merge-tree.c

   1 #include "cache.h"
   2 #include "diff.h"
   3
   4 static const char merge_tree_usage[] = "git-merge-tree <base-tree> <branch1> <branch2>";
   5 static int resolve_directories = 1;
   6
   7 static void merge_trees(struct tree_desc t[3], const char *base);
   8
   9 static void *fill_tree_descriptor(struct tree_desc *desc, const unsigned char *sha1)
  10 {
  11         unsigned long size = 0;
  12         void *buf = NULL;
  13
  14         if (sha1) {
  15                 buf = read_object_with_reference(sha1, "tree", &size, NULL);
  16                 if (!buf)
  17                         die("unable to read tree %s", sha1_to_hex(sha1));
  18         }
  19         desc->size = size;
  20         desc->buf = buf;
  21         return buf;
  22 }
  23
  24 struct name_entry {
  25         const unsigned char *sha1;
  26         const char *path;
  27         unsigned int mode;
  28         int pathlen;
  29 };
  30
  31 static void entry_clear(struct name_entry *a)
  32 {
  33         memset(a, 0, sizeof(*a));
  34 }
  35
  36 static int entry_compare(struct name_entry *a, struct name_entry *b)
  37 {
  38         return base_name_compare(
  39                         a->path, a->pathlen, a->mode,
  40                         b->path, b->pathlen, b->mode);
  41 }
  42
  43 static void entry_extract(struct tree_desc *t, struct name_entry *a)
  44 {
  45         a->sha1 = tree_entry_extract(t, &a->path, &a->mode);
  46         a->pathlen = strlen(a->path);
  47 }
  48
  49 /* An empty entry never compares same, not even to another empty entry */
  50 static int same_entry(struct name_entry *a, struct name_entry *b)
  51 {
  52         return  a->sha1 &&
  53                 b->sha1 &&
  54                 !memcmp(a->sha1, b->sha1, 20) &&
  55                 a->mode == b->mode;
  56 }
  57
  58 static void resolve(const char *base, struct name_entry *result)
  59 {
  60         printf("0 %06o %s %s%s\n", result->mode, sha1_to_hex(result->sha1), base, result->path);
  61 }
  62
  63 static int unresolved_directory(const char *base, struct name_entry n[3])
  64 {
  65         int baselen;
  66         char *newbase;
  67         struct name_entry *p;
  68         struct tree_desc t[3];
  69         void *buf0, *buf1, *buf2;
  70
  71         if (!resolve_directories)
  72                 return 0;
  73         p = n;
  74         if (!p->mode) {
  75                 p++;
  76                 if (!p->mode)
  77                         p++;
  78         }
  79         if (!S_ISDIR(p->mode))
  80                 return 0;
  81         baselen = strlen(base);
  82         newbase = xmalloc(baselen + p->pathlen + 2);
  83         memcpy(newbase, base, baselen);
  84         memcpy(newbase + baselen, p->path, p->pathlen);
  85         memcpy(newbase + baselen + p->pathlen, "/", 2);
  86
  87         buf0 = fill_tree_descriptor(t+0, n[0].sha1);
  88         buf1 = fill_tree_descriptor(t+1, n[1].sha1);
  89         buf2 = fill_tree_descriptor(t+2, n[2].sha1);
  90         merge_trees(t, newbase);
  91
  92         free(buf0);
  93         free(buf1);
  94         free(buf2);
  95         free(newbase);
  96         return 1;
  97 }
  98
  99 static void unresolved(const char *base, struct name_entry n[3])
 100 {
 101         if (unresolved_directory(base, n))
 102                 return;
 103         printf("1 %06o %s %s%s\n", n[0].mode, sha1_to_hex(n[0].sha1), base, n[0].path);
 104         printf("2 %06o %s %s%s\n", n[1].mode, sha1_to_hex(n[1].sha1), base, n[1].path);
 105         printf("3 %06o %s %s%s\n", n[2].mode, sha1_to_hex(n[2].sha1), base, n[2].path);
 106 }
 107
 108 /*
 109  * Merge two trees together (t[1] and t[2]), using a common base (t[0])
 110  * as the origin.
