Fix closure void return anywhere (wurstscript#1172)

Author: Frotty

de.peeeq.wurstscript/src/main/java/de/peeeq/wurstscript/validation/WurstValidator.java

@@ -2052,7 +2052,8 @@ private void visit(Modifiers modifiers) {
     private void visit(StmtReturn s) {
         if (s.attrNearestExprStatementsBlock() != null) {
             ExprStatementsBlock e = s.attrNearestExprStatementsBlock();
-            if (!isClosureImplementationBlock(e) && e.getReturnStmt() != s) {
+            boolean closureImplementationBlock = isClosureImplementationBlock(e);
+            if (!closureImplementationBlock && e.getReturnStmt() != s) {
                 s.addError("Return in a statements block can only be at the end.");
                 return;
             }
@@ -2062,7 +2063,9 @@ private void visit(StmtReturn s) {
                     s.addError("Cannot return void from statements block.");
                 }
             } else {
-                s.addError("Cannot have empty return statement in statements block.");
+                if (!closureImplementationBlock || !closureReturnsVoid(e)) {
+                    s.addError("Cannot have empty return statement in statements block.");
+                }
             }
         } else {
             FunctionImplementation func = s.attrNearestFuncDef();
@@ -2079,6 +2082,16 @@ private boolean isClosureImplementationBlock(ExprStatementsBlock block) {
         return parent instanceof ExprClosure && ((ExprClosure) parent).getImplementation() == block;
     }
 
+    private boolean closureReturnsVoid(ExprStatementsBlock block) {
+        Element parent = block.getParent();
+        if (!(parent instanceof ExprClosure)) {
+            return false;
+        }
+        ExprClosure closure = (ExprClosure) parent;
+        FuncLink abstractMethod = closure.attrClosureAbstractMethod();
+        return abstractMethod != null && abstractMethod.getReturnType().isVoid();
+    }
+
     private void checkReturnInFunc(StmtReturn s, FunctionImplementation func) {
         WurstType returnType = func.attrReturnTyp();
         if (s.getReturnedObj() instanceof Expr) {

de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/ClosureTests.java

@@ -499,6 +499,27 @@ public void closure_multipleEarlyReturns_inStatementsBlock() {
         );
     }
 
+    @Test
+    public void closure_multipleEmptyEarlyReturns_inVoidStatementsBlock() {
+        testAssertOkLines(true,
+                "package test",
+                "native testSuccess()",
+                "interface FnVoid",
+                "    function run()",
+                "function call(FnVoid f)",
+                "    f.run()",
+                "int x = 0",
+                "init",
+                "    call() ->",
+                "        x = 1",
+                "        if true",
+                "            return",
+                "        x = 2",
+                "    if x == 1",
+                "        testSuccess()"
+        );
+    }
+
     @Test
     public void statementsBlockOutsideClosure_stillRequiresReturnAtEnd() {
         testAssertErrorsLines(false, "Return in a statements block can only be at the end.",