summaryrefslogtreecommitdiff
path: root/read-tree.c
blob: f8dc509a1f999fcbcccc6936477ddc80c9d063cc (plain)
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
/*
 * GIT - The information manager from hell
 *
 * Copyright (C) Linus Torvalds, 2005
 */
#include "cache.h"

static int stage = 0;

static int unpack_tree(unsigned char *sha1)
{
	void *buffer;
	unsigned long size;

	buffer = read_object_with_reference(sha1, "tree", &size, 0);
	if (!buffer)
		return -1;
	return read_tree(buffer, size, stage);
}

static char *lockfile_name;

static void remove_lock_file(void)
{
	if (lockfile_name)
		unlink(lockfile_name);
}

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.
 *
 * _Any_ other merge is left to user policy.  That includes "both
 * created the same file", and "both removed the same file" - which are
 * trivial, but the user might still want to _note_ it. 
 */
static struct cache_entry *merge_entries(struct cache_entry *a,
					 struct cache_entry *b,
					 struct cache_entry *c)
{
	int len = ce_namelen(a);

	/*
	 * Are they all the same filename? We won't do
	 * any name merging
	 */
	if (ce_namelen(b) != len ||
	    ce_namelen(c) != len ||
	    memcmp(a->name, b->name, len) ||
	    memcmp(a->name, c->name, len))
		return NULL;

	/*
	 * 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 (same(b,c))
		return c;
	if (same(a,b))
		return c;
	if (same(a,c))
		return b;
	return NULL;
}

static void trivially_merge_cache(struct cache_entry **src, int nr)
{
	static struct cache_entry null_entry;
	struct cache_entry **dst = src;
	struct cache_entry *old = &null_entry;

	while (nr) {
		struct cache_entry *ce, *result;

		ce = src[0];

		/* We throw away original cache entries except for the stat information */
		if (!ce_stage(ce)) {
			old = ce;
			src++;
			nr--;
			active_nr--;
			continue;
		}
		if (nr > 2 && (result = merge_entries(ce, src[1], src[2])) != NULL) {
			/*
			 * See if we can re-use the old CE directly?
			 * That way we get the uptodate stat info.
			 */
			if (path_matches(result, old) && same(result, old))
				*result = *old;
			ce = result;
			ce->ce_flags &= ~htons(CE_STAGEMASK);
			src += 2;
			nr -= 2;
			active_nr -= 2;
		}
		*dst++ = ce;
		src++;
		nr--;
	}
}

static void merge_stat_info(struct cache_entry **src, int nr)
{
	static struct cache_entry null_entry;
	struct cache_entry **dst = src;
	struct cache_entry *old = &null_entry;

	while (nr) {
		struct cache_entry *ce;

		ce = src[0];

		/* We throw away original cache entries except for the stat information */
		if (!ce_stage(ce)) {
			old = ce;
			src++;
			nr--;
			active_nr--;
			continue;
		}
		if (path_matches(ce, old) && same(ce, old))
			*ce = *old;
		ce->ce_flags &= ~htons(CE_STAGEMASK);
		*dst++ = ce;
		src++;
		nr--;
	}
}

static char *read_tree_usage = "read-tree (<sha> | -m <sha1> [<sha2> <sha3>])";

int main(int argc, char **argv)
{
	int i, newfd, merge;
	unsigned char sha1[20];
	static char lockfile[MAXPATHLEN+1];
	const char *indexfile = get_index_file();

	snprintf(lockfile, sizeof(lockfile), "%s.lock", indexfile);

	newfd = open(lockfile, O_RDWR | O_CREAT | O_EXCL, 0600);
	if (newfd < 0)
		die("unable to create new cachefile");
	atexit(remove_lock_file);
	lockfile_name = lockfile;

	merge = 0;
	for (i = 1; i < argc; i++) {
		const char *arg = argv[i];

		/* "-m" stands for "merge", meaning we start in stage 1 */
		if (!strcmp(arg, "-m")) {
			int i;
			if (stage)
				die("-m needs to come first");
			read_cache();
			for (i = 0; i < active_nr; i++) {
				if (ce_stage(active_cache[i]))
					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 (merge) {
		switch (stage) {
		case 4:	/* Three-way merge */
			trivially_merge_cache(active_cache, active_nr);
			break;
		case 2:	/* Just read a tree, merge with old cache contents */
			merge_stat_info(active_cache, active_nr);
			break;
		default:
			die("just how do you expect me to merge %d trees?", stage-1);
		}
	}
	if (write_cache(newfd, active_cache, active_nr) || rename(lockfile, indexfile))
		die("unable to write new index file");
	lockfile_name = NULL;
	return 0;
}