2 * GIT - The information manager from hell
4 * Copyright (C) Linus Torvalds, 2005
11 static int unpack_tree(unsigned char *sha1)
17 buffer = read_object_with_reference(sha1, "tree", &size, NULL);
20 ret = read_tree(buffer, size, stage);
25 static int path_matches(struct cache_entry *a, struct cache_entry *b)
27 int len = ce_namelen(a);
28 return ce_namelen(b) == len &&
29 !memcmp(a->name, b->name, len);
32 static int same(struct cache_entry *a, struct cache_entry *b)
34 return a->ce_mode == b->ce_mode &&
35 !memcmp(a->sha1, b->sha1, 20);
40 * This removes all trivial merges that don't change the tree
41 * and collapses them to state 0.
43 static struct cache_entry *merge_entries(struct cache_entry *a,
44 struct cache_entry *b,
45 struct cache_entry *c)
48 * Ok, all three entries describe the same
49 * filename, but maybe the contents or file
52 * The trivial cases end up being the ones where two
53 * out of three files are the same:
54 * - both destinations the same, trivially take either
55 * - one of the destination versions hasn't changed,
58 * The "all entries exactly the same" case falls out as
59 * a special case of any of the "two same" cases.
61 * Here "a" is "original", and "b" and "c" are the two
62 * trees we are merging.
76 * When a CE gets turned into an unmerged entry, we
77 * want it to be up-to-date
79 static void verify_uptodate(struct cache_entry *ce)
83 if (!lstat(ce->name, &st)) {
84 unsigned changed = ce_match_stat(ce, &st);
91 die("Entry '%s' not uptodate. Cannot merge.", ce->name);
95 * If the old tree contained a CE that isn't even in the
96 * result, that's always a problem, regardless of whether
97 * it's up-to-date or not (ie it can be a file that we
98 * have updated but not committed yet).
100 static void reject_merge(struct cache_entry *ce)
102 die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
105 static int merged_entry_internal(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst, int allow_dirty)
107 merge->ce_flags |= htons(CE_UPDATE);
110 * See if we can re-use the old CE directly?
111 * That way we get the uptodate stat info.
113 * This also removes the UPDATE flag on
116 if (same(old, merge)) {
118 } else if (!allow_dirty) {
119 verify_uptodate(old);
122 merge->ce_flags &= ~htons(CE_STAGEMASK);
127 static int merged_entry_allow_dirty(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
129 return merged_entry_internal(merge, old, dst, 1);
132 static int merged_entry(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
134 return merged_entry_internal(merge, old, dst, 0);
137 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old, struct cache_entry **dst)
140 verify_uptodate(old);
146 static int causes_df_conflict(struct cache_entry *ce, int stage,
147 struct cache_entry **dst_,
148 struct cache_entry **next_,
151 /* This is called during the merge operation and walking
152 * the active_cache[] array is messy, because it is in the
153 * middle of overlapping copy operation. The invariants
155 * (1) active_cache points at the first (zeroth) entry.
156 * (2) up to dst pointer are resolved entries.
157 * (3) from the next pointer (head-inclusive) to the tail
158 * of the active_cache array have the remaining paths
159 * to be processed. There can be a gap between dst
160 * and next. Note that next is called "src" in the
161 * merge_cache() function, and tail is the original
162 * end of active_cache array when merge_cache() started.
163 * (4) the path corresponding to *ce is not found in (2)
164 * or (3). It is in the gap.
166 * active_cache -----......+++++++++++++.
170 const char *path = ce->name;
171 int namelen = ce_namelen(ce);
173 next = next_ - active_cache;
174 dst = dst_ - active_cache;
176 for (i = 0; i < tail; i++) {
178 const char *one, *two;
179 if (dst <= i && i < next)
181 ce = active_cache[i];
182 if (ce_stage(ce) != stage)
184 /* If ce->name is a prefix of path, then path is a file
185 * that hangs underneath ce->name, which is bad.
186 * If path is a prefix of ce->name, then it is the
187 * other way around which also is bad.
189 entlen = ce_namelen(ce);
190 if (namelen == entlen)
192 if (namelen < entlen) {
201 if (memcmp(one, two, len))
209 static int threeway_merge(struct cache_entry *stages[4],
210 struct cache_entry **dst,
211 struct cache_entry **next, int tail)
213 struct cache_entry *old = stages[0];
214 struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
215 struct cache_entry *merge;
219 if (!a && b && c && same(b, c)) {
220 if (old && !same(b, old))
222 return merged_entry_allow_dirty(b, old, dst);
224 /* #2ALT and #3ALT */
225 if (!a && (!!b != !!c)) {
227 * The reason we need to worry about directory/file
228 * conflicts only in #2ALT and #3ALT case is this:
230 * (1) For all other cases that read-tree internally
231 * resolves a path, we always have such a path in
232 * *both* stage2 and stage3 when we begin.
