Re: [PATCH] git-add--interactive.perl: Permit word-based diff

On Tue, Jun 18, 2013 at 11:12:59PM +0200, Mark Abraham wrote:

Right. My point is that the colorized version always lines up with the "real" to-apply version line-for-line. But the word diff version does not.

If we assume that they line up hunk for hunk (that is, --color-words comes up with the same number of hunks, but the contents of each hunk may be different), then swapping "colorized line diff" for "word diff" in the presentation version (i.e., your patch) is fine. I think this is the case with the current --word-diff, so the only question would be one of not wanting to paint ourselves into a corner with implementation details. I think that is OK, as if we later wanted to change --word-diff to coalesce hunks, we could continue to support a "--hunk-based-word-diff" mode for this type of operation that cares about matching the normal diff hunks.

If we assume that the presentation version lines up line for line within each hunk, then it is safe to do hunk-level operations like splitting. That works with the current colorized diffs, but not with word-diff. I think you can construct a case where doing a hunk-split from the selection menu causes us to display a word-diff that is not the equivalent of what would be applied if it is selected.

For example:

	# make a file and add it to the index
	cat >file <<-\EOF
	a
	c
	d
	e
	f
	EOF
	git add file

	# now fix the missing letter, tweak the wrapping, and add some new
	# content
	cat >file <<\EOF
	a b c d e
	f
	g h i j k
	EOF

The regular diff has 7 lines:

	$ git diff
	diff --git a/file b/file
	index dffa0a4..3a7aeb4 100644
	--- a/file
	+++ b/file
	@@ -1,5 +1,3 @@ f
	-a
	-c
	-d
	-e
	+a b c d e
	 f
	+g h i j k

But the word diff has only 3:

	$ git diff --word-diff
	diff --git a/file b/file
	index dffa0a4..3a7aeb4 100644
	--- a/file
	+++ b/file
	@@ -1,5 +1,3 @@ f
	a {+b+} c d e
	f
	{+g h i j k+}

If I run "git add -p" with your patch and choose "s" to split the hunk, I will still be shown:

	Stage this hunk [y,n,q,a,d,/,s,e,?]? s
	Split into 2 hunks.
	@@ -1,5 +1,2 @@
	a b c d e
	f
	g h i j k
	Stage this hunk [y,n,q,a,d,/,j,J,g,e,?]?

If I say "yes" here, I get shown the next hunk, which has no lines at all. Let's imagine I say "no". What gets applied? Only the first change (rewrapping and adding "b"). But not the addition of "g" through "k", even though they were shown in the presentation of the hunk that I said "yes" to.

So I think if we want to do a word-diff for the presentation, it would probably make sense to shut off line-level manipulation like hunk-splitting.

I wonder if it should go even a step below there: always generate the normal diff for presentation, and then have an interactive key to show the --word-diff of it.

I find I often do not know until I get to a very ugly documentation diff with paragraph rewrapping that I wanted word-diff (and I would _not_ want it for my code hunks, just for the documentation hunk).

And as a bonus, it is easier to implement, since the logic is all within the hunk-selection menu.

-Peff