Re: [PATCH 1/2] diff: do not display hunk context under -W

Am 15.02.21 um 20:24 schrieb Ævar Arnfjörð Bjarmason:

On Mon, Feb 15 2021, René Scharfe. wrote:

quoted

Your reasoning applies to patches generated without -W as well.  If the
precontext contains a function line then the @@ line should not contain
a function comment.  However, e.g. with this:

-- snip --
cat >a <<EOF
func a

func b
1
2
3
EOF
sed 's/3/three/' <a >b
diff -up a b
-- snap --

... I get this:

--- a	2021-02-15 18:30:21.000000000 +0100
+++ b	2021-02-15 18:30:21.000000000 +0100

@@ -3,4 +3,4 @@ func a
 func b
 1
 2
-3
+three

So diff(1) shows the previous function line.  git diff does the same.

The behaviour of diff(1) and git diff does make sense to me: It's easy
to implement and the only downside is that it produces extra output in
some cases.

I can understand that users would rather have a tidy diff without
distractions, though.  So I like the output change you propose.

Does GNU diff have something like git's -W, both "diff -U 0 -F func a b"
and "diff -U 0 -p a b" don't extend the context window as we do.

Exactly my point: GNU diff doesn't have something like -W, but still can
show an unchanged function at the @@ line, because it searches upwards
starting just above the first shown line, and the name of the actually
changed function might be in one of the shown lines.

I don't think the patch I'm submitting here would make sense for GNU
diff, since there it just shows the context without being guaranteed to
show the full set of lines leading up to it under -W, but with Git diff
we do that, so I think it makes sense to omit the context.

Given the goal to show the name of the changed function it *would* make
sense to start searching at the first changed line instead.

quoted

However, I'm not sure it would be a good idea to clear @@ lines of hunks
generated without -W that have function lines in their precontext, even
though it would be a logical thing to do.

Yes, I don't think that's a good idea either. I think it only makes
sense under -W where the user explicitly asks "show me the function this
change was in", and we're (before this patch) showing different context
on the basis of emergent behavior.

Right, -W never needs diff(1)'s -p, while the case is less clear for
diffs generated without -W.

René