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 #include "promisor-remote.h"
   8
   9 static int should_break(struct repository *r,
  10                         struct diff_filespec *src,
  11                         struct diff_filespec *dst,
  12                         int break_score,
  13                         int *merge_score_p)
  14 {
  15         /* dst is recorded as a modification of src.  Are they so
  16          * different that we are better off recording this as a pair
  17          * of delete and create?
  18          *
  19          * There are two criteria used in this algorithm.  For the
  20          * purposes of helping later rename/copy, we take both delete
  21          * and insert into account and estimate the amount of "edit".
  22          * If the edit is very large, we break this pair so that
  23          * rename/copy can pick the pieces up to match with other
  24          * files.
  25          *
  26          * On the other hand, we would want to ignore inserts for the
  27          * pure "complete rewrite" detection.  As long as most of the
  28          * existing contents were removed from the file, it is a
  29          * complete rewrite, and if sizable chunk from the original
  30          * still remains in the result, it is not a rewrite.  It does
  31          * not matter how much or how little new material is added to
  32          * the file.
  33          *
  34          * The score we leave for such a broken filepair uses the
  35          * latter definition so that later clean-up stage can find the
  36          * pieces that should not have been broken according to the
  37          * latter definition after rename/copy runs, and merge the
  38          * broken pair that have a score lower than given criteria
  39          * back together.  The break operation itself happens
  40          * according to the former definition.
  41          *
  42          * The minimum_edit parameter tells us when to break (the
  43          * amount of "edit" required for us to consider breaking the
  44          * pair).  We leave the amount of deletion in *merge_score_p
  45          * when we return.
  46          *
  47          * The value we return is 1 if we want the pair to be broken,
  48          * or 0 if we do not.
  49          */
  50         unsigned long delta_size, max_size;
  51         unsigned long src_copied, literal_added, src_removed;
  52
  53         struct diff_populate_filespec_options options = { 0 };
  54
  55         *merge_score_p = 0; /* assume no deletion --- "do not break"
  56                              * is the default.
  57                              */
  58
  59         if (S_ISREG(src->mode) != S_ISREG(dst->mode)) {
  60                 *merge_score_p = (int)MAX_SCORE;
  61                 return 1; /* even their types are different */
  62         }
  63
  64         if (src->oid_valid && dst->oid_valid &&
  65             oideq(&src->oid, &dst->oid))
  66                 return 0; /* they are the same */
  67
  68         if (r == the_repository && repo_has_promisor_remote(the_repository)) {
  69                 options.missing_object_cb = diff_queued_diff_prefetch;
  70                 options.missing_object_data = r;
  71         }
  72
  73         if (diff_populate_filespec(r, src, &options) ||
  74             diff_populate_filespec(r, dst, &options))
  75                 return 0; /* error but caught downstream */
  76
  77         max_size = ((src->size > dst->size) ? src->size : dst->size);
  78         if (max_size < MINIMUM_BREAK_SIZE)
  79                 return 0; /* we do not break too small filepair */
  80
  81         if (!src->size)
  82                 return 0; /* we do not let empty files get renamed */
  83
  84         if (diffcore_count_changes(r, src, dst,
  85                                    &src->cnt_data, &dst->cnt_data,
  86                                    &src_copied, &literal_added))
  87                 return 0;
  88
  89         /* sanity */
  90         if (src->size < src_copied)
  91                 src_copied = src->size;
  92         if (dst->size < literal_added + src_copied) {
  93                 if (src_copied < dst->size)
  94                         literal_added = dst->size - src_copied;
  95                 else
  96                         literal_added = 0;
  97         }
  98         src_removed = src->size - src_copied;
  99
 100         /* Compute merge-score, which is "how much is removed
 101          * from the source material".  The clean-up stage will
 102          * merge the surviving pair together if the score is
 103          * less than the minimum, after rename/copy runs.
