mercurial/dirs.c

obsolescence: add test for the "branch replacement" logic during push, case D6

Mercurial checks for the introduction of new heads on push. Evolution comes
into play to detect if existing branches on the server are being replaced by
some of the new one we push.

The current code for this logic is very basic (eg: issue4354) and was poorly
tested. We have a better implementation coming in the evolve extension fixing
these issues and with more serious tests coverage. In the process of upstreaming
this improved logic, we start with adding the test case that are already passing
with the current implementation. Once they are all in, we'll upstream the better
implementation and the extra test cases.

See inline documentation for details about the test case added in this
changeset.

/*
 dirs.c - dynamic directory diddling for dirstates

 Copyright 2013 Facebook

 This software may be used and distributed according to the terms of
 the GNU General Public License, incorporated herein by reference.
*/

#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include "util.h"

#ifdef IS_PY3K
#define PYLONG_VALUE(o) ((PyLongObject *)o)->ob_digit[1]
#else
#define PYLONG_VALUE(o) PyInt_AS_LONG(o)
#endif

/*
 * This is a multiset of directory names, built from the files that
 * appear in a dirstate or manifest.
 *
 * A few implementation notes:
 *
 * We modify Python integers for refcounting, but those integers are
 * never visible to Python code.
 *
 * We mutate strings in-place, but leave them immutable once they can
 * be seen by Python code.
 */
typedef struct {
	PyObject_HEAD
	PyObject *dict;
} dirsObject;

static inline Py_ssize_t _finddir(const char *path, Py_ssize_t pos)
{
	while (pos != -1) {
		if (path[pos] == '/')
			break;
		pos -= 1;
	}

	return pos;
}

static int _addpath(PyObject *dirs, PyObject *path)
{
	const char *cpath = PyBytes_AS_STRING(path);
	Py_ssize_t pos = PyBytes_GET_SIZE(path);
	PyObject *key = NULL;
	int ret = -1;

	/* This loop is super critical for performance. That's why we inline
	* access to Python structs instead of going through a supported API.
	* The implementation, therefore, is heavily dependent on CPython
	* implementation details. We also commit violations of the Python
	* "protocol" such as mutating immutable objects. But since we only
	* mutate objects created in this function or in other well-defined
	* locations, the references are known so these violations should go
	* unnoticed. The code for adjusting the length of a PyBytesObject is
	* essentially a minimal version of _PyBytes_Resize. */
	while ((pos = _finddir(cpath, pos - 1)) != -1) {
		PyObject *val;

		/* It's likely that every prefix already has an entry
		   in our dict. Try to avoid allocating and
		   deallocating a string for each prefix we check. */
		if (key != NULL)
			((PyBytesObject *)key)->ob_shash = -1;
		else {
			/* Force Python to not reuse a small shared string. */
			key = PyBytes_FromStringAndSize(cpath,
							 pos < 2 ? 2 : pos);
			if (key == NULL)
				goto bail;
		}
		/* Py_SIZE(o) refers to the ob_size member of the struct. Yes,
		* assigning to what looks like a function seems wrong. */
		Py_SIZE(key) = pos;
		((PyBytesObject *)key)->ob_sval[pos] = '\0';

		val = PyDict_GetItem(dirs, key);
		if (val != NULL) {
			PYLONG_VALUE(val) += 1;
			break;
		}

		/* Force Python to not reuse a small shared int. */
#ifdef IS_PY3K
		val = PyLong_FromLong(0x1eadbeef);
#else
		val = PyInt_FromLong(0x1eadbeef);
#endif

		if (val == NULL)
			goto bail;

		PYLONG_VALUE(val) = 1;
		ret = PyDict_SetItem(dirs, key, val);
		Py_DECREF(val);
		if (ret == -1)
			goto bail;
		Py_CLEAR(key);
	}
	ret = 0;

bail:
	Py_XDECREF(key);

	return ret;
}

static int _delpath(PyObject *dirs, PyObject *path)
{
	char *cpath = PyBytes_AS_STRING(path);
	Py_ssize_t pos = PyBytes_GET_SIZE(path);
	PyObject *key = NULL;
	int ret = -1;

	while ((pos = _finddir(cpath, pos - 1)) != -1) {
		PyObject *val;

		key = PyBytes_FromStringAndSize(cpath, pos);

		if (key == NULL)
			goto bail;

		val = PyDict_GetItem(dirs, key);
		if (val == NULL) {
			PyErr_SetString(PyExc_ValueError,
					"expected a value, found none");
			goto bail;
		}

		if (--PYLONG_VALUE(val) <= 0) {
			if (PyDict_DelItem(dirs, key) == -1)
				goto bail;
		} else
			break;
		Py_CLEAR(key);
	}
	ret = 0;

bail:
	Py_XDECREF(key);

