summaryrefslogtreecommitdiff
path: root/rerere.c
blob: d4929a66ae9e6ba63a87c4663968b466bc4a4bfb (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
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
#include "cache.h"
#include "lockfile.h"
#include "string-list.h"
#include "rerere.h"
#include "xdiff-interface.h"
#include "dir.h"
#include "resolve-undo.h"
#include "ll-merge.h"
#include "attr.h"
#include "pathspec.h"
#include "sha1-lookup.h"
 
#define RESOLVED 0
#define PUNTED 1
#define THREE_STAGED 2
void *RERERE_RESOLVED = &RERERE_RESOLVED;
 
/* if rerere_enabled == -1, fall back to detection of .git/rr-cache */
static int rerere_enabled = -1;
 
/* automatically update cleanly resolved paths to the index */
static int rerere_autoupdate;
 
static char *merge_rr_path;
 
static int rerere_dir_nr;
static int rerere_dir_alloc;
 
#define RR_HAS_POSTIMAGE 1
#define RR_HAS_PREIMAGE 2
static struct rerere_dir {
	unsigned char sha1[20];
	int status_alloc, status_nr;
	unsigned char *status;
} **rerere_dir;
 
static void free_rerere_dirs(void)
{
	int i;
	for (i = 0; i < rerere_dir_nr; i++) {
		free(rerere_dir[i]->status);
		free(rerere_dir[i]);
	}
	free(rerere_dir);
	rerere_dir_nr = rerere_dir_alloc = 0;
	rerere_dir = NULL;
}
 
static void free_rerere_id(struct string_list_item *item)
{
	free(item->util);
}
 
static const char *rerere_id_hex(const struct rerere_id *id)
{
	return sha1_to_hex(id->collection->sha1);
}
 
static void fit_variant(struct rerere_dir *rr_dir, int variant)
{
	variant++;
	ALLOC_GROW(rr_dir->status, variant, rr_dir->status_alloc);
	if (rr_dir->status_nr < variant) {
		memset(rr_dir->status + rr_dir->status_nr,
		       '\0', variant - rr_dir->status_nr);
		rr_dir->status_nr = variant;
	}
}
 
static void assign_variant(struct rerere_id *id)
{
	int variant;
	struct rerere_dir *rr_dir = id->collection;
 
	variant = id->variant;
	if (variant < 0) {
		for (variant = 0; variant < rr_dir->status_nr; variant++)
			if (!rr_dir->status[variant])
				break;
	}
	fit_variant(rr_dir, variant);
	id->variant = variant;
}
 
const char *rerere_path(const struct rerere_id *id, const char *file)
{
	if (!file)
		return git_path("rr-cache/%s", rerere_id_hex(id));
 
	if (id->variant <= 0)
		return git_path("rr-cache/%s/%s", rerere_id_hex(id), file);
 
	return git_path("rr-cache/%s/%s.%d",
			rerere_id_hex(id), file, id->variant);
}
 
static int is_rr_file(const char *name, const char *filename, int *variant)
{
	const char *suffix;
	char *ep;
 
	if (!strcmp(name, filename)) {
		*variant = 0;
		return 1;
	}
	if (!skip_prefix(name, filename, &suffix) || *suffix != '.')
		return 0;
 
	errno = 0;
	*variant = strtol(suffix + 1, &ep, 10);
	if (errno || *ep)
		return 0;
	return 1;
}
 
static void scan_rerere_dir(struct rerere_dir *rr_dir)
{
	struct dirent *de;
	DIR *dir = opendir(git_path("rr-cache/%s", sha1_to_hex(rr_dir->sha1)));
 
	if (!dir)
		return;
	while ((de = readdir(dir)) != NULL) {
		int variant;
 
		if (is_rr_file(de->d_name, "postimage", &variant)) {
			fit_variant(rr_dir, variant);
			rr_dir->status[variant] |= RR_HAS_POSTIMAGE;
		} else if (is_rr_file(de->d_name, "preimage", &variant)) {
			fit_variant(rr_dir, variant);
			rr_dir->status[variant] |= RR_HAS_PREIMAGE;
		}
	}
	closedir(dir);
}
 
static const unsigned char *rerere_dir_sha1(size_t i, void *table)
{
	struct rerere_dir **rr_dir = table;
	return rr_dir[i]->sha1;
}
 
static struct rerere_dir *find_rerere_dir(const char *hex)
{
	unsigned char sha1[20];
	struct rerere_dir *rr_dir;
	int pos;
 
	if (get_sha1_hex(hex, sha1))
		return NULL; /* BUG */
	pos = sha1_pos(sha1, rerere_dir, rerere_dir_nr, rerere_dir_sha1);
	if (pos < 0) {
		rr_dir = xmalloc(sizeof(*rr_dir));
		hashcpy(rr_dir->sha1, sha1);
		rr_dir->status = NULL;
		rr_dir->status_nr = 0;
		rr_dir->status_alloc = 0;
		pos = -1 - pos;
 
