Re: [PATCH 6/8] checkout: add --cached option

[Thomas Gummerer <t.gummerer@gmail.com>]

On 12/10, Elijah Newren wrote:
> On Sun, Dec 9, 2018 at 12:05 PM Thomas Gummerer <t.gummerer@gmail.com> wrote:
> >
> > Add a new --cached option to git checkout, which works only on the
> > index, but not the working tree, similar to what 'git reset <tree-ish>
> > -- <pathspec>... does.  Indeed the tests are adapted from the 'git
> > reset' tests.
> >
> > In the longer term the idea is to potentially deprecate 'git reset
> > <tree-ish> -- <pathspec>...', so the 'git reset' command becomes only
> > about re-pointing the HEAD, and not also about copying entries from
> > <tree-ish> to the index.
> >
> > Note that 'git checkout' by default works in overlay mode, meaning
> > files that match the pathspec that don't exist in <tree-ish>, but
> > exist in the index would not be removed.  'git checkout --no-overlay
> > --cached' can be used to get the same behaviour as 'git reset
> > <tree-ish> -- <pathspec>'.
> 
> I think this argues _even more_ that --no-overlay should be the
> default.  Your series is valuable even if we don't push on that, I'm
> just being noisy about what I think would be an even better world.

I think just having that mode in 'git restore-files' Duy is working on
may have to be enough for now.

> Also, I don't think I've mentioned it yet, but I'm really excited
> about this series and what you're doing.  It's super cool.  (Which I
> expected when I saw the description of the desired behavior, but I'm
> also liking and contemplating re-using some code...)

Thanks :)

> > One thing this patch doesn't currently deal with is conflicts.
> > Currently 'git checkout --{ours,theirs} -- <file-with-conflicts>'
> > doesn't do anything with the index, so the --cached option just
> > mirrors that behaviour.  But given it doesn't even deal with
> > conflicts, the '--cached' option doesn't make much sense when no
> > <tree-ish> is given.  As it operates only on the index, it's always a
> > no-op if no tree-ish is given.
> >
> > Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
> > ---
> >
> > Maybe we can just disallow --cached without <tree-ish> given for now,
> > and possibly later allow it with some different behaviour for
> > conflicts, not sure what the best way forward here is.  We can also
> > just make it update the index as appropriate, and have it behave
> > different than 'git checkout' curerntly does when handling conflicts?
> 
> Huh?
>   "git checkout -- <path>"
> means update <path> from the index, meaning the index is left alone
> (it's the source) and only the working tree is touched.
> 
> When you add a flag named --cached to only update the index and not
> the working tree, then the index becomes the sole destination.
> 
> Now we combine: no tree is specified means the index is the source of
> the writing, and --cached being specified means the index is the sole
> destination of the writing.  Thus, you have a no-op.  If the user
> specifies --cached and no tree, you should immediately exit with a
> message along the lines of "Nothing to do; no tree given and --cached
> specified."  The presence of conflicts seems completely irrelevant to
> me here.

Ah yeah you're right, thanks for a sanity check.  The command I was
most worried about was 'git checkout --cached --{ours,theirs} -- <pathspec>', 
which I thought should update the index.  But as we don't give any
tree-ish, I'm not sure anymore it should.  Maybe just always exiting
with the message you mention above is the right thing to do.

