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git/xdiff/xmerge.c
Junio C Hamano 73eb40eeaa git-merge-file --ours, --theirs 
Sometimes people want their conflicting merges autoresolved by
favouring upstream changes.  The standard answer they are given is
to run "git diff --name-only | xargs git checkout MERGE_HEAD --" in
such a case.  This is to accept automerge results for the paths that
are fully resolved automatically, while taking their version of the
file in full for paths that have conflicts.

This is problematic on two counts.

One is that this is not exactly what these people want.  It discards
all changes they did on their branch for any paths that conflicted.
They usually want to salvage as much automerge result as possible in
a conflicted file, and want to take the upstream change only in the
conflicted part.

This patch teaches two new modes of operation to the lowest-lever
merge machinery, xdl_merge().  Instead of leaving the conflicted
lines from both sides enclosed in <<<, ===, and >>> markers, the
conflicts are resolved favouring our side or their side of changes.

A larger problem is that this tends to encourage a bad workflow by
allowing people to record such a mixed up half-merged result as a
full commit without auditing.  This commit does not tackle this
issue at all.  In git, we usually give long enough rope to users
with strange wishes as long as the risky features are not enabled by
default, and this is such a risky feature.

Signed-off-by: Avery Pennarun <apenwarr@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2009-11-29 23:11:46 -08:00

591 lines
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/*
* LibXDiff by Davide Libenzi ( File Differential Library )
* Copyright (C) 2003-2006 Davide Libenzi, Johannes E. Schindelin
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* Davide Libenzi <davidel@xmailserver.org>
*
*/
#include "xinclude.h"
typedef struct s_xdmerge {
struct s_xdmerge *next;
/*
* 0 = conflict,
* 1 = no conflict, take first,
* 2 = no conflict, take second.
*/
int mode;
/*
* These point at the respective postimages. E.g. <i1,chg1> is
* how side #1 wants to change the common ancestor; if there is no
* overlap, lines before i1 in the postimage of side #1 appear
* in the merge result as a region touched by neither side.
*/
long i1, i2;
long chg1, chg2;
/*
* These point at the preimage; of course there is just one
* preimage, that is from the shared common ancestor.
*/
long i0;
long chg0;
} xdmerge_t;
static int xdl_append_merge(xdmerge_t **merge, int mode,
long i0, long chg0,
long i1, long chg1,
long i2, long chg2)
{
xdmerge_t *m = *merge;
if (m && (i1 <= m->i1 + m->chg1 || i2 <= m->i2 + m->chg2)) {
if (mode != m->mode)
m->mode = 0;
m->chg0 = i0 + chg0 - m->i0;
m->chg1 = i1 + chg1 - m->i1;
m->chg2 = i2 + chg2 - m->i2;
} else {
m = xdl_malloc(sizeof(xdmerge_t));
if (!m)
return -1;
m->next = NULL;
m->mode = mode;
m->i0 = i0;
m->chg0 = chg0;
m->i1 = i1;
m->chg1 = chg1;
m->i2 = i2;
m->chg2 = chg2;
if (*merge)
(*merge)->next = m;
*merge = m;
}
return 0;
}
static int xdl_cleanup_merge(xdmerge_t *c)
{
int count = 0;
xdmerge_t *next_c;
/* were there conflicts? */
for (; c; c = next_c) {
if (c->mode == 0)
count++;
next_c = c->next;
free(c);
}
return count;
}
static int xdl_merge_cmp_lines(xdfenv_t *xe1, int i1, xdfenv_t *xe2, int i2,
