LibJS: Implement basic execution of "switch" statements

The "break" keyword now unwinds to the nearest ScopeType::Breakable.
There's no support for break labels yet, but we'll get there too.

Libraries/LibJS/AST.cpp

@@ -873,7 +873,31 @@ Value ThrowStatement::execute(Interpreter& interpreter) const
 
 Value SwitchStatement::execute(Interpreter& interpreter) const
 {
-    (void)interpreter;
+    auto discriminant_result = m_discriminant->execute(interpreter);
+    if (interpreter.exception())
+        return {};
+
+    bool falling_through = false;
+
+    for (auto& switch_case : m_cases) {
+        if (!falling_through && switch_case.test()) {
+            auto test_result = switch_case.test()->execute(interpreter);
+            if (interpreter.exception())
+                return {};
+            if (!eq(discriminant_result, test_result).to_boolean())
+                continue;
+        }
+        falling_through = true;
+
+        for (auto& statement : switch_case.consequent()) {
+            statement.execute(interpreter);
+            if (interpreter.exception())
+                return {};
+            if (interpreter.should_unwind())
+                return {};
+        }
+    }
+
     return {};
 }
 
@@ -885,7 +909,7 @@ Value SwitchCase::execute(Interpreter& interpreter) const
 
 Value BreakStatement::execute(Interpreter& interpreter) const
 {
-    (void)interpreter;
+    interpreter.unwind(ScopeType::Breakable);
     return {};
 }
 

Libraries/LibJS/AST.h

@@ -715,6 +715,9 @@ public:
     {
     }
 
+    const Expression* test() const { return m_test; }
+    const NonnullRefPtrVector<Statement>& consequent() const { return m_consequent; }
+
     virtual void dump(int indent) const override;
     virtual Value execute(Interpreter&) const override;
 

Libraries/LibJS/Interpreter.h

@@ -42,6 +42,7 @@ enum class ScopeType {
     Function,
     Block,
     Try,
+    Breakable,
 };
 
 struct Variable {
@@ -78,6 +79,7 @@ public:
     Heap& heap() { return m_heap; }
 
     void unwind(ScopeType type) { m_unwind_until = type; }
+    bool should_unwind() const { return m_unwind_until != ScopeType::None; }
 
     Optional<Value> get_variable(const FlyString& name);
     void set_variable(const FlyString& name, Value, bool first_assignment = false);

Libraries/LibJS/Tests/switch-basic-2.js

@@ -0,0 +1,10 @@
+var a = "foo";
+
+switch (a + "bar") {
+case 1:
+	break;
+case "foobar":
+case 2:
+        console.log("PASS");
+	break;
+}

Libraries/LibJS/Tests/switch-basic-3.js

@@ -0,0 +1,6 @@
+var a = "foo";
+
+switch (100) {
+default:
+        console.log("PASS");
+}

Libraries/LibJS/Tests/switch-basic.js

@@ -0,0 +1,10 @@
+switch (1 + 2) {
+case 3:
+	console.log("PASS");
+	break;
+case 5:
+case 1:
+	break;
+default:
+	break;
+}