		/* Make sure the array is big enough ... */
		ALLOC_GROW(rerere_dir, rerere_dir_nr + 1, rerere_dir_alloc);
		/* ... and add it in. */
		rerere_dir_nr++;
		memmove(rerere_dir + pos + 1, rerere_dir + pos,
			(rerere_dir_nr - pos - 1) * sizeof(*rerere_dir));
		rerere_dir[pos] = rr_dir;
		scan_rerere_dir(rr_dir);
	}
	return rerere_dir[pos];
}
 
static int has_rerere_resolution(const struct rerere_id *id)
{
	const int both = RR_HAS_POSTIMAGE|RR_HAS_PREIMAGE;
	int variant = id->variant;
 
	if (variant < 0)
		return 0;
	return ((id->collection->status[variant] & both) == both);
}
 
static struct rerere_id *new_rerere_id_hex(char *hex)
{
	struct rerere_id *id = xmalloc(sizeof(*id));
	id->collection = find_rerere_dir(hex);
	id->variant = -1; /* not known yet */
	return id;
}
 
static struct rerere_id *new_rerere_id(unsigned char *sha1)
{
	return new_rerere_id_hex(sha1_to_hex(sha1));
}
 
/*
 * $GIT_DIR/MERGE_RR file is a collection of records, each of which is
 * "conflict ID", a HT and pathname, terminated with a NUL, and is
 * used to keep track of the set of paths that "rerere" may need to
 * work on (i.e. what is left by the previous invocation of "git
 * rerere" during the current conflict resolution session).
 */
static void read_rr(struct string_list *rr)
{
	struct strbuf buf = STRBUF_INIT;
	FILE *in = fopen(merge_rr_path, "r");
 
	if (!in)
		return;
	while (!strbuf_getwholeline(&buf, in, '\0')) {
		char *path;
		unsigned char sha1[20];
		struct rerere_id *id;
		int variant;
 
		/* There has to be the hash, tab, path and then NUL */
		if (buf.len < 42 || get_sha1_hex(buf.buf, sha1))
			die("corrupt MERGE_RR");
 
		if (buf.buf[40] != '.') {
			variant = 0;
			path = buf.buf + 40;
		} else {
			errno = 0;
			variant = strtol(buf.buf + 41, &path, 10);
			if (errno)
				die("corrupt MERGE_RR");
		}
		if (*(path++) != '\t')
			die("corrupt MERGE_RR");
		buf.buf[40] = '\0';
		id = new_rerere_id_hex(buf.buf);
		id->variant = variant;
		string_list_insert(rr, path)->util = id;
	}
	strbuf_release(&buf);
	fclose(in);
}
 
static struct lock_file write_lock;
 
static int write_rr(struct string_list *rr, int out_fd)
{
	int i;
	for (i = 0; i < rr->nr; i++) {
		struct strbuf buf = STRBUF_INIT;
		struct rerere_id *id;
 
		assert(rr->items[i].util != RERERE_RESOLVED);
 
		id = rr->items[i].util;
		if (!id)
			continue;
		assert(id->variant >= 0);
		if (0 < id->variant)
			strbuf_addf(&buf, "%s.%d\t%s%c",
				    rerere_id_hex(id), id->variant,
				    rr->items[i].string, 0);
		else
			strbuf_addf(&buf, "%s\t%s%c",
				    rerere_id_hex(id),
				    rr->items[i].string, 0);
 
		if (write_in_full(out_fd, buf.buf, buf.len) != buf.len)
			die("unable to write rerere record");
 
		strbuf_release(&buf);
	}
	if (commit_lock_file(&write_lock) != 0)
		die("unable to write rerere record");
	return 0;
}
 
/*
 * "rerere" interacts with conflicted file contents using this I/O
 * abstraction.  It reads a conflicted contents from one place via
 * "getline()" method, and optionally can write it out after
 * normalizing the conflicted hunks to the "output".  Subclasses of
 * rerere_io embed this structure at the beginning of their own
 * rerere_io object.
 */
struct rerere_io {
	int (*getline)(struct strbuf *, struct rerere_io *);
	FILE *output;
	int wrerror;
	/* some more stuff */
};
 
static void ferr_write(const void *p, size_t count, FILE *fp, int *err)
{
	if (!count || *err)
		return;
	if (fwrite(p, count, 1, fp) != 1)
		*err = errno;
}
 
static inline void ferr_puts(const char *s, FILE *fp, int *err)
{
	ferr_write(s, strlen(s), fp, err);
}
 
static void rerere_io_putstr(const char *str, struct rerere_io *io)
{
	if (io->output)
		ferr_puts(str, io->output, &io->wrerror);
}
 
