Re: [PATCH] Add --show-touched option to show "diff --git" line when contents are unchanged

Junio C Hamano [off-list ref] writes:

Matthieu Moy [off-list ref] writes:

quoted

Also, is there any particular reason not to update the index stat
information when files are found to be identical?

Very much --- diff is a read-only operation.

"git-status $args" on the other hand is a preview of "what would
happen if I say 'git-commit $args'", and in order to compute
that, you would fundamentally need to be able to write into the
object store.  In a special case of giving empty $args it can be
read-only.

Can you give an example where it _could_ not be read-only?

The commit Dscho quoted earlier was to hack that around so that
"git-status" can pretend to be a read-only operation in a repository
you do not have write permission to.

I really, really, really, don't understand your argument.

There are two different concepts:

* Should git-diff be "read-only for the user"?
  (i.e. external specification)

* Should git-diff be actually read-only for the filesystem?
  (i.e. implementation)


"read-only for the user" is a user-interface thing. It just means that
running

$ git-diff >& /dev/null; whatever

will give the same result as

$ whatever

In another context, "cat", for example, is a read-only operation for
the user. I can run "cat whatever-file" without influencing the
behavior of subsequent operations. Now, somewhere in the kernel of my
OS, I do hope that reading this file will have side-effects (putting
the file in the cache, and why not decide to physically move the file
on disk).


Here, obviously, git-diff is a read-only operation for the user. I
don't expect git-diff to modify the behavior of subsequent commands,
but I appreciate if git-diff can improve the speed of subsequent
commands.

Now, both of us agree that git-status should not be read-only for the
filesystem, both of us agree that git-diff should be read-only for the
user, but we disagree on the two other cases.

In the same way, I expect git-status to be read-only for the user. You
say "what _would_ happen _if_ I say commit $args". But you don't
commit, the sentence is conditionnal. I don't expect any tool to have
visible side-effects when I say "what would happen if ...".

-- 
Matthieu