 111  *
 112  * This walks the (sorted) trees in lock-step, checking every possible
 113  * name. Note that directories automatically sort differently from other
 114  * files (see "base_name_compare"), so you'll never see file/directory
 115  * conflicts, because they won't ever compare the same.
 116  *
 117  * IOW, if a directory changes to a filename, it will automatically be
 118  * seen as the directory going away, and the filename being created.
 119  *
 120  * Think of this as a three-way diff.
 121  *
 122  * The output will be either:
 123  *  - successful merge
 124  *       "0 mode sha1 filename"
 125  *    NOTE NOTE NOTE! FIXME! We really really need to walk the index
 126  *    in parallel with this too!
 127  *
 128  *  - conflict:
 129  *      "1 mode sha1 filename"
 130  *      "2 mode sha1 filename"
 131  *      "3 mode sha1 filename"
 132  *    where not all of the 1/2/3 lines may exist, of course.
 133  *
 134  * The successful merge rules are the same as for the three-way merge
 135  * in git-read-tree.
 136  */
 137 static void merge_trees(struct tree_desc t[3], const char *base)
 138 {
 139         for (;;) {
 140                 struct name_entry entry[3];
 141                 unsigned int mask = 0;
 142                 int i, last;
 143
 144                 last = -1;
 145                 for (i = 0; i < 3; i++) {
 146                         if (!t[i].size)
 147                                 continue;
 148                         entry_extract(t+i, entry+i);
 149                         if (last >= 0) {
 150                                 int cmp = entry_compare(entry+i, entry+last);
 151
 152                                 /*
 153                                  * Is the new name bigger than the old one?
 154                                  * Ignore it
 155                                  */
 156                                 if (cmp > 0)
 157                                         continue;
 158                                 /*
 159                                  * Is the new name smaller than the old one?
 160                                  * Ignore all old ones
 161                                  */
 162                                 if (cmp < 0)
 163                                         mask = 0;
 164                         }
 165                         mask |= 1u << i;
 166                         last = i;
 167                 }
 168                 if (!mask)
 169                         break;
 170
 171                 /*
 172                  * Update the tree entries we've walked, and clear
 173                  * all the unused name-entries.
 174                  */
 175                 for (i = 0; i < 3; i++) {
 176                         if (mask & (1u << i)) {
 177                                 update_tree_entry(t+i);
 178                                 continue;
 179                         }
 180                         entry_clear(entry + i);
 181                 }
 182
 183                 /* Same in both? */
 184                 if (same_entry(entry+1, entry+2)) {
 185                         if (entry[0].sha1) {
 186                                 resolve(base, entry+1);
 187                                 continue;
 188                         }
 189                 }
 190
 191                 if (same_entry(entry+0, entry+1)) {
 192                         if (entry[2].sha1) {
 193                                 resolve(base, entry+2);
 194                                 continue;
 195                         }
 196                 }
 197
 198                 if (same_entry(entry+0, entry+2)) {
 199                         if (entry[1].sha1) {
 200                                 resolve(base, entry+1);
 201                                 continue;
 202                         }
 203                 }
 204
 205                 unresolved(base, entry);
 206         }
 207 }
 208
 209 static void *get_tree_descriptor(struct tree_desc *desc, const char *rev)
 210 {
 211         unsigned char sha1[20];
 212         void *buf;
 213
 214         if (get_sha1(rev, sha1) < 0)
 215                 die("unknown rev %s", rev);
 216         buf = fill_tree_descriptor(desc, sha1);
 217         if (!buf)
 218                 die("%s is not a tree", rev);
 219         return buf;
 220 }
 221
 222 int main(int argc, char **argv)
 223 {
 224         struct tree_desc t[3];
 225         void *buf1, *buf2, *buf3;
 226
 227         if (argc < 4)
 228                 usage(merge_tree_usage);
 229
 230         buf1 = get_tree_descriptor(t+0, argv[1]);
 231         buf2 = get_tree_descriptor(t+1, argv[2]);
 232         buf3 = get_tree_descriptor(t+2, argv[3]);
 233         merge_trees(t, "");
 234         free(buf1);
 235         free(buf2);
 236         free(buf3);
 237         return 0;
 238 }