eval: keep references to function contexts

Otherwise the "this" context might be gc'ed before the function can access it.
This bug manifested itself with long chained expressions such as:

    require("fs").open("file.txt").read(10)

The file handle produced by open() was gc'ed before invoking read() on it due
to the evaluation not increasing its refcount.

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

1 files changed, 9 insertions, 3 deletions

diff --git a/eval.c b/eval.c
index 1e8d9a3..0f1d7b2 100644
--- a/eval.c
+++ b/eval.c
@@ -1326,7 +1326,9 @@ ut_execute_op(struct ut_state *state, uint32_t off)
 
 	case T_LABEL:
 		scope = ut_getref(state, off, &key);
-		state->ctx = scope;
+
+		ut_putval(state->ctx);
+		state->ctx = json_object_get(scope);
 
 		val = ut_getval(scope, key);
 		ut_putval(scope);
@@ -1335,7 +1337,9 @@ ut_execute_op(struct ut_state *state, uint32_t off)
 
 	case T_DOT:
 		scope = ut_getref_required(state, off, &key);
-		state->ctx = scope;
+
+		ut_putval(state->ctx);
+		state->ctx = json_object_get(scope);
 
 		if (!key)
 			return scope;
@@ -1349,7 +1353,9 @@ ut_execute_op(struct ut_state *state, uint32_t off)
 		/* postfix access */
 		if (op->is_postfix) {
 			scope = ut_getref_required(state, off, &key);
-			state->ctx = scope;
+
+			ut_putval(state->ctx);
+			state->ctx = json_object_get(scope);
 
 			if (!key)
 				return scope;