1 #include "cache.h"
2 #include "tree.h"
3 #include "tree-walk.h"
4 #include "object-store.h"
5
score_missing(unsigned mode)6 static int score_missing(unsigned mode)
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
score_differs(unsigned mode1,unsigned mode2)19 static int score_differs(unsigned mode1, unsigned mode2)
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
score_matches(unsigned mode1,unsigned mode2)32 static int score_matches(unsigned mode1, unsigned mode2)
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
fill_tree_desc_strict(struct tree_desc * desc,const struct object_id * hash)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
base_name_entries_compare(const struct name_entry * a,const struct name_entry * b)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 */
score_trees(const struct object_id * hash1,const struct object_id * hash2)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);
102 update_tree_entry(&one);
103 } else if (cmp > 0) {
104 /* path2 does not appear in one */
105 score += score_missing(two.entry.mode);
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 } else {
114 /* same subtree or blob */
115 score += score_matches(one.entry.mode,
116 two.entry.mode);
117 }
118 update_tree_entry(&one);
119 update_tree_entry(&two);
120 }
121 }
122 free(one_buf);
123 free(two_buf);
124 return score;
125 }
126
127 /*
128 * Match one itself and its subtrees with two and pick the best match.
129 */
match_trees(const struct object_id * hash1,const struct object_id * hash2,int * best_score,char ** best_match,const char * base,int recurse_limit)130 static void match_trees(const struct object_id *hash1,
131 const struct object_id *hash2,
132 int *best_score,
133 char **best_match,
134 const char *base,
135 int recurse_limit)
136 {
137 struct tree_desc one;
138 void *one_buf = fill_tree_desc_strict(&one, hash1);
139
140 while (one.size) {
141 const char *path;
142 const struct object_id *elem;
143 unsigned short mode;
144 int score;
145
146 elem = tree_entry_extract(&one, &path, &mode);
147 if (!S_ISDIR(mode))
148 goto next;
149 score = score_trees(elem, hash2);
150 if (*best_score < score) {
151 free(*best_match);
152 *best_match = xstrfmt("%s%s", base, path);
153 *best_score = score;
154 }
155 if (recurse_limit) {
156 char *newbase = xstrfmt("%s%s/", base, path);
157 match_trees(elem, hash2, best_score, best_match,
158 newbase, recurse_limit - 1);
159 free(newbase);
160 }
161
162 next:
163 update_tree_entry(&one);
164 }
165 free(one_buf);
166 }
167
168 /*
169 * A tree "oid1" has a subdirectory at "prefix". Come up with a tree object by
170 * replacing it with another tree "oid2".
171 */
splice_tree(const struct object_id * oid1,const char * prefix,const struct object_id * oid2,struct object_id * result)172 static int splice_tree(const struct object_id *oid1, const char *prefix,
173 const struct object_id *oid2, struct object_id *result)
174 {
175 char *subpath;
176 int toplen;
177 char *buf;
178 unsigned long sz;
179 struct tree_desc desc;
180 unsigned char *rewrite_here;
181 const struct object_id *rewrite_with;
182 struct object_id subtree;
183 enum object_type type;
184 int status;
185
186 subpath = strchrnul(prefix, '/');
187 toplen = subpath - prefix;
188 if (*subpath)
189 subpath++;
190
191 buf = read_object_file(oid1, &type, &sz);
192 if (!buf)
193 die("cannot read tree %s", oid_to_hex(oid1));
194 init_tree_desc(&desc, buf, sz);
195
196 rewrite_here = NULL;
197 while (desc.size) {
198 const char *name;
199 unsigned short mode;
200
201 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", name,
206 oid_to_hex(oid1));
207
208 /*
209 * We cast here for two reasons:
210 *
211 * - to flip the "char *" (for the path) to "unsigned
212 * char *" (for the hash stored after it)
213 *
214 * - to discard the "const"; this is OK because we
215 * know it points into our non-const "buf"
216 */
217 rewrite_here = (unsigned char *)(desc.entry.path +
218 strlen(desc.entry.path) +
219 1);
220 break;
221 }
222 update_tree_entry(&desc);
223 }
224 if (!rewrite_here)
225 die("entry %.*s not found in tree %s", toplen, prefix,
226 oid_to_hex(oid1));
227 if (*subpath) {
228 struct object_id tree_oid;
229 oidread(&tree_oid, rewrite_here);
230 status = splice_tree(&tree_oid, subpath, oid2, &subtree);
231 if (status)
232 return status;
233 rewrite_with = &subtree;
234 } else {
235 rewrite_with = oid2;
236 }
237 hashcpy(rewrite_here, rewrite_with->hash);
238 status = write_object_file(buf, sz, tree_type, result);
239 free(buf);
240 return status;
241 }
242
243 /*
244 * We are trying to come up with a merge between one and two that
245 * results in a tree shape similar to one. The tree two might
246 * correspond to a subtree of one, in which case it needs to be
247 * shifted down by prefixing otherwise empty directories. On the
248 * other hand, it could cover tree one and we might need to pick a
249 * subtree of it.
