When invoked with a file path argment, the `render()` function executes
the specified path as ucode script, optionally setting a different
execution scope for the invoked file, and captures the produced output
in a string.

If the specified path is relative, it is treated as being relative to the
source file currently being executed or the current working directory in
case the interpreter executes code from stdin or a command line argument.

Throws an exception if the given path value is not a string.

Throws an exception if a scope argument is specified and not a valid object.

Throws an exception if the given path could not be found or opened.

Throws an exception if the given file could not be compiled.

When invoked with a function value, `render()` invokes the function, passes
all remaining arugments to it and captures any produces output in a string.

Returns a string containing the captured output of the executed file or
function.

-- Testcase --
{%
	let real_printf = printf;

	printf("%.J\n", [
		// include by relative path
		render("files/include.uc"),

		// include by absolute path
		render(TESTFILES_PATH + "/include.uc"),

		// include with overridden scope
		render("files/include.uc", {
			printf: function(...args) {
				real_printf("This is the wrapped printf() getting called!\n");

				return real_printf(...args);
			}
		}),

		// include with isolated scope
		render("files/include.uc", proto({
			printf: function(...args) {
				real_printf("This is the wrapped printf() getting called!\n");

				return real_printf(...args);
			}
		}, {}))
	]);
%}
-- End --

-- File include.uc --
{%
	printf("This is the include file running! Can I access the global env? %s\n",
		REQUIRE_SEARCH_PATH ? "Yes!" : "No.");
%}
-- End --

-- Expect stdout --
[
	"This is the include file running! Can I access the global env? Yes!\n",
	"This is the include file running! Can I access the global env? Yes!\n",
	"This is the wrapped printf() getting called!\nThis is the include file running! Can I access the global env? Yes!\n",
	"This is the wrapped printf() getting called!\nThis is the include file running! Can I access the global env? No.\n"
]
-- End --


An invalid path value triggers an exception.

-- Testcase --
{%
	render(true);
%}
-- End --

-- Expect stderr --
Type error: Passed filename is not a string
In line 2, byte 13:

 `    render(true);`
  Near here -----^


-- End --


An invalid scope value triggers an exception.

-- Testcase --
{%
	render("test", true);
%}
-- End --

-- Expect stderr --
Type error: Passed scope value is not an object
In line 2, byte 21:

 `    render("test", true);`
  Near here -------------^


-- End --


A not found file triggers an exception.

-- Testcase --
{%
	render("files/doesnotexist.uc");
%}
-- End --

-- Expect stderr --
Runtime error: Include file not found
In line 2, byte 32:

 `    render("files/doesnotexist.uc");`
  Near here ------------------------^


-- End --


A compilation error in the file triggers an exception.

-- Testcase --
{%
	render("files/broken.uc");
%}
-- End --

-- File broken.uc --
{%
	// Unclosed object to force syntax error
	return {
%}
-- End --

-- Expect stderr --
Runtime error: Unable to compile source file './files/broken.uc':

  | Syntax error: Expecting label
  | In line 4, byte 1:
  |
  |  `    return {`
  |   Near here --^

In line 2, byte 26:

 `    render("files/broken.uc");`
  Near here ------------------^


-- End --


Rendering a function value will capture it's output.

-- Testcase --
{%
	name = "world";

	printf("%.J\n", [
		render(print, "Test"),
		render(loadstring("Hello, {{ name }}!")),
		render(function(name) {
			include("files/greeting.uc", { name })
		}, "Bob")
	]);
%}
-- End --

-- File greeting.uc --
Hello, {{ name }}
-- End --

-- Expect stdout --
[
	"Test",
	"Hello, world!",
	"Hello, Bob\n"
]
-- End --