Merge branch 'jk/commit-C-pick-empty'
[git] / match-trees.c
1 #include "cache.h"
2 #include "tree.h"
3 #include "tree-walk.h"
4
5 static int score_missing(unsigned mode, const char *path)
6 {
7         int score;
8
9         if (S_ISDIR(mode))
10                 score = -1000;
11         else if (S_ISLNK(mode))
12                 score = -500;
13         else
14                 score = -50;
15         return score;
16 }
17
18 static int score_differs(unsigned mode1, unsigned mode2, const char *path)
19 {
20         int score;
21
22         if (S_ISDIR(mode1) != S_ISDIR(mode2))
23                 score = -100;
24         else if (S_ISLNK(mode1) != S_ISLNK(mode2))
25                 score = -50;
26         else
27                 score = -5;
28         return score;
29 }
30
31 static int score_matches(unsigned mode1, unsigned mode2, const char *path)
32 {
33         int score;
34
35         /* Heh, we found SHA-1 collisions between different kind of objects */
36         if (S_ISDIR(mode1) != S_ISDIR(mode2))
37                 score = -100;
38         else if (S_ISLNK(mode1) != S_ISLNK(mode2))
39                 score = -50;
40
41         else if (S_ISDIR(mode1))
42                 score = 1000;
43         else if (S_ISLNK(mode1))
44                 score = 500;
45         else
46                 score = 250;
47         return score;
48 }
49
50 static void *fill_tree_desc_strict(struct tree_desc *desc,
51                                    const unsigned char *hash)
52 {
53         void *buffer;
54         enum object_type type;
55         unsigned long size;
56
57         buffer = read_sha1_file(hash, &type, &size);
58         if (!buffer)
59                 die("unable to read tree (%s)", sha1_to_hex(hash));
60         if (type != OBJ_TREE)
61                 die("%s is not a tree", sha1_to_hex(hash));
62         init_tree_desc(desc, buffer, size);
63         return buffer;
64 }
65
66 static int base_name_entries_compare(const struct name_entry *a,
67                                      const struct name_entry *b)
68 {
69         return base_name_compare(a->path, tree_entry_len(a), a->mode,
70                                  b->path, tree_entry_len(b), b->mode);
71 }
72
73 /*
74  * Inspect two trees, and give a score that tells how similar they are.
75  */
76 static int score_trees(const unsigned char *hash1, const unsigned char *hash2)
77 {
78         struct tree_desc one;
79         struct tree_desc two;
80         void *one_buf = fill_tree_desc_strict(&one, hash1);
81         void *two_buf = fill_tree_desc_strict(&two, hash2);
82         int score = 0;
83
84         for (;;) {
85                 struct name_entry e1, e2;
86                 int got_entry_from_one = tree_entry(&one, &e1);
87                 int got_entry_from_two = tree_entry(&two, &e2);
88                 int cmp;
89
90                 if (got_entry_from_one && got_entry_from_two)
91                         cmp = base_name_entries_compare(&e1, &e2);
92                 else if (got_entry_from_one)
93                         /* two lacks this entry */
94                         cmp = -1;
95                 else if (got_entry_from_two)
96                         /* two has more entries */
97                         cmp = 1;
98                 else
99                         break;
100
101                 if (cmp < 0)
102                         /* path1 does not appear in two */
103                         score += score_missing(e1.mode, e1.path);
104                 else if (cmp > 0)
105                         /* path2 does not appear in one */
106                         score += score_missing(e2.mode, e2.path);
107                 else if (hashcmp(e1.sha1, e2.sha1))
108                         /* they are different */
109                         score += score_differs(e1.mode, e2.mode, e1.path);
110                 else
111                         /* same subtree or blob */
112                         score += score_matches(e1.mode, e2.mode, e1.path);
113         }
114         free(one_buf);
115         free(two_buf);
116         return score;
117 }
118
119 /*
120  * Match one itself and its subtrees with two and pick the best match.
121  */
122 static void match_trees(const unsigned char *hash1,
123                         const unsigned char *hash2,
124                         int *best_score,
125                         char **best_match,
126                         const char *base,
127                         int recurse_limit)
128 {
129         struct tree_desc one;
130         void *one_buf = fill_tree_desc_strict(&one, hash1);
131
132         while (one.size) {
133                 const char *path;
134                 const unsigned char *elem;
135                 unsigned mode;
136                 int score;
137
138                 elem = tree_entry_extract(&one, &path, &mode);
139                 if (!S_ISDIR(mode))
140                         goto next;
141                 score = score_trees(elem, hash2);
142                 if (*best_score < score) {
143                         char *newpath;
144                         newpath = xmalloc(strlen(base) + strlen(path) + 1);
145                         sprintf(newpath, "%s%s", base, path);
146                         free(*best_match);
147                         *best_match = newpath;
148                         *best_score = score;
149                 }
150                 if (recurse_limit) {
151                         char *newbase;
152                         newbase = xmalloc(strlen(base) + strlen(path) + 2);
153                         sprintf(newbase, "%s%s/", base, path);
154                         match_trees(elem, hash2, best_score, best_match,
155                                     newbase, recurse_limit - 1);
156                         free(newbase);
157                 }
158
159         next:
160                 update_tree_entry(&one);
161         }
162         free(one_buf);
163 }
164
165 /*
166  * A tree "hash1" has a subdirectory at "prefix".  Come up with a
167  * tree object by replacing it with another tree "hash2".
