stdio: add rename(2) binding.

Closes #228, #229
* specs/posix_stdio_spec.yaml (rename): Specify behaviour of
posix.stdio.rename.
* ext/posix/stdio.c (Prename): Bind rename(2).
(posix_stdio_fns): Export Prename.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>

ext/posix/stdio.c

@@ -98,12 +98,36 @@ Pfdopen(lua_State *L)	/** fdopen(fd, mode) */
 	return 1;
 }
 
+/***
+Change the name or location of a file
+@function rename
+@tparam string oldpath
+@tparam string newpath
+@treturn[1] int `0` if successful
+@return[2] nil
+@treturn[2] string error message
+@treturn[2] int errnum
+@see rename(2)
+@usage
+local ok, errmsg = P.rename (oldpath, newpath)
+if not ok then error (errmsg) end
+*/
+static int
+Prename(lua_State *L)	/** rename(oldpath, newpath) */
+{
+	const char *oldpath = luaL_checkstring(L, 1);
+	const char *newpath = luaL_checkstring(L, 2);
+	checknargs(L, 2);
+	return pushresult(L, rename(oldpath, newpath), NULL);
+}
+
 
 static const luaL_Reg posix_stdio_fns[] =
 {
 	LPOSIX_FUNC( Pctermid		),
 	LPOSIX_FUNC( Pfileno		),
 	LPOSIX_FUNC( Pfdopen		),
+	LPOSIX_FUNC( Prename		),
 	{NULL, NULL}
 };
 

specs/posix_stdio_spec.yaml

@@ -1,12 +1,12 @@
 specify posix.stdio:
 - before:
     stdio = require "posix.stdio"
+    unistd = require "posix.unistd"
 
 
 - describe fdopen:
     - before:
         fdopen = stdio.fdopen
-        unistd = require "posix.unistd"
         STDOUT_FILENO = unistd.STDOUT_FILENO
         f = fdopen (STDOUT_FILENO, "w")
 
@@ -19,3 +19,27 @@ specify posix.stdio:
     - it writes to the duplicated stream:
         -- Lua 5.1 file.write returns true; > 5.1 returns file handle
         expect (f:write ("writing to fdopen(stdout)\n")).not_to_be (nil)
+
+
+- describe rename:
+    - before:
+        rename = stdio.rename
+        fd, path = require "posix.stdlib".mkstemp (template)
+    - after:
+        unistd.close (fd)
+        os.remove (path)
+
+    - context with bad arguments:
+        badargs.diagnose (rename, "(string,string)")
+
+    - it renames an existing file:
+        newpath = path .. ".renamed"
+        expect (fd).not_to_be (nil)
+        unistd.write (fd, "rename me")
+        rename (path, newpath)
+        expect (io.open (path, "r")).to_be (nil)
+        fh = io.open (newpath, "r")
+        expect (fh).not_to_be (nil)
+        expect (fh:read ()).to_be "rename me"
+        fh:close ()
+        rename (newpath, path)