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diffcore-break.c
Junio C Hamano authored
Starting from a single file, A, if you create B as a copy of A (and
possibly make some edit) and then make extensive change to A, you
will see:
$ git diff -C --name-status
C89 A B
M A
which is expected. However, if you ask the same question in a
different way, you see this:
$ git diff -B -M --name-status
R89 A B
M100 A
telling us that A was rename-edited into B (as if "A will no longer
exist as the result") and at the same time A itself was extensively
edited.
In this case, because the resulting tree still does have file A
(even if it has contents vastly different from the original), we
should use "C"opy, not "R"ename, to avoid hinting that A somehow
goes away.
Two existing tests were depending on the wrong behaviour, and fixed.
Signed-off-by: 
Junio C Hamano <gitster@pobox.com> diffcore-break.c 9.00 KiB
/*
* Copyright (C) 2005 Junio C Hamano
*/
#include "cache.h"
#include "diff.h"
#include "diffcore.h"
static int should_break(struct diff_filespec *src,
struct diff_filespec *dst,
int break_score,
int *merge_score_p)
{
/* dst is recorded as a modification of src. Are they so
* different that we are better off recording this as a pair
* of delete and create?
*
* There are two criteria used in this algorithm. For the
* purposes of helping later rename/copy, we take both delete
* and insert into account and estimate the amount of "edit".
* If the edit is very large, we break this pair so that
* rename/copy can pick the pieces up to match with other
* files.
*
* On the other hand, we would want to ignore inserts for the
* pure "complete rewrite" detection. As long as most of the
* existing contents were removed from the file, it is a
* complete rewrite, and if sizable chunk from the original
* still remains in the result, it is not a rewrite. It does
* not matter how much or how little new material is added to
* the file.
*
* The score we leave for such a broken filepair uses the
* latter definition so that later clean-up stage can find the
* pieces that should not have been broken according to the
* latter definition after rename/copy runs, and merge the
* broken pair that have a score lower than given criteria
* back together. The break operation itself happens
* according to the former definition.
*
* The minimum_edit parameter tells us when to break (the
* amount of "edit" required for us to consider breaking the
* pair). We leave the amount of deletion in *merge_score_p
* when we return.
*
* The value we return is 1 if we want the pair to be broken,
* or 0 if we do not.
*/
unsigned long delta_size, max_size;
unsigned long src_copied, literal_added, src_removed;
*merge_score_p = 0; /* assume no deletion --- "do not break"
* is the default.
*/
if (S_ISREG(src->mode) != S_ISREG(dst->mode)) {
*merge_score_p = (int)MAX_SCORE;
return 1; /* even their types are different */
}
if (src->sha1_valid && dst->sha1_valid &&
!hashcmp(src->sha1, dst->sha1))
return 0; /* they are the same */
if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
return 0; /* error but caught downstream */
max_size = ((src->size > dst->size) ? src->size : dst->size);
if (max_size < MINIMUM_BREAK_SIZE)
return 0; /* we do not break too small filepair */
if (!src->size)
return 0; /* we do not let empty files get renamed */
if (diffcore_count_changes(src, dst,
&src->cnt_data, &dst->cnt_data,
0,
&src_copied, &literal_added))
return 0;
/* sanity */
if (src->size < src_copied)
src_copied = src->size;
if (dst->size < literal_added + src_copied) {
if (src_copied < dst->size)
literal_added = dst->size - src_copied;
else
literal_added = 0;
}
src_removed = src->size - src_copied;
/* Compute merge-score, which is "how much is removed
* from the source material". The clean-up stage will
* merge the surviving pair together if the score is
* less than the minimum, after rename/copy runs.
*/
*merge_score_p = (int)(src_removed * MAX_SCORE / src->size);
if (*merge_score_p > break_score)
return 1;
/* Extent of damage, which counts both inserts and
* deletes.
*/
delta_size = src_removed + literal_added;
if (delta_size * MAX_SCORE / max_size < break_score)
return 0;
/* If you removed a lot without adding new material, that is
* not really a rewrite.
*/
if ((src->size * break_score < src_removed * MAX_SCORE) &&
(literal_added * 20 < src_removed) &&
(literal_added * 20 < src_copied))
return 0;
return 1;
}
void diffcore_break(int break_score)
{
struct diff_queue_struct *q = &diff_queued_diff;
struct diff_queue_struct outq;
/* When the filepair has this much edit (insert and delete),
* it is first considered to be a rewrite and broken into a
* create and delete filepair. This is to help breaking a
* file that had too much new stuff added, possibly from
* moving contents from another file, so that rename/copy can
* match it with the other file.
*
* int break_score; we reuse incoming parameter for this.