/*
 * Write a conflict marker to io->output (if defined).
 */
static void rerere_io_putconflict(int ch, int size, struct rerere_io *io)
{
	char buf[64];
 
	while (size) {
		if (size <= sizeof(buf) - 2) {
			memset(buf, ch, size);
			buf[size] = '\n';
			buf[size + 1] = '\0';
			size = 0;
		} else {
			int sz = sizeof(buf) - 1;
 
			/*
			 * Make sure we will not write everything out
			 * in this round by leaving at least 1 byte
			 * for the next round, giving the next round
			 * a chance to add the terminating LF.  Yuck.
			 */
			if (size <= sz)
				sz -= (sz - size) + 1;
			memset(buf, ch, sz);
			buf[sz] = '\0';
			size -= sz;
		}
		rerere_io_putstr(buf, io);
	}
}
 
static void rerere_io_putmem(const char *mem, size_t sz, struct rerere_io *io)
{
	if (io->output)
		ferr_write(mem, sz, io->output, &io->wrerror);
}
 
/*
 * Subclass of rerere_io that reads from an on-disk file
 */
struct rerere_io_file {
	struct rerere_io io;
	FILE *input;
};
 
/*
 * ... and its getline() method implementation
 */
static int rerere_file_getline(struct strbuf *sb, struct rerere_io *io_)
{
	struct rerere_io_file *io = (struct rerere_io_file *)io_;
	return strbuf_getwholeline(sb, io->input, '\n');
}
 
/*
 * Require the exact number of conflict marker letters, no more, no
 * less, followed by SP or any whitespace
 * (including LF).
 */
static int is_cmarker(char *buf, int marker_char, int marker_size)
{
	int want_sp;
 
	/*
	 * The beginning of our version and the end of their version
	 * always are labeled like "<<<<< ours" or ">>>>> theirs",
	 * hence we set want_sp for them.  Note that the version from
	 * the common ancestor in diff3-style output is not always
	 * labelled (e.g. "||||| common" is often seen but "|||||"
	 * alone is also valid), so we do not set want_sp.
	 */
	want_sp = (marker_char == '<') || (marker_char == '>');
 
	while (marker_size--)
		if (*buf++ != marker_char)
			return 0;
	if (want_sp && *buf != ' ')
		return 0;
	return isspace(*buf);
}
 
/*
 * Read contents a file with conflicts, normalize the conflicts
 * by (1) discarding the common ancestor version in diff3-style,
 * (2) reordering our side and their side so that whichever sorts
 * alphabetically earlier comes before the other one, while
 * computing the "conflict ID", which is just an SHA-1 hash of
 * one side of the conflict, NUL, the other side of the conflict,
 * and NUL concatenated together.
 *
 * Return the number of conflict hunks found.
 *
 * NEEDSWORK: the logic and theory of operation behind this conflict
 * normalization may deserve to be documented somewhere, perhaps in
 * Documentation/technical/rerere.txt.
 */
static int handle_path(unsigned char *sha1, struct rerere_io *io, int marker_size)
{
	git_SHA_CTX ctx;
	int hunk_no = 0;
	enum {
		RR_CONTEXT = 0, RR_SIDE_1, RR_SIDE_2, RR_ORIGINAL
	} hunk = RR_CONTEXT;
	struct strbuf one = STRBUF_INIT, two = STRBUF_INIT;
	struct strbuf buf = STRBUF_INIT;
 
	if (sha1)
		git_SHA1_Init(&ctx);
 
	while (!io->getline(&buf, io)) {
		if (is_cmarker(buf.buf, '<', marker_size)) {
			if (hunk != RR_CONTEXT)
				goto bad;
			hunk = RR_SIDE_1;
		} else if (is_cmarker(buf.buf, '|', marker_size)) {
			if (hunk != RR_SIDE_1)
				goto bad;
			hunk = RR_ORIGINAL;
		} else if (is_cmarker(buf.buf, '=', marker_size)) {
			if (hunk != RR_SIDE_1 && hunk != RR_ORIGINAL)
				goto bad;
			hunk = RR_SIDE_2;
		} else if (is_cmarker(buf.buf, '>', marker_size)) {
			if (hunk != RR_SIDE_2)
				goto bad;
			if (strbuf_cmp(&one, &two) > 0)
				strbuf_swap(&one, &two);
			hunk_no++;
			hunk = RR_CONTEXT;
			rerere_io_putconflict('<', marker_size, io);
			rerere_io_putmem(one.buf, one.len, io);
			rerere_io_putconflict('=', marker_size, io);
			rerere_io_putmem(two.buf, two.len, io);
			rerere_io_putconflict('>', marker_size, io);
			if (sha1) {
				git_SHA1_Update(&ctx, one.buf ? one.buf : "",
					    one.len + 1);
				git_SHA1_Update(&ctx, two.buf ? two.buf : "",
					    two.len + 1);
			}
			strbuf_reset(&one);
			strbuf_reset(&two);
		} else if (hunk == RR_SIDE_1)
			strbuf_addbuf(&one, &buf);
		else if (hunk == RR_ORIGINAL)
			; /* discard */
		else if (hunk == RR_SIDE_2)
			strbuf_addbuf(&two, &buf);
		else
			rerere_io_putstr(buf.buf, io);
		continue;
	bad:
		hunk = 99; /* force error exit */
		break;
	}
	strbuf_release(&one);
	strbuf_release(&two);
	strbuf_release(&buf);
 
	if (sha1)
		git_SHA1_Final(sha1, &ctx);
	if (hunk != RR_CONTEXT)
		return -1;
	return hunk_no;
}
 
