view mercurial/mpatch.c @ 42050:03f6480bfdda

unshelve: disable unshelve during merge (issue5123)

As stated in the issue5123, unshelve can destroy the second parent of
the context when tried to unshelve with an uncommitted merge. This
patch makes unshelve to abort when called with an uncommitted merge.

See how shelve.mergefiles works. Commit structure looks like this:
```
... -> pctx -> tmpwctx -> shelvectx
                  /
                 /
        second
        merge parent

pctx = parent before merging working context(first merge parent)
tmpwctx = commited working directory after merge(with two parents)
shelvectx = shelved context
```
shelve.mergefiles first updates to pctx then it reverts shelvectx to pctx with:

```
cmdutil.revert(ui, repo, shelvectx, repo.dirstate.parents(),
                       *pathtofiles(repo, files),
                       **{'no_backup': True})
```

Reverting tmpwctx files that were merged from second parent to pctx makes them
added because they are not in pctx.

Changing this revert operation is crucial to restore parents after unshelve.
This is a complicated issue as this is not fixing a regression. Thus, for the
time being, unshelve during an uncommitted merge can be aborted.

(Details taken from http://mercurial.808500.n3.nabble.com/PATCH-V3-shelve-restore-parents-after-unshelve-issue5123-tt4036858.html#a4037408)

Differential Revision: https://phab.mercurial-scm.org/D6169

/*
 mpatch.c - efficient binary patching for Mercurial

 This implements a patch algorithm that's O(m + nlog n) where m is the
 size of the output and n is the number of patches.

 Given a list of binary patches, it unpacks each into a hunk list,
 then combines the hunk lists with a treewise recursion to form a
 single hunk list. This hunk list is then applied to the original
 text.

 The text (or binary) fragments are copied directly from their source
 Python objects into a preallocated output string to avoid the
 allocation of intermediate Python objects. Working memory is about 2x
 the total number of hunks.

 Copyright 2005, 2006 Matt Mackall <[e-mail]>

 This software may be used and distributed according to the terms
 of the GNU General Public License, incorporated herein by reference.
*/

#include <limits.h>
#include <stdlib.h>
#include <string.h>

#include "bitmanipulation.h"
#include "compat.h"
#include "mpatch.h"

/* VC9 doesn't include bool and lacks stdbool.h based on cext/util.h */
#if defined(_MSC_VER) || __STDC_VERSION__ < 199901L
#define true 1
#define false 0
typedef unsigned char bool;
#else
#include <stdbool.h>
#endif

static struct mpatch_flist *lalloc(ssize_t size)
{
	struct mpatch_flist *a = NULL;

	if (size < 1) {
		size = 1;
	}

	a = (struct mpatch_flist *)malloc(sizeof(struct mpatch_flist));
	if (a) {
		a->base = (struct mpatch_frag *)malloc(
		    sizeof(struct mpatch_frag) * size);
		if (a->base) {
			a->head = a->tail = a->base;
			return a;
		}
		free(a);
	}
	return NULL;
}

void mpatch_lfree(struct mpatch_flist *a)
{
	if (a) {
		free(a->base);
		free(a);
	}
}

static ssize_t lsize(struct mpatch_flist *a)
{
	return a->tail - a->head;
}

/* add helper to add src and *dest iff it won't overflow */
static inline bool safeadd(int src, int *dest)
{
	if ((src > 0) == (*dest > 0)) {
		if (*dest > 0) {
			if (src > (INT_MAX - *dest)) {
				return false;
			}
		} else {
			if (src < (INT_MIN - *dest)) {
				return false;
			}
		}
	}
	*dest += src;
	return true;
}

/* subtract src from dest and store result in dest */
static inline bool safesub(int src, int *dest)
{
	if (((src > 0) && (*dest < INT_MIN + src)) ||
	    ((src < 0) && (*dest > INT_MAX + src))) {
		return false;
	}
	*dest -= src;
	return true;
}

/* move hunks in source that are less cut to dest, compensating
   for changes in offset. the last hunk may be split if necessary.
*/
static int gather(struct mpatch_flist *dest, struct mpatch_flist *src, int cut,
                  int offset)
{
	struct mpatch_frag *d = dest->tail, *s = src->head;
	int postend, c, l;

	while (s != src->tail) {
		int soffset = s->start;
		if (!safeadd(offset, &soffset)) {
			break; /* add would overflow, oh well */
		}
		if (soffset >= cut) {
			break; /* we've gone far enough */
		}

		postend = offset;
		if (!safeadd(s->start, &postend) ||
		    !safeadd(s->len, &postend)) {
			break;
		}
		if (postend <= cut) {
			/* save this hunk */
			int tmp = s->start;
			if (!safesub(s->end, &tmp)) {
				break;
			}
			if (!safeadd(s->len, &tmp)) {
				break;
			}
			if (!safeadd(tmp, &offset)) {
				break; /* add would overflow, oh well */
			}
			*d++ = *s++;
		} else {
			/* break up this hunk */
			c = cut;
			if (!safesub(offset, &c)) {
				break;
			}
			if (s->end < c) {
				c = s->end;
			}
			l = cut - offset - s->start;
			if (s->len < l) {
				l = s->len;
			}

			offset += s->start + l - c;

			d->start = s->start;
			d->end = c;
			d->len = l;
			d->data = s->data;
			d++;
			s->start = c;
			s->len = s->len - l;
			s->data = s->data + l;

			break;
		}
	}

	dest->tail = d;
	src->head = s;
	return offset;
}

/* like gather, but with no output list */
static int discard(struct mpatch_flist *src, int cut, int offset)
{
	struct mpatch_frag *s = src->head;
	int postend, c, l;