233 * Traditionally, the behaviour has been even
234 * stricter and we did not resolve a path without
235 * initially being in all of stage1, 2, and 3.
237 * (2) When read-tree finishes, all resolved paths (i.e.
238 * the paths that are in stage0) must have come from
239 * either stage2 or stage3. It is not possible to
240 * have a stage0 path as a result of a merge if
241 * neither stage2 nor stage3 had that path.
243 * (3) It is guaranteed that just after reading the
244 * stages, each stage cannot have directory/file
245 * conflicts on its own, because they are populated
246 * by reading hierarchy of a tree. Combined with
247 * (1) and (2) above, this means that no matter what
248 * combination of paths we take from stage2 and
249 * stage3 as a result of a merge, they cannot cause
250 * a directory/file conflict situation (otherwise
251 * the "guilty" path would have already had such a
252 * conflict in the original stage, either stage2
253 * or stage3). Although its stage2 is synthesized
254 * by overlaying the current index on top of "our
255 * head" tree, --emu23 case also has this guarantee,
256 * by calling add_cache_entry() to create such stage2
259 * (4) Only #2ALT and #3ALT lack the guarantee (1).
260 * They resolve paths that exist only in stage2
261 * or stage3. The stage2 tree may have a file DF
262 * while stage3 tree may have a file DF/DF. If
263 * #2ALT and #3ALT rules happen to apply to both
264 * of them, we would end up having DF (coming from
265 * stage2) and DF/DF (from stage3) in the result.
266 * When we attempt to resolve a path that exists
267 * only in stage2, we need to make sure there is
268 * no path that would conflict with it in stage3
272 if (!causes_df_conflict(c, 2, dst, next, tail) &&
273 (!old || same(c, old)))
274 return merged_entry_allow_dirty(c, old, dst);
277 if (!causes_df_conflict(b, 3, dst, next, tail) &&
278 (!old || same(b, old)))
279 return merged_entry_allow_dirty(b, old, dst);
281 /* otherwise we will apply the original rule */
284 * If we have an entry in the index cache ("old"), then we want
285 * to make sure that it matches any entries in stage 2 ("first
289 if (!b || !same(old, b))
292 merge = merge_entries(a, b, c);
294 return merged_entry(merge, old, dst);
296 verify_uptodate(old);
298 if (a) { *dst++ = a; count++; }
299 if (b) { *dst++ = b; count++; }
300 if (c) { *dst++ = c; count++; }
307 * The rule is to "carry forward" what is in the index without losing
308 * information across a "fast forward", favoring a successful merge
309 * over a merge failure when it makes sense. For details of the
310 * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
313 static int twoway_merge(struct cache_entry **src, struct cache_entry **dst,
314 struct cache_entry **next, int tail)
316 struct cache_entry *current = src[0];
317 struct cache_entry *oldtree = src[1], *newtree = src[2];
323 if ((!oldtree && !newtree) || /* 4 and 5 */
324 (!oldtree && newtree &&
325 same(current, newtree)) || /* 6 and 7 */
326 (oldtree && newtree &&
327 same(oldtree, newtree)) || /* 14 and 15 */
328 (oldtree && newtree &&
329 !same(oldtree, newtree) && /* 18 and 19*/
330 same(current, newtree))) {
334 else if (oldtree && !newtree && same(current, oldtree)) {
336 return deleted_entry(oldtree, current, dst);
338 else if (oldtree && newtree &&
339 same(current, oldtree) && !same(current, newtree)) {
341 return merged_entry(newtree, current, dst);
344 /* all other failures */
348 return merged_entry(newtree, current, dst);
350 return deleted_entry(oldtree, current, dst);
354 * Two-way merge emulated with three-way merge.
356 * This treats "read-tree -m H M" by transforming it internally
357 * into "read-tree -m H I+H M", where I+H is a tree that would
358 * contain the contents of the current index file, overlayed on
359 * top of H. Unlike the traditional two-way merge, this leaves
360 * the stages in the resulting index file and lets the user resolve
361 * the merge conflicts using standard tools for three-way merge.
363 * This function is just to set-up such an arrangement, and the
364 * actual merge uses threeway_merge() function.
366 static void setup_emu23(void)
368 /* stage0 contains I, stage1 H, stage2 M.
369 * move stage2 to stage3, and create stage2 entries
370 * by scanning stage0 and stage1 entries.
