view mercurial/cext/bdiff.c @ 45214:6063c1857d0a stable

exchange: backout changeset c26335fa4225

Changeset c26335fa4225 has good intends but introduce significant behavior
regressions for multiple important cases. In short there are many case where
push would have caught instability creation/propagation that are no longer
covered.  These behavior have been covered for many years and even if some
related case are not currently caught, the covered one should not be regressed.

The next four changesets introduce tests for some of these cases. However we
could produce many more tests cases since the area is wide and they are many
possible combination. (And we should cover them when getting back to this issue)

Since 5.5 is one week away, the most reasonable approach seems to back this out
while we devise a new way to move forward that preserve the current behavior,
catch more issues and also improves the situation that c26335fa4225 target.


In addition to the behavior change, c26335fa4225 also introduced output
changes. These output changes does not requires a backout per-se, but are part of
the same changeset. However they come with a couple of issues that also requires
attention:

1) the bulk of the error message have been shoehorned into a multiple line abort
message. This seems quite different from what we usually do. The abort message
should be a compact and efficient message, with extra details being issued as
normal error output beforehand. (with --verbose/--quiet) support.

2) the current output is unbounded, so if there is many (tens, hundreds,
thousands, …) of unstable/obsolete changeset involved in the push, the output
can quickly become a scary and un-usuable wall of text. So we need some
limitation here (same as we have with the remote head list that says A, B , C
and # others).

/*
 bdiff.c - efficient binary diff extension for Mercurial

 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.

 Based roughly on Python difflib
*/

#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>

#include "bdiff.h"
#include "bitmanipulation.h"
#include "thirdparty/xdiff/xdiff.h"
#include "util.h"

static PyObject *blocks(PyObject *self, PyObject *args)
{
	PyObject *sa, *sb, *rl = NULL, *m;
	struct bdiff_line *a, *b;
	struct bdiff_hunk l, *h;
	int an, bn, count, pos = 0;

	l.next = NULL;

	if (!PyArg_ParseTuple(args, "SS:bdiff", &sa, &sb)) {
		return NULL;
	}

	an = bdiff_splitlines(PyBytes_AsString(sa), PyBytes_Size(sa), &a);
	bn = bdiff_splitlines(PyBytes_AsString(sb), PyBytes_Size(sb), &b);

	if (!a || !b) {
		goto nomem;
	}

	count = bdiff_diff(a, an, b, bn, &l);
	if (count < 0) {
		goto nomem;
	}

	rl = PyList_New(count);
	if (!rl) {
		goto nomem;
	}

	for (h = l.next; h; h = h->next) {
		m = Py_BuildValue("iiii", h->a1, h->a2, h->b1, h->b2);
		PyList_SetItem(rl, pos, m);
		pos++;
	}

nomem:
	free(a);
	free(b);
	bdiff_freehunks(l.next);
	return rl ? rl : PyErr_NoMemory();
}

static PyObject *bdiff(PyObject *self, PyObject *args)
{
	Py_buffer ba, bb;
	char *rb, *ia, *ib;
	PyObject *result = NULL;
	struct bdiff_line *al = NULL, *bl = NULL;
	struct bdiff_hunk l, *h;
	int an, bn, count;
	Py_ssize_t len = 0, la, lb, li = 0, lcommon = 0, lmax;
	PyThreadState *_save = NULL;

	l.next = NULL;

	if (!PyArg_ParseTuple(args, PY23("s*s*:bdiff", "y*y*:bdiff"), &ba,
	                      &bb)) {
		return NULL;
	}

	if (!PyBuffer_IsContiguous(&ba, 'C') || ba.ndim > 1) {
		PyErr_SetString(PyExc_ValueError, "bdiff input not contiguous");
		goto cleanup;
	}

	if (!PyBuffer_IsContiguous(&bb, 'C') || bb.ndim > 1) {
		PyErr_SetString(PyExc_ValueError, "bdiff input not contiguous");
		goto cleanup;
	}

	la = ba.len;
	lb = bb.len;

	if (la > UINT_MAX || lb > UINT_MAX) {
		PyErr_SetString(PyExc_ValueError, "bdiff inputs too large");
		goto cleanup;
	}

