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git/xdiff/xmerge.c
Junio C Hamano 83133740d9 xmerge.c: "diff3 -m" style clips merge reduction level to EAGER or less 
When showing a conflicting merge result, and "--diff3 -m" style is asked
for, this patch makes sure that the merge reduction level does not exceed
XDL_MERGE_EAGER.  This is because "diff3 -m" style output would not make
sense for anything more aggressive than XDL_MERGE_EAGER, because of the
way how the merge reduction works.

"git merge-file" no longer has to force MERGE_EAGER when "--diff3" is
asked for because of this change.

Suppose a common ancestor (shared preimage) is modified to postimage #1
and #2 (each letter represents one line):

                     #####
    postimage#1: 1234ABCDE789
                    |    /
                    |   /
    preimage:    123456789
                    |   \
    postimage#2: 1234AXYE789
                     ####

XDL_MERGE_MINIMAL and XDL_MERGE_EAGER would:

 (1) find the s/56/ABCDE/ done on one side and s/56/AXYE/ done on the
     other side,

 (2) notice that they touch an overlapping area, and

 (3) mark it as a conflict, "ABCDE vs AXYE".

The difference between the two algorithms is that EAGER drops the hunk
altogether if the postimages match (i.e. both sides modified the same
way), while MINIMAL keeps it.  There is no other operation performed to
the hunk.  As the result, lines marked with "#" in the above picure will
be in the RCS merge style output like this (letters <, = and > represent
conflict marker lines):

    output:      1234<ABCDE=AXYE>789    ; with MINIMAL/EAGER

The part from the preimage that corresponds to these conflicting changes
is "56", which is what "diff3 -m" style output adds to it:

    output:      1234<ABCDE|56=AXYE>789 ; in "diff3 -m" style

Now, XDL_MERGE_ZEALOUS looks at the differences between the changes two
postimages made in order to reduce the number of lines in the conflicting
regions.  It notices that both sides start their new contents with "A",
and excludes it from the output (it also excludes "E" for the same
reason).  The conflict that used to be "ABCDE vs AXYE" is now "BCD vs XY":

    output:      1234A<BCD=XY>E789      ; with ZEALOUS

There could even be matching parts between two postimages in the middle.
Instead of one side rewriting the shared "56" to "ABCDE" and the other
side to "AXYE", imagine the case where the postimages are "ABCDE" and
"AXCYE", in which case instead of having one conflicted hunk "BCD vs XY",
you would have two conflicting hunks "B vs X" and "D vs Y".

In either case, once you reduce "ABCDE vs AXYE" to "BCD vs XY" (or "ABCDE
vs AXCYE" to "B vs X" and "D vs Y"), there is no part from the preimage
that corresponds to the conflicting change made in both postimages
anymore.  In other words, conflict reduced by ZEALOUS algorithm cannot be
expressed in "diff3 -m" style.  Representing the last illustration like
this is misleading to say the least:

    output:      1234A<BCD|56=XY>E789   ; broken "diff3 -m" style

because the preimage was not ...4A56E... to begin with.  "A" and "E" are
common only between the postimages.

Even worse, once a single conflicting hunk is split into multiple ones
(recall the example of breaking "ABCDE vs AXCYE" to "B vs X" and "D vs
Y"), there is no sane way to distribute the preimage text across split
conflicting hunks.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-08-30 19:41:43 -07:00

587 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,
xdmerge_t *m, char *dest, int style)
{
int size, i;
for (size = i = 0; m; m = m->next) {
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;
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,
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, 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 || xscr2) {
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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