diff-tree: fix up comparison of "interesting" sub-trees
[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"
7
8 static int stage = 0;
9
10 static int unpack_tree(unsigned char *sha1)
11 {
12         void *buffer;
13         unsigned long size;
14         int ret;
15
16         buffer = read_object_with_reference(sha1, "tree", &size, 0);
17         if (!buffer)
18                 return -1;
19         ret = read_tree(buffer, size, stage);
20         free(buffer);
21         return ret;
22 }
23
24 static char *lockfile_name;
25
26 static void remove_lock_file(void)
27 {
28         if (lockfile_name)
29                 unlink(lockfile_name);
30 }
31
32 static int path_matches(struct cache_entry *a, struct cache_entry *b)
33 {
34         int len = ce_namelen(a);
35         return ce_namelen(b) == len &&
36                 !memcmp(a->name, b->name, len);
37 }
38
39 static int same(struct cache_entry *a, struct cache_entry *b)
40 {
41         return a->ce_mode == b->ce_mode && 
42                 !memcmp(a->sha1, b->sha1, 20);
43 }
44
45
46 /*
47  * This removes all trivial merges that don't change the tree
48  * and collapses them to state 0.
49  *
50  * _Any_ other merge is left to user policy.  That includes "both
51  * created the same file", and "both removed the same file" - which are
52  * trivial, but the user might still want to _note_ it. 
53  */
54 static struct cache_entry *merge_entries(struct cache_entry *a,
55                                          struct cache_entry *b,
56                                          struct cache_entry *c)
57 {
58         int len = ce_namelen(a);
59
60         /*
61          * Are they all the same filename? We won't do
62          * any name merging
63          */
64         if (ce_namelen(b) != len ||
65             ce_namelen(c) != len ||
66             memcmp(a->name, b->name, len) ||
67             memcmp(a->name, c->name, len))
68                 return NULL;
69
70         /*
71          * Ok, all three entries describe the same
72          * filename, but maybe the contents or file
73          * mode have changed?
74          *
75          * The trivial cases end up being the ones where two
76          * out of three files are the same:
77          *  - both destinations the same, trivially take either
78          *  - one of the destination versions hasn't changed,
79          *    take the other.
80          *
81          * The "all entries exactly the same" case falls out as
82          * a special case of any of the "two same" cases.
83          *
84          * Here "a" is "original", and "b" and "c" are the two
85          * trees we are merging.
86          */
87         if (same(b,c))
88                 return c;
89         if (same(a,b))
90                 return c;
91         if (same(a,c))
92                 return b;
93         return NULL;
94 }
95
96 static void trivially_merge_cache(struct cache_entry **src, int nr)
97 {
98         static struct cache_entry null_entry;
99         struct cache_entry **dst = src;
100         struct cache_entry *old = &null_entry;
101
102         while (nr) {
103                 struct cache_entry *ce, *result;
104
105                 ce = src[0];
106
107                 /* We throw away original cache entries except for the stat information */
108                 if (!ce_stage(ce)) {
109                         old = ce;
110                         src++;
111                         nr--;
112                         active_nr--;
113                         continue;
114                 }
115                 if (nr > 2 && (result = merge_entries(ce, src[1], src[2])) != NULL) {
116                         /*
117                          * See if we can re-use the old CE directly?
118                          * That way we get the uptodate stat info.
119                          */
120                         if (path_matches(result, old) && same(result, old))
121                                 *result = *old;
122                         ce = result;
123                         ce->ce_flags &= ~htons(CE_STAGEMASK);
124                         src += 2;
125                         nr -= 2;
126                         active_nr -= 2;
127                 }
128                 *dst++ = ce;
129                 src++;
130                 nr--;
131         }
132 }
133
134 static void merge_stat_info(struct cache_entry **src, int nr)
135 {
136         static struct cache_entry null_entry;
137         struct cache_entry **dst = src;
138         struct cache_entry *old = &null_entry;
139
140         while (nr) {
141                 struct cache_entry *ce;
142
143                 ce = src[0];
144
145                 /* We throw away original cache entries except for the stat information */
146                 if (!ce_stage(ce)) {
147                         old = ce;
148                         src++;
149                         nr--;
150                         active_nr--;
151                         continue;
152                 }
153                 if (path_matches(ce, old) && same(ce, old))
154                         *ce = *old;
155                 ce->ce_flags &= ~htons(CE_STAGEMASK);
156                 *dst++ = ce;
157                 src++;
158                 nr--;
159         }
160 }
161
162 static char *read_tree_usage = "read-tree (<sha> | -m <sha1> [<sha2> <sha3>])";
163
164 int main(int argc, char **argv)
165 {
166         int i, newfd, merge;
167         unsigned char sha1[20];
168         static char lockfile[MAXPATHLEN+1];
169         const char *indexfile = get_index_file();
170
171         snprintf(lockfile, sizeof(lockfile), "%s.lock", indexfile);
172
173         newfd = open(lockfile, O_RDWR | O_CREAT | O_EXCL, 0600);
174         if (newfd < 0)
175                 die("unable to create new cachefile");
176         atexit(remove_lock_file);
177         lockfile_name = lockfile;
178
179         merge = 0;
180         for (i = 1; i < argc; i++) {
181                 const char *arg = argv[i];
182
183                 /* "-m" stands for "merge", meaning we start in stage 1 */
184                 if (!strcmp(arg, "-m")) {
185                         int i;
186                         if (stage)
187                                 die("-m needs to come first");
188                         read_cache();
189                         for (i = 0; i < active_nr; i++) {
190                                 if (ce_stage(active_cache[i]))
191                                         die("you need to resolve your current index first");
192                         }
193                         stage = 1;
194                         merge = 1;
195                         continue;
196                 }
197                 if (get_sha1(arg, sha1) < 0)
198                         usage(read_tree_usage);
199                 if (stage > 3)
200                         usage(read_tree_usage);
201                 if (unpack_tree(sha1) < 0)
202                         die("failed to unpack tree object %s", arg);
203                 stage++;
204         }
205         if (merge) {
206                 switch (stage) {
207                 case 4: /* Three-way merge */
208                         trivially_merge_cache(active_cache, active_nr);
209                         break;
210                 case 2: /* Just read a tree, merge with old cache contents */
211                         merge_stat_info(active_cache, active_nr);
212                         break;
213                 default:
214                         die("just how do you expect me to merge %d trees?", stage-1);
215                 }
216         }
217         if (write_cache(newfd, active_cache, active_nr) || rename(lockfile, indexfile))
218                 die("unable to write new index file");
219         lockfile_name = NULL;
220         return 0;
221 }