Documentation/stash: remove mention of git reset --hard
[git.git] / diffcore-break.c
blobc64359f489c87910b9d41756918dacda49276004
1 /*
2 * Copyright (C) 2005 Junio C Hamano
3 */
4 #include "cache.h"
5 #include "diff.h"
6 #include "diffcore.h"
8 static int should_break(struct diff_filespec *src,
9 struct diff_filespec *dst,
10 int break_score,
11 int *merge_score_p)
13 /* dst is recorded as a modification of src. Are they so
14 * different that we are better off recording this as a pair
15 * of delete and create?
17 * There are two criteria used in this algorithm. For the
18 * purposes of helping later rename/copy, we take both delete
19 * and insert into account and estimate the amount of "edit".
20 * If the edit is very large, we break this pair so that
21 * rename/copy can pick the pieces up to match with other
22 * files.
24 * On the other hand, we would want to ignore inserts for the
25 * pure "complete rewrite" detection. As long as most of the
26 * existing contents were removed from the file, it is a
27 * complete rewrite, and if sizable chunk from the original
28 * still remains in the result, it is not a rewrite. It does
29 * not matter how much or how little new material is added to
30 * the file.
32 * The score we leave for such a broken filepair uses the
33 * latter definition so that later clean-up stage can find the
34 * pieces that should not have been broken according to the
35 * latter definition after rename/copy runs, and merge the
36 * broken pair that have a score lower than given criteria
37 * back together. The break operation itself happens
38 * according to the former definition.
40 * The minimum_edit parameter tells us when to break (the
41 * amount of "edit" required for us to consider breaking the
42 * pair). We leave the amount of deletion in *merge_score_p
43 * when we return.
45 * The value we return is 1 if we want the pair to be broken,
46 * or 0 if we do not.
48 unsigned long delta_size, max_size;
49 unsigned long src_copied, literal_added, src_removed;
51 *merge_score_p = 0; /* assume no deletion --- "do not break"
52 * is the default.
55 if (S_ISREG(src->mode) != S_ISREG(dst->mode)) {
56 *merge_score_p = (int)MAX_SCORE;
57 return 1; /* even their types are different */
60 if (src->oid_valid && dst->oid_valid &&
61 !oidcmp(&src->oid, &dst->oid))
62 return 0; /* they are the same */
64 if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
65 return 0; /* error but caught downstream */
67 max_size = ((src->size > dst->size) ? src->size : dst->size);
68 if (max_size < MINIMUM_BREAK_SIZE)
69 return 0; /* we do not break too small filepair */
71 if (!src->size)
72 return 0; /* we do not let empty files get renamed */
74 if (diffcore_count_changes(src, dst,
75 &src->cnt_data, &dst->cnt_data,
76 &src_copied, &literal_added))
77 return 0;
79 /* sanity */
80 if (src->size < src_copied)
81 src_copied = src->size;
82 if (dst->size < literal_added + src_copied) {
83 if (src_copied < dst->size)
84 literal_added = dst->size - src_copied;
85 else
86 literal_added = 0;
88 src_removed = src->size - src_copied;
90 /* Compute merge-score, which is "how much is removed
91 * from the source material". The clean-up stage will
92 * merge the surviving pair together if the score is
93 * less than the minimum, after rename/copy runs.
95 *merge_score_p = (int)(src_removed * MAX_SCORE / src->size);
96 if (*merge_score_p > break_score)
97 return 1;
99 /* Extent of damage, which counts both inserts and
100 * deletes.
102 delta_size = src_removed + literal_added;
103 if (delta_size * MAX_SCORE / max_size < break_score)
104 return 0;
106 /* If you removed a lot without adding new material, that is
107 * not really a rewrite.
109 if ((src->size * break_score < src_removed * MAX_SCORE) &&
110 (literal_added * 20 < src_removed) &&
111 (literal_added * 20 < src_copied))
112 return 0;
114 return 1;
117 void diffcore_break(int break_score)
119 struct diff_queue_struct *q = &diff_queued_diff;
120 struct diff_queue_struct outq;
122 /* When the filepair has this much edit (insert and delete),
123 * it is first considered to be a rewrite and broken into a
124 * create and delete filepair. This is to help breaking a
125 * file that had too much new stuff added, possibly from
126 * moving contents from another file, so that rename/copy can
127 * match it with the other file.
129 * int break_score; we reuse incoming parameter for this.
132 /* After a pair is broken according to break_score and
133 * subjected to rename/copy, both of them may survive intact,
134 * due to lack of suitable rename/copy peer. Or, the caller
135 * may be calling us without using rename/copy. When that
136 * happens, we merge the broken pieces back into one
137 * modification together if the pair did not have more than
138 * this much delete. For this computation, we do not take
139 * insert into account at all. If you start from a 100-line
140 * file and delete 97 lines of it, it does not matter if you
141 * add 27 lines to it to make a new 30-line file or if you add
142 * 997 lines to it to make a 1000-line file. Either way what
143 * you did was a rewrite of 97%. On the other hand, if you
144 * delete 3 lines, keeping 97 lines intact, it does not matter
145 * if you add 3 lines to it to make a new 100-line file or if
146 * you add 903 lines to it to make a new 1000-line file.