250 */
shift_tree(struct repository * r,const struct object_id * hash1,const struct object_id * hash2,struct object_id * shifted,int depth_limit)251 void shift_tree(struct repository *r,
252 const struct object_id *hash1,
253 const struct object_id *hash2,
254 struct object_id *shifted,
255 int depth_limit)
256 {
257 char *add_prefix;
258 char *del_prefix;
259 int add_score, del_score;
260
261 /*
262 * NEEDSWORK: this limits the recursion depth to hardcoded
263 * value '2' to avoid excessive overhead.
264 */
265 if (!depth_limit)
266 depth_limit = 2;
267
268 add_score = del_score = score_trees(hash1, hash2);
269 add_prefix = xcalloc(1, 1);
270 del_prefix = xcalloc(1, 1);
271
272 /*
273 * See if one's subtree resembles two; if so we need to prefix
274 * two with a few fake trees to match the prefix.
275 */
276 match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit);
277
278 /*
279 * See if two's subtree resembles one; if so we need to
280 * pick only subtree of two.
281 */
282 match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit);
283
284 /* Assume we do not have to do any shifting */
285 oidcpy(shifted, hash2);
286
287 if (add_score < del_score) {
288 /* We need to pick a subtree of two */
289 unsigned short mode;
290
291 if (!*del_prefix)
292 return;
293
294 if (get_tree_entry(r, hash2, del_prefix, shifted, &mode))
295 die("cannot find path %s in tree %s",
296 del_prefix, oid_to_hex(hash2));
297 return;
298 }
299
300 if (!*add_prefix)
301 return;
302
303 splice_tree(hash1, add_prefix, hash2, shifted);
304 }
305
306 /*
307 * The user says the trees will be shifted by this much.
308 * Unfortunately we cannot fundamentally tell which one to
309 * be prefixed, as recursive merge can work in either direction.
310 */
shift_tree_by(struct repository * r,const struct object_id * hash1,const struct object_id * hash2,struct object_id * shifted,const char * shift_prefix)311 void shift_tree_by(struct repository *r,
312 const struct object_id *hash1,
313 const struct object_id *hash2,
314 struct object_id *shifted,
315 const char *shift_prefix)
316 {
317 struct object_id sub1, sub2;
318 unsigned short mode1, mode2;
319 unsigned candidate = 0;
320
321 /* Can hash2 be a tree at shift_prefix in tree hash1? */
322 if (!get_tree_entry(r, hash1, shift_prefix, &sub1, &mode1) &&
323 S_ISDIR(mode1))
324 candidate |= 1;
325
326 /* Can hash1 be a tree at shift_prefix in tree hash2? */
327 if (!get_tree_entry(r, hash2, shift_prefix, &sub2, &mode2) &&
328 S_ISDIR(mode2))
329 candidate |= 2;
330
331 if (candidate == 3) {
332 /* Both are plausible -- we need to evaluate the score */
333 int best_score = score_trees(hash1, hash2);
334 int score;
335
336 candidate = 0;
337 score = score_trees(&sub1, hash2);
338 if (score > best_score) {
339 candidate = 1;
340 best_score = score;
341 }
342 score = score_trees(&sub2, hash1);
343 if (score > best_score)
344 candidate = 2;
345 }
346
347 if (!candidate) {
348 /* Neither is plausible -- do not shift */
349 oidcpy(shifted, hash2);
350 return;
351 }
352
353 if (candidate == 1)
354 /*
355 * shift tree2 down by adding shift_prefix above it
356 * to match tree1.
357 */
358 splice_tree(hash1, shift_prefix, hash2, shifted);
359 else
360 /*
361 * shift tree2 up by removing shift_prefix from it
362 * to match tree1.
363 */
364 oidcpy(shifted, &sub2);
365 }
366