	while (s != src->tail) {
		int cmpcut = s->start;
		if (!safeadd(offset, &cmpcut)) {
			break;
		}
		if (cmpcut >= cut) {
			break;
		}

		postend = offset;
		if (!safeadd(s->start, &postend)) {
			break;
		}
		if (!safeadd(s->len, &postend)) {
			break;
		}
		if (postend <= cut) {
			/* do the subtraction first to avoid UB integer overflow
			 */
			int tmp = s->start;
			if (!safesub(s->end, &tmp)) {
				break;
			}
			if (!safeadd(s->len, &tmp)) {
				break;
			}
			if (!safeadd(tmp, &offset)) {
				break;
			}
			s++;
		} else {
			c = cut;
			if (!safesub(offset, &c)) {
				break;
			}
			if (s->end < c) {
				c = s->end;
			}
			l = cut - offset - s->start;
			if (s->len < l) {
				l = s->len;
			}

			offset += s->start + l - c;
			s->start = c;
			s->len = s->len - l;
			s->data = s->data + l;

			break;
		}
	}

	src->head = s;
	return offset;
}

/* combine hunk lists a and b, while adjusting b for offset changes in a/
   this deletes a and b and returns the resultant list. */
static struct mpatch_flist *combine(struct mpatch_flist *a,
                                    struct mpatch_flist *b)
{
	struct mpatch_flist *c = NULL;
	struct mpatch_frag *bh, *ct;
	int offset = 0, post;

	if (a && b) {
		c = lalloc((lsize(a) + lsize(b)) * 2);
	}

	if (c) {

		for (bh = b->head; bh != b->tail; bh++) {
			/* save old hunks */
			offset = gather(c, a, bh->start, offset);

			/* discard replaced hunks */
			post = discard(a, bh->end, offset);

			/* insert new hunk */
			ct = c->tail;
			ct->start = bh->start;
			ct->end = bh->end;
			if (!safesub(offset, &(ct->start)) ||
			    !safesub(post, &(ct->end))) {
				/* It was already possible to exit
				 * this function with a return value
				 * of NULL before the safesub()s were
				 * added, so this should be fine. */
				mpatch_lfree(c);
				c = NULL;
				goto done;
			}
			ct->len = bh->len;
			ct->data = bh->data;
			c->tail++;
			offset = post;
		}

		/* hold on to tail from a */
		memcpy(c->tail, a->head, sizeof(struct mpatch_frag) * lsize(a));
		c->tail += lsize(a);
	}
done:
	mpatch_lfree(a);
	mpatch_lfree(b);
	return c;
}

/* decode a binary patch into a hunk list */
int mpatch_decode(const char *bin, ssize_t len, struct mpatch_flist **res)
{
	struct mpatch_flist *l;
	struct mpatch_frag *lt;
	int pos = 0;

	/* assume worst case size, we won't have many of these lists */
	l = lalloc(len / 12 + 1);
	if (!l) {
		return MPATCH_ERR_NO_MEM;
	}

	lt = l->tail;

	/* We check against len-11 to ensure we have at least 12 bytes
	   left in the patch so we can read our three be32s out of it. */
	while (pos >= 0 && pos < (len - 11)) {
		lt->start = getbe32(bin + pos);
		lt->end = getbe32(bin + pos + 4);
		lt->len = getbe32(bin + pos + 8);
		if (lt->start < 0 || lt->start > lt->end || lt->len < 0) {
			break; /* sanity check */
		}
		if (!safeadd(12, &pos)) {
			break;
		}
		lt->data = bin + pos;
		if (!safeadd(lt->len, &pos)) {
			break;
		}
		lt++;
	}

	if (pos != len) {
		mpatch_lfree(l);
		return MPATCH_ERR_CANNOT_BE_DECODED;
	}

	l->tail = lt;
	*res = l;
	return 0;
}

/* calculate the size of resultant text */
ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l)
{
	ssize_t outlen = 0, last = 0;
	struct mpatch_frag *f = l->head;

	while (f != l->tail) {
		if (f->start < last || f->end > len) {
			return MPATCH_ERR_INVALID_PATCH;
		}
		outlen += f->start - last;
		last = f->end;
		outlen += f->len;
		f++;
	}

	outlen += len - last;
	return outlen;
}

int mpatch_apply(char *buf, const char *orig, ssize_t len,
                 struct mpatch_flist *l)
{
	struct mpatch_frag *f = l->head;
	int last = 0;
	char *p = buf;

	while (f != l->tail) {
		if (f->start < last || f->start > len || f->end > len ||
		    last < 0) {
			return MPATCH_ERR_INVALID_PATCH;
		}
		memcpy(p, orig + last, f->start - last);
		p += f->start - last;
		memcpy(p, f->data, f->len);
		last = f->end;
		p += f->len;
		f++;
	}
	if (last < 0) {
		return MPATCH_ERR_INVALID_PATCH;
	}
	memcpy(p, orig + last, len - last);
	return 0;
}

/* recursively generate a patch of all bins between start and end */
struct mpatch_flist *
mpatch_fold(void *bins, struct mpatch_flist *(*get_next_item)(void *, ssize_t),
            ssize_t start, ssize_t end)
{
	ssize_t len;

	if (start + 1 == end) {
		/* trivial case, output a decoded list */
		return get_next_item(bins, start);
	}

	/* divide and conquer, memory management is elsewhere */
	len = (end - start) / 2;
	return combine(mpatch_fold(bins, get_next_item, start, start + len),
	               mpatch_fold(bins, get_next_item, start + len, end));
}