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 const char *sha1_to_hex_zero(const unsigned char *sha1)
  59 {
  60         if (sha1)
  61                 return sha1_to_hex(sha1);
  62         return "0000000000000000000000000000000000000000";
  63 }
  64
  65 static void resolve(const char *base, struct name_entry *branch1, struct name_entry *result)
  66 {
  67         char branch1_sha1[50];
  68
  69         /* If it's already branch1, don't bother showing it */
  70         if (!branch1)
  71                 return;
  72         memcpy(branch1_sha1, sha1_to_hex_zero(branch1->sha1), 41);
  73
  74         printf("0 %06o->%06o %s->%s %s%s\n",
  75                 branch1->mode, result->mode,
  76                 branch1_sha1, sha1_to_hex_zero(result->sha1),
  77                 base, result->path);
  78 }
  79
  80 static int unresolved_directory(const char *base, struct name_entry n[3])
  81 {
  82         int baselen;
  83         char *newbase;
  84         struct name_entry *p;
  85         struct tree_desc t[3];
  86         void *buf0, *buf1, *buf2;
  87
  88         if (!resolve_directories)
  89                 return 0;
  90         p = n;
  91         if (!p->mode) {
  92                 p++;
  93                 if (!p->mode)
  94                         p++;
  95         }
  96         if (!S_ISDIR(p->mode))
  97                 return 0;
  98         baselen = strlen(base);
  99         newbase = xmalloc(baselen + p->pathlen + 2);
 100         memcpy(newbase, base, baselen);
 101         memcpy(newbase + baselen, p->path, p->pathlen);
 102         memcpy(newbase + baselen + p->pathlen, "/", 2);
 103
 104         buf0 = fill_tree_descriptor(t+0, n[0].sha1);
 105         buf1 = fill_tree_descriptor(t+1, n[1].sha1);
 106         buf2 = fill_tree_descriptor(t+2, n[2].sha1);
 107         merge_trees(t, newbase);
 108
 109         free(buf0);
 110         free(buf1);
 111         free(buf2);
 112         free(newbase);
 113         return 1;
 114 }
 115
 116 static void unresolved(const char *base, struct name_entry n[3])
 117 {
 118         if (unresolved_directory(base, n))
 119                 return;
 120         if (n[0].sha1)
 121                 printf("1 %06o %s %s%s\n", n[0].mode, sha1_to_hex(n[0].sha1), base, n[0].path);
 122         if (n[1].sha1)
 123                 printf("2 %06o %s %s%s\n", n[1].mode, sha1_to_hex(n[1].sha1), base, n[1].path);
 124         if (n[2].sha1)
 125                 printf("3 %06o %s %s%s\n", n[2].mode, sha1_to_hex(n[2].sha1), base, n[2].path);
 126 }
 127
 128 /*
 129  * Merge two trees together (t[1] and t[2]), using a common base (t[0])
 130  * as the origin.
 131  *
 132  * This walks the (sorted) trees in lock-step, checking every possible
 133  * name. Note that directories automatically sort differently from other
 134  * files (see "base_name_compare"), so you'll never see file/directory
 135  * conflicts, because they won't ever compare the same.
 136  *
 137  * IOW, if a directory changes to a filename, it will automatically be
 138  * seen as the directory going away, and the filename being created.
 139  *
 140  * Think of this as a three-way diff.
 141  *
 142  * The output will be either:
 143  *  - successful merge
 144  *       "0 mode sha1 filename"
 145  *    NOTE NOTE NOTE! FIXME! We really really need to walk the index
 146  *    in parallel with this too!
 147  *
 148  *  - conflict:
 149  *      "1 mode sha1 filename"
 150  *      "2 mode sha1 filename"
 151  *      "3 mode sha1 filename"
 152  *    where not all of the 1/2/3 lines may exist, of course.
 153  *
 154  * The successful merge rules are the same as for the three-way merge
 155  * in git-read-tree.
 156  */
 157 static void merge_trees(struct tree_desc t[3], const char *base)
 158 {
 159         for (;;) {
 160                 struct name_entry entry[3];
 161                 unsigned int mask = 0;
 162                 int i, last;
 163
 164                 last = -1;
 165                 for (i = 0; i < 3; i++) {
 166                         if (!t[i].size)
 167                                 continue;
 168                         entry_extract(t+i, entry+i);
 169                         if (last >= 0) {
 170                                 int cmp = entry_compare(entry+i, entry+last);
 171
 172                                 /*
 173                                  * Is the new name bigger than the old one?
 174                                  * Ignore it
 175                                  */
 176                                 if (cmp > 0)
 177                                         continue;
 178                                 /*
 179                                  * Is the new name smaller than the old one?
 180                                  * Ignore all old ones
 181                                  */
 182                                 if (cmp < 0)
 183                                         mask = 0;
 184                         }
 185                         mask |= 1u << i;
 186                         last = i;
 187                 }
 188                 if (!mask)
 189                         break;
 190
 191                 /*
 192                  * Update the tree entries we've walked, and clear
 193                  * all the unused name-entries.
 194                  */
 195                 for (i = 0; i < 3; i++) {
 196                         if (mask & (1u << i)) {
 197                                 update_tree_entry(t+i);
 198                                 continue;
 199                         }
 200                         entry_clear(entry + i);
 201                 }
 202
 203                 /* Same in both? */
 204                 if (same_entry(entry+1, entry+2)) {
 205                         if (entry[0].sha1) {
 206                                 resolve(base, NULL, entry+1);
 207                                 continue;
 208                         }
 209                 }
 210
 211                 if (same_entry(entry+0, entry+1)) {
 212                         if (entry[2].sha1 && !S_ISDIR(entry[2].mode)) {
 213                                 resolve(base, entry+1, entry+2);
 214                                 continue;
 215                         }
 216                 }
 217
 218                 if (same_entry(entry+0, entry+2)) {
 219                         if (entry[1].sha1 && !S_ISDIR(entry[1].mode)) {
 220                                 resolve(base, NULL, entry+1);
 221                                 continue;
 222                         }
 223                 }
 224
 225                 unresolved(base, entry);
 226         }
 227 }
 228
 229 static void *get_tree_descriptor(struct tree_desc *desc, const char *rev)
 230 {
 231         unsigned char sha1[20];
 232         void *buf;
 233
 234         if (get_sha1(rev, sha1) < 0)
 235                 die("unknown rev %s", rev);
 236         buf = fill_tree_descriptor(desc, sha1);
 237         if (!buf)
 238                 die("%s is not a tree", rev);
 239         return buf;
 240 }
 241
 242 int main(int argc, char **argv)
 243 {
 244         struct tree_desc t[3];
 245         void *buf1, *buf2, *buf3;
 246
 247         if (argc < 4)
 248                 usage(merge_tree_usage);
 249
 250         buf1 = get_tree_descriptor(t+0, argv[1]);
 251         buf2 = get_tree_descriptor(t+1, argv[2]);
 252         buf3 = get_tree_descriptor(t+2, argv[3]);
 253         merge_trees(t, "");
 254         free(buf1);
 255         free(buf2);
 256         free(buf3);
 257         return 0;
 258 }