1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
|
/*
* GIT - The information manager from hell
*
* Copyright (C) Linus Torvalds, 2005
*/
#include "cache.h"
static int stage = 0;
static int update = 0;
static int unpack_tree(unsigned char *sha1)
{
void *buffer;
unsigned long size;
int ret;
buffer = read_object_with_reference(sha1, "tree", &size, NULL);
if (!buffer)
return -1;
ret = read_tree(buffer, size, stage);
free(buffer);
return ret;
}
static int path_matches(struct cache_entry *a, struct cache_entry *b)
{
int len = ce_namelen(a);
return ce_namelen(b) == len &&
!memcmp(a->name, b->name, len);
}
static int same(struct cache_entry *a, struct cache_entry *b)
{
return a->ce_mode == b->ce_mode &&
!memcmp(a->sha1, b->sha1, 20);
}
/*
* This removes all trivial merges that don't change the tree
* and collapses them to state 0.
*/
static struct cache_entry *merge_entries(struct cache_entry *a,
struct cache_entry *b,
struct cache_entry *c)
{
/*
* Ok, all three entries describe the same
* filename, but maybe the contents or file
* mode have changed?
*
* The trivial cases end up being the ones where two
* out of three files are the same:
* - both destinations the same, trivially take either
* - one of the destination versions hasn't changed,
* take the other.
*
* The "all entries exactly the same" case falls out as
* a special case of any of the "two same" cases.
*
* Here "a" is "original", and "b" and "c" are the two
* trees we are merging.
*/
if (a && b && c) {
if (same(b,c))
return c;
if (same(a,b))
return c;
if (same(a,c))
return b;
}
return NULL;
}
/*
* When a CE gets turned into an unmerged entry, we
* want it to be up-to-date
*/
static void verify_uptodate(struct cache_entry *ce)
{
struct stat st;
if (!lstat(ce->name, &st)) {
unsigned changed = ce_match_stat(ce, &st);
if (!changed)
return;
errno = 0;
}
if (errno == ENOENT)
return;
die("Entry '%s' not uptodate. Cannot merge.", ce->name);
}
/*
* If the old tree contained a CE that isn't even in the
* result, that's always a problem, regardless of whether
* it's up-to-date or not (ie it can be a file that we
* have updated but not committed yet).
*/
static void reject_merge(struct cache_entry *ce)
{
die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
}
static int merged_entry(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
{
merge->ce_flags |= htons(CE_UPDATE);
if (old) {
/*
* See if we can re-use the old CE directly?
* That way we get the uptodate stat info.
*
* This also removes the UPDATE flag on
* a match.
*/
if (same(old, merge)) {
*merge = *old;
} else {
verify_uptodate(old);
}
}
merge->ce_flags &= ~htons(CE_STAGEMASK);
*dst++ = merge;
return 1;
}
static int deleted_entry(struct cache_entry *ce, struct cache_entry *old, struct cache_entry **dst)
{
if (old)
verify_uptodate(old);
ce->ce_mode = 0;
*dst++ = ce;
return 1;
}
static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **dst)
{
struct cache_entry *old = stages[0];
struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
struct cache_entry *merge;
int count;
/*
* If we have an entry in the index cache ("old"), then we want
* to make sure that it matches any entries in stage 2 ("first
* branch", aka "b").
*/
if (old) {
if (!b || !same(old, b))
return -1;
}
merge = merge_entries(a, b, c);
if (merge)
return merged_entry(merge, old, dst);
if (old)
verify_uptodate(old);
count = 0;
if (a) { *dst++ = a; count++; }
if (b) { *dst++ = b; count++; }
if (c) { *dst++ = c; count++; }
return count;
}
/*
* Two-way merge.
*
* The rule is to "carry forward" what is in the index without losing
* information across a "fast forward", favoring a successful merge
* over a merge failure when it makes sense. For details of the
* "carry forward" rule, please see <Documentation/git-read-tree.txt>.
