view mercurial/thirdparty/xdiff/xemit.c @ 36671:34e2ff1f9cd8

xdiff: vendor xdiff library from git

Vendor git's xdiff library from git commit
d7c6c2369d7c6c2369ac21141b7c6cceaebc6414ec3da14ad using GPL2+ license.

There is another recent user report that hg diff generates suboptimal
result. It seems the fix to issue4074 isn't good enough. I crafted some
other interesting cases, and hg diff barely has any advantage compared with
gnu diffutils or git diff.

| testcase | gnu diffutils |      hg diff |   git diff |
|          |    lines time |   lines time | lines time |
| patience |        6 0.00 |     602 0.08 |     6 0.00 |
|   random |    91772 0.90 |  109462 0.70 | 91772 0.24 |
|     json |        2 0.03 | 1264814 1.81 |     2 0.29 |

"lines" means the size of the output, i.e. the count of "+/-" lines. "time"
means seconds needed to do the calculation. Both are the smaller the better.
"hg diff" counts Python startup overhead.

Git and GNU diffutils generate optimal results. For the "json" case, git can
have an optimization that does a scan for common prefix and suffix first,
and match them if the length is greater than half of the text. See
https://neil.fraser.name/news/2006/03/12/. That would make git the fastest
for all above cases.

About testcases:

patience:
Aiming for the weakness of the greedy "patience diff" algorithm.  Using
git's patience diff option would also get suboptimal result. Generated using
the Python script:

```
open('a', 'w').write('\n'.join(list('a' + 'x' * 300 + 'u' + 'x' * 700 + 'a\n')))
open('b', 'w').write('\n'.join(list('b' + 'x' * 700 + 'u' + 'x' * 300 + 'b\n')))
```

random:
Generated using the script in `test-issue4074.t`. It practically makes the
algorithm suffer. Impressively, git wins in both performance and diff
quality.

json:
The recent user reported case. It's a single line movement near the end of a
very large (800K lines) JSON file.

Test Plan:
Code taken as-is.

Differential Revision: https://phab.mercurial-scm.org/D2572

# no-check-commit for vendored code

/*
 *  LibXDiff by Davide Libenzi ( File Differential Library )
 *  Copyright (C) 2003	Davide Libenzi
 *
 *  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, see
 *  <http://www.gnu.org/licenses/>.
 *
 *  Davide Libenzi <[e-mail]>
 *
 */

#include "xinclude.h"

static long xdl_get_rec(xdfile_t *xdf, long ri, char const **rec) {

	*rec = xdf->recs[ri]->ptr;

	return xdf->recs[ri]->size;
}


static int xdl_emit_record(xdfile_t *xdf, long ri, char const *pre, xdemitcb_t *ecb) {
	long size, psize = strlen(pre);
	char const *rec;

	size = xdl_get_rec(xdf, ri, &rec);
	if (xdl_emit_diffrec(rec, size, pre, psize, ecb) < 0) {

		return -1;
	}

	return 0;
}


/*
 * Starting at the passed change atom, find the latest change atom to be included
 * inside the differential hunk according to the specified configuration.
 * Also advance xscr if the first changes must be discarded.
 */
xdchange_t *xdl_get_hunk(xdchange_t **xscr, xdemitconf_t const *xecfg)
{
	xdchange_t *xch, *xchp, *lxch;
	long max_common = 2 * xecfg->ctxlen + xecfg->interhunkctxlen;
	long max_ignorable = xecfg->ctxlen;
	unsigned long ignored = 0; /* number of ignored blank lines */