/*
 * Scan the path for conflicts, do the "handle_path()" thing above, and
 * return the number of conflict hunks found.
 */
static int handle_file(const char *path, unsigned char *sha1, const char *output)
{
	int hunk_no = 0;
	struct rerere_io_file io;
	int marker_size = ll_merge_marker_size(path);
 
	memset(&io, 0, sizeof(io));
	io.io.getline = rerere_file_getline;
	io.input = fopen(path, "r");
	io.io.wrerror = 0;
	if (!io.input)
		return error("Could not open %s", path);
 
	if (output) {
		io.io.output = fopen(output, "w");
		if (!io.io.output) {
			fclose(io.input);
			return error("Could not write %s", output);
		}
	}
 
	hunk_no = handle_path(sha1, (struct rerere_io *)&io, marker_size);
 
	fclose(io.input);
	if (io.io.wrerror)
		error("There were errors while writing %s (%s)",
		      path, strerror(io.io.wrerror));
	if (io.io.output && fclose(io.io.output))
		io.io.wrerror = error("Failed to flush %s: %s",
				      path, strerror(errno));
 
	if (hunk_no < 0) {
		if (output)
			unlink_or_warn(output);
		return error("Could not parse conflict hunks in %s", path);
	}
	if (io.io.wrerror)
		return -1;
	return hunk_no;
}
 
/*
 * Look at a cache entry at "i" and see if it is not conflicting,
 * conflicting and we are willing to handle, or conflicting and
 * we are unable to handle, and return the determination in *type.
 * Return the cache index to be looked at next, by skipping the
 * stages we have already looked at in this invocation of this
 * function.
 */
static int check_one_conflict(int i, int *type)
{
	const struct cache_entry *e = active_cache[i];
 
	if (!ce_stage(e)) {
		*type = RESOLVED;
		return i + 1;
	}
 
	*type = PUNTED;
	while (ce_stage(active_cache[i]) == 1)
		i++;
 
	/* Only handle regular files with both stages #2 and #3 */
	if (i + 1 < active_nr) {
		const struct cache_entry *e2 = active_cache[i];
		const struct cache_entry *e3 = active_cache[i + 1];
		if (ce_stage(e2) == 2 &&
		    ce_stage(e3) == 3 &&
		    ce_same_name(e, e3) &&
		    S_ISREG(e2->ce_mode) &&
		    S_ISREG(e3->ce_mode))
			*type = THREE_STAGED;
	}
 
	/* Skip the entries with the same name */
	while (i < active_nr && ce_same_name(e, active_cache[i]))
		i++;
	return i;
}
 
/*
 * Scan the index and find paths that have conflicts that rerere can
 * handle, i.e. the ones that has both stages #2 and #3.
 *
 * NEEDSWORK: we do not record or replay a previous "resolve by
 * deletion" for a delete-modify conflict, as that is inherently risky
 * without knowing what modification is being discarded.  The only
 * safe case, i.e. both side doing the deletion and modification that
 * are identical to the previous round, might want to be handled,
 * though.
 */
static int find_conflict(struct string_list *conflict)
{
	int i;
	if (read_cache() < 0)
		return error("Could not read index");
 
	for (i = 0; i < active_nr;) {
		int conflict_type;
		const struct cache_entry *e = active_cache[i];
		i = check_one_conflict(i, &conflict_type);
		if (conflict_type == THREE_STAGED)
			string_list_insert(conflict, (const char *)e->name);
	}
	return 0;
}
 
/*
 * The merge_rr list is meant to hold outstanding conflicted paths
 * that rerere could handle.  Abuse the list by adding other types of
 * entries to allow the caller to show "rerere remaining".
 *
 * - Conflicted paths that rerere does not handle are added
 * - Conflicted paths that have been resolved are marked as such
 *   by storing RERERE_RESOLVED to .util field (where conflict ID
 *   is expected to be stored).
 *
 * Do *not* write MERGE_RR file out after calling this function.
 *
 * NEEDSWORK: we may want to fix the caller that implements "rerere
 * remaining" to do this without abusing merge_rr.
 */
int rerere_remaining(struct string_list *merge_rr)
{
	int i;
	if (read_cache() < 0)
		return error("Could not read index");
 
	for (i = 0; i < active_nr;) {
		int conflict_type;
		const struct cache_entry *e = active_cache[i];
		i = check_one_conflict(i, &conflict_type);
		if (conflict_type == PUNTED)
			string_list_insert(merge_rr, (const char *)e->name);
		else if (conflict_type == RESOLVED) {
			struct string_list_item *it;
			it = string_list_lookup(merge_rr, (const char *)e->name);
			if (it != NULL) {
				free_rerere_id(it);
				it->util = RERERE_RESOLVED;
			}
		}
	}
	return 0;
}
 
