickaxe-all when -S is used would also
   make sense.

[Footnote]

*1* I wrote the following before reading Jeff's response where I explained it already; it should say the same thing so if you read the message Jeff pointed at, you don't have to read this, but I didn't want to waste my typing, so ...

  The log dataflow is:

  - revision walker finds commits one-by-one, but limiting the commits
    to the ones that touch the paths in the pathspec.

  - each found commit and its ancestor(s) are given to the diff
    machinery, in order to skip the commit if there is no difference,
    and also as a side effect to show the diff.

  - diff front-end collects paths in the commit pair, limited by the
    pathspec given.  however, this can be countermanded with full-diff.

  - diffcore does its thing---compares the collected paths, ignoring
    changes between pairs that do not satisfy pickaxe filter (if given).

    - when pickaxe is in effect, usually paths that do not satisfy the
      pickaxe filter is _discarded_ even if they are different between
      the parent and the child.

    - pickaxe-all however prevents the above.  If even one path
      satisifies the pickaxe filter, all paths survive.

  - if there are still changes after the above computation, the change
    is shown in diff form (when -p is given).

For example, "log -Shello -- world/" would:

  a) limit to commits that touch something in world/ directory;

  b) compare commit and its parents but limit this comparison in world/
     directory.

  c) if some compared file have different number of "hello" in parent and
     child, diff for only those files is shown.

  Giving --full-diff affects step b.  files outside world/ will also be
  inspected in step c and the ones that changes the number of "hello"
  are shown even if outside world/

  Giving --pickaxe affects step c.