ecd40cc393fad70a15ca4efbdab4a2049ea8aefe
1/*
2 * GIT - The information manager from hell
3 *
4 * Copyright (C) Linus Torvalds, 2005
5 */
6#include "cache.h"
7static int stage = 0;
9static int update = 0;
10static int unpack_tree(unsigned char *sha1)
12{
13 void *buffer;
14 unsigned long size;
15 int ret;
16 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}
24static 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}
31static 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}
37/*
40 * This removes all trivial merges that don't change the tree
41 * and collapses them to state 0.
42 */
43static 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}
74/*
76 * When a CE gets turned into an unmerged entry, we
77 * want it to be up-to-date
78 */
79static void verify_uptodate(struct cache_entry *ce)
80{
81 struct stat st;
82 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}
93/*
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 */
100static void reject_merge(struct cache_entry *ce)
101{
102 die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
103}
104static int merged_entry_internal(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst, int allow_dirty)
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 if (!allow_dirty) {
119 verify_uptodate(old);
120 }
121 }
122 merge->ce_flags &= ~htons(CE_STAGEMASK);
123 *dst++ = merge;
124 return 1;
125}
126static int merged_entry_allow_dirty(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
128{
129 return merged_entry_internal(merge, old, dst, 1);
130}
131static int merged_entry(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
133{
134 return merged_entry_internal(merge, old, dst, 0);
135}
136static int deleted_entry(struct cache_entry *ce, struct cache_entry *old, struct cache_entry **dst)
138{
139 if (old)
140 verify_uptodate(old);
141 ce->ce_mode = 0;
142 *dst++ = ce;
143 return 1;
144}
145static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **dst)
147{
148 struct cache_entry *old = stages[0];
149 struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
150 struct cache_entry *merge;
151 int count;
152 /* #5ALT */
154 if (!a && b && c && same(b, c)) {
155 if (old && !same(b, old))
156 return -1;
157 return merged_entry_allow_dirty(b, old, dst);
158 }
159 /*
160 * If we have an entry in the index cache ("old"), then we want
161 * to make sure that it matches any entries in stage 2 ("first
162 * branch", aka "b").
163 */
164 if (old) {
165 if (!b || !same(old, b))
166 return -1;
167 }
168 merge = merge_entries(a, b, c);
169 if (merge)
170 return merged_entry(merge, old, dst);
171 if (old)
172 verify_uptodate(old);
173 count = 0;
174 if (a) { *dst++ = a; count++; }
175 if (b) { *dst++ = b; count++; }
176 if (c) { *dst++ = c; count++; }
177 return count;
178}
179/*
181 * Two-way merge.
182 *
183 * The rule is to "carry forward" what is in the index without losing
184 * information across a "fast forward", favoring a successful merge
185 * over a merge failure when it makes sense. For details of the
186 * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
187 *
188 */
189static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
190{
191 struct cache_entry *current = src[0];
192 struct cache_entry *oldtree = src[1], *newtree = src[2];
193 if (src[3])
195 return -1;
196 if (current) {
198 if ((!oldtree && !newtree) || /* 4 and 5 */
199 (!oldtree && newtree &&
200 same(current, newtree)) || /* 6 and 7 */
201 (oldtree && newtree &&
202 same(oldtree, newtree)) || /* 14 and 15 */
203 (oldtree && newtree &&
204 !same(oldtree, newtree) && /* 18 and 19*/
205 same(current, newtree))) {
206 *dst++ = current;
207 return 1;
208 }
209 else if (oldtree && !newtree && same(current, oldtree)) {
210 /* 10 or 11 */
211 return deleted_entry(oldtree, current, dst);
212 }
213 else if (oldtree && newtree &&
214 same(current, oldtree) && !same(current, newtree)) {
215 /* 20 or 21 */
216 return merged_entry(newtree, current, dst);
217 }
218 else
219 /* all other failures */
220 return -1;
221 }
222 else if (newtree)
223 return merged_entry(newtree, current, dst);
224 else
225 return deleted_entry(oldtree, current, dst);
226}
227/*
229 * Two-way merge emulated with three-way merge.
230 *
231 * This treats "read-tree -m H M" by transforming it internally
232 * into "read-tree -m H I+H M", where I+H is a tree that would
233 * contain the contents of the current index file, overlayed on
234 * top of H. Unlike the traditional two-way merge, this leaves
235 * the stages in the resulting index file and lets the user resolve
236 * the merge conflicts using standard tools for three-way merge.
237 *
238 * This function is just to set-up such an arrangement, and the
239 * actual merge uses threeway_merge() function.
240 */
241static void setup_emu23(void)
242{
243 /* stage0 contains I, stage1 H, stage2 M.
244 * move stage2 to stage3, and create stage2 entries
245 * by scanning stage0 and stage1 entries.
246 */
247 int i, namelen, size;
248 struct cache_entry *ce, *stage2;
249 for (i = 0; i < active_nr; i++) {
251 ce = active_cache[i];
252 if (ce_stage(ce) != 2)
253 continue;
254 /* hoist them up to stage 3 */
255 namelen = ce_namelen(ce);
256 ce->ce_flags = create_ce_flags(namelen, 3);
257 }
258 for (i = 0; i < active_nr; i++) {
260 ce = active_cache[i];
261 if (ce_stage(ce) > 1)
262 continue;
263 namelen = ce_namelen(ce);
264 size = cache_entry_size(namelen);
265 stage2 = xmalloc(size);
266 memcpy(stage2, ce, size);
267 stage2->ce_flags = create_ce_flags(namelen, 2);
268 if (add_cache_entry(stage2, ADD_CACHE_OK_TO_ADD) < 0)
269 die("cannot merge index and our head tree");
270 /* We are done with this name, so skip to next name */
272 while (i < active_nr &&
273 ce_namelen(active_cache[i]) == namelen &&
274 !memcmp(active_cache[i]->name, ce->name, namelen))
275 i++;
276 i--; /* compensate for the loop control */
277 }
278}
279/*
281 * One-way merge.