*/
/* After a pair is broken according to break_score and
* subjected to rename/copy, both of them may survive intact,
* due to lack of suitable rename/copy peer. Or, the caller
* may be calling us without using rename/copy. When that
* happens, we merge the broken pieces back into one
* modification together if the pair did not have more than
* this much delete. For this computation, we do not take
* insert into account at all. If you start from a 100-line * file and delete 97 lines of it, it does not matter if you
* add 27 lines to it to make a new 30-line file or if you add
* 997 lines to it to make a 1000-line file. Either way what
* you did was a rewrite of 97%. On the other hand, if you
* delete 3 lines, keeping 97 lines intact, it does not matter
* if you add 3 lines to it to make a new 100-line file or if
* you add 903 lines to it to make a new 1000-line file.
* Either way you did a lot of additions and not a rewrite.
* This merge happens to catch the latter case. A merge_score
* of 80% would be a good default value (a broken pair that
* has score lower than merge_score will be merged back
* together).
*/
int merge_score;
int i;
/* See comment on DEFAULT_BREAK_SCORE and
* DEFAULT_MERGE_SCORE in diffcore.h
*/
merge_score = (break_score >> 16) & 0xFFFF;
break_score = (break_score & 0xFFFF);
if (!break_score)
break_score = DEFAULT_BREAK_SCORE;
if (!merge_score)
merge_score = DEFAULT_MERGE_SCORE;
DIFF_QUEUE_CLEAR(&outq);
for (i = 0; i < q->nr; i++) {
struct diff_filepair *p = q->queue[i];
int score;
/*
* We deal only with in-place edit of blobs.
* We do not break anything else.
*/
if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
object_type(p->one->mode) == OBJ_BLOB &&
object_type(p->two->mode) == OBJ_BLOB &&
!strcmp(p->one->path, p->two->path)) {
if (should_break(p->one, p->two,
break_score, &score)) {
/* Split this into delete and create */
struct diff_filespec *null_one, *null_two;
struct diff_filepair *dp;
/* Set score to 0 for the pair that
* needs to be merged back together
* should they survive rename/copy.
* Also we do not want to break very
* small files.
*/
if (score < merge_score)
score = 0;
/* deletion of one */
null_one = alloc_filespec(p->one->path);
dp = diff_queue(&outq, p->one, null_one);
dp->score = score;
dp->broken_pair = 1;
/* creation of two */
null_two = alloc_filespec(p->two->path);
dp = diff_queue(&outq, null_two, p->two);
dp->score = score;
dp->broken_pair = 1;
diff_free_filespec_blob(p->one);
diff_free_filespec_blob(p->two); free(p); /* not diff_free_filepair(), we are
* reusing one and two here.
*/
continue;
}
}
diff_free_filespec_data(p->one);
diff_free_filespec_data(p->two);
diff_q(&outq, p);
}
free(q->queue);
*q = outq;
return;
}
static void merge_broken(struct diff_filepair *p,
struct diff_filepair *pp,
struct diff_queue_struct *outq)
{
/* p and pp are broken pairs we want to merge */
struct diff_filepair *c = p, *d = pp, *dp;
if (DIFF_FILE_VALID(p->one)) {
/* this must be a delete half */
d = p; c = pp;
}
/* Sanity check */
if (!DIFF_FILE_VALID(d->one))
die("internal error in merge #1");
if (DIFF_FILE_VALID(d->two))
die("internal error in merge #2");
if (DIFF_FILE_VALID(c->one))
die("internal error in merge #3");
if (!DIFF_FILE_VALID(c->two))
die("internal error in merge #4");
dp = diff_queue(outq, d->one, c->two);
dp->score = p->score;
/*
* We will be one extra user of the same src side of the
* broken pair, if it was used as the rename source for other
* paths elsewhere. Increment to mark that the path stays
* in the resulting tree.
*/
d->one->rename_used++;
diff_free_filespec_data(d->two);
diff_free_filespec_data(c->one);
free(d);
free(c);
}
void diffcore_merge_broken(void)
{
struct diff_queue_struct *q = &diff_queued_diff;
struct diff_queue_struct outq;
int i, j;
DIFF_QUEUE_CLEAR(&outq);
for (i = 0; i < q->nr; i++) {
struct diff_filepair *p = q->queue[i];
if (!p)
/* we already merged this with its peer */
continue;
else if (p->broken_pair &&
!strcmp(p->one->path, p->two->path)) {
/* If the peer also survived rename/copy, then
* we merge them back together.
*/
for (j = i + 1; j < q->nr; j++) { struct diff_filepair *pp = q->queue[j];
if (pp->broken_pair &&
!strcmp(pp->one->path, pp->two->path) &&
!strcmp(p->one->path, pp->two->path)) {
/* Peer survived. Merge them */
merge_broken(p, pp, &outq);
q->queue[j] = NULL;
break;
}
}
if (q->nr <= j)
/* The peer did not survive, so we keep
* it in the output.
*/
diff_q(&outq, p);
}
else
diff_q(&outq, p);
}
free(q->queue);
*q = outq;
return;
}