 104          */
 105         *merge_score_p = (int)(src_removed * MAX_SCORE / src->size);
 106         if (*merge_score_p > break_score)
 107                 return 1;
 108
 109         /* Extent of damage, which counts both inserts and
 110          * deletes.
 111          */
 112         delta_size = src_removed + literal_added;
 113         if (delta_size * MAX_SCORE / max_size < break_score)
 114                 return 0;
 115
 116         /* If you removed a lot without adding new material, that is
 117          * not really a rewrite.
 118          */
 119         if ((src->size * break_score < src_removed * MAX_SCORE) &&
 120             (literal_added * 20 < src_removed) &&
 121             (literal_added * 20 < src_copied))
 122                 return 0;
 123
 124         return 1;
 125 }
 126
 127 void diffcore_break(struct repository *r, int break_score)
 128 {
 129         struct diff_queue_struct *q = &diff_queued_diff;
 130         struct diff_queue_struct outq;
 131
 132         /* When the filepair has this much edit (insert and delete),
 133          * it is first considered to be a rewrite and broken into a
 134          * create and delete filepair.  This is to help breaking a
 135          * file that had too much new stuff added, possibly from
 136          * moving contents from another file, so that rename/copy can
 137          * match it with the other file.
 138          *
 139          * int break_score; we reuse incoming parameter for this.
 140          */
 141
 142         /* After a pair is broken according to break_score and
 143          * subjected to rename/copy, both of them may survive intact,
 144          * due to lack of suitable rename/copy peer.  Or, the caller
 145          * may be calling us without using rename/copy.  When that
 146          * happens, we merge the broken pieces back into one
 147          * modification together if the pair did not have more than
 148          * this much delete.  For this computation, we do not take
 149          * insert into account at all.  If you start from a 100-line
 150          * file and delete 97 lines of it, it does not matter if you
 151          * add 27 lines to it to make a new 30-line file or if you add
 152          * 997 lines to it to make a 1000-line file.  Either way what
 153          * you did was a rewrite of 97%.  On the other hand, if you
 154          * delete 3 lines, keeping 97 lines intact, it does not matter
 155          * if you add 3 lines to it to make a new 100-line file or if
 156          * you add 903 lines to it to make a new 1000-line file.
 157          * Either way you did a lot of additions and not a rewrite.
 158          * This merge happens to catch the latter case.  A merge_score
 159          * of 80% would be a good default value (a broken pair that
 160          * has score lower than merge_score will be merged back
 161          * together).
 162          */
 163         int merge_score;
 164         int i;
 165
 166         /* See comment on DEFAULT_BREAK_SCORE and
 167          * DEFAULT_MERGE_SCORE in diffcore.h
 168          */
 169         merge_score = (break_score >> 16) & 0xFFFF;
 170         break_score = (break_score & 0xFFFF);
 171
 172         if (!break_score)
 173                 break_score = DEFAULT_BREAK_SCORE;
 174         if (!merge_score)
 175                 merge_score = DEFAULT_MERGE_SCORE;
 176
 177         DIFF_QUEUE_CLEAR(&outq);
 178
 179         for (i = 0; i < q->nr; i++) {
 180                 struct diff_filepair *p = q->queue[i];
 181                 int score;
 182
 183                 /*
 184                  * We deal only with in-place edit of blobs.
 185                  * We do not break anything else.
 186                  */
 187                 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
 188                     object_type(p->one->mode) == OBJ_BLOB &&
 189                     object_type(p->two->mode) == OBJ_BLOB &&
 190                     !strcmp(p->one->path, p->two->path)) {
 191                         if (should_break(r, p->one, p->two,
 192                                          break_score, &score)) {
 193                                 /* Split this into delete and create */
 194                                 struct diff_filespec *null_one, *null_two;
 195                                 struct diff_filepair *dp;
 196
 197                                 /* Set score to 0 for the pair that
 198                                  * needs to be merged back together
 199                                  * should they survive rename/copy.
 200                                  * Also we do not want to break very
 201                                  * small files.
