f2a8bb53a1c4338b0bccb6a44df5cdcdb8d74aed
1 /*
2 * GIT - The information manager from hell
3 *
4 * Copyright (C) Linus Torvalds, 2005
5 */
6 #include "cache.h"
8 static int stage = 0;
9 static int update = 0;
11 static int unpack_tree(unsigned char *sha1)
12 {
13 void *buffer;
14 unsigned long size;
15 int ret;
17 buffer = read_object_with_reference(sha1, "tree", &size, NULL);
18 if (!buffer)
19 return -1;
20 ret = read_tree(buffer, size, stage);
21 free(buffer);
22 return ret;
23 }
25 static int path_matches(struct cache_entry *a, struct cache_entry *b)
26 {
27 int len = ce_namelen(a);
28 return ce_namelen(b) == len &&
29 !memcmp(a->name, b->name, len);
30 }
32 static int same(struct cache_entry *a, struct cache_entry *b)
33 {
34 return a->ce_mode == b->ce_mode &&
35 !memcmp(a->sha1, b->sha1, 20);
36 }
39 /*
40 * This removes all trivial merges that don't change the tree
41 * and collapses them to state 0.
42 */
43 static struct cache_entry *merge_entries(struct cache_entry *a,
44 struct cache_entry *b,
45 struct cache_entry *c)
46 {
47 /*
48 * Ok, all three entries describe the same
49 * filename, but maybe the contents or file
50 * mode have changed?
51 *
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,
56 * take the other.
57 *
58 * The "all entries exactly the same" case falls out as
59 * a special case of any of the "two same" cases.
60 *
61 * Here "a" is "original", and "b" and "c" are the two
62 * trees we are merging.
63 */
64 if (a && b && c) {
65 if (same(b,c))
66 return c;
67 if (same(a,b))
68 return c;
69 if (same(a,c))
70 return b;
71 }
72 return NULL;
73 }
75 /*
76 * When a CE gets turned into an unmerged entry, we
77 * want it to be up-to-date
78 */
79 static void verify_uptodate(struct cache_entry *ce)
80 {
81 struct stat st;
83 if (!lstat(ce->name, &st)) {
84 unsigned changed = ce_match_stat(ce, &st);
85 if (!changed)
86 return;
87 errno = 0;
88 }
89 if (errno == ENOENT)
90 return;
91 die("Entry '%s' not uptodate. Cannot merge.", ce->name);
92 }
94 /*
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).
99 */
100 static void reject_merge(struct cache_entry *ce)
101 {
102 die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
103 }
105 static int merged_entry(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
106 {
107 merge->ce_flags |= htons(CE_UPDATE);
108 if (old) {
109 /*
110 * See if we can re-use the old CE directly?
111 * That way we get the uptodate stat info.
112 *
113 * This also removes the UPDATE flag on
114 * a match.
115 */
116 if (same(old, merge)) {
117 *merge = *old;
118 } else {
119 verify_uptodate(old);
120 }
121 }
122 merge->ce_flags &= ~htons(CE_STAGEMASK);
123 *dst++ = merge;
124 return 1;
125 }
127 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old, struct cache_entry **dst)
128 {
129 if (old)
130 verify_uptodate(old);
131 ce->ce_mode = 0;
132 *dst++ = ce;
133 return 1;
134 }
136 static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **dst)
137 {
138 struct cache_entry *old = stages[0];
139 struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
140 struct cache_entry *merge;
141 int count;
143 /*
144 * If we have an entry in the index cache ("old"), then we want
145 * to make sure that it matches any entries in stage 2 ("first
146 * branch", aka "b").
147 */
148 if (old) {
149 if (!b || !same(old, b))
150 return -1;
151 }
152 merge = merge_entries(a, b, c);
153 if (merge)
154 return merged_entry(merge, old, dst);
155 if (old)
156 verify_uptodate(old);
157 count = 0;
158 if (a) { *dst++ = a; count++; }
159 if (b) { *dst++ = b; count++; }
160 if (c) { *dst++ = c; count++; }
161 return count;
162 }
164 /*
165 * Two-way merge.