	_save = PyEval_SaveThread();

	lmax = la > lb ? lb : la;
	for (ia = ba.buf, ib = bb.buf; li < lmax && *ia == *ib;
	     ++li, ++ia, ++ib) {
		if (*ia == '\n') {
			lcommon = li + 1;
		}
	}
	/* we can almost add: if (li == lmax) lcommon = li; */

	an = bdiff_splitlines((char *)ba.buf + lcommon, la - lcommon, &al);
	bn = bdiff_splitlines((char *)bb.buf + lcommon, lb - lcommon, &bl);
	if (!al || !bl) {
		PyErr_NoMemory();
		goto cleanup;
	}

	count = bdiff_diff(al, an, bl, bn, &l);
	if (count < 0) {
		PyErr_NoMemory();
		goto cleanup;
	}

	/* calculate length of output */
	la = lb = 0;
	for (h = l.next; h; h = h->next) {
		if (h->a1 != la || h->b1 != lb) {
			len += 12 + bl[h->b1].l - bl[lb].l;
		}
		la = h->a2;
		lb = h->b2;
	}
	PyEval_RestoreThread(_save);
	_save = NULL;

	result = PyBytes_FromStringAndSize(NULL, len);

	if (!result) {
		goto cleanup;
	}

	/* build binary patch */
	rb = PyBytes_AsString(result);
	la = lb = 0;

	for (h = l.next; h; h = h->next) {
		if (h->a1 != la || h->b1 != lb) {
			len = bl[h->b1].l - bl[lb].l;
			putbe32((uint32_t)(al[la].l + lcommon - al->l), rb);
			putbe32((uint32_t)(al[h->a1].l + lcommon - al->l),
			        rb + 4);
			putbe32((uint32_t)len, rb + 8);
			memcpy(rb + 12, bl[lb].l, len);
			rb += 12 + len;
		}
		la = h->a2;
		lb = h->b2;
	}

cleanup:
	if (_save) {
		PyEval_RestoreThread(_save);
	}
	PyBuffer_Release(&ba);
	PyBuffer_Release(&bb);
	free(al);
	free(bl);
	bdiff_freehunks(l.next);
	return result;
}

/*
 * If allws != 0, remove all whitespace (' ', \t and \r). Otherwise,
 * reduce whitespace sequences to a single space and trim remaining whitespace
 * from end of lines.
 */
static PyObject *fixws(PyObject *self, PyObject *args)
{
	PyObject *s, *result = NULL;
	char allws, c;
	const char *r;
	Py_ssize_t i, rlen, wlen = 0;
	char *w;

	if (!PyArg_ParseTuple(args, "Sb:fixws", &s, &allws)) {
		return NULL;
	}
	r = PyBytes_AsString(s);
	rlen = PyBytes_Size(s);

	w = (char *)PyMem_Malloc(rlen ? rlen : 1);
	if (!w) {
		goto nomem;
	}

	for (i = 0; i != rlen; i++) {
		c = r[i];
		if (c == ' ' || c == '\t' || c == '\r') {
			if (!allws && (wlen == 0 || w[wlen - 1] != ' ')) {
				w[wlen++] = ' ';
			}
		} else if (c == '\n' && !allws && wlen > 0 &&
		           w[wlen - 1] == ' ') {
			w[wlen - 1] = '\n';
		} else {
			w[wlen++] = c;
		}
	}

	result = PyBytes_FromStringAndSize(w, wlen);

nomem:
	PyMem_Free(w);
	return result ? result : PyErr_NoMemory();
}

static bool sliceintolist(PyObject *list, Py_ssize_t destidx,
                          const char *source, Py_ssize_t len)
{
	PyObject *sliced = PyBytes_FromStringAndSize(source, len);
	if (sliced == NULL) {
		return false;
	}
	PyList_SET_ITEM(list, destidx, sliced);
	return true;
}

