update comment references to sha1_object_info()
[git] / match-trees.c
1 #include "cache.h"
2 #include "tree.h"
3 #include "tree-walk.h"
4 #include "object-store.h"
5
6 static int score_missing(unsigned mode, const char *path)
7 {
8         int score;
9
10         if (S_ISDIR(mode))
11                 score = -1000;
12         else if (S_ISLNK(mode))
13                 score = -500;
14         else
15                 score = -50;
16         return score;
17 }
18
19 static int score_differs(unsigned mode1, unsigned mode2, const char *path)
20 {
21         int score;
22
23         if (S_ISDIR(mode1) != S_ISDIR(mode2))
24                 score = -100;
25         else if (S_ISLNK(mode1) != S_ISLNK(mode2))
26                 score = -50;
27         else
28                 score = -5;
29         return score;
30 }
31
32 static int score_matches(unsigned mode1, unsigned mode2, const char *path)
33 {
34         int score;
35
36         /* Heh, we found SHA-1 collisions between different kind of objects */
37         if (S_ISDIR(mode1) != S_ISDIR(mode2))
38                 score = -100;
39         else if (S_ISLNK(mode1) != S_ISLNK(mode2))
40                 score = -50;
41
42         else if (S_ISDIR(mode1))
43                 score = 1000;
44         else if (S_ISLNK(mode1))
45                 score = 500;
46         else
47                 score = 250;
48         return score;
49 }
50
51 static void *fill_tree_desc_strict(struct tree_desc *desc,
52                                    const struct object_id *hash)
53 {
54         void *buffer;
55         enum object_type type;
56         unsigned long size;
57
58         buffer = read_object_file(hash, &type, &size);
59         if (!buffer)
60                 die("unable to read tree (%s)", oid_to_hex(hash));
61         if (type != OBJ_TREE)
62                 die("%s is not a tree", oid_to_hex(hash));
63         init_tree_desc(desc, buffer, size);
64         return buffer;
65 }
66
67 static int base_name_entries_compare(const struct name_entry *a,
68                                      const struct name_entry *b)
69 {
70         return base_name_compare(a->path, tree_entry_len(a), a->mode,
71                                  b->path, tree_entry_len(b), b->mode);
72 }
73
74 /*
75  * Inspect two trees, and give a score that tells how similar they are.
76  */
77 static int score_trees(const struct object_id *hash1, const struct object_id *hash2)
78 {
79         struct tree_desc one;
80         struct tree_desc two;
81         void *one_buf = fill_tree_desc_strict(&one, hash1);
82         void *two_buf = fill_tree_desc_strict(&two, hash2);
83         int score = 0;
84
85         for (;;) {
86                 int cmp;
87
88                 if (one.size && two.size)
89                         cmp = base_name_entries_compare(&one.entry, &two.entry);
90                 else if (one.size)
91                         /* two lacks this entry */
92                         cmp = -1;
93                 else if (two.size)
94                         /* two has more entries */
95                         cmp = 1;
96                 else
97                         break;
98
99                 if (cmp < 0) {
100                         /* path1 does not appear in two */
101                         score += score_missing(one.entry.mode, one.entry.path);
102                         update_tree_entry(&one);
103                 } else if (cmp > 0) {
104                         /* path2 does not appear in one */
105                         score += score_missing(two.entry.mode, two.entry.path);
106                         update_tree_entry(&two);
107                 } else {
108                         /* path appears in both */
109                         if (!oideq(one.entry.oid, two.entry.oid)) {
110                                 /* they are different */
111                                 score += score_differs(one.entry.mode,
112                                                        two.entry.mode,
113                                                        one.entry.path);
114                         } else {
115                                 /* same subtree or blob */
116                                 score += score_matches(one.entry.mode,
117                                                        two.entry.mode,
118                                                        one.entry.path);
119                         }
120                         update_tree_entry(&one);
121                         update_tree_entry(&two);
122                 }
123         }
124         free(one_buf);
125         free(two_buf);
126         return score;
127 }
128
129 /*
130  * Match one itself and its subtrees with two and pick the best match.
131  */
132 static void match_trees(const struct object_id *hash1,
133                         const struct object_id *hash2,
134                         int *best_score,
135                         char **best_match,
136                         const char *base,
137                         int recurse_limit)
138 {
139         struct tree_desc one;
140         void *one_buf = fill_tree_desc_strict(&one, hash1);
141
142         while (one.size) {
143                 const char *path;
144                 const struct object_id *elem;
145                 unsigned mode;
146                 int score;
147
148                 elem = tree_entry_extract(&one, &path, &mode);
149                 if (!S_ISDIR(mode))
150                         goto next;
151                 score = score_trees(elem, hash2);
152                 if (*best_score < score) {
153                         free(*best_match);
154                         *best_match = xstrfmt("%s%s", base, path);
155                         *best_score = score;
156                 }
157                 if (recurse_limit) {
158                         char *newbase = xstrfmt("%s%s/", base, path);
159                         match_trees(elem, hash2, best_score, best_match,
160                                     newbase, recurse_limit - 1);
161                         free(newbase);
162                 }
163
164         next:
165                 update_tree_entry(&one);
166         }
167         free(one_buf);
168 }
169
170 /*
171  * A tree "oid1" has a subdirectory at "prefix".  Come up with a tree object by
172  * replacing it with another tree "oid2".