147 * Either way you did a lot of additions and not a rewrite.
148 * This merge happens to catch the latter case. A merge_score
149 * of 80% would be a good default value (a broken pair that
150 * has score lower than merge_score will be merged back
151 * together).
153 int merge_score;
154 int i;
156 /* See comment on DEFAULT_BREAK_SCORE and
157 * DEFAULT_MERGE_SCORE in diffcore.h
159 merge_score = (break_score >> 16) & 0xFFFF;
160 break_score = (break_score & 0xFFFF);
162 if (!break_score)
163 break_score = DEFAULT_BREAK_SCORE;
164 if (!merge_score)
165 merge_score = DEFAULT_MERGE_SCORE;
167 DIFF_QUEUE_CLEAR(&outq);
169 for (i = 0; i < q->nr; i++) {
170 struct diff_filepair *p = q->queue[i];
171 int score;
174 * We deal only with in-place edit of blobs.
175 * We do not break anything else.
177 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
178 object_type(p->one->mode) == OBJ_BLOB &&
179 object_type(p->two->mode) == OBJ_BLOB &&
180 !strcmp(p->one->path, p->two->path)) {
181 if (should_break(p->one, p->two,
182 break_score, &score)) {
183 /* Split this into delete and create */
184 struct diff_filespec *null_one, *null_two;
185 struct diff_filepair *dp;
187 /* Set score to 0 for the pair that
188 * needs to be merged back together
189 * should they survive rename/copy.
190 * Also we do not want to break very
191 * small files.
193 if (score < merge_score)
194 score = 0;
196 /* deletion of one */
197 null_one = alloc_filespec(p->one->path);
198 dp = diff_queue(&outq, p->one, null_one);
199 dp->score = score;
200 dp->broken_pair = 1;
202 /* creation of two */
203 null_two = alloc_filespec(p->two->path);
204 dp = diff_queue(&outq, null_two, p->two);
205 dp->score = score;
206 dp->broken_pair = 1;
208 diff_free_filespec_blob(p->one);
209 diff_free_filespec_blob(p->two);
210 free(p); /* not diff_free_filepair(), we are
211 * reusing one and two here.
213 continue;
216 diff_free_filespec_data(p->one);
217 diff_free_filespec_data(p->two);
218 diff_q(&outq, p);
220 free(q->queue);
221 *q = outq;
223 return;
226 static void merge_broken(struct diff_filepair *p,
227 struct diff_filepair *pp,
228 struct diff_queue_struct *outq)
230 /* p and pp are broken pairs we want to merge */
231 struct diff_filepair *c = p, *d = pp, *dp;
232 if (DIFF_FILE_VALID(p->one)) {
233 /* this must be a delete half */
234 d = p; c = pp;
236 /* Sanity check */
237 if (!DIFF_FILE_VALID(d->one))
238 die("internal error in merge #1");
239 if (DIFF_FILE_VALID(d->two))
240 die("internal error in merge #2");
241 if (DIFF_FILE_VALID(c->one))
242 die("internal error in merge #3");
243 if (!DIFF_FILE_VALID(c->two))
244 die("internal error in merge #4");
246 dp = diff_queue(outq, d->one, c->two);
247 dp->score = p->score;
249 * We will be one extra user of the same src side of the
250 * broken pair, if it was used as the rename source for other
251 * paths elsewhere. Increment to mark that the path stays
252 * in the resulting tree.
254 d->one->rename_used++;
255 diff_free_filespec_data(d->two);
256 diff_free_filespec_data(c->one);
257 free(d);
258 free(c);
261 void diffcore_merge_broken(void)
263 struct diff_queue_struct *q = &diff_queued_diff;
264 struct diff_queue_struct outq;
265 int i, j;
267 DIFF_QUEUE_CLEAR(&outq);
269 for (i = 0; i < q->nr; i++) {
270 struct diff_filepair *p = q->queue[i];
271 if (!p)
272 /* we already merged this with its peer */
273 continue;
274 else if (p->broken_pair &&
275 !strcmp(p->one->path, p->two->path)) {
276 /* If the peer also survived rename/copy, then
277 * we merge them back together.
279 for (j = i + 1; j < q->nr; j++) {
280 struct diff_filepair *pp = q->queue[j];
281 if (pp->broken_pair &&
282 !strcmp(pp->one->path, pp->two->path) &&
283 !strcmp(p->one->path, pp->two->path)) {
284 /* Peer survived. Merge them */
285 merge_broken(p, pp, &outq);
286 q->queue[j] = NULL;
287 break;
290 if (q->nr <= j)
291 /* The peer did not survive, so we keep
292 * it in the output.
294 diff_q(&outq, p);
296 else
297 diff_q(&outq, p);
299 free(q->queue);
300 *q = outq;
302 return;