	/* remove ignorable changes that are too far before other changes */
	for (xchp = *xscr; xchp && xchp->ignore; xchp = xchp->next) {
		xch = xchp->next;

		if (xch == NULL ||
		    xch->i1 - (xchp->i1 + xchp->chg1) >= max_ignorable)
			*xscr = xch;
	}

	if (*xscr == NULL)
		return NULL;

	lxch = *xscr;

	for (xchp = *xscr, xch = xchp->next; xch; xchp = xch, xch = xch->next) {
		long distance = xch->i1 - (xchp->i1 + xchp->chg1);
		if (distance > max_common)
			break;

		if (distance < max_ignorable && (!xch->ignore || lxch == xchp)) {
			lxch = xch;
			ignored = 0;
		} else if (distance < max_ignorable && xch->ignore) {
			ignored += xch->chg2;
		} else if (lxch != xchp &&
			   xch->i1 + ignored - (lxch->i1 + lxch->chg1) > max_common) {
			break;
		} else if (!xch->ignore) {
			lxch = xch;
			ignored = 0;
		} else {
			ignored += xch->chg2;
		}
	}

	return lxch;
}


static long def_ff(const char *rec, long len, char *buf, long sz, void *priv)
{
	if (len > 0 &&
			(isalpha((unsigned char)*rec) || /* identifier? */
			 *rec == '_' || /* also identifier? */
			 *rec == '$')) { /* identifiers from VMS and other esoterico */
		if (len > sz)
			len = sz;
		while (0 < len && isspace((unsigned char)rec[len - 1]))
			len--;
		memcpy(buf, rec, len);
		return len;
	}
	return -1;
}

static long match_func_rec(xdfile_t *xdf, xdemitconf_t const *xecfg, long ri,
			   char *buf, long sz)
{
	const char *rec;
	long len = xdl_get_rec(xdf, ri, &rec);
	if (!xecfg->find_func)
		return def_ff(rec, len, buf, sz, xecfg->find_func_priv);
	return xecfg->find_func(rec, len, buf, sz, xecfg->find_func_priv);
}

static int is_func_rec(xdfile_t *xdf, xdemitconf_t const *xecfg, long ri)
{
	char dummy[1];
	return match_func_rec(xdf, xecfg, ri, dummy, sizeof(dummy)) >= 0;
}

struct func_line {
	long len;
	char buf[80];
};

static long get_func_line(xdfenv_t *xe, xdemitconf_t const *xecfg,
			  struct func_line *func_line, long start, long limit)
{
	long l, size, step = (start > limit) ? -1 : 1;
	char *buf, dummy[1];

	buf = func_line ? func_line->buf : dummy;
	size = func_line ? sizeof(func_line->buf) : sizeof(dummy);

	for (l = start; l != limit && 0 <= l && l < xe->xdf1.nrec; l += step) {
		long len = match_func_rec(&xe->xdf1, xecfg, l, buf, size);
		if (len >= 0) {
			if (func_line)
				func_line->len = len;
			return l;
		}
	}
	return -1;
}

static int is_empty_rec(xdfile_t *xdf, long ri)
{
	const char *rec;
	long len = xdl_get_rec(xdf, ri, &rec);

	while (len > 0 && XDL_ISSPACE(*rec)) {
		rec++;
		len--;
	}
	return !len;
}

int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
		  xdemitconf_t const *xecfg) {
	long s1, s2, e1, e2, lctx;
	xdchange_t *xch, *xche;
	long funclineprev = -1;
	struct func_line func_line = { 0 };

	for (xch = xscr; xch; xch = xche->next) {
		xche = xdl_get_hunk(&xch, xecfg);
		if (!xch)
			break;

		s1 = XDL_MAX(xch->i1 - xecfg->ctxlen, 0);
		s2 = XDL_MAX(xch->i2 - xecfg->ctxlen, 0);

		if (xecfg->flags & XDL_EMIT_FUNCCONTEXT) {
			long fs1, i1 = xch->i1;

			/* Appended chunk? */
			if (i1 >= xe->xdf1.nrec) {
				long i2 = xch->i2;

				/*
				 * We don't need additional context if
				 * a whole function was added.
				 */
				while (i2 < xe->xdf2.nrec) {
					if (is_func_rec(&xe->xdf2, xecfg, i2))
						goto post_context_calculation;
					i2++;
				}

