diffcore: fix iteration order of identical files during rename detection

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>

diff --git a/diffcore-rename.c b/diffcore-rename.c
index af1fe08861e6862985ac8fb9311b17568cb9e547..69fcf77be02df4160dfaa04380d0a262b9d4aa02 100644 (file)
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -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 */

diff --git a/t/t4001-diff-rename.sh b/t/t4001-diff-rename.sh
index 2f327b749588af7eda57187cba4d365233a25ef9..ed90c6c6f984979bfc250d277486550cb5129e30 100755 (executable)
--- a/t/t4001-diff-rename.sh
+++ b/t/t4001-diff-rename.sh
@@ -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;