Re: RFE: Discard hunks during `git add -p`

[Jeff King]

On Wed, Nov 02, 2016 at 06:11:14PM -0400, Jeff King wrote:

> > Being able to discard hunks (reset working copy to index contents) 
> > during add-p would alleviate the (quite broad) hard reset.
> 
> As Konstantin pointed out, you can already discard interactively with
> "git checkout -p". It might be nice to be able to do both in the same
> run, and turn the "yes/no" decision into "yes/no/discard".
> 
> In theory it should be easy, as the same code drives the hunk selector
> for both commands. It's just a matter of which command we feed the
> selected hunks to. I don't know if there would be corner cases around
> hunk-editing and splitting, though. The "add" phase should never touch
> the working tree file itself, so any hunks present from the initial list
> should still apply cleanly during the "discard" phase.

The patch is something like the one below, which worked for me in a very
trivial test. I won't be surprised if there are some corner cases it's
missing. At the very least, coalesce_overlapping_hunks() needs to learn
about the differences between "apply" and "discard" hunks (and not
coalesce them!).

I don't have immediate plans for this, so if somebody wants to pick it
up and run with it, be my guest.

-Peff

diff --git a/git-add--interactive.perl b/git-add--interactive.perl
index ee3d81269..43651435a 100755
--- a/git-add--interactive.perl
+++ b/git-add--interactive.perl
@@ -109,6 +109,7 @@ my %patch_modes = (
                PARTICIPLE => 'staging',
                FILTER => 'file-only',
                IS_REVERSE => 0,
+               DISCARD => sub { apply_patch 'apply -R', @_; },
        },
        'stash' => {
                DIFF => 'diff-index -p HEAD',
@@ -1325,6 +1326,11 @@ sub patch_update_file {
                my ($prev, $next, $other, $undecided, $i);
                $other = '';
 
+               my $discard = exists $patch_mode_flavour{DISCARD};
+               if ($discard) {
+                       $other .= ',D';
+               }
+
                if ($num <= $ix) {
                        $ix = 0;
                }
@@ -1384,6 +1390,9 @@ sub patch_update_file {
                        elsif ($line =~ /^n/i) {
                                $hunk[$ix]{USE} = 0;
                        }
+                       elsif ($discard && $line =~ /^D/) {
+                               $hunk[$ix]{USE} = -1;
+                       }
                        elsif ($line =~ /^a/i) {
                                while ($ix < $num) {
                                        if (!defined $hunk[$ix]{USE}) {
@@ -1539,9 +1548,12 @@ sub patch_update_file {
 
        my $n_lofs = 0;
        my @result = ();
+       my @discard = ();
        for (@hunk) {
-               if ($_->{USE}) {
+               if ($_->{USE} > 0) {
                        push @result, @{$_->{TEXT}};
+               } elsif ($_->{USE} < 0) {
+                       push @discard, @{$_->{TEXT}};
                }
        }
 
@@ -1552,6 +1564,13 @@ sub patch_update_file {
                refresh();
        }
 
+       if (@discard) {
+               my @patch = reassemble_patch($head->{TEXT}, @discard);
+               my $apply_routine = $patch_mode_flavour{DISCARD};
+               &$apply_routine(@patch);
+               refresh();
+       }
+
        print "\n";
        return $quit;
 }