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diffcore: fix iteration order of identical files during rename detection

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If the two paths 'dir/A/file' and 'dir/B/file' have identical content
and the parent directory is renamed, e.g. 'git mv dir other-dir', then
diffcore reports the following exact renames:

    renamed:    dir/B/file -> other-dir/A/file
    renamed:    dir/A/file -> other-dir/B/file

While technically not wrong, this is confusing not only for the user,
but also for git commands that make decisions based on rename
information, e.g. 'git log --follow other-dir/A/file' follows
'dir/B/file' past the rename.

This behavior is a side effect of commit v2.0.0-rc4~8^2~14
(diffcore-rename.c: simplify finding exact renames, 2013-11-14): the
hashmap storing sources returns entries from the same bucket, i.e.
sources matching the current destination, in LIFO order.  Thus the
iteration first examines 'other-dir/A/file' and 'dir/B/file' and, upon
finding identical content and basename, reports an exact rename.

Other hashmap users are apparently happy with the current iteration
order over the entries of a bucket.  Changing the iteration order
would risk upsetting other hashmap users and would increase the memory
footprint of each bucket by a pointer to the tail element.

Fill the hashmap with source entries in reverse order to restore the
original exact rename detection behavior.

Reported-by: Bill Okara <billokara@gmail.com>
Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
SZEDER Gábor 2016-03-30 10:35:07 +02:00 committed by Junio C Hamano
parent 765428699a
commit ca4e3ca029
2 changed files with 15 additions and 2 deletions
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6
diffcore-rename.c
View File

@ -340,9 +340,11 @@ static int find_exact_renames(struct diff_options *options)
int i, renames = 0;
struct hashmap file_table;
/* Add all sources to the hash table */
/* Add all sources to the hash table in reverse order, because
* later on they will be retrieved in LIFO order.
*/
hashmap_init(&file_table, NULL, rename_src_nr);
for (i = 0; i < rename_src_nr; i++)
for (i = rename_src_nr-1; i >= 0; i--)
insert_file_table(&file_table, i, rename_src[i].p->one);
/* Walk the destinations and find best source match */

11
t/t4001-diff-rename.sh
View File

@ -77,6 +77,17 @@ test_expect_success 'favour same basenames even with minor differences' '
git show HEAD:path1 | sed "s/15/16/" > subdir/path1 &&
git status | test_i18ngrep "renamed: .*path1 -> subdir/path1"'
test_expect_success 'two files with same basename and same content' '
git reset --hard &&
mkdir -p dir/A dir/B &&
cp path1 dir/A/file &&
cp path1 dir/B/file &&
git add dir &&
git commit -m 2 &&
git mv dir other-dir &&
git status | test_i18ngrep "renamed: .*dir/A/file -> other-dir/A/file"
'
test_expect_success 'setup for many rename source candidates' '
git reset --hard &&
for i in 0 1 2 3 4 5 6 7 8 9;