173  */
174 static int splice_tree(const struct object_id *oid1, const char *prefix,
175                        const struct object_id *oid2, struct object_id *result)
176 {
177         char *subpath;
178         int toplen;
179         char *buf;
180         unsigned long sz;
181         struct tree_desc desc;
182         struct object_id *rewrite_here;
183         const struct object_id *rewrite_with;
184         struct object_id subtree;
185         enum object_type type;
186         int status;
187
188         subpath = strchrnul(prefix, '/');
189         toplen = subpath - prefix;
190         if (*subpath)
191                 subpath++;
192
193         buf = read_object_file(oid1, &type, &sz);
194         if (!buf)
195                 die("cannot read tree %s", oid_to_hex(oid1));
196         init_tree_desc(&desc, buf, sz);
197
198         rewrite_here = NULL;
199         while (desc.size) {
200                 const char *name;
201                 unsigned mode;
202                 const struct object_id *oid;
203
204                 oid = tree_entry_extract(&desc, &name, &mode);
205                 if (strlen(name) == toplen &&
206                     !memcmp(name, prefix, toplen)) {
207                         if (!S_ISDIR(mode))
208                                 die("entry %s in tree %s is not a tree", name,
209                                     oid_to_hex(oid1));
210                         rewrite_here = (struct object_id *)oid;
211                         break;
212                 }
213                 update_tree_entry(&desc);
214         }
215         if (!rewrite_here)
216                 die("entry %.*s not found in tree %s", toplen, prefix,
217                     oid_to_hex(oid1));
218         if (*subpath) {
219                 status = splice_tree(rewrite_here, subpath, oid2, &subtree);
220                 if (status)
221                         return status;
222                 rewrite_with = &subtree;
223         } else {
224                 rewrite_with = oid2;
225         }
226         oidcpy(rewrite_here, rewrite_with);
227         status = write_object_file(buf, sz, tree_type, result);
228         free(buf);
229         return status;
230 }
231
232 /*
233  * We are trying to come up with a merge between one and two that
234  * results in a tree shape similar to one.  The tree two might
235  * correspond to a subtree of one, in which case it needs to be
236  * shifted down by prefixing otherwise empty directories.  On the
237  * other hand, it could cover tree one and we might need to pick a
238  * subtree of it.
239  */
240 void shift_tree(const struct object_id *hash1,
241                 const struct object_id *hash2,
242                 struct object_id *shifted,
243                 int depth_limit)
244 {
245         char *add_prefix;
246         char *del_prefix;
247         int add_score, del_score;
248
249         /*
250          * NEEDSWORK: this limits the recursion depth to hardcoded
251          * value '2' to avoid excessive overhead.
252          */
253         if (!depth_limit)
254                 depth_limit = 2;
255
256         add_score = del_score = score_trees(hash1, hash2);
257         add_prefix = xcalloc(1, 1);
258         del_prefix = xcalloc(1, 1);
259
260         /*
261          * See if one's subtree resembles two; if so we need to prefix
262          * two with a few fake trees to match the prefix.
263          */
264         match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit);
265
266         /*
267          * See if two's subtree resembles one; if so we need to
268          * pick only subtree of two.
269          */
270         match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit);
271
272         /* Assume we do not have to do any shifting */
273         oidcpy(shifted, hash2);
274
275         if (add_score < del_score) {
276                 /* We need to pick a subtree of two */
277                 unsigned mode;
278
279                 if (!*del_prefix)
280                         return;
281
282                 if (get_tree_entry(hash2, del_prefix, shifted, &mode))
283                         die("cannot find path %s in tree %s",
284                             del_prefix, oid_to_hex(hash2));
285                 return;
286         }
287
288         if (!*add_prefix)
289                 return;
290
291         splice_tree(hash1, add_prefix, hash2, shifted);
292 }
293
294 /*
295  * The user says the trees will be shifted by this much.
296  * Unfortunately we cannot fundamentally tell which one to
297  * be prefixed, as recursive merge can work in either direction.
298  */
299 void shift_tree_by(const struct object_id *hash1,
300                    const struct object_id *hash2,
301                    struct object_id *shifted,
302                    const char *shift_prefix)
303 {
304         struct object_id sub1, sub2;
305         unsigned mode1, mode2;
306         unsigned candidate = 0;
307
308         /* Can hash2 be a tree at shift_prefix in tree hash1? */
309         if (!get_tree_entry(hash1, shift_prefix, &sub1, &mode1) &&
310             S_ISDIR(mode1))
311                 candidate |= 1;
312
313         /* Can hash1 be a tree at shift_prefix in tree hash2? */
314         if (!get_tree_entry(hash2, shift_prefix, &sub2, &mode2) &&
315             S_ISDIR(mode2))
316                 candidate |= 2;
317
318         if (candidate == 3) {
319                 /* Both are plausible -- we need to evaluate the score */
320                 int best_score = score_trees(hash1, hash2);
321                 int score;
322
323                 candidate = 0;
324                 score = score_trees(&sub1, hash2);
325                 if (score > best_score) {
326                         candidate = 1;
327                         best_score = score;
328                 }
329                 score = score_trees(&sub2, hash1);
330                 if (score > best_score)
331                         candidate = 2;
332         }
333
334         if (!candidate) {
335                 /* Neither is plausible -- do not shift */
336                 oidcpy(shifted, hash2);
337                 return;
338         }
339
340         if (candidate == 1)
341                 /*
342                  * shift tree2 down by adding shift_prefix above it
343                  * to match tree1.
344                  */
345                 splice_tree(hash1, shift_prefix, hash2, shifted);
346         else
347                 /*
348                  * shift tree2 up by removing shift_prefix from it
349                  * to match tree1.
350                  */
351                 oidcpy(shifted, &sub2);
352 }