Re: Wrong tabs in terminal output for git diff

[Jeff King <peff@peff.net>]

On Sat, Jun 12, 2021 at 04:10:04PM -0700, Phil Hord wrote:

> On Fri, Jun 11, 2021 at 12:30 PM Timothy Madden <terminatorul@gmail.com> wrote:
> > For git diff and git show commands, terminal output appears with wrong
> > tab stops (missaligned).
> >
> > Because diff operation inserts a new column at character position 1, for
> > the +, - and space characters, the diff content appears shifted to the
> > right by 1 column. But not the tab stop positions. So relative to the
> > text, the tab stops now appear off-by-one (shifted to the left).
> 
> I think "fixing" this would require modifying the diff output so it
> would no longer be correct. If we accept that a switch can make a
> incorrect diff for display only, though, it seems something could be
> done here.

We do have a few "display only" modes. You mentioned --color-words, but
--textconv is similar (and of course --ext-diff can generate whatever it
wants). I'm not sure how helpful that is, though, because humans end up
needing to look at "real" diffs that can be applied often enough (and as
you note, changing those would break them).

This could be addressed at the viewing layer, though, which is what's
converting the tabstops to screen positions. For example, "less -x9,17"
adjusts the tab stops in the pager to account for the extra leading
character (and you can put it into $LESS or $GIT_PAGER to have it kick
in automatically).

> I think the only approach that can fix the alignment, however, is to
> remove the +/- prefix markers altogether.  We do this now with the
> `--color-words` switch. This kind of solution only works if there is
> some way to indicate added/removed lines other than the line-prefix
> marker; ANSI color codes, for example.  Would that work for your
> needs, or were you thinking of something else?

There are other diff-viewing projects which can be used as a Git pager
to do stuff like this. E.g.:

  https://github.com/so-fancy/diff-so-fancy

-Peff