*
*/
static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
{
struct cache_entry *current = src[0];
struct cache_entry *oldtree = src[1], *newtree = src[2];
if (src[3])
return -1;
if (current) {
if ((!oldtree && !newtree) || /* 4 and 5 */
(!oldtree && newtree &&
same(current, newtree)) || /* 6 and 7 */
(oldtree && newtree &&
same(oldtree, newtree)) || /* 14 and 15 */
(oldtree && newtree &&
!same(oldtree, newtree) && /* 18 and 19*/
same(current, newtree))) {
*dst++ = current;
return 1;
}
else if (oldtree && !newtree && same(current, oldtree)) {
/* 10 or 11 */
return deleted_entry(oldtree, current, dst);
}
else if (oldtree && newtree &&
same(current, oldtree) && !same(current, newtree)) {
/* 20 or 21 */
return merged_entry(newtree, current, dst);
}
else
/* all other failures */
return -1;
}
else if (newtree)
return merged_entry(newtree, current, dst);
else
return deleted_entry(oldtree, current, dst);
}
/*
* One-way merge.
*
* The rule is:
* - take the stat information from stage0, take the data from stage1
*/
static int oneway_merge(struct cache_entry **src, struct cache_entry **dst)
{
struct cache_entry *old = src[0];
struct cache_entry *a = src[1];
if (src[2] || src[3])
return -1;
if (!a)
return 0;
if (old && same(old, a)) {
*dst++ = old;
return 1;
}
return merged_entry(a, NULL, dst);
}
static void check_updates(struct cache_entry **src, int nr)
{
static struct checkout state = {
.base_dir = "",
.force = 1,
.quiet = 1,
.refresh_cache = 1,
};
unsigned short mask = htons(CE_UPDATE);
while (nr--) {
struct cache_entry *ce = *src++;
if (!ce->ce_mode) {
if (update)
unlink(ce->name);
continue;
}
if (ce->ce_flags & mask) {
ce->ce_flags &= ~mask;
if (update)
checkout_entry(ce, &state);
}
}
}
typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **);
static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
{
struct cache_entry **dst = src;
while (nr) {
int entries;
struct cache_entry *name, *ce, *stages[4] = { NULL, };
name = ce = *src;
for (;;) {
int stage = ce_stage(ce);
stages[stage] = ce;
ce = *++src;
active_nr--;
if (!--nr)
break;
if (!path_matches(ce, name))
break;
}
entries = fn(stages, dst);
if (entries < 0)
reject_merge(name);
dst += entries;
active_nr += entries;
}
check_updates(active_cache, active_nr);
}
static int read_cache_unmerged(void)
{
int i, deleted;
struct cache_entry **dst;
read_cache();
dst = active_cache;
deleted = 0;
for (i = 0; i < active_nr; i++) {
struct cache_entry *ce = active_cache[i];
if (ce_stage(ce)) {
deleted++;
continue;
}
if (deleted)
*dst = ce;
dst++;
}
active_nr -= deleted;
return deleted;
}
static char *read_tree_usage = "git-read-tree (<sha> | -m [-u] <sha1> [<sha2> [<sha3>]])";
static struct cache_file cache_file;
int main(int argc, char **argv)
{
int i, newfd, merge, reset;
unsigned char sha1[20];
newfd = hold_index_file_for_update(&cache_file, get_index_file());
if (newfd < 0)
die("unable to create new cachefile");
merge = 0;
reset = 0;
for (i = 1; i < argc; i++) {
const char *arg = argv[i];
/* "-u" means "update", meaning that a merge will update the working directory */
if (!strcmp(arg, "-u")) {
update = 1;
continue;
}
/* This differs from "-m" in that we'll silently ignore unmerged entries */
if (!strcmp(arg, "--reset")) {
if (stage || merge)
usage(read_tree_usage);
reset = 1;
merge = 1;
stage = 1;
read_cache_unmerged();
}
/* "-m" stands for "merge", meaning we start in stage 1 */
if (!strcmp(arg, "-m")) {
if (stage || merge)
usage(read_tree_usage);
if (read_cache_unmerged())
die("you need to resolve your current index first");
stage = 1;
merge = 1;
continue;
}
if (get_sha1(arg, sha1) < 0)
usage(read_tree_usage);
if (stage > 3)
usage(read_tree_usage);
if (unpack_tree(sha1) < 0)
die("failed to unpack tree object %s", arg);
stage++;
}
if (update && !merge)
usage(read_tree_usage);
if (merge) {
static const merge_fn_t merge_function[] = {
[1] = oneway_merge,
[2] = twoway_merge,
[3] = threeway_merge,
};
if (stage < 2 || stage > 4)
die("just how do you expect me to merge %d trees?", stage-1);
merge_cache(active_cache, active_nr, merge_function[stage-1]);
}
if (write_cache(newfd, active_cache, active_nr) ||
commit_index_file(&cache_file))
die("unable to write new index file");
return 0;
}
|