int line_count, long flags)
{
int i;
xrecord_t **rec1 = xe1->xdf2.recs + i1;
xrecord_t **rec2 = xe2->xdf2.recs + i2;
for (i = 0; i < line_count; i++) {
int result = xdl_recmatch(rec1[i]->ptr, rec1[i]->size,
rec2[i]->ptr, rec2[i]->size, flags);
if (!result)
return -1;
}
return 0;
}
static int xdl_recs_copy_0(int use_orig, xdfenv_t *xe, int i, int count, int add_nl, char *dest)
{
xrecord_t **recs;
int size = 0;
recs = (use_orig ? xe->xdf1.recs : xe->xdf2.recs) + i;
if (count < 1)
return 0;
for (i = 0; i < count; size += recs[i++]->size)
if (dest)
memcpy(dest + size, recs[i]->ptr, recs[i]->size);
if (add_nl) {
i = recs[count - 1]->size;
if (i == 0 || recs[count - 1]->ptr[i - 1] != '\n') {
if (dest)
dest[size] = '\n';
size++;
}
}
return size;
}
static int xdl_recs_copy(xdfenv_t *xe, int i, int count, int add_nl, char *dest)
{
return xdl_recs_copy_0(0, xe, i, count, add_nl, dest);
}
static int xdl_orig_copy(xdfenv_t *xe, int i, int count, int add_nl, char *dest)
{
return xdl_recs_copy_0(1, xe, i, count, add_nl, dest);
}
static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
xdfenv_t *xe2, const char *name2,
int size, int i, int style,
xdmerge_t *m, char *dest)
{
const int marker_size = 7;
int marker1_size = (name1 ? strlen(name1) + 1 : 0);
int marker2_size = (name2 ? strlen(name2) + 1 : 0);
int j;
/* Before conflicting part */
size += xdl_recs_copy(xe1, i, m->i1 - i, 0,
dest ? dest + size : NULL);
if (!dest) {
size += marker_size + 1 + marker1_size;
} else {
for (j = 0; j < marker_size; j++)
dest[size++] = '<';
if (marker1_size) {
dest[size] = ' ';
memcpy(dest + size + 1, name1, marker1_size - 1);
size += marker1_size;
}
dest[size++] = '\n';
}
/* Postimage from side #1 */
size += xdl_recs_copy(xe1, m->i1, m->chg1, 1,
dest ? dest + size : NULL);
if (style == XDL_MERGE_DIFF3) {
/* Shared preimage */
if (!dest) {
size += marker_size + 1;
} else {
for (j = 0; j < marker_size; j++)
dest[size++] = '|';
dest[size++] = '\n';
}
size += xdl_orig_copy(xe1, m->i0, m->chg0, 1,
dest ? dest + size : NULL);
}
if (!dest) {
size += marker_size + 1;
} else {
for (j = 0; j < marker_size; j++)
dest[size++] = '=';
dest[size++] = '\n';
}
/* Postimage from side #2 */
size += xdl_recs_copy(xe2, m->i2, m->chg2, 1,
dest ? dest + size : NULL);
if (!dest) {
size += marker_size + 1 + marker2_size;
} else {
for (j = 0; j < marker_size; j++)
dest[size++] = '>';
if (marker2_size) {
dest[size] = ' ';
memcpy(dest + size + 1, name2, marker2_size - 1);
size += marker2_size;
}
dest[size++] = '\n';
}
return size;
}
static int xdl_fill_merge_buffer(xdfenv_t *xe1, const char *name1,
xdfenv_t *xe2, const char *name2,
int favor,
xdmerge_t *m, char *dest, int style)
{
int size, i;
for (size = i = 0; m; m = m->next) {
if (favor && !m->mode)
m->mode = favor;
if (m->mode == 0)
size = fill_conflict_hunk(xe1, name1, xe2, name2,
size, i, style, m, dest);
else if (m->mode == 1)
size += xdl_recs_copy(xe1, i, m->i1 + m->chg1 - i, 0,
dest ? dest + size : NULL);
else if (m->mode == 2)
size += xdl_recs_copy(xe2, m->i2 - m->i1 + i,
m->i1 + m->chg2 - i, 0,
dest ? dest + size : NULL);
else
continue;
i = m->i1 + m->chg1;
}
size += xdl_recs_copy(xe1, i, xe1->xdf2.nrec - i, 0,
dest ? dest + size : NULL);
return size;
}
/*
* Sometimes, changes are not quite identical, but differ in only a few
* lines. Try hard to show only these few lines as conflicting.