372 int i, namelen, size;
373 struct cache_entry *ce, *stage2;
375 for (i = 0; i < active_nr; i++) {
376 ce = active_cache[i];
377 if (ce_stage(ce) != 2)
379 /* hoist them up to stage 3 */
380 namelen = ce_namelen(ce);
381 ce->ce_flags = create_ce_flags(namelen, 3);
384 for (i = 0; i < active_nr; i++) {
385 ce = active_cache[i];
386 if (ce_stage(ce) > 1)
388 namelen = ce_namelen(ce);
389 size = cache_entry_size(namelen);
390 stage2 = xmalloc(size);
391 memcpy(stage2, ce, size);
392 stage2->ce_flags = create_ce_flags(namelen, 2);
393 if (add_cache_entry(stage2, ADD_CACHE_OK_TO_ADD) < 0)
394 die("cannot merge index and our head tree");
396 /* We are done with this name, so skip to next name */
397 while (i < active_nr &&
398 ce_namelen(active_cache[i]) == namelen &&
399 !memcmp(active_cache[i]->name, ce->name, namelen))
401 i--; /* compensate for the loop control */
409 * - take the stat information from stage0, take the data from stage1
411 static int oneway_merge(struct cache_entry **src, struct cache_entry **dst,
412 struct cache_entry **next, int tail)
414 struct cache_entry *old = src[0];
415 struct cache_entry *a = src[1];
417 if (src[2] || src[3])
422 if (old && same(old, a)) {
426 return merged_entry(a, NULL, dst);
429 static void check_updates(struct cache_entry **src, int nr)
431 static struct checkout state = {
437 unsigned short mask = htons(CE_UPDATE);
439 struct cache_entry *ce = *src++;
445 if (ce->ce_flags & mask) {
446 ce->ce_flags &= ~mask;
448 checkout_entry(ce, &state);
453 typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **, struct cache_entry **, int);
455 static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
457 struct cache_entry **dst = src;
462 struct cache_entry *name, *ce, *stages[4] = { NULL, };
466 int stage = ce_stage(ce);
472 if (!path_matches(ce, name))
476 entries = fn(stages, dst, src, tail);
480 active_nr += entries;
482 check_updates(active_cache, active_nr);
485 static int read_cache_unmerged(void)
488 struct cache_entry **dst;
493 for (i = 0; i < active_nr; i++) {
494 struct cache_entry *ce = active_cache[i];
503 active_nr -= deleted;
507 static char *read_tree_usage = "git-read-tree (<sha> | -m [-u] <sha1> [<sha2> [<sha3>]])";
509 static struct cache_file cache_file;
511 int main(int argc, char **argv)
513 int i, newfd, merge, reset, emu23;
514 unsigned char sha1[20];
516 newfd = hold_index_file_for_update(&cache_file, get_index_file());
518 die("unable to create new cachefile");
523 for (i = 1; i < argc; i++) {
524 const char *arg = argv[i];
526 /* "-u" means "update", meaning that a merge will update the working directory */
527 if (!strcmp(arg, "-u")) {
532 /* This differs from "-m" in that we'll silently ignore unmerged entries */
533 if (!strcmp(arg, "--reset")) {
534 if (stage || merge || emu23)
535 usage(read_tree_usage);
539 read_cache_unmerged();
542 /* "-m" stands for "merge", meaning we start in stage 1 */
543 if (!strcmp(arg, "-m")) {
544 if (stage || merge || emu23)
545 usage(read_tree_usage);
546 if (read_cache_unmerged())
547 die("you need to resolve your current index first");
553 /* "-emu23" uses 3-way merge logic to perform fast-forward */
554 if (!strcmp(arg, "--emu23")) {
555 if (stage || merge || emu23)
556 usage(read_tree_usage);
557 if (read_cache_unmerged())
558 die("you need to resolve your current index first");
559 merge = emu23 = stage = 1;
563 if (get_sha1(arg, sha1) < 0)
564 usage(read_tree_usage);
566 usage(read_tree_usage);
567 if (unpack_tree(sha1) < 0)
568 die("failed to unpack tree object %s", arg);
571 if (update && !merge)
572 usage(read_tree_usage);
574 static const merge_fn_t merge_function[] = {
577 [3] = threeway_merge,
581 if (stage < 2 || stage > 4)
582 die("just how do you expect me to merge %d trees?", stage-1);
583 if (emu23 && stage != 3)
584 die("--emu23 takes only two trees");
585 fn = merge_function[stage-1];
586 if (stage == 3 && emu23) {
588 fn = merge_function[3];
590 merge_cache(active_cache, active_nr, fn);
592 if (write_cache(newfd, active_cache, active_nr) ||
593 commit_index_file(&cache_file))
594 die("unable to write new index file");