166 *
167 * The rule is to "carry forward" what is in the index without losing
168 * information across a "fast forward", favoring a successful merge
169 * over a merge failure when it makes sense. For details of the
170 * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
171 *
172 */
173 static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
174 {
175 struct cache_entry *current = src[0];
176 struct cache_entry *oldtree = src[1], *newtree = src[2];
178 if (src[3])
179 return -1;
181 if (current) {
182 if ((!oldtree && !newtree) || /* 4 and 5 */
183 (!oldtree && newtree &&
184 same(current, newtree)) || /* 6 and 7 */
185 (oldtree && newtree &&
186 same(oldtree, newtree)) || /* 14 and 15 */
187 (oldtree && newtree &&
188 !same(oldtree, newtree) && /* 18 and 19*/
189 same(current, newtree))) {
190 *dst++ = current;
191 return 1;
192 }
193 else if (oldtree && !newtree && same(current, oldtree)) {
194 /* 10 or 11 */
195 return deleted_entry(oldtree, current, dst);
196 }
197 else if (oldtree && newtree &&
198 same(current, oldtree) && !same(current, newtree)) {
199 /* 20 or 21 */
200 return merged_entry(newtree, current, dst);
201 }
202 else
203 /* all other failures */
204 return -1;
205 }
206 else if (newtree)
207 return merged_entry(newtree, current, dst);
208 else
209 return deleted_entry(oldtree, current, dst);
210 }
212 /*
213 * Two-way merge emulated with three-way merge.
214 *
215 * This treats "read-tree -m H M" by transforming it internally
216 * into "read-tree -m H I+H M", where I+H is a tree that would
217 * contain the contents of the current index file, overlayed on
218 * top of H. Unlike the traditional two-way merge, this leaves
219 * the stages in the resulting index file and lets the user resolve
220 * the merge conflicts using standard tools for three-way merge.
221 *
222 * This function is just to set-up such an arrangement, and the
223 * actual merge uses threeway_merge() function.
224 */
225 static void setup_emu23(void)
226 {
227 /* stage0 contains I, stage1 H, stage2 M.
228 * move stage2 to stage3, and create stage2 entries
229 * by scanning stage0 and stage1 entries.
230 */
231 int i, namelen, size;
232 struct cache_entry *ce, *stage2;
234 for (i = 0; i < active_nr; i++) {
235 ce = active_cache[i];
236 if (ce_stage(ce) != 2)
237 continue;
238 /* hoist them up to stage 3 */
239 namelen = ce_namelen(ce);
240 ce->ce_flags = create_ce_flags(namelen, 3);
241 }
243 for (i = 0; i < active_nr; i++) {
244 ce = active_cache[i];
245 if (ce_stage(ce) > 1)
246 continue;
247 namelen = ce_namelen(ce);
248 size = cache_entry_size(namelen);
249 stage2 = xmalloc(size);
250 memcpy(stage2, ce, size);
251 stage2->ce_flags = create_ce_flags(namelen, 2);
252 if (add_cache_entry(stage2, ADD_CACHE_OK_TO_ADD) < 0)
253 die("cannot merge index and our head tree");
255 /* We are done with this name, so skip to next name */
256 while (i < active_nr &&
257 ce_namelen(active_cache[i]) == namelen &&
258 !memcmp(active_cache[i]->name, ce->name, namelen))
259 i++;
260 i--; /* compensate for the loop control */
261 }
262 }
264 /*
265 * One-way merge.
