From fe2efbb2fc816263e3e6d5d51e9edc70179348ba Mon Sep 17 00:00:00 2001
From: Luke Wilde <lukew@serenityos.org>
Date: Sun, 17 Jul 2022 19:25:23 +0100
Subject: [PATCH] LibJS/Bytecode: Implement initializers for array binding
 patterns

---
 .../Libraries/LibJS/Bytecode/ASTCodegen.cpp     | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
index 4201467660..5a4e8dd37f 100644
--- a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
@@ -1270,6 +1270,8 @@ static Bytecode::CodeGenerationErrorOr<void> generate_array_binding_pattern_byte
         VERIFY(name.has<Empty>());
 
         if (is_rest) {
+            VERIFY(!initializer);
+
             if (first) {
                 // The iterator has not been called, and is thus known to be not exhausted
                 generator.emit<Bytecode::Op::Load>(iterator_reg);
@@ -1358,6 +1360,21 @@ static Bytecode::CodeGenerationErrorOr<void> generate_array_binding_pattern_byte
         // pattern if necessary.
         generator.switch_to_basic_block(create_binding_block);
 
+        if (initializer) {
+            auto& value_is_undefined_block = generator.make_block();
+            auto& value_is_not_undefined_block = generator.make_block();
+
+            generator.emit<Bytecode::Op::JumpUndefined>().set_targets(
+                Bytecode::Label { value_is_undefined_block },
+                Bytecode::Label { value_is_not_undefined_block });
+
+            generator.switch_to_basic_block(value_is_undefined_block);
+            TRY(initializer->generate_bytecode(generator));
+            generator.emit<Bytecode::Op::Jump>(Bytecode::Label { value_is_not_undefined_block });
+
+            generator.switch_to_basic_block(value_is_not_undefined_block);
+        }
+
         TRY(assign_accumulator_to_alias(alias));
 
         first = false;