168  */
169 static int splice_tree(const unsigned char *hash1,
170                        const char *prefix,
171                        const unsigned char *hash2,
172                        unsigned char *result)
173 {
174         char *subpath;
175         int toplen;
176         char *buf;
177         unsigned long sz;
178         struct tree_desc desc;
179         unsigned char *rewrite_here;
180         const unsigned char *rewrite_with;
181         unsigned char subtree[20];
182         enum object_type type;
183         int status;
184
185         subpath = strchrnul(prefix, '/');
186         toplen = subpath - prefix;
187         if (*subpath)
188                 subpath++;
189
190         buf = read_sha1_file(hash1, &type, &sz);
191         if (!buf)
192                 die("cannot read tree %s", sha1_to_hex(hash1));
193         init_tree_desc(&desc, buf, sz);
194
195         rewrite_here = NULL;
196         while (desc.size) {
197                 const char *name;
198                 unsigned mode;
199                 const unsigned char *sha1;
200
201                 sha1 = tree_entry_extract(&desc, &name, &mode);
202                 if (strlen(name) == toplen &&
203                     !memcmp(name, prefix, toplen)) {
204                         if (!S_ISDIR(mode))
205                                 die("entry %s in tree %s is not a tree",
206                                     name, sha1_to_hex(hash1));
207                         rewrite_here = (unsigned char *) sha1;
208                         break;
209                 }
210                 update_tree_entry(&desc);
211         }
212         if (!rewrite_here)
213                 die("entry %.*s not found in tree %s",
214                     toplen, prefix, sha1_to_hex(hash1));
215         if (*subpath) {
216                 status = splice_tree(rewrite_here, subpath, hash2, subtree);
217                 if (status)
218                         return status;
219                 rewrite_with = subtree;
220         }
221         else
222                 rewrite_with = hash2;
223         hashcpy(rewrite_here, rewrite_with);
224         status = write_sha1_file(buf, sz, tree_type, result);
225         free(buf);
226         return status;
227 }
228
229 /*
230  * We are trying to come up with a merge between one and two that
231  * results in a tree shape similar to one.  The tree two might
232  * correspond to a subtree of one, in which case it needs to be
233  * shifted down by prefixing otherwise empty directories.  On the
234  * other hand, it could cover tree one and we might need to pick a
235  * subtree of it.
236  */
237 void shift_tree(const unsigned char *hash1,
238                 const unsigned char *hash2,
239                 unsigned char *shifted,
240                 int depth_limit)
241 {
242         char *add_prefix;
243         char *del_prefix;
244         int add_score, del_score;
245
246         /*
247          * NEEDSWORK: this limits the recursion depth to hardcoded
248          * value '2' to avoid excessive overhead.
249          */
250         if (!depth_limit)
251                 depth_limit = 2;
252
253         add_score = del_score = score_trees(hash1, hash2);
254         add_prefix = xcalloc(1, 1);
255         del_prefix = xcalloc(1, 1);
256
257         /*
258          * See if one's subtree resembles two; if so we need to prefix
259          * two with a few fake trees to match the prefix.
260          */
261         match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit);
262
263         /*
264          * See if two's subtree resembles one; if so we need to
265          * pick only subtree of two.
266          */
267         match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit);
268
269         /* Assume we do not have to do any shifting */
270         hashcpy(shifted, hash2);
271
272         if (add_score < del_score) {
273                 /* We need to pick a subtree of two */
274                 unsigned mode;
275
276                 if (!*del_prefix)
277                         return;
278
279                 if (get_tree_entry(hash2, del_prefix, shifted, &mode))
280                         die("cannot find path %s in tree %s",
281                             del_prefix, sha1_to_hex(hash2));
282                 return;
283         }
284
285         if (!*add_prefix)
286                 return;
287
288         splice_tree(hash1, add_prefix, hash2, shifted);
289 }
290
291 /*
292  * The user says the trees will be shifted by this much.
293  * Unfortunately we cannot fundamentally tell which one to
294  * be prefixed, as recursive merge can work in either direction.
295  */
296 void shift_tree_by(const unsigned char *hash1,
297                    const unsigned char *hash2,
298                    unsigned char *shifted,
299                    const char *shift_prefix)
300 {
301         unsigned char sub1[20], sub2[20];
302         unsigned mode1, mode2;
303         unsigned candidate = 0;
304
305         /* Can hash2 be a tree at shift_prefix in tree hash1? */
306         if (!get_tree_entry(hash1, shift_prefix, sub1, &mode1) &&
307             S_ISDIR(mode1))
308                 candidate |= 1;
309
310         /* Can hash1 be a tree at shift_prefix in tree hash2? */
311         if (!get_tree_entry(hash2, shift_prefix, sub2, &mode2) &&
312             S_ISDIR(mode2))
313                 candidate |= 2;
314
315         if (candidate == 3) {
316                 /* Both are plausible -- we need to evaluate the score */
317                 int best_score = score_trees(hash1, hash2);
318                 int score;
319
320                 candidate = 0;
321                 score = score_trees(sub1, hash2);
322                 if (score > best_score) {
323                         candidate = 1;
324                         best_score = score;
325                 }
326                 score = score_trees(sub2, hash1);
327                 if (score > best_score)
328                         candidate = 2;
329         }
330
331         if (!candidate) {
332                 /* Neither is plausible -- do not shift */
333                 hashcpy(shifted, hash2);
334                 return;
335         }
336
337         if (candidate == 1)
338                 /*
339                  * shift tree2 down by adding shift_prefix above it
340                  * to match tree1.
341                  */
342                 splice_tree(hash1, shift_prefix, hash2, shifted);
343         else
344                 /*
345                  * shift tree2 up by removing shift_prefix from it
346                  * to match tree1.
347                  */
348                 hashcpy(shifted, sub2);
349 }