/*
 * Try using the given conflict resolution "ID" to see
 * if that recorded conflict resolves cleanly what we
 * got in the "cur".
 */
static int try_merge(const struct rerere_id *id, const char *path,
		     mmfile_t *cur, mmbuffer_t *result)
{
	int ret;
	mmfile_t base = {NULL, 0}, other = {NULL, 0};
 
	if (read_mmfile(&base, rerere_path(id, "preimage")) ||
	    read_mmfile(&other, rerere_path(id, "postimage")))
		ret = 1;
	else
		/*
		 * A three-way merge. Note that this honors user-customizable
		 * low-level merge driver settings.
		 */
		ret = ll_merge(result, path, &base, NULL, cur, "", &other, "", NULL);
 
	free(base.ptr);
	free(other.ptr);
 
	return ret;
}
 
/*
 * Find the conflict identified by "id"; the change between its
 * "preimage" (i.e. a previous contents with conflict markers) and its
 * "postimage" (i.e. the corresponding contents with conflicts
 * resolved) may apply cleanly to the contents stored in "path", i.e.
 * the conflict this time around.
 *
 * Returns 0 for successful replay of recorded resolution, or non-zero
 * for failure.
 */
static int merge(const struct rerere_id *id, const char *path)
{
	FILE *f;
	int ret;
	mmfile_t cur = {NULL, 0};
	mmbuffer_t result = {NULL, 0};
 
	/*
	 * Normalize the conflicts in path and write it out to
	 * "thisimage" temporary file.
	 */
	if ((handle_file(path, NULL, rerere_path(id, "thisimage")) < 0) ||
	    read_mmfile(&cur, rerere_path(id, "thisimage"))) {
		ret = 1;
		goto out;
	}
 
	ret = try_merge(id, path, &cur, &result);
	if (ret)
		goto out;
 
	/*
	 * A successful replay of recorded resolution.
	 * Mark that "postimage" was used to help gc.
	 */
	if (utime(rerere_path(id, "postimage"), NULL) < 0)
		warning("failed utime() on %s: %s",
			rerere_path(id, "postimage"),
			strerror(errno));
 
	/* Update "path" with the resolution */
	f = fopen(path, "w");
	if (!f)
		return error("Could not open %s: %s", path,
			     strerror(errno));
	if (fwrite(result.ptr, result.size, 1, f) != 1)
		error("Could not write %s: %s", path, strerror(errno));
	if (fclose(f))
		return error("Writing %s failed: %s", path,
			     strerror(errno));
 
out:
	free(cur.ptr);
	free(result.ptr);
 
	return ret;
}
 
static struct lock_file index_lock;
 
static void update_paths(struct string_list *update)
{
	int i;
 
	hold_locked_index(&index_lock, 1);
 
	for (i = 0; i < update->nr; i++) {
		struct string_list_item *item = &update->items[i];
		if (add_file_to_cache(item->string, 0))
			exit(128);
		fprintf(stderr, "Staged '%s' using previous resolution.\n",
			item->string);
	}
 
	if (active_cache_changed) {
		if (write_locked_index(&the_index, &index_lock, COMMIT_LOCK))
			die("Unable to write new index file");
	} else
		rollback_lock_file(&index_lock);
}
 
static void remove_variant(struct rerere_id *id)
{
	unlink_or_warn(rerere_path(id, "postimage"));
	unlink_or_warn(rerere_path(id, "preimage"));
	id->collection->status[id->variant] = 0;
}
 
/*
 * The path indicated by rr_item may still have conflict for which we
 * have a recorded resolution, in which case replay it and optionally
 * update it.  Or it may have been resolved by the user and we may
 * only have the preimage for that conflict, in which case the result
 * needs to be recorded as a resolution in a postimage file.
 */
static void do_rerere_one_path(struct string_list_item *rr_item,
			       struct string_list *update)
{
	const char *path = rr_item->string;
	struct rerere_id *id = rr_item->util;
	struct rerere_dir *rr_dir = id->collection;
	int variant;
 
	variant = id->variant;
 
	/* Has the user resolved it already? */
	if (variant >= 0) {
		if (!handle_file(path, NULL, NULL)) {
			copy_file(rerere_path(id, "postimage"), path, 0666);
			id->collection->status[variant] |= RR_HAS_POSTIMAGE;
			fprintf(stderr, "Recorded resolution for '%s'.\n", path);
			free_rerere_id(rr_item);
			rr_item->util = NULL;
			return;
		}
		/*
		 * There may be other variants that can cleanly
		 * replay.  Try them and update the variant number for
		 * this one.
		 */
	}
 
