fix: ✨ allow empty return in void functions

TODO.md

@@ -3,7 +3,7 @@
 ## Bug fixes
 - [x] Parser expects exactly one newline at the end of the file
 - [x] Disallow return in top level
-- [ ] Allow return void
+- [x] Allow return void
 
 ## Refactoring
 - [ ] Replace SourceLocation by Span

src/Backend/Codegen.cpp

@@ -339,19 +339,24 @@ void Codegen::visit(FuncDecl *node) {
     //    auto instrs = deferStack.top();
     //    deferStack.pop();
 
-    if (visit(node->getReturnType()) == Builder->getVoidTy())
+    if (visit(node->getReturnType()) == Builder->getVoidTy() && !isReturn)
         Builder->CreateRetVoid();
 
+    isReturn = false;
+
+    // Verify function
     std::string output;
     llvm::raw_string_ostream oss(output);
     if (llvm::verifyFunction(*F, &oss)) {
         F->print(outs());
         throw CodegenError("Invalid Function {}\n{}", node->getName(), output);
     }
 
+    // Insert Function to Symbol Table
     Scope = Scope->getParent();
     Scope->insertSymbol(node->getName(), F, F->getFunctionType());
 
+    // Reset Insert Point to Top Level
     Builder->SetInsertPoint(&TopLevelFunc->back());
 }
 
@@ -422,7 +427,11 @@ void Codegen::visit(Return *node) {
     if (Builder->GetInsertBlock()->getParent() == TopLevelFunc)
         throw CodegenError("Return statements are not allowed at top-level\n");
 
-    Builder->CreateRet(visit(node->getValue()));
+    isReturn = true;
+    if (node->getValue() == nullptr)
+        Builder->CreateRetVoid();
+    else
+        Builder->CreateRet(visit(node->getValue()));
 }
 
 void Codegen::visit(Defer * /*node*/) {

src/Backend/Codegen.h

@@ -44,6 +44,7 @@ namespace lesma {
         std::stack<std::vector<llvm::Value *>> deferStack;
         llvm::Function *TopLevelFunc;
         bool isBreak = false;
+        bool isReturn = false;
 
     public:
         std::vector<ThreadSafeModule> Modules;

src/Frontend/Parser.cpp

@@ -305,6 +305,10 @@ Statement *Parser::ParseContinue() {
 Statement *Parser::ParseReturn() {
     auto loc = Peek()->loc;
     Consume(TokenType::RETURN);
+    if (Check(TokenType::NEWLINE) || Peek()->type == TokenType::EOF_TOKEN) {
+        ConsumeNewline();
+        return reinterpret_cast<Statement *>(new Return(loc, nullptr));
+    }
     auto val = ParseExpression();
     ConsumeNewline();
     return reinterpret_cast<Statement *>(new Return(loc, val));