*/
static int xdl_refine_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
xpparam_t const *xpp)
{
for (; m; m = m->next) {
mmfile_t t1, t2;
xdfenv_t xe;
xdchange_t *xscr, *x;
int i1 = m->i1, i2 = m->i2;
/* let's handle just the conflicts */
if (m->mode)
continue;
/* no sense refining a conflict when one side is empty */
if (m->chg1 == 0 || m->chg2 == 0)
continue;
/*
* This probably does not work outside git, since
* we have a very simple mmfile structure.
*/
t1.ptr = (char *)xe1->xdf2.recs[m->i1]->ptr;
t1.size = xe1->xdf2.recs[m->i1 + m->chg1 - 1]->ptr
+ xe1->xdf2.recs[m->i1 + m->chg1 - 1]->size - t1.ptr;
t2.ptr = (char *)xe2->xdf2.recs[m->i2]->ptr;
t2.size = xe2->xdf2.recs[m->i2 + m->chg2 - 1]->ptr
+ xe2->xdf2.recs[m->i2 + m->chg2 - 1]->size - t2.ptr;
if (xdl_do_diff(&t1, &t2, xpp, &xe) < 0)
return -1;
if (xdl_change_compact(&xe.xdf1, &xe.xdf2, xpp->flags) < 0 ||
xdl_change_compact(&xe.xdf2, &xe.xdf1, xpp->flags) < 0 ||
xdl_build_script(&xe, &xscr) < 0) {
xdl_free_env(&xe);
return -1;
}
if (!xscr) {
/* If this happens, the changes are identical. */
xdl_free_env(&xe);
m->mode = 4;
continue;
}
x = xscr;
m->i1 = xscr->i1 + i1;
m->chg1 = xscr->chg1;
m->i2 = xscr->i2 + i2;
m->chg2 = xscr->chg2;
while (xscr->next) {
xdmerge_t *m2 = xdl_malloc(sizeof(xdmerge_t));
if (!m2) {
xdl_free_env(&xe);
xdl_free_script(x);
return -1;
}
xscr = xscr->next;
m2->next = m->next;
m->next = m2;
m = m2;
m->mode = 0;
m->i1 = xscr->i1 + i1;
m->chg1 = xscr->chg1;
m->i2 = xscr->i2 + i2;
m->chg2 = xscr->chg2;
}
xdl_free_env(&xe);
xdl_free_script(x);
}
return 0;
}
static int line_contains_alnum(const char *ptr, long size)
{
while (size--)
if (isalnum(*(ptr++)))
return 1;
return 0;
}
static int lines_contain_alnum(xdfenv_t *xe, int i, int chg)
{
for (; chg; chg--, i++)
if (line_contains_alnum(xe->xdf2.recs[i]->ptr,
xe->xdf2.recs[i]->size))
return 1;
return 0;
}
/*
* This function merges m and m->next, marking everything between those hunks
* as conflicting, too.
*/
static void xdl_merge_two_conflicts(xdmerge_t *m)
{
xdmerge_t *next_m = m->next;
m->chg1 = next_m->i1 + next_m->chg1 - m->i1;
m->chg2 = next_m->i2 + next_m->chg2 - m->i2;
m->next = next_m->next;
free(next_m);
}
/*
* If there are less than 3 non-conflicting lines between conflicts,
* it appears simpler -- because it takes up less (or as many) lines --
* if the lines are moved into the conflicts.