	/* Does any existing resolution apply cleanly? */
	for (variant = 0; variant < rr_dir->status_nr; variant++) {
		const int both = RR_HAS_PREIMAGE | RR_HAS_POSTIMAGE;
		struct rerere_id vid = *id;
 
		if ((rr_dir->status[variant] & both) != both)
			continue;
 
		vid.variant = variant;
		if (merge(&vid, path))
			continue; /* failed to replay */
 
		/*
		 * If there already is a different variant that applies
		 * cleanly, there is no point maintaining our own variant.
		 */
		if (0 <= id->variant && id->variant != variant)
			remove_variant(id);
 
		if (rerere_autoupdate)
			string_list_insert(update, path);
		else
			fprintf(stderr,
				"Resolved '%s' using previous resolution.\n",
				path);
		free_rerere_id(rr_item);
		rr_item->util = NULL;
		return;
	}
 
	/* None of the existing one applies; we need a new variant */
	assign_variant(id);
 
	variant = id->variant;
	handle_file(path, NULL, rerere_path(id, "preimage"));
	if (id->collection->status[variant] & RR_HAS_POSTIMAGE) {
		const char *path = rerere_path(id, "postimage");
		if (unlink(path))
			die_errno("cannot unlink stray '%s'", path);
		id->collection->status[variant] &= ~RR_HAS_POSTIMAGE;
	}
	id->collection->status[variant] |= RR_HAS_PREIMAGE;
	fprintf(stderr, "Recorded preimage for '%s'\n", path);
}
 
static int do_plain_rerere(struct string_list *rr, int fd)
{
	struct string_list conflict = STRING_LIST_INIT_DUP;
	struct string_list update = STRING_LIST_INIT_DUP;
	int i;
 
	find_conflict(&conflict);
 
	/*
	 * MERGE_RR records paths with conflicts immediately after
	 * merge failed.  Some of the conflicted paths might have been
	 * hand resolved in the working tree since then, but the
	 * initial run would catch all and register their preimages.
	 */
	for (i = 0; i < conflict.nr; i++) {
		struct rerere_id *id;
		unsigned char sha1[20];
		const char *path = conflict.items[i].string;
		int ret;
 
		if (string_list_has_string(rr, path))
			continue;
 
		/*
		 * Ask handle_file() to scan and assign a
		 * conflict ID.  No need to write anything out
		 * yet.
		 */
		ret = handle_file(path, sha1, NULL);
		if (ret < 1)
			continue;
 
		id = new_rerere_id(sha1);
		string_list_insert(rr, path)->util = id;
 
		/* Ensure that the directory exists. */
		mkdir_in_gitdir(rerere_path(id, NULL));
	}
 
	for (i = 0; i < rr->nr; i++)
		do_rerere_one_path(&rr->items[i], &update);
 
	if (update.nr)
		update_paths(&update);
 
	return write_rr(rr, fd);
}
 
static void git_rerere_config(void)
{
	git_config_get_bool("rerere.enabled", &rerere_enabled);
	git_config_get_bool("rerere.autoupdate", &rerere_autoupdate);
	git_config(git_default_config, NULL);
}
 
static int is_rerere_enabled(void)
{
	const char *rr_cache;
	int rr_cache_exists;
 
	if (!rerere_enabled)
		return 0;
 
	rr_cache = git_path("rr-cache");
	rr_cache_exists = is_directory(rr_cache);
	if (rerere_enabled < 0)
		return rr_cache_exists;
 
	if (!rr_cache_exists && mkdir_in_gitdir(rr_cache))
		die("Could not create directory %s", rr_cache);
	return 1;
}
 
int setup_rerere(struct string_list *merge_rr, int flags)
{
	int fd;
 
	git_rerere_config();
	if (!is_rerere_enabled())
		return -1;
 
	if (flags & (RERERE_AUTOUPDATE|RERERE_NOAUTOUPDATE))
		rerere_autoupdate = !!(flags & RERERE_AUTOUPDATE);
	merge_rr_path = git_pathdup("MERGE_RR");
	fd = hold_lock_file_for_update(&write_lock, merge_rr_path,
				       LOCK_DIE_ON_ERROR);
	read_rr(merge_rr);
	return fd;
}
 
/*
 * The main entry point that is called internally from codepaths that
 * perform mergy operations, possibly leaving conflicted index entries
 * and working tree files.
 */
int rerere(int flags)
{
	struct string_list merge_rr = STRING_LIST_INIT_DUP;
	int fd, status;
 
	fd = setup_rerere(&merge_rr, flags);
	if (fd < 0)
		return 0;
	status = do_plain_rerere(&merge_rr, fd);
	free_rerere_dirs();
	return status;
}
 
