diffcore-break.c

   1 /*
   2  * Copyright (C) 2005 Junio C Hamano
   3  */
   4 #include "cache.h"
   5 #include "diff.h"
   6 #include "diffcore.h"
   7
   8 static int should_break(struct diff_filespec *src,
   9                         struct diff_filespec *dst,
  10                         int break_score,
  11                         int *merge_score_p)
  12 {
  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?
  16          *
  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.
  23          *
  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.
  31          *
  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.
  39          *
  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.
  44          *
  45          * The value we return is 1 if we want the pair to be broken,
  46          * or 0 if we do not.
  47          */
  48         unsigned long delta_size, max_size;
  49         unsigned long src_copied, literal_added, src_removed;
  50
  51         *merge_score_p = 0; /* assume no deletion --- "do not break"
  52                              * is the default.
  53                              */
  54
  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 */
  58         }
  59
  60         if (src->oid_valid && dst->oid_valid &&
  61             oideq(&src->oid, &dst->oid))
  62                 return 0; /* they are the same */
  63
  64         if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
  65                 return 0; /* error but caught downstream */
  66
  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 */
  70
  71         if (!src->size)
  72                 return 0; /* we do not let empty files get renamed */
  73
  74         if (diffcore_count_changes(src, dst,
  75                                    &src->cnt_data, &dst->cnt_data,
  76                                    &src_copied, &literal_added))
  77                 return 0;
  78
  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;
  87         }
  88         src_removed = src->size - src_copied;
  89
  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.
  94          */
  95         *merge_score_p = (int)(src_removed * MAX_SCORE / src->size);
  96         if (*merge_score_p > break_score)
  97                 return 1;
  98
  99         /* Extent of damage, which counts both inserts and
 100          * deletes.
 101          */
 102         delta_size = src_removed + literal_added;
 103         if (delta_size * MAX_SCORE / max_size < break_score)
 104                 return 0;
 105
 106         /* If you removed a lot without adding new material, that is
 107          * not really a rewrite.
 108          */
 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;
 113
 114         return 1;
 115 }
 116
 117 void diffcore_break(int break_score)
 118 {
 119         struct diff_queue_struct *q = &diff_queued_diff;
 120         struct diff_queue_struct outq;
 121
 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.
 128          *
 129          * int break_score; we reuse incoming parameter for this.
 130          */
 131
 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).
 152          */
 153         int merge_score;
 154         int i;
 155
 156         /* See comment on DEFAULT_BREAK_SCORE and
 157          * DEFAULT_MERGE_SCORE in diffcore.h
 158          */
 159         merge_score = (break_score >> 16) & 0xFFFF;
 160         break_score = (break_score & 0xFFFF);
 161
 162         if (!break_score)
 163                 break_score = DEFAULT_BREAK_SCORE;
 164         if (!merge_score)
 165                 merge_score = DEFAULT_MERGE_SCORE;
 166
 167         DIFF_QUEUE_CLEAR(&outq);
 168
 169         for (i = 0; i < q->nr; i++) {
 170                 struct diff_filepair *p = q->queue[i];
 171                 int score;
 172
 173                 /*
 174                  * We deal only with in-place edit of blobs.
 175                  * We do not break anything else.
 176                  */
 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;
 186
 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.
 192                                  */
 193                                 if (score < merge_score)
 194                                         score = 0;
 195
 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;
 201
 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;
 207
 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.
 212                                           */
 213                                 continue;
 214                         }
 215                 }
 216                 diff_free_filespec_data(p->one);
 217                 diff_free_filespec_data(p->two);
 218                 diff_q(&outq, p);
 219         }
 220         free(q->queue);
 221         *q = outq;
 222
 223         return;
 224 }
 225
 226 static void merge_broken(struct diff_filepair *p,
 227                          struct diff_filepair *pp,
 228                          struct diff_queue_struct *outq)
 229 {
 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;
 235         }
 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");
 245
 246         dp = diff_queue(outq, d->one, c->two);
 247         dp->score = p->score;
 248         /*
 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.
 253          */
 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);
 259 }
 260
 261 void diffcore_merge_broken(void)
 262 {
 263         struct diff_queue_struct *q = &diff_queued_diff;
 264         struct diff_queue_struct outq;
 265         int i, j;
 266
 267         DIFF_QUEUE_CLEAR(&outq);
 268
 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.
 278                          */
 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;
 288                                 }
 289                         }
 290                         if (q->nr <= j)
 291                                 /* The peer did not survive, so we keep
 292                                  * it in the output.
 293                                  */
 294                                 diff_q(&outq, p);
 295                 }
 296                 else
 297                         diff_q(&outq, p);
 298         }
 299         free(q->queue);
 300         *q = outq;
 301
 302         return;
 303 }