*/
static int xdl_simplify_non_conflicts(xdfenv_t *xe1, xdmerge_t *m,
int simplify_if_no_alnum)
{
int result = 0;
if (!m)
return result;
for (;;) {
xdmerge_t *next_m = m->next;
int begin, end;
if (!next_m)
return result;
begin = m->i1 + m->chg1;
end = next_m->i1;
if (m->mode != 0 || next_m->mode != 0 ||
(end - begin > 3 &&
(!simplify_if_no_alnum ||
lines_contain_alnum(xe1, begin, end - begin)))) {
m = next_m;
} else {
result++;
xdl_merge_two_conflicts(m);
}
}
}
/*
* level == 0: mark all overlapping changes as conflict
* level == 1: mark overlapping changes as conflict only if not identical
* level == 2: analyze non-identical changes for minimal conflict set
* level == 3: analyze non-identical changes for minimal conflict set, but
* treat hunks not containing any letter or number as conflicting
*
* returns < 0 on error, == 0 for no conflicts, else number of conflicts
*/
static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1, const char *name1,
xdfenv_t *xe2, xdchange_t *xscr2, const char *name2,
int flags, xpparam_t const *xpp, mmbuffer_t *result) {
xdmerge_t *changes, *c;
int i0, i1, i2, chg0, chg1, chg2;
int level = flags & XDL_MERGE_LEVEL_MASK;
int style = flags & XDL_MERGE_STYLE_MASK;
int favor = XDL_MERGE_FAVOR(flags);
if (style == XDL_MERGE_DIFF3) {
/*
* "diff3 -m" output does not make sense for anything
* more aggressive than XDL_MERGE_EAGER.
*/
if (XDL_MERGE_EAGER < level)
level = XDL_MERGE_EAGER;
}
c = changes = NULL;
while (xscr1 && xscr2) {
if (!changes)
changes = c;
if (xscr1->i1 + xscr1->chg1 < xscr2->i1) {
i0 = xscr1->i1;
i1 = xscr1->i2;
i2 = xscr2->i2 - xscr2->i1 + xscr1->i1;
chg0 = xscr1->chg1;
chg1 = xscr1->chg2;
chg2 = xscr1->chg1;
if (xdl_append_merge(&c, 1,
i0, chg0, i1, chg1, i2, chg2)) {
xdl_cleanup_merge(changes);
return -1;
}
xscr1 = xscr1->next;
continue;
}
if (xscr2->i1 + xscr2->chg1 < xscr1->i1) {
i0 = xscr2->i1;
i1 = xscr1->i2 - xscr1->i1 + xscr2->i1;
i2 = xscr2->i2;
chg0 = xscr2->chg1;
chg1 = xscr2->chg1;
chg2 = xscr2->chg2;
if (xdl_append_merge(&c, 2,
i0, chg0, i1, chg1, i2, chg2)) {
xdl_cleanup_merge(changes);
return -1;
}
xscr2 = xscr2->next;
continue;
}
if (level == XDL_MERGE_MINIMAL || xscr1->i1 != xscr2->i1 ||
xscr1->chg1 != xscr2->chg1 ||
xscr1->chg2 != xscr2->chg2 ||
xdl_merge_cmp_lines(xe1, xscr1->i2,
xe2, xscr2->i2,
xscr1->chg2, xpp->flags)) {
/* conflict */
int off = xscr1->i1 - xscr2->i1;
int ffo = off + xscr1->chg1 - xscr2->chg1;
i0 = xscr1->i1;
i1 = xscr1->i2;
i2 = xscr2->i2;
if (off > 0) {
i0 -= off;
i1 -= off;
}
else
i2 += off;
chg0 = xscr1->i1 + xscr1->chg1 - i0;
chg1 = xscr1->i2 + xscr1->chg2 - i1;
chg2 = xscr2->i2 + xscr2->chg2 - i2;
if (ffo < 0) {
chg0 -= ffo;
chg1 -= ffo;
} else
chg2 += ffo;
