compiler: optimize function return opcode generation

Track last emitted statement type in compiled code and only generate final
`return null` opcodes if there is no preceeding `return` statement.

Also use this statement tracking to avoid emitting invalid return opcodes
for arrow function bodies with trailing empty statements.

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

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/custom/99_bugs/41_compiler_invalid_return_opcode b/tests/custom/99_bugs/41_compiler_invalid_return_opcode
new file mode 100644
index 0000000..a97dae9
--- /dev/null
+++ b/tests/custom/99_bugs/41_compiler_invalid_return_opcode
@@ -0,0 +1,20 @@
+When compiling an arrow function body with a trailing loop or conditional
+statement having an empty body, the emitted return code incorrectly
+overwrote the target address of the jump instruction.
+
+-- Testcase --
+(() => {
+	if(0)
+		;
+})();
+
+print("OK\n");
+-- End --
+
+-- Args --
+-R
+-- End --
+
+-- Expect stdout --
+OK
+-- End --