lib: extend render() to support function values

Extend the `render()` function to accept a function value as first argument,
which allows running arbitrary ucode functions and capturing their output.

This is especially useful in conjunction with `loadfile()` or `loadstring()`
to dynamically compile templates and rendering their output into a string.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 6 insertions, 1 deletions

diff --git a/lib.c b/lib.c
index d5e02a5..5d76cc8 100644
--- a/lib.c
+++ b/lib.c
@@ -2484,8 +2484,13 @@ uc_render(uc_vm_t *vm, size_t nargs)
 	prev = vm->output;
 	vm->output = mem;
 
+	/* execute function */
+	if (ucv_is_callable(uc_fn_arg(0)))
+		(void) uc_vm_call(vm, false, nargs - 1);
+
 	/* execute include */
-	(void) uc_include_common(vm, nargs, false);
+	else
+		(void) uc_include_common(vm, nargs, false);
 
 	/* restore previous VM output */
 	vm->output = prev;