				/*
				 * Otherwise get more context from the
				 * pre-image.
				 */
				i1 = xe->xdf1.nrec - 1;
			}

			fs1 = get_func_line(xe, xecfg, NULL, i1, -1);
			while (fs1 > 0 && !is_empty_rec(&xe->xdf1, fs1 - 1) &&
			       !is_func_rec(&xe->xdf1, xecfg, fs1 - 1))
				fs1--;
			if (fs1 < 0)
				fs1 = 0;
			if (fs1 < s1) {
				s2 -= s1 - fs1;
				s1 = fs1;
			}
		}

 post_context_calculation:
		lctx = xecfg->ctxlen;
		lctx = XDL_MIN(lctx, xe->xdf1.nrec - (xche->i1 + xche->chg1));
		lctx = XDL_MIN(lctx, xe->xdf2.nrec - (xche->i2 + xche->chg2));

		e1 = xche->i1 + xche->chg1 + lctx;
		e2 = xche->i2 + xche->chg2 + lctx;

		if (xecfg->flags & XDL_EMIT_FUNCCONTEXT) {
			long fe1 = get_func_line(xe, xecfg, NULL,
						 xche->i1 + xche->chg1,
						 xe->xdf1.nrec);
			while (fe1 > 0 && is_empty_rec(&xe->xdf1, fe1 - 1))
				fe1--;
			if (fe1 < 0)
				fe1 = xe->xdf1.nrec;
			if (fe1 > e1) {
				e2 += fe1 - e1;
				e1 = fe1;
			}

			/*
			 * Overlap with next change?  Then include it
			 * in the current hunk and start over to find
			 * its new end.
			 */
			if (xche->next) {
				long l = XDL_MIN(xche->next->i1,
						 xe->xdf1.nrec - 1);
				if (l - xecfg->ctxlen <= e1 ||
				    get_func_line(xe, xecfg, NULL, l, e1) < 0) {
					xche = xche->next;
					goto post_context_calculation;
				}
			}
		}

		/*
		 * Emit current hunk header.
		 */

		if (xecfg->flags & XDL_EMIT_FUNCNAMES) {
			get_func_line(xe, xecfg, &func_line,
				      s1 - 1, funclineprev);
			funclineprev = s1 - 1;
		}
		if (xdl_emit_hunk_hdr(s1 + 1, e1 - s1, s2 + 1, e2 - s2,
				      func_line.buf, func_line.len, ecb) < 0)
			return -1;

		/*
		 * Emit pre-context.
		 */
		for (; s2 < xch->i2; s2++)
			if (xdl_emit_record(&xe->xdf2, s2, " ", ecb) < 0)
				return -1;

		for (s1 = xch->i1, s2 = xch->i2;; xch = xch->next) {
			/*
			 * Merge previous with current change atom.
			 */
			for (; s1 < xch->i1 && s2 < xch->i2; s1++, s2++)
				if (xdl_emit_record(&xe->xdf2, s2, " ", ecb) < 0)
					return -1;

			/*
			 * Removes lines from the first file.
			 */
			for (s1 = xch->i1; s1 < xch->i1 + xch->chg1; s1++)
				if (xdl_emit_record(&xe->xdf1, s1, "-", ecb) < 0)
					return -1;

			/*
			 * Adds lines from the second file.
			 */
			for (s2 = xch->i2; s2 < xch->i2 + xch->chg2; s2++)
				if (xdl_emit_record(&xe->xdf2, s2, "+", ecb) < 0)
					return -1;

			if (xch == xche)
				break;
			s1 = xch->i1 + xch->chg1;
			s2 = xch->i2 + xch->chg2;
		}

		/*
		 * Emit post-context.
		 */
		for (s2 = xche->i2 + xche->chg2; s2 < e2; s2++)
			if (xdl_emit_record(&xe->xdf2, s2, " ", ecb) < 0)
				return -1;
	}

	return 0;
}