if (xdl_append_merge(&c, 0,
i0, chg0, i1, chg1, i2, chg2)) {
xdl_cleanup_merge(changes);
return -1;
}
}
i1 = xscr1->i1 + xscr1->chg1;
i2 = xscr2->i1 + xscr2->chg1;
if (i1 >= i2)
xscr2 = xscr2->next;
if (i2 >= i1)
xscr1 = xscr1->next;
}
while (xscr1) {
if (!changes)
changes = c;
i0 = xscr1->i1;
i1 = xscr1->i2;
i2 = xscr1->i1 + xe2->xdf2.nrec - xe2->xdf1.nrec;
chg0 = xscr1->chg1;
chg1 = xscr1->chg2;
chg2 = xscr1->chg1;
if (xdl_append_merge(&c, 1,
i0, chg0, i1, chg1, i2, chg2)) {
xdl_cleanup_merge(changes);
return -1;
}
xscr1 = xscr1->next;
}
while (xscr2) {
if (!changes)
changes = c;
i0 = xscr2->i1;
i1 = xscr2->i1 + xe1->xdf2.nrec - xe1->xdf1.nrec;
i2 = xscr2->i2;
chg0 = xscr2->chg1;
chg1 = xscr2->chg1;
chg2 = xscr2->chg2;
if (xdl_append_merge(&c, 2,
i0, chg0, i1, chg1, i2, chg2)) {
xdl_cleanup_merge(changes);
return -1;
}
xscr2 = xscr2->next;
}
if (!changes)
changes = c;
/* refine conflicts */
if (XDL_MERGE_ZEALOUS <= level &&
(xdl_refine_conflicts(xe1, xe2, changes, xpp) < 0 ||
xdl_simplify_non_conflicts(xe1, changes,
XDL_MERGE_ZEALOUS < level) < 0)) {
xdl_cleanup_merge(changes);
return -1;
}
/* output */
if (result) {
int size = xdl_fill_merge_buffer(xe1, name1, xe2, name2,
favor, changes, NULL, style);
result->ptr = xdl_malloc(size);
if (!result->ptr) {
xdl_cleanup_merge(changes);
return -1;
}
result->size = size;
xdl_fill_merge_buffer(xe1, name1, xe2, name2, favor, changes,
result->ptr, style);
}
return xdl_cleanup_merge(changes);
}
int xdl_merge(mmfile_t *orig, mmfile_t *mf1, const char *name1,
mmfile_t *mf2, const char *name2,
xpparam_t const *xpp, int flags, mmbuffer_t *result) {
xdchange_t *xscr1, *xscr2;
xdfenv_t xe1, xe2;
int status;
result->ptr = NULL;
result->size = 0;
if (xdl_do_diff(orig, mf1, xpp, &xe1) < 0 ||
xdl_do_diff(orig, mf2, xpp, &xe2) < 0) {
return -1;
}
if (xdl_change_compact(&xe1.xdf1, &xe1.xdf2, xpp->flags) < 0 ||
xdl_change_compact(&xe1.xdf2, &xe1.xdf1, xpp->flags) < 0 ||
xdl_build_script(&xe1, &xscr1) < 0) {
xdl_free_env(&xe1);
return -1;
}
if (xdl_change_compact(&xe2.xdf1, &xe2.xdf2, xpp->flags) < 0 ||
xdl_change_compact(&xe2.xdf2, &xe2.xdf1, xpp->flags) < 0 ||
xdl_build_script(&xe2, &xscr2) < 0) {
xdl_free_env(&xe2);
return -1;
}
status = 0;
if (!xscr1) {
result->ptr = xdl_malloc(mf2->size);
memcpy(result->ptr, mf2->ptr, mf2->size);
result->size = mf2->size;
} else if (!xscr2) {
result->ptr = xdl_malloc(mf1->size);
memcpy(result->ptr, mf1->ptr, mf1->size);
result->size = mf1->size;
} else {
status = xdl_do_merge(&xe1, xscr1, name1,
&xe2, xscr2, name2,
flags, xpp, result);
}
xdl_free_script(xscr1);
xdl_free_script(xscr2);
xdl_free_env(&xe1);
xdl_free_env(&xe2);
return status;
}
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