	return ret;
}

static int dirs_fromdict(PyObject *dirs, PyObject *source, char skipchar)
{
	PyObject *key, *value;
	Py_ssize_t pos = 0;

	while (PyDict_Next(source, &pos, &key, &value)) {
		if (!PyBytes_Check(key)) {
			PyErr_SetString(PyExc_TypeError, "expected string key");
			return -1;
		}
		if (skipchar) {
			if (!dirstate_tuple_check(value)) {
				PyErr_SetString(PyExc_TypeError,
						"expected a dirstate tuple");
				return -1;
			}
			if (((dirstateTupleObject *)value)->state == skipchar)
				continue;
		}

		if (_addpath(dirs, key) == -1)
			return -1;
	}

	return 0;
}

static int dirs_fromiter(PyObject *dirs, PyObject *source)
{
	PyObject *iter, *item = NULL;
	int ret;

	iter = PyObject_GetIter(source);
	if (iter == NULL)
		return -1;

	while ((item = PyIter_Next(iter)) != NULL) {
		if (!PyBytes_Check(item)) {
			PyErr_SetString(PyExc_TypeError, "expected string");
			break;
		}

		if (_addpath(dirs, item) == -1)
			break;
		Py_CLEAR(item);
	}

	ret = PyErr_Occurred() ? -1 : 0;
	Py_DECREF(iter);
	Py_XDECREF(item);
	return ret;
}

/*
 * Calculate a refcounted set of directory names for the files in a
 * dirstate.
 */
static int dirs_init(dirsObject *self, PyObject *args)
{
	PyObject *dirs = NULL, *source = NULL;
	char skipchar = 0;
	int ret = -1;

	self->dict = NULL;

	if (!PyArg_ParseTuple(args, "|Oc:__init__", &source, &skipchar))
		return -1;

	dirs = PyDict_New();

	if (dirs == NULL)
		return -1;

	if (source == NULL)
		ret = 0;
	else if (PyDict_Check(source))
		ret = dirs_fromdict(dirs, source, skipchar);
	else if (skipchar)
		PyErr_SetString(PyExc_ValueError,
				"skip character is only supported "
				"with a dict source");
	else
		ret = dirs_fromiter(dirs, source);

	if (ret == -1)
		Py_XDECREF(dirs);
	else
		self->dict = dirs;

	return ret;
}

PyObject *dirs_addpath(dirsObject *self, PyObject *args)
{
	PyObject *path;

	if (!PyArg_ParseTuple(args, "O!:addpath", &PyBytes_Type, &path))
		return NULL;

	if (_addpath(self->dict, path) == -1)
		return NULL;

	Py_RETURN_NONE;
}

static PyObject *dirs_delpath(dirsObject *self, PyObject *args)
{
	PyObject *path;

	if (!PyArg_ParseTuple(args, "O!:delpath", &PyBytes_Type, &path))
		return NULL;

	if (_delpath(self->dict, path) == -1)
		return NULL;

	Py_RETURN_NONE;
}

static int dirs_contains(dirsObject *self, PyObject *value)
{
	return PyBytes_Check(value) ? PyDict_Contains(self->dict, value) : 0;
}

static void dirs_dealloc(dirsObject *self)
{
	Py_XDECREF(self->dict);
	PyObject_Del(self);
}

static PyObject *dirs_iter(dirsObject *self)
{
	return PyObject_GetIter(self->dict);
}

static PySequenceMethods dirs_sequence_methods;

static PyMethodDef dirs_methods[] = {
	{"addpath", (PyCFunction)dirs_addpath, METH_VARARGS, "add a path"},
	{"delpath", (PyCFunction)dirs_delpath, METH_VARARGS, "remove a path"},
	{NULL} /* Sentinel */
};

static PyTypeObject dirsType = { PyVarObject_HEAD_INIT(NULL, 0) };

void dirs_module_init(PyObject *mod)
{
	dirs_sequence_methods.sq_contains = (objobjproc)dirs_contains;
	dirsType.tp_name = "parsers.dirs";
	dirsType.tp_new = PyType_GenericNew;
	dirsType.tp_basicsize = sizeof(dirsObject);
	dirsType.tp_dealloc = (destructor)dirs_dealloc;
	dirsType.tp_as_sequence = &dirs_sequence_methods;
	dirsType.tp_flags = Py_TPFLAGS_DEFAULT;
	dirsType.tp_doc = "dirs";
	dirsType.tp_iter = (getiterfunc)dirs_iter;
	dirsType.tp_methods = dirs_methods;
	dirsType.tp_init = (initproc)dirs_init;

	if (PyType_Ready(&dirsType) < 0)
		return;
	Py_INCREF(&dirsType);

	PyModule_AddObject(mod, "dirs", (PyObject *)&dirsType);
}