266 *
267 * The rule is:
268 * - take the stat information from stage0, take the data from stage1
269 */
270 static int oneway_merge(struct cache_entry **src, struct cache_entry **dst)
271 {
272 struct cache_entry *old = src[0];
273 struct cache_entry *a = src[1];
275 if (src[2] || src[3])
276 return -1;
278 if (!a)
279 return 0;
280 if (old && same(old, a)) {
281 *dst++ = old;
282 return 1;
283 }
284 return merged_entry(a, NULL, dst);
285 }
287 static void check_updates(struct cache_entry **src, int nr)
288 {
289 static struct checkout state = {
290 .base_dir = "",
291 .force = 1,
292 .quiet = 1,
293 .refresh_cache = 1,
294 };
295 unsigned short mask = htons(CE_UPDATE);
296 while (nr--) {
297 struct cache_entry *ce = *src++;
298 if (!ce->ce_mode) {
299 if (update)
300 unlink(ce->name);
301 continue;
302 }
303 if (ce->ce_flags & mask) {
304 ce->ce_flags &= ~mask;
305 if (update)
306 checkout_entry(ce, &state);
307 }
308 }
309 }
311 typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **);
313 static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
314 {
315 struct cache_entry **dst = src;
317 while (nr) {
318 int entries;
319 struct cache_entry *name, *ce, *stages[4] = { NULL, };
321 name = ce = *src;
322 for (;;) {
323 int stage = ce_stage(ce);
324 stages[stage] = ce;
325 ce = *++src;
326 active_nr--;
327 if (!--nr)
328 break;
329 if (!path_matches(ce, name))
330 break;
331 }
333 entries = fn(stages, dst);
334 if (entries < 0)
335 reject_merge(name);
336 dst += entries;
337 active_nr += entries;
338 }
339 check_updates(active_cache, active_nr);
340 }
342 static int read_cache_unmerged(void)
343 {
344 int i, deleted;
345 struct cache_entry **dst;
347 read_cache();
348 dst = active_cache;
349 deleted = 0;
350 for (i = 0; i < active_nr; i++) {
351 struct cache_entry *ce = active_cache[i];
352 if (ce_stage(ce)) {
353 deleted++;
354 continue;
355 }
356 if (deleted)
357 *dst = ce;
358 dst++;
359 }
360 active_nr -= deleted;
361 return deleted;
362 }
364 static char *read_tree_usage = "git-read-tree (<sha> | -m [-u] <sha1> [<sha2> [<sha3>]])";
366 static struct cache_file cache_file;
368 int main(int argc, char **argv)
369 {
370 int i, newfd, merge, reset, emu23;
371 unsigned char sha1[20];
373 newfd = hold_index_file_for_update(&cache_file, get_index_file());
374 if (newfd < 0)
375 die("unable to create new cachefile");
377 merge = 0;
378 reset = 0;
379 emu23 = 0;
380 for (i = 1; i < argc; i++) {
381 const char *arg = argv[i];
383 /* "-u" means "update", meaning that a merge will update the working directory */
384 if (!strcmp(arg, "-u")) {
385 update = 1;
386 continue;
387 }
389 /* This differs from "-m" in that we'll silently ignore unmerged entries */
390 if (!strcmp(arg, "--reset")) {
391 if (stage || merge || emu23)
392 usage(read_tree_usage);
393 reset = 1;
394 merge = 1;
395 stage = 1;
396 read_cache_unmerged();
397 }
399 /* "-m" stands for "merge", meaning we start in stage 1 */
400 if (!strcmp(arg, "-m")) {
401 if (stage || merge || emu23)
402 usage(read_tree_usage);
403 if (read_cache_unmerged())
404 die("you need to resolve your current index first");
405 stage = 1;
406 merge = 1;
407 continue;
408 }
410 /* "-emu23" uses 3-way merge logic to perform fast-forward */
411 if (!strcmp(arg, "--emu23")) {
412 if (stage || merge || emu23)
413 usage(read_tree_usage);
414 if (read_cache_unmerged())
415 die("you need to resolve your current index first");
416 merge = emu23 = stage = 1;
417 continue;
418 }
420 if (get_sha1(arg, sha1) < 0)
421 usage(read_tree_usage);
422 if (stage > 3)
423 usage(read_tree_usage);
424 if (unpack_tree(sha1) < 0)
425 die("failed to unpack tree object %s", arg);
426 stage++;
427 }
428 if (update && !merge)
429 usage(read_tree_usage);
430 if (merge) {
431 static const merge_fn_t merge_function[] = {
432 [1] = oneway_merge,
433 [2] = twoway_merge,
434 [3] = threeway_merge,
435 };
436 merge_fn_t fn;
438 if (stage < 2 || stage > 4)
439 die("just how do you expect me to merge %d trees?", stage-1);
440 if (emu23 && stage != 3)
441 die("--emu23 takes only two trees");
442 fn = merge_function[stage-1];
443 if (stage == 3 && emu23) {
444 setup_emu23();
445 fn = merge_function[3];
446 }
447 merge_cache(active_cache, active_nr, fn);
448 }
449 if (write_cache(newfd, active_cache, active_nr) ||
450 commit_index_file(&cache_file))
451 die("unable to write new index file");
452 return 0;
453 }