/*
 * Subclass of rerere_io that reads from an in-core buffer that is a
 * strbuf
 */
struct rerere_io_mem {
	struct rerere_io io;
	struct strbuf input;
};
 
/*
 * ... and its getline() method implementation
 */
static int rerere_mem_getline(struct strbuf *sb, struct rerere_io *io_)
{
	struct rerere_io_mem *io = (struct rerere_io_mem *)io_;
	char *ep;
	size_t len;
 
	strbuf_release(sb);
	if (!io->input.len)
		return -1;
	ep = memchr(io->input.buf, '\n', io->input.len);
	if (!ep)
		ep = io->input.buf + io->input.len;
	else if (*ep == '\n')
		ep++;
	len = ep - io->input.buf;
	strbuf_add(sb, io->input.buf, len);
	strbuf_remove(&io->input, 0, len);
	return 0;
}
 
static int handle_cache(const char *path, unsigned char *sha1, const char *output)
{
	mmfile_t mmfile[3] = {{NULL}};
	mmbuffer_t result = {NULL, 0};
	const struct cache_entry *ce;
	int pos, len, i, hunk_no;
	struct rerere_io_mem io;
	int marker_size = ll_merge_marker_size(path);
 
	/*
	 * Reproduce the conflicted merge in-core
	 */
	len = strlen(path);
	pos = cache_name_pos(path, len);
	if (0 <= pos)
		return -1;
	pos = -pos - 1;
 
	while (pos < active_nr) {
		enum object_type type;
		unsigned long size;
 
		ce = active_cache[pos++];
		if (ce_namelen(ce) != len || memcmp(ce->name, path, len))
			break;
		i = ce_stage(ce) - 1;
		if (!mmfile[i].ptr) {
			mmfile[i].ptr = read_sha1_file(ce->sha1, &type, &size);
			mmfile[i].size = size;
		}
	}
	for (i = 0; i < 3; i++)
		if (!mmfile[i].ptr && !mmfile[i].size)
			mmfile[i].ptr = xstrdup("");
 
	/*
	 * NEEDSWORK: handle conflicts from merges with
	 * merge.renormalize set, too?
	 */
	ll_merge(&result, path, &mmfile[0], NULL,
		 &mmfile[1], "ours",
		 &mmfile[2], "theirs", NULL);
	for (i = 0; i < 3; i++)
		free(mmfile[i].ptr);
 
	memset(&io, 0, sizeof(io));
	io.io.getline = rerere_mem_getline;
	if (output)
		io.io.output = fopen(output, "w");
	else
		io.io.output = NULL;
	strbuf_init(&io.input, 0);
	strbuf_attach(&io.input, result.ptr, result.size, result.size);
 
	/*
	 * Grab the conflict ID and optionally write the original
	 * contents with conflict markers out.
	 */
	hunk_no = handle_path(sha1, (struct rerere_io *)&io, marker_size);
	strbuf_release(&io.input);
	if (io.io.output)
		fclose(io.io.output);
	return hunk_no;
}
 
static int rerere_forget_one_path(const char *path, struct string_list *rr)
{
	const char *filename;
	struct rerere_id *id;
	unsigned char sha1[20];
	int ret;
	struct string_list_item *item;
 
	/*
	 * Recreate the original conflict from the stages in the
	 * index and compute the conflict ID
	 */
	ret = handle_cache(path, sha1, NULL);
	if (ret < 1)
		return error("Could not parse conflict hunks in '%s'", path);
 
	/* Nuke the recorded resolution for the conflict */
	id = new_rerere_id(sha1);
 
	for (id->variant = 0;
	     id->variant < id->collection->status_nr;
	     id->variant++) {
		mmfile_t cur = { NULL, 0 };
		mmbuffer_t result = {NULL, 0};
		int cleanly_resolved;
 
		if (!has_rerere_resolution(id))
			continue;
 
		handle_cache(path, sha1, rerere_path(id, "thisimage"));
		if (read_mmfile(&cur, rerere_path(id, "thisimage"))) {
			free(cur.ptr);
			error("Failed to update conflicted state in '%s'", path);
			goto fail_exit;
		}
		cleanly_resolved = !try_merge(id, path, &cur, &result);
		free(result.ptr);
		free(cur.ptr);
		if (cleanly_resolved)
			break;
	}
 
	if (id->collection->status_nr <= id->variant) {
		error("no remembered resolution for '%s'", path);
		goto fail_exit;
	}
 
	filename = rerere_path(id, "postimage");
	if (unlink(filename)) {
		if (errno == ENOENT)
			error("no remembered resolution for %s", path);
		else
			error("cannot unlink %s: %s", filename, strerror(errno));
		goto fail_exit;
	}
 
	/*
	 * Update the preimage so that the user can resolve the
	 * conflict in the working tree, run us again to record
	 * the postimage.
	 */
	handle_cache(path, sha1, rerere_path(id, "preimage"));
	fprintf(stderr, "Updated preimage for '%s'\n", path);
 
