contrib/fuzz/xdiff.cc

simplestore: use a custom store for the simple store repo

Before, we used the default store, which was based on fncache
and dotencode. After attempting to port tests to work with the
simple store, I realized that fncache was more trouble than it is
worth.

This commit implements a proper store type for the simple repo -
one that isn't based off fncache.

This causes a number of new test failures because of tests
expecting the full fncache store filename encoding. I may
extend the store format in a subsequent commit to take the
filename encoding parts of fncache that we can take
(basically everything except hash encoding, since that isn't
reversible). But for now, let's use encoded store.

As part of this, we implement proper requirements support for
repos created with the simple store. This should have been
done from the beginning, as a requirement is needed to lock
out clients that don't understand a storage format.

A new hghave feature advertising the presence of fncache in repos
has been added. Most tests touching the fncache are now conditional
on that feature.

Other tests have added the optional repo requirement to output.

Differential Revision: https://phab.mercurial-scm.org/D3095

/*
 * xdiff.cc - fuzzer harness for thirdparty/xdiff
 *
 * Copyright 2018, Google Inc.
 *
 * This software may be used and distributed according to the terms of
 * the GNU General Public License, incorporated herein by reference.
 */
#include "thirdparty/xdiff/xdiff.h"
#include <inttypes.h>
#include <stdlib.h>

extern "C" {

int hunk_consumer(long a1, long a2, long b1, long b2, void *priv)
{
	// TODO: probably also test returning -1 from this when things break?
	return 0;
}

int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
{
	if (!Size) {
		return 0;
	}
	// figure out a random point in [0, Size] to split our input.
	size_t split = Data[0] / 255.0 * Size;

	mmfile_t a, b;

	// `a` input to diff is data[1:split]
	a.ptr = (char *)Data + 1;
	// which has len split-1
	a.size = split - 1;
	// `b` starts at the next byte after `a` ends
	b.ptr = a.ptr + a.size;
	b.size = Size - split;
	xpparam_t xpp = {
	    XDF_INDENT_HEURISTIC, /* flags */
	};
	xdemitconf_t xecfg = {
	    XDL_EMIT_BDIFFHUNK, /* flags */
	    hunk_consumer,      /* hunk_consume_func */
	};
	xdemitcb_t ecb = {
	    NULL, /* priv */
	};
	xdl_diff(&a, &b, &xpp, &xecfg, &ecb);
	return 0; // Non-zero return values are reserved for future use.
}

#ifdef HG_FUZZER_INCLUDE_MAIN
int main(int argc, char **argv)
{
	const char data[] = "asdf";
	return LLVMFuzzerTestOneInput((const uint8_t *)data, 4);
}
#endif

} // extern "C"