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[git.git] / read-tree.c
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;
10 static int unpack_tree(unsigned char *sha1)
11 {
12         void *buffer;
13         unsigned long size;
15         buffer = read_tree_with_tree_or_commit_sha1(sha1, &size, 0);
16         if (!buffer)
17                 return -1;
18         return read_tree(buffer, size, stage);
19 }
21 static char *lockfile_name;
23 static void remove_lock_file(void)
24 {
25         if (lockfile_name)
26                 unlink(lockfile_name);
27 }
29 static int path_matches(struct cache_entry *a, struct cache_entry *b)
30 {
31         int len = ce_namelen(a);
32         return ce_namelen(b) == len &&
33                 !memcmp(a->name, b->name, len);
34 }
36 static int same(struct cache_entry *a, struct cache_entry *b)
37 {
38         return a->ce_mode == b->ce_mode && 
39                 !memcmp(a->sha1, b->sha1, 20);
40 }
43 /*
44  * This removes all trivial merges that don't change the tree
45  * and collapses them to state 0.
46  *
47  * _Any_ other merge is left to user policy.  That includes "both
48  * created the same file", and "both removed the same file" - which are
49  * trivial, but the user might still want to _note_ it. 
50  */
51 static struct cache_entry *merge_entries(struct cache_entry *a,
52                                          struct cache_entry *b,
53                                          struct cache_entry *c)
54 {
55         int len = ce_namelen(a);
57         /*
58          * Are they all the same filename? We won't do
59          * any name merging
60          */
61         if (ce_namelen(b) != len ||
62             ce_namelen(c) != len ||
63             memcmp(a->name, b->name, len) ||
64             memcmp(a->name, c->name, len))
65                 return NULL;
67         /*
68          * Ok, all three entries describe the same
69          * filename, but maybe the contents or file
70          * mode have changed?
71          *
72          * The trivial cases end up being the ones where two
73          * out of three files are the same:
74          *  - both destinations the same, trivially take either
75          *  - one of the destination versions hasn't changed,
76          *    take the other.
77          *
78          * The "all entries exactly the same" case falls out as
79          * a special case of any of the "two same" cases.
80          *
81          * Here "a" is "original", and "b" and "c" are the two
82          * trees we are merging.
83          */
84         if (same(b,c))
85                 return c;
86         if (same(a,b))
87                 return c;
88         if (same(a,c))
89                 return b;
90         return NULL;
91 }
93 static void trivially_merge_cache(struct cache_entry **src, int nr)
94 {
95         static struct cache_entry null_entry;
96         struct cache_entry **dst = src;
97         struct cache_entry *old = &null_entry;
99         while (nr) {
100                 struct cache_entry *ce, *result;
102                 ce = src[0];
104                 /* We throw away original cache entries except for the stat information */
105                 if (!ce_stage(ce)) {
106                         old = ce;
107                         src++;
108                         nr--;
109                         active_nr--;
110                         continue;
111                 }
112                 if (nr > 2 && (result = merge_entries(ce, src[1], src[2])) != NULL) {
113                         /*
114                          * See if we can re-use the old CE directly?
115                          * That way we get the uptodate stat info.
116                          */
117                         if (path_matches(result, old) && same(result, old))
118                                 *result = *old;
119                         ce = result;
120                         ce->ce_flags &= ~htons(CE_STAGEMASK);
121                         src += 2;
122                         nr -= 2;
123                         active_nr -= 2;
124                 }
125                 *dst++ = ce;
126                 src++;
127                 nr--;
128         }
131 static void merge_stat_info(struct cache_entry **src, int nr)
133         static struct cache_entry null_entry;
134         struct cache_entry **dst = src;
135         struct cache_entry *old = &null_entry;
137         while (nr) {
138                 struct cache_entry *ce;
140                 ce = src[0];
142                 /* We throw away original cache entries except for the stat information */
143                 if (!ce_stage(ce)) {
144                         old = ce;
145                         src++;
146                         nr--;
147                         active_nr--;
148                         continue;
149                 }
150                 if (path_matches(ce, old) && same(ce, old))
151                         *ce = *old;
152                 ce->ce_flags &= ~htons(CE_STAGEMASK);
153                 *dst++ = ce;
154                 src++;
155                 nr--;
156         }
159 static char *read_tree_usage = "read-tree (<sha> | -m <sha1> [<sha2> <sha3>])";
161 int main(int argc, char **argv)
163         int i, newfd, merge;
164         unsigned char sha1[20];
165         static char lockfile[MAXPATHLEN+1];
166         const char *indexfile = get_index_file();
168         snprintf(lockfile, sizeof(lockfile), "%s.lock", indexfile);
170         newfd = open(lockfile, O_RDWR | O_CREAT | O_EXCL, 0600);
171         if (newfd < 0)
172                 die("unable to create new cachefile");
173         atexit(remove_lock_file);
174         lockfile_name = lockfile;
176         merge = 0;
177         for (i = 1; i < argc; i++) {
178                 const char *arg = argv[i];
180                 /* "-m" stands for "merge", meaning we start in stage 1 */
181                 if (!strcmp(arg, "-m")) {
182                         int i;
183                         if (stage)
184                                 die("-m needs to come first");
185                         read_cache();
186                         for (i = 0; i < active_nr; i++) {
187                                 if (ce_stage(active_cache[i]))
188                                         die("you need to resolve your current index first");
189                         }
190                         stage = 1;
191                         merge = 1;
192                         continue;
193                 }
194                 if (get_sha1_hex(arg, sha1) < 0)
195                         usage(read_tree_usage);
196                 if (stage > 3)
197                         usage(read_tree_usage);
198                 if (unpack_tree(sha1) < 0)
199                         die("failed to unpack tree object %s", arg);
200                 stage++;
201         }
202         if (merge) {
203                 switch (stage) {
204                 case 4: /* Three-way merge */
205                         trivially_merge_cache(active_cache, active_nr);
206                         break;
207                 case 2: /* Just read a tree, merge with old cache contents */
208                         merge_stat_info(active_cache, active_nr);
209                         break;
210                 default:
211                         die("just how do you expect me to merge %d trees?", stage-1);
212                 }
213         }
214         if (write_cache(newfd, active_cache, active_nr) || rename(lockfile, indexfile))
215                 die("unable to write new index file");
216         lockfile_name = NULL;
217         return 0;