> >  builtin/checkout.c         |  26 ++++++++--
> >  t/t2016-checkout-patch.sh  |   8 +++
> >  t/t2026-checkout-cached.sh | 103 +++++++++++++++++++++++++++++++++++++
> >  t/t9902-completion.sh      |   1 +
> >  4 files changed, 135 insertions(+), 3 deletions(-)
> >  create mode 100755 t/t2026-checkout-cached.sh
> >
> > diff --git a/builtin/checkout.c b/builtin/checkout.c
> > index 0aef35bbc4..6ba85e9de5 100644
> > --- a/builtin/checkout.c
> > +++ b/builtin/checkout.c
> > @@ -45,6 +45,7 @@ struct checkout_opts {
> >         int ignore_other_worktrees;
> >         int show_progress;
> >         int overlay_mode;
> > +       int cached;
> >         /*
> >          * If new checkout options are added, skip_merge_working_tree
> >          * should be updated accordingly.
> > @@ -288,6 +289,10 @@ static int checkout_paths(const struct checkout_opts *opts,
> >                 die(_("Cannot update paths and switch to branch '%s' at the same time."),
> >                     opts->new_branch);
> >
> > +       if (opts->patch_mode && opts->cached)
> > +               return run_add_interactive(revision, "--patch=reset",
> > +                                          &opts->pathspec);
> > +
> >         if (opts->patch_mode)
> >                 return run_add_interactive(revision, "--patch=checkout",
> >                                            &opts->pathspec);
> > @@ -319,7 +324,9 @@ static int checkout_paths(const struct checkout_opts *opts,
> >                                  * the current index, which means that it should
> >                                  * be removed.
> >                                  */
> > -                               ce->ce_flags |= CE_MATCHED | CE_REMOVE | CE_WT_REMOVE;
> > +                               ce->ce_flags |= CE_MATCHED | CE_REMOVE;
> > +                               if (!opts->cached)
> > +                                       ce->ce_flags |= CE_WT_REMOVE;
> >                                 continue;
> >                         } else {
> >                                 /*
> > @@ -392,6 +399,9 @@ static int checkout_paths(const struct checkout_opts *opts,
> >         for (pos = 0; pos < active_nr; pos++) {
> >                 struct cache_entry *ce = active_cache[pos];
> >                 if (ce->ce_flags & CE_MATCHED) {
> > +                       if (opts->cached) {
> > +                               continue;
> > +                       }
> >                         if (!ce_stage(ce)) {
> >                                 errs |= checkout_entry(ce, &state, NULL);
> >                                 continue;
> > @@ -571,6 +581,11 @@ static int skip_merge_working_tree(const struct checkout_opts *opts,
> >          * not tested here
> >          */
> >
> > +       /*
> > +        * opts->cached cannot be used with switching branches so is
> > +        * not tested here
> > +        */
> > +
> >         /*
> >          * If we aren't creating a new branch any changes or updates will
> >          * happen in the existing branch.  Since that could only be updating
> > @@ -1207,9 +1222,13 @@ static int checkout_branch(struct checkout_opts *opts,
> >                 die(_("'%s' cannot be used with switching branches"),
> >                     "--patch");
> >
> > -       if (!opts->overlay_mode)
> > +       if (opts->overlay_mode != -1)
> > +               die(_("'%s' cannot be used with switching branches"),
> > +                   "--overlay/--no-overlay");
> > +
> > +       if (opts->cached)
> >                 die(_("'%s' cannot be used with switching branches"),
> > -                   "--no-overlay");
> > +                   "--cached");
> >
> >         if (opts->writeout_stage)
> >                 die(_("'%s' cannot be used with switching branches"),
> > @@ -1300,6 +1319,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
> >                             PARSE_OPT_OPTARG, option_parse_recurse_submodules_worktree_updater },
> >                 OPT_BOOL(0, "progress", &opts.show_progress, N_("force progress reporting")),
> >                 OPT_BOOL(0, "overlay", &opts.overlay_mode, N_("use overlay mode")),
> > +               OPT_BOOL(0, "cached", &opts.cached, N_("work on the index only")),
> >                 OPT_END(),
> >         };
> >
> > diff --git a/t/t2016-checkout-patch.sh b/t/t2016-checkout-patch.sh
> > index 47aeb0b167..e8774046e0 100755
> > --- a/t/t2016-checkout-patch.sh
> > +++ b/t/t2016-checkout-patch.sh
> > @@ -108,6 +108,14 @@ test_expect_success PERL 'path limiting works: foo inside dir' '
> >         verify_state dir/foo head head
> >  '
> >
> > +test_expect_success PERL 'git checkout --cached -p' '
> > +       set_and_save_state dir/foo work work &&
> > +       test_write_lines n y | git checkout --cached -p >output &&
> > +       verify_state dir/foo work head &&
> > +       verify_saved_state bar &&
> > +       test_i18ngrep "Unstage" output
> > +'
> > +