	/*
	 * And remember that we can record resolution for this
	 * conflict when the user is done.
	 */
	item = string_list_insert(rr, path);
	free_rerere_id(item);
	item->util = id;
	fprintf(stderr, "Forgot resolution for %s\n", path);
	return 0;
 
fail_exit:
	free(id);
	return -1;
}
 
int rerere_forget(struct pathspec *pathspec)
{
	int i, fd;
	struct string_list conflict = STRING_LIST_INIT_DUP;
	struct string_list merge_rr = STRING_LIST_INIT_DUP;
 
	if (read_cache() < 0)
		return error("Could not read index");
 
	fd = setup_rerere(&merge_rr, RERERE_NOAUTOUPDATE);
 
	/*
	 * The paths may have been resolved (incorrectly);
	 * recover the original conflicted state and then
	 * find the conflicted paths.
	 */
	unmerge_cache(pathspec);
	find_conflict(&conflict);
	for (i = 0; i < conflict.nr; i++) {
		struct string_list_item *it = &conflict.items[i];
		if (!match_pathspec(pathspec, it->string,
				    strlen(it->string), 0, NULL, 0))
			continue;
		rerere_forget_one_path(it->string, &merge_rr);
	}
	return write_rr(&merge_rr, fd);
}
 
/*
 * Garbage collection support
 */
 
static time_t rerere_created_at(struct rerere_id *id)
{
	struct stat st;
 
	return stat(rerere_path(id, "preimage"), &st) ? (time_t) 0 : st.st_mtime;
}
 
static time_t rerere_last_used_at(struct rerere_id *id)
{
	struct stat st;
 
	return stat(rerere_path(id, "postimage"), &st) ? (time_t) 0 : st.st_mtime;
}
 
/*
 * Remove the recorded resolution for a given conflict ID
 */
static void unlink_rr_item(struct rerere_id *id)
{
	unlink_or_warn(rerere_path(id, "thisimage"));
	remove_variant(id);
	id->collection->status[id->variant] = 0;
}
 
static void prune_one(struct rerere_id *id, time_t now,
		      int cutoff_resolve, int cutoff_noresolve)
{
	time_t then;
	int cutoff;
 
	then = rerere_last_used_at(id);
	if (then)
		cutoff = cutoff_resolve;
	else {
		then = rerere_created_at(id);
		if (!then)
			return;
		cutoff = cutoff_noresolve;
	}
	if (then < now - cutoff * 86400)
		unlink_rr_item(id);
}
 
void rerere_gc(struct string_list *rr)
{
	struct string_list to_remove = STRING_LIST_INIT_DUP;
	DIR *dir;
	struct dirent *e;
	int i;
	time_t now = time(NULL);
	int cutoff_noresolve = 15;
	int cutoff_resolve = 60;
 
	git_config_get_int("gc.rerereresolved", &cutoff_resolve);
	git_config_get_int("gc.rerereunresolved", &cutoff_noresolve);
	git_config(git_default_config, NULL);
	dir = opendir(git_path("rr-cache"));
	if (!dir)
		die_errno("unable to open rr-cache directory");
	/* Collect stale conflict IDs ... */
	while ((e = readdir(dir))) {
		struct rerere_dir *rr_dir;
		struct rerere_id id;
		int now_empty;
 
		if (is_dot_or_dotdot(e->d_name))
			continue;
		rr_dir = find_rerere_dir(e->d_name);
		if (!rr_dir)
			continue; /* or should we remove e->d_name? */
 
		now_empty = 1;
		for (id.variant = 0, id.collection = rr_dir;
		     id.variant < id.collection->status_nr;
		     id.variant++) {
			prune_one(&id, now, cutoff_resolve, cutoff_noresolve);
			if (id.collection->status[id.variant])
				now_empty = 0;
		}
		if (now_empty)
			string_list_append(&to_remove, e->d_name);
	}
	closedir(dir);
 
	/* ... and then remove the empty directories */
	for (i = 0; i < to_remove.nr; i++)
		rmdir(git_path("rr-cache/%s", to_remove.items[i].string));
	string_list_clear(&to_remove, 0);
}
 
/*
 * During a conflict resolution, after "rerere" recorded the
 * preimages, abandon them if the user did not resolve them or
 * record their resolutions.  And drop $GIT_DIR/MERGE_RR.
 *
 * NEEDSWORK: shouldn't we be calling this from "reset --hard"?
 */
void rerere_clear(struct string_list *merge_rr)
{
	int i;
 
	for (i = 0; i < merge_rr->nr; i++) {
		struct rerere_id *id = merge_rr->items[i].util;
		if (!has_rerere_resolution(id)) {
			unlink_rr_item(id);
			rmdir(rerere_path(id, NULL));
		}
	}
	unlink_or_warn(git_path("MERGE_RR"));
}