282 *
283 * The rule is:
284 * - take the stat information from stage0, take the data from stage1
285 */
286static int oneway_merge(struct cache_entry **src, struct cache_entry **dst)
287{
288 struct cache_entry *old = src[0];
289 struct cache_entry *a = src[1];
290 if (src[2] || src[3])
292 return -1;
293 if (!a)
295 return 0;
296 if (old && same(old, a)) {
297 *dst++ = old;
298 return 1;
299 }
300 return merged_entry(a, NULL, dst);
301}
302static void check_updates(struct cache_entry **src, int nr)
304{
305 static struct checkout state = {
306 .base_dir = "",
307 .force = 1,
308 .quiet = 1,
309 .refresh_cache = 1,
310 };
311 unsigned short mask = htons(CE_UPDATE);
312 while (nr--) {
313 struct cache_entry *ce = *src++;
314 if (!ce->ce_mode) {
315 if (update)
316 unlink(ce->name);
317 continue;
318 }
319 if (ce->ce_flags & mask) {
320 ce->ce_flags &= ~mask;
321 if (update)
322 checkout_entry(ce, &state);
323 }
324 }
325}
326typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **);
328static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
330{
331 struct cache_entry **dst = src;
332 while (nr) {
334 int entries;
335 struct cache_entry *name, *ce, *stages[4] = { NULL, };
336 name = ce = *src;
338 for (;;) {
339 int stage = ce_stage(ce);
340 stages[stage] = ce;
341 ce = *++src;
342 active_nr--;
343 if (!--nr)
344 break;
345 if (!path_matches(ce, name))
346 break;
347 }
348 entries = fn(stages, dst);
350 if (entries < 0)
351 reject_merge(name);
352 dst += entries;
353 active_nr += entries;
354 }
355 check_updates(active_cache, active_nr);
356}
357static int read_cache_unmerged(void)
359{
360 int i, deleted;
361 struct cache_entry **dst;
362 read_cache();
364 dst = active_cache;
365 deleted = 0;
366 for (i = 0; i < active_nr; i++) {
367 struct cache_entry *ce = active_cache[i];
368 if (ce_stage(ce)) {
369 deleted++;
370 continue;
371 }
372 if (deleted)
373 *dst = ce;
374 dst++;
375 }
376 active_nr -= deleted;
377 return deleted;
378}
379static char *read_tree_usage = "git-read-tree (<sha> | -m [-u] <sha1> [<sha2> [<sha3>]])";
381static struct cache_file cache_file;
383int main(int argc, char **argv)
385{
386 int i, newfd, merge, reset, emu23;
387 unsigned char sha1[20];
388 newfd = hold_index_file_for_update(&cache_file, get_index_file());
390 if (newfd < 0)
391 die("unable to create new cachefile");
392 merge = 0;
394 reset = 0;
395 emu23 = 0;
396 for (i = 1; i < argc; i++) {
397 const char *arg = argv[i];
398 /* "-u" means "update", meaning that a merge will update the working directory */
400 if (!strcmp(arg, "-u")) {
401 update = 1;
402 continue;
403 }
404 /* This differs from "-m" in that we'll silently ignore unmerged entries */
406 if (!strcmp(arg, "--reset")) {
407 if (stage || merge || emu23)
408 usage(read_tree_usage);
409 reset = 1;
410 merge = 1;
411 stage = 1;
412 read_cache_unmerged();
413 }
414 /* "-m" stands for "merge", meaning we start in stage 1 */
416 if (!strcmp(arg, "-m")) {
417 if (stage || merge || emu23)
418 usage(read_tree_usage);
419 if (read_cache_unmerged())
420 die("you need to resolve your current index first");
421 stage = 1;
422 merge = 1;
423 continue;
424 }
425 /* "-emu23" uses 3-way merge logic to perform fast-forward */
427 if (!strcmp(arg, "--emu23")) {
428 if (stage || merge || emu23)
429 usage(read_tree_usage);
430 if (read_cache_unmerged())
431 die("you need to resolve your current index first");
432 merge = emu23 = stage = 1;
433 continue;
434 }
435 if (get_sha1(arg, sha1) < 0)
437 usage(read_tree_usage);
438 if (stage > 3)
439 usage(read_tree_usage);
440 if (unpack_tree(sha1) < 0)
441 die("failed to unpack tree object %s", arg);
442 stage++;
443 }
444 if (update && !merge)
445 usage(read_tree_usage);
446 if (merge) {
447 static const merge_fn_t merge_function[] = {
448 [1] = oneway_merge,
449 [2] = twoway_merge,
450 [3] = threeway_merge,
451 };
452 merge_fn_t fn;
453 if (stage < 2 || stage > 4)
455 die("just how do you expect me to merge %d trees?", stage-1);
456 if (emu23 && stage != 3)
457 die("--emu23 takes only two trees");
458 fn = merge_function[stage-1];
459 if (stage == 3 && emu23) {
460 setup_emu23();
461 fn = merge_function[3];
462 }
463 merge_cache(active_cache, active_nr, fn);
464 }
465 if (write_cache(newfd, active_cache, active_nr) ||
466 commit_index_file(&cache_file))
467 die("unable to write new index file");
468 return 0;
469}