static PyObject *splitnewlines(PyObject *self, PyObject *args)
{
	const char *text;
	Py_ssize_t nelts = 0, size, i, start = 0;
	PyObject *result = NULL;

	if (!PyArg_ParseTuple(args, PY23("s#", "y#"), &text, &size)) {
		goto abort;
	}
	if (!size) {
		return PyList_New(0);
	}
	/* This loops to size-1 because if the last byte is a newline,
	 * we don't want to perform a split there. */
	for (i = 0; i < size - 1; ++i) {
		if (text[i] == '\n') {
			++nelts;
		}
	}
	if ((result = PyList_New(nelts + 1)) == NULL) {
		goto abort;
	}
	nelts = 0;
	for (i = 0; i < size - 1; ++i) {
		if (text[i] == '\n') {
			if (!sliceintolist(result, nelts++, text + start,
			                   i - start + 1)) {
				goto abort;
			}
			start = i + 1;
		}
	}
	if (!sliceintolist(result, nelts++, text + start, size - start)) {
		goto abort;
	}
	return result;
abort:
	Py_XDECREF(result);
	return NULL;
}

static int hunk_consumer(int64_t a1, int64_t a2, int64_t b1, int64_t b2,
                         void *priv)
{
	PyObject *rl = (PyObject *)priv;
	PyObject *m = Py_BuildValue("LLLL", a1, a2, b1, b2);
	int r;
	if (!m) {
		return -1;
	}
	r = PyList_Append(rl, m);
	Py_DECREF(m);
	return r;
}

static PyObject *xdiffblocks(PyObject *self, PyObject *args)
{
	Py_ssize_t la, lb;
	mmfile_t a, b;
	PyObject *rl;

	xpparam_t xpp = {
	    XDF_INDENT_HEURISTIC, /* flags */
	};
	xdemitconf_t xecfg = {
	    XDL_EMIT_BDIFFHUNK, /* flags */
	    hunk_consumer,      /* hunk_consume_func */
	};
	xdemitcb_t ecb = {
	    NULL, /* priv */
	};

	if (!PyArg_ParseTuple(args, PY23("s#s#", "y#y#"), &a.ptr, &la, &b.ptr,
	                      &lb)) {
		return NULL;
	}

	a.size = la;
	b.size = lb;

	rl = PyList_New(0);
	if (!rl) {
		return PyErr_NoMemory();
	}

	ecb.priv = rl;

	if (xdl_diff(&a, &b, &xpp, &xecfg, &ecb) != 0) {
		Py_DECREF(rl);
		return PyErr_NoMemory();
	}

	return rl;
}

static char mdiff_doc[] = "Efficient binary diff.";

static PyMethodDef methods[] = {
    {"bdiff", bdiff, METH_VARARGS, "calculate a binary diff\n"},
    {"blocks", blocks, METH_VARARGS, "find a list of matching lines\n"},
    {"fixws", fixws, METH_VARARGS, "normalize diff whitespaces\n"},
    {"splitnewlines", splitnewlines, METH_VARARGS,
     "like str.splitlines, but only split on newlines\n"},
    {"xdiffblocks", xdiffblocks, METH_VARARGS,
     "find a list of matching lines using xdiff algorithm\n"},
    {NULL, NULL},
};

static const int version = 3;

#ifdef IS_PY3K
static struct PyModuleDef bdiff_module = {
    PyModuleDef_HEAD_INIT, "bdiff", mdiff_doc, -1, methods,
};

PyMODINIT_FUNC PyInit_bdiff(void)
{
	PyObject *m;
	m = PyModule_Create(&bdiff_module);
	PyModule_AddIntConstant(m, "version", version);
	return m;
}
#else
PyMODINIT_FUNC initbdiff(void)
{
	PyObject *m;
	m = Py_InitModule3("bdiff", methods, mdiff_doc);
	PyModule_AddIntConstant(m, "version", version);
}
#endif