Re: [RFC PATCH 2/5] format-patch: add --range-diff option to embed diff in cover letter

[Eric Sunshine <sunshine@sunshineco.com>]

On Thu, Jul 26, 2018 at 6:56 AM Johannes Schindelin
<Johannes.Schindelin@gmx.de> wrote:
> On Tue, 17 Jul 2018, Eric Sunshine wrote:
> > On Tue, Jul 17, 2018 at 6:31 AM Johannes Schindelin
> > <Johannes.Schindelin@gmx.de> wrote:
> > > BTW I like to have an extra space in front of all the range-diff lines, to
> > > make it easier to discern them from the rest.
> >
> > I'm not sure what you mean. Perhaps I'm misreading your comment.
>
> Sorry, I was really unclear.
>
> In the cover letters sent out by GitGitGadget (or earlier, my
> mail-patch-series.sh command), I took pains to indent the entire
> range-diff (or interdiff) with a single space. That is, the footer
> "Range-diff vs v<n>:" is not indented at all, but all subsequent lines of
> the range-diff have a leading space.
>
> The original reason was to stop confusing `git apply` when sending an
> interdiff as part of a single patch without a cover letter (in which case
> mail-patch-series.sh inserted the interdiff below the `---` marker, and
> the interdiff would have looked like the start of the real diff
> otherwise).

The new version[1] likewise indents the interdiff to avoid confusing
git-am / git-apply.

[1]: https://public-inbox.org/git/20180722095717.17912-1-sunshine@sunshineco.com/

> In the meantime, I got used to this indentation so much that I do not want
> to miss it, it is a relatively easy and intuitive visual marker.
>
> This, however, will be harder to achieve now that you are using the
> libified range-diff.

I toyed with indenting the range-diff in both the cover letter and
below the "---" line in a patch. With the libified range-diff, doing
so involves modifying the range-diff implementation (rather than
having the consumer of the range-diff manage the indentation locally),
so it adds a bit of complexity to show_range_diff(), though perhaps
not too much.

However, I opted against it for a few reasons. First, "header" lines
apart, all lines of the range-diff are already indented, and the
existing indentation was sufficient (for me, at least) as a visual
marker. Second, range-diffs tend to be _wide_, especially the header
lines, and I was loath to make it wider by indenting more. Third, due
to the existing indentation of the diff proper, a range-diff won't
confuse git-am / git-apply, nor will the unindented header lines, so
extra indentation seemed superfluous.

> > > > @@ -1438,6 +1480,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
> > > > +     const char *range_diff = NULL;
> > >
> > > Maybe `range_diff_opt`? It's not exactly the range diff that is contained
> > > in this variable.
> >
> > I could, though I was trying to keep it shorter rather than longer.
> > This is still the same in the re-roll, but I can rename it if you
> > insist.
>
> I think it will confuse me in the future if I read `range_diff` and even
> the data type suggests that it could hold the output of a `git range-diff
> <options>` run.
>
> So I would like to insist.

In the new version[1], this variable is named 'rdiff_prev' (the
"previous" version against which the range-diff is to be generated).

> > > > +format_patch () {
> > > > +     title=$1 &&
> > > > +     range=$2 &&
> > > > +     test_expect_success "format-patch --range-diff ($title)" '
> > > > +             git format-patch --stdout --cover-letter --range-diff=$range \
> > > > +                     master..unmodified >actual &&
> > > > +             grep "= 1: .* s/5/A" actual &&
> > > > +             grep "= 2: .* s/4/A" actual &&
> > > > +             grep "= 3: .* s/11/B" actual &&
> > > > +             grep "= 4: .* s/12/B" actual
> > >
> > > I guess this might make sense if `format_patch` was not a function, but it
> > > is specifically marked as a function... so... shouldn't these `grep`s also
> > > be using function parameters?
> >
> > A later patch adds a second test which specifies the same ranges but
> > in a different way, so the result will be the same, hence the
> > hard-coded grep'ing. The function avoids repetition across the two
> > tests. I suppose I could do this a bit differently, though, to avoid
> > pretending it's a general-purpose function.
>
> If you can think of a way that would make this easier to read for, say,
> myself if I ever find myself debugging a regression caught by this test, I
> would appreciate that.

In the new version, the function is gone; it looks like this:

--- >8 ---
for prev in topic master..topic
do
    test_expect_success "format-patch --range-diff=$prev" '
        git format-patch --stdout --cover-letter --range-diff=$prev \
            master..unmodified >actual &&
        grep "= 1: .* s/5/A" actual &&
        grep "= 2: .* s/4/A" actual &&
        grep "= 3: .* s/11/B" actual &&
        grep "= 4: .* s/12/B" actual
    '
done
--- >8 ---