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checkout: prevent losing staged changes with --merge 

When --merge is specified, we may need to do a real merge (instead of
three-way tree unpacking), the steps are best seen in git-checkout.sh
version before it's removed:

    # Match the index to the working tree, and do a three-way.
    git diff-files --name-only | git update-index --remove --stdin &&
    work=`git write-tree` &&
    git read-tree $v --reset -u $new || exit

    git merge-recursive $old -- $new $work

    # Do not register the cleanly merged paths in the index yet.
    # this is not a real merge before committing, but just carrying
    # the working tree changes along.
    unmerged=`git ls-files -u`
    git read-tree $v --reset $new
    case "$unmerged" in
    '')     ;;
    *)
            (
                    z40=0000000000000000000000000000000000000000
                    echo "$unmerged" |
                    sed -e 's/^[0-7]* [0-9a-f]* /'"0 $z40 /"
                    echo "$unmerged"
            ) | git update-index --index-info
            ;;
    esac

Notice the last 'read-tree --reset' step. We restore worktree back to
'new' tree after worktree's messed up by merge-recursive. If there are
staged changes before this whole command sequence is executed, they
are lost because they are unlikely part of the 'new' tree to be
restored.

There is no easy way to fix this. Elijah may have something up his
sleeves [1], but until then, check if there are staged changes and
refuse to run and lose them. The user would need to do "git reset" to
continue in this case.

A note about the test update. 'checkout -m' in that test will fail
because a deletion is staged. This 'checkout -m' was previously needed
to verify quietness behavior of unpack-trees. But a different check
has been put in place in the last patch. We can safely drop
'checkout -m' now.

[1] CABPp-BFoL_U=bzON4SEMaQSKU2TKwnOgNqjt5MUaOejTKGUJxw@mail.gmail.com

Reported-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Nguyễn Thái Ngọc Duy 2019-03-22 16:31:38 +07:00 committed by Junio C Hamano
parent 3e41485d85
commit 6eff409e8a
2 changed files with 11 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
builtin/checkout.c
View File

@ -725,7 +725,10 @@ static int merge_working_tree(const struct checkout_opts *opts,
*/
struct tree *result;
struct tree *work;
struct tree *old_tree;
struct merge_options o;
struct strbuf sb = STRBUF_INIT;
if (!opts->merge)
return 1;
@ -735,6 +738,12 @@ static int merge_working_tree(const struct checkout_opts *opts,
*/
if (!old_branch_info->commit)
return 1;
old_tree = get_commit_tree(old_branch_info->commit);
if (repo_index_has_changes(the_repository, old_tree, &sb))
die(_("cannot continue with staged changes in "
"the following files:\n%s"), sb.buf);
strbuf_release(&sb);
/* Do more real merge */
@ -772,7 +781,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
ret = merge_trees(&o,
get_commit_tree(new_branch_info->commit),
work,
get_commit_tree(old_branch_info->commit),
old_tree,
&result);
if (ret < 0)
exit(128);

10
t/t7201-co.sh
View File

@ -224,15 +224,7 @@ test_expect_success 'switch to another branch while carrying a deletion' '
test_i18ngrep overwritten errs &&
test_must_fail git read-tree --quiet -m -u HEAD simple 2>errs &&
test_must_be_empty errs &&
git checkout --merge simple 2>errs &&
test_i18ngrep ! overwritten errs &&
git ls-files -u &&
test_must_fail git cat-file -t :0:two &&
test "$(git cat-file -t :1:two)" = blob &&
test "$(git cat-file -t :2:two)" = blob &&
test_must_fail git cat-file -t :3:two
test_must_be_empty errs
'
test_expect_success 'checkout to detach HEAD (with advice declined)' '