debugmergestate: make templated
Our IntelliJ team wants to be able to read the merge state in order to
help the user resolve merge conflicts. They had so far been reading
file contents from p1() and p2() and their merge base. That is not
ideal for several reasons (merge base is not necessarily the "graft
base", renames are not handled, commands like `hg update -m` is not
handled). It will get especially bad as of my D7827. This patch makes
the output s a templated. I haven't bothered to make it complete
(e.g. merge driver states are not handled), but it's probably good
enough as a start.
I've done a web search for "debugmergestate" and I can't find any
indication that any tools currently rely on its output. If it turns
out that we get bug reports for it once this is released, I won't
object to backing this patch out on the stable branch (and then
perhaps replace it by a separate command, or put it behind a new
flag).
The changes in test-backout.t are interesting, in particular this:
```
- other path: foo (node not stored in v1 format)
+ other path: (node foo)
```
I wonder if that means that we actually read v1 format
incorrectly. That seems to be an old format that was switched away
from in 2014, so it doesn't matter now anyway.
Differential Revision: https://phab.mercurial-scm.org/D8120
/*
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 <mpm@selenic.com>
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));
}