D7105: dirs: reject consecutive slashes in paths

[Yuya Nishihara]

> diff --git a/mercurial/cext/dirs.c b/mercurial/cext/dirs.c
> --- a/mercurial/cext/dirs.c
> +++ b/mercurial/cext/dirs.c
> @@ -52,6 +52,7 @@
>  {
>  	const char *cpath = PyBytes_AS_STRING(path);
>  	Py_ssize_t pos = PyBytes_GET_SIZE(path);
> +	Py_ssize_t prev_pos = -1;
>  	PyObject *key = NULL;
>  	int ret = -1;
>  
> @@ -64,6 +65,13 @@
>  	 * locations, the references are known so these violations should go
>  	 * unnoticed. */
>  	while ((pos = _finddir(cpath, pos - 1)) != -1) {
> +		if (pos && prev_pos == pos + 1) {

Maybe it's better to reject leading "/" and trailing "/".

> +			PyErr_SetString(
> +			    PyExc_ValueError,
> +			    "invalid empty directory name in dirs.c _addpath");
> +			return -1;

`goto bail;` is the way to error out from this function, though it doesn't
matter here.