mercurial/cext/dirs.c

interfaces: introduce and use a protocol class for the `charencoding` module

See f2832de2a46c for details when this was done for the `bdiff` module.

This lets us dump the hack where the `pure` implementation was imported during
the type checking phase to provide signatures for the module methods it
provides.  Now the protocol classes are starting to shine, because these methods
are provided by `pure.charencoding` and `cext.parsers`, and references to
`cffi.charencoding` and `cext.charencoding` are forwarded to them as appropriate
by the `policy` module.  But none of that matters, as long as the module
returned provides the listed methods.

The interface was copy/pasted from the `pure` module, but `jsonescapeu8fallback`
is omitted because it is accessed from the `pure` module directly when the
escaping fails in the primary module's `jsonescapeu8()`.

/*
 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 <string.h>

#include "util.h"

#if PY_VERSION_HEX >= 0x030C00A5
#define PYLONG_VALUE(o) ((PyLongObject *)o)->long_value.ob_digit[0]
#else
#define PYLONG_VALUE(o) ((PyLongObject *)o)->ob_digit[0]
#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.
 */
/* clang-format off */
typedef struct {
	PyObject_HEAD
	PyObject *dict;
} dirsObject;
/* clang-format on */

static inline Py_ssize_t _finddir(const char *path, Py_ssize_t pos)
{
	while (pos != -1) {
		if (path[pos] == '/')
			break;
		pos -= 1;
	}
	if (pos == -1) {
		return 0;
	}

	return pos;
}

/* Mercurial will fail to run on directory hierarchies deeper than
 * this constant, so we should try and keep this constant as big as
 * possible.
 */
#define MAX_DIRS_DEPTH 2048

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;
	size_t num_slashes = 0;

	/* 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. */
	while ((pos = _finddir(cpath, pos - 1)) != -1) {
		PyObject *val;
		++num_slashes;
		if (num_slashes > MAX_DIRS_DEPTH) {
			PyErr_SetString(PyExc_ValueError,
			                "Directory hierarchy too deep.");
			goto bail;
		}

		/* Sniff for trailing slashes, a marker of an invalid input. */
		if (pos > 0 && cpath[pos - 1] == '/') {
			PyErr_SetString(
			    PyExc_ValueError,
			    "found invalid consecutive slashes in path");
			goto bail;
		}

		key = PyBytes_FromStringAndSize(cpath, pos);
		if (key == NULL)
			goto bail;

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

		/* Force Python to not reuse a small shared int. */
		val = PyLong_FromLong(0x1eadbeef);

		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, bool only_tracked)
{
	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 (only_tracked) {
			if (!dirstate_tuple_check(value)) {
				PyErr_SetString(PyExc_TypeError,
				                "expected a dirstate tuple");
				return -1;
			}
			if (!(((dirstateItemObject *)value)->flags &
			      dirstate_flag_wc_tracked))
				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 *kwargs)
{
	PyObject *dirs = NULL, *source = NULL;
	int only_tracked = 0;
	int ret = -1;
	static char *keywords_name[] = {"map", "only_tracked", NULL};

	self->dict = NULL;

	if (!PyArg_ParseTupleAndKeywords(args, kwargs, "|Oi:__init__",
	                                 keywords_name, &source, &only_tracked))
		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, (bool)only_tracked);
	else if (only_tracked)
		PyErr_SetString(PyExc_ValueError,
		                "`only_tracked` 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);
}