Fix incorrect path taken when rescue nested inside a rescue/else

lib/natalie/compiler/instructions/try_instruction.rb

@@ -49,16 +49,14 @@ def generate(transform)
           code << '} catch(ExceptionObject *exception) {'
 
           code << 'auto exception_was = env->exception()'
-
-          code << 'GlobalEnv::the()->set_rescued(true)'
           code << 'env->set_exception(exception)'
 
           transform.with_same_scope(catch_body) do |t|
             code << t.transform(@discard_catch_result ? nil : "#{result} =")
           end
 
-          code << 'if (exception_was) env->set_exception(exception_was)'
-          code << 'else env->clear_exception()'
+          code << 'env->set_exception(exception_was)'
+          code << 'GlobalEnv::the()->set_rescued(true)'
 
           code << '}'
         end

src/env.cpp

@@ -264,11 +264,9 @@ Value Env::exception_object() {
 
 ExceptionObject *Env::exception() {
     auto e = this;
-    for (;;) {
+    while (e) {
         if (e->m_exception)
             return e->m_exception;
-        if (!e->m_caller)
-            break;
         e = e->m_caller;
     }
     return nullptr;

src/kernel_module.cpp

@@ -473,9 +473,8 @@ Value KernelModule::puts(Env *env, Args args) {
 
 Value KernelModule::raise(Env *env, Value klass, Value message) {
     if (!klass) {
-        if (env->exception())
-            klass = env->exception();
-        else {
+        klass = env->exception();
+        if (!klass) {
             klass = find_top_level_const(env, "RuntimeError"_s);
             message = new StringObject { "" };
         }

test/natalie/rescue_test.rb

@@ -123,6 +123,49 @@ def test_until2
       end
       $!.message.should == 'foo'
     end
+    $!.should be_nil
+
+    begin
+      raise 'foo'
+    rescue
+      begin
+      rescue
+      else
+        $!.message.should == 'foo'
+      end
+      $!.message.should == 'foo'
+    end
+  end
+
+  it 'does not get confused by nested rescues' do
+    ran = []
+    begin
+      raise 'foo'
+    rescue
+      ran << :rescue
+      begin
+      rescue
+      end
+    else
+      ran << :else
+    end
+    ran.should == [:rescue]
+  end
+
+  it 'does not get confused by an unused LocalJumpError' do
+    ran = []
+    l = -> {
+      begin
+        raise 'foo'
+      rescue
+        ran << :rescue
+        nil.tap { return 'bar' if false } # return here could raise a LocalJumpError, but doesn't
+      else
+        ran << :else
+      end
+    }
+    l.call
+    ran.should == [:rescue]
   end
 end