 202                                  */
 203                                 if (score < merge_score)
 204                                         score = 0;
 205
 206                                 /* deletion of one */
 207                                 null_one = alloc_filespec(p->one->path);
 208                                 dp = diff_queue(&outq, p->one, null_one);
 209                                 dp->score = score;
 210                                 dp->broken_pair = 1;
 211
 212                                 /* creation of two */
 213                                 null_two = alloc_filespec(p->two->path);
 214                                 dp = diff_queue(&outq, null_two, p->two);
 215                                 dp->score = score;
 216                                 dp->broken_pair = 1;
 217
 218                                 diff_free_filespec_blob(p->one);
 219                                 diff_free_filespec_blob(p->two);
 220                                 free(p); /* not diff_free_filepair(), we are
 221                                           * reusing one and two here.
 222                                           */
 223                                 continue;
 224                         }
 225                 }
 226                 diff_free_filespec_data(p->one);
 227                 diff_free_filespec_data(p->two);
 228                 diff_q(&outq, p);
 229         }
 230         free(q->queue);
 231         *q = outq;
 232
 233         return;
 234 }
 235
 236 static void merge_broken(struct diff_filepair *p,
 237                          struct diff_filepair *pp,
 238                          struct diff_queue_struct *outq)
 239 {
 240         /* p and pp are broken pairs we want to merge */
 241         struct diff_filepair *c = p, *d = pp, *dp;
 242         if (DIFF_FILE_VALID(p->one)) {
 243                 /* this must be a delete half */
 244                 d = p; c = pp;
 245         }
 246         /* Sanity check */
 247         if (!DIFF_FILE_VALID(d->one))
 248                 die("internal error in merge #1");
 249         if (DIFF_FILE_VALID(d->two))
 250                 die("internal error in merge #2");
 251         if (DIFF_FILE_VALID(c->one))
 252                 die("internal error in merge #3");
 253         if (!DIFF_FILE_VALID(c->two))
 254                 die("internal error in merge #4");
 255
 256         dp = diff_queue(outq, d->one, c->two);
 257         dp->score = p->score;
 258         /*
 259          * We will be one extra user of the same src side of the
 260          * broken pair, if it was used as the rename source for other
 261          * paths elsewhere.  Increment to mark that the path stays
 262          * in the resulting tree.
 263          */
 264         d->one->rename_used++;
 265         diff_free_filespec_data(d->two);
 266         diff_free_filespec_data(c->one);
 267         free(d);
 268         free(c);
 269 }
 270
 271 void diffcore_merge_broken(void)
 272 {
 273         struct diff_queue_struct *q = &diff_queued_diff;
 274         struct diff_queue_struct outq;
 275         int i, j;
 276
 277         DIFF_QUEUE_CLEAR(&outq);
 278
 279         for (i = 0; i < q->nr; i++) {
 280                 struct diff_filepair *p = q->queue[i];
 281                 if (!p)
 282                         /* we already merged this with its peer */
 283                         continue;
 284                 else if (p->broken_pair &&
 285                          !strcmp(p->one->path, p->two->path)) {
 286                         /* If the peer also survived rename/copy, then
 287                          * we merge them back together.
 288                          */
 289                         for (j = i + 1; j < q->nr; j++) {
 290                                 struct diff_filepair *pp = q->queue[j];
 291                                 if (pp->broken_pair &&
 292                                     !strcmp(pp->one->path, pp->two->path) &&
 293                                     !strcmp(p->one->path, pp->two->path)) {
 294                                         /* Peer survived.  Merge them */
 295                                         merge_broken(p, pp, &outq);
 296                                         q->queue[j] = NULL;
 297                                         goto next;
 298                                 }
 299                         }
 300                         /* The peer did not survive, so we keep
 301                          * it in the output.
 302                          */
 303                         diff_q(&outq, p);
 304                 }
 305                 else
 306                         diff_q(&outq, p);
 307 next:;
 308         }
 309         free(q->queue);
 310         *q = outq;
 311
 312         return;
 313 }