compiler: ensure that arrow functions with block bodies return no value

Follow ES6 semantics and ensure that arrow functions with a block body
don't implicitly return the value of the last executed statement.

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

1 files changed, 24 insertions, 1 deletions

diff --git a/tests/custom/00_syntax/19_arrow_functions b/tests/custom/00_syntax/19_arrow_functions
index 8dcce6c..761705b 100644
--- a/tests/custom/00_syntax/19_arrow_functions
+++ b/tests/custom/00_syntax/19_arrow_functions
@@ -38,7 +38,7 @@ test
 
 	// parentheses may be omitted if arrow function takes only one argument
 	test4_fn = a => {
-		a * 2;
+		return a * 2;
 	};
 
 	// curly braces may be omitted if function body is a single expression
@@ -122,3 +122,26 @@ In line 2, byte 10:
 	(a + 1) => { print("test\n") }
 %}
 -- End --
+
+
+Arrow functions consisting of a single expression implicitly return the expression
+results. Arrow functions having a statement block as body do not return any result
+by default but may return explictly.
+
+-- Expect stdout --
+[
+	4,
+	null,
+	4
+]
+-- End --
+
+-- Testcase --
+{%
+	printf("%.J\n", [
+		(() => 2 * 2)(),
+		(() => { 2 * 2 })(),
+		(() => { return 2 * 2 })()
+	]);
+%}
+-- End --