> >  test_expect_success PERL 'none of this moved HEAD' '
> >         verify_saved_head
> >  '
> > diff --git a/t/t2026-checkout-cached.sh b/t/t2026-checkout-cached.sh
> > new file mode 100755
> > index 0000000000..1b66192727
> > --- /dev/null
> > +++ b/t/t2026-checkout-cached.sh
> > @@ -0,0 +1,103 @@
> > +#!/bin/sh
> > +
> > +test_description='checkout --cached <pathspec>'
> > +
> > +. ./test-lib.sh
> > +
> > +test_expect_success 'checkout --cached <pathspec>' '
> > +       echo 1 >file1 &&
> > +       echo 2 >file2 &&
> > +       git add file1 file2 &&
> > +       test_tick &&
> > +       git commit -m files &&
> > +       git rm file2 &&
> > +       echo 3 >file3 &&
> > +       echo 4 >file1 &&
> > +       git add file1 file3 &&
> > +       git checkout --cached HEAD -- file1 file2 &&
> > +       test_must_fail git diff --quiet &&
> > +
> > +       cat >expect <<-\EOF &&
> > +       diff --git a/file1 b/file1
> > +       index d00491f..b8626c4 100644
> > +       --- a/file1
> > +       +++ b/file1
> > +       @@ -1 +1 @@
> > +       -1
> > +       +4
> > +       diff --git a/file2 b/file2
> > +       deleted file mode 100644
> > +       index 0cfbf08..0000000
> > +       --- a/file2
> > +       +++ /dev/null
> > +       @@ -1 +0,0 @@
> > +       -2
> > +       EOF
> > +       git diff >actual &&
> > +       test_cmp expect actual &&
> > +
> > +       cat >expect <<-\EOF &&
> > +       diff --git a/file3 b/file3
> > +       new file mode 100644
> > +       index 0000000..00750ed
> > +       --- /dev/null
> > +       +++ b/file3
> > +       @@ -0,0 +1 @@
> > +       +3
> > +       EOF
> > +       git diff --cached >actual &&
> > +       test_cmp expect actual
> > +'
> > +
> > +test_expect_success 'checking out an unmodified path is a no-op' '
> > +       git reset --hard &&
> > +       git checkout --cached HEAD -- file1 &&
> > +       git diff-files --exit-code &&
> > +       git diff-index --cached --exit-code HEAD
> > +'
> > +
> > +test_expect_success 'checking out specific path that is unmerged' '
> > +       test_commit file3 file3 &&
> > +       git rm --cached file2 &&
> > +       echo 1234 >file2 &&
> > +       F1=$(git rev-parse HEAD:file1) &&
> > +       F2=$(git rev-parse HEAD:file2) &&
> > +       F3=$(git rev-parse HEAD:file3) &&
> > +       {
> > +               echo "100644 $F1 1      file2" &&
> > +               echo "100644 $F2 2      file2" &&
> > +               echo "100644 $F3 3      file2"
> > +       } | git update-index --index-info &&
> > +       git ls-files -u &&
> > +       git checkout --cached HEAD file2 &&
> > +       test_must_fail git diff --quiet &&
> > +       git diff-index --exit-code --cached HEAD
> > +'
> > +
> > +test_expect_success '--cached without --no-overlay does not remove entry from index' '
> > +       test_must_fail git checkout --cached HEAD^ file3 &&
> > +       git ls-files --error-unmatch -- file3
> > +'
> > +
> > +test_expect_success 'file is removed from the index with --no-overlay' '
> > +       git checkout --cached --no-overlay HEAD^ file3 &&
> > +       test_path_is_file file3 &&
> > +       test_must_fail git ls-files --error-unmatch -- file3
> > +'
> > +
> > +test_expect_success 'test checkout --cached --no-overlay at given paths' '
> > +       mkdir sub &&
> > +       >sub/file1 &&
> > +       >sub/file2 &&
> > +       git update-index --add sub/file1 sub/file2 &&
> > +       T=$(git write-tree) &&
> > +       git checkout --cached --no-overlay HEAD sub/file2 &&
> > +       test_must_fail git diff --quiet &&
> > +       U=$(git write-tree) &&
> 
> Do we need to worry at all about losing the exit status of write-tree
> in either invocation?  In particular, if the second one for U fails
> somehow, we'd end up with $U being a blank string and we'd still
> probably get "$T" != "$U" below.

Hmm this seems to be a fairly common pattern in our test suite:

$ git grep -F '$(git write-tree)' t/* | wc -l
112

But maybe it's just something we used to do, but should move away
from.  Just writing the output to a file shouldn't be much harder
either, I'll do that in the next iteration.

> You also had some rev-parse invocations hidden in a sub-shell in both
> this patch and patch 5, but subsequent commands relied on non-empty
> output out of those, so I figured those were fine.  This one might be
> too, but I thought I'd at least mention it.
> 
> > +       echo "$T" &&
> > +       echo "$U" &&
> > +       test_must_fail git diff-index --cached --exit-code "$T" &&
> > +       test "$T" != "$U"
> > +'
> > +
> > +test_done
> > diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
> > index a3fd9a9630..cbc304ace8 100755
> > --- a/t/t9902-completion.sh
> > +++ b/t/t9902-completion.sh
> > @@ -1437,6 +1437,7 @@ test_expect_success 'double dash "git checkout"' '
> >         --no-quiet Z
> >         --no-... Z
> >         --overlay Z
> > +       --cached Z
> >         EOF
> >  '
> >
> > --
> > 2.20.0.405.gbc1bbc6f85