GROOVY-11685: STC: null or void return within closure expression (#2243)

Author: eric-milles

src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java

@@ -2397,7 +2397,7 @@ public void visitReturnStatement(final ReturnStatement statement) {
 
     protected ClassNode checkReturnType(final ReturnStatement statement) {
         Expression expression = statement.getExpression();
-        ClassNode type = getType(expression);
+        var type = statement.isReturningNullOrVoid() ? VOID_TYPE : getType(expression); // GROOVY-11685
 
         TypeCheckingContext.EnclosingClosure enclosingClosure = typeCheckingContext.getEnclosingClosure();
         if (enclosingClosure != null) {
@@ -2419,7 +2419,8 @@ protected ClassNode checkReturnType(final ReturnStatement statement) {
                 } else if (statement.isReturningNullOrVoid() ? !isPrimitiveType(inferredReturnType) // GROOVY-7713, GROOVY-8202
                      : GenericsUtils.buildWildcardType(wrapTypeIfNecessary(inferredReturnType)).isCompatibleWith(wrapTypeIfNecessary(type))) {
                     type = inferredReturnType; // GROOVY-8310, GROOVY-10082, GROOVY-10091, GROOVY-10128, GROOVY-10306: allow simple covariance
-                } else if (!isPrimitiveVoid(type) && !extension.handleIncompatibleReturnType(statement, type)) { // GROOVY-10277: incompatible
+                } else if ((statement.isReturningNullOrVoid() || !isPrimitiveVoid(type)) && !extension.handleIncompatibleReturnType(statement, type)) {
+                    // GROOVY-10277, GROOVY-11490: incompatible return statement (null for primitive or inconvertible type)
                     String value = (statement.isReturningNullOrVoid() ? "null" : "value of type " + prettyPrintType(type));
                     String which = (enclosingClosure.getClosureExpression() instanceof LambdaExpression ? "lambda" : "closure");
                     addStaticTypeError("Cannot return " + value + " for " + which + " expecting " + prettyPrintType(inferredReturnType), expression);

src/test/groovy/groovy/transform/stc/ClosuresSTCTest.groovy

@@ -429,6 +429,23 @@ class ClosuresSTCTest extends StaticTypeCheckingTestCase {
         '''
     }
 
+    // GROOVY-11685
+    void testCollect3() {
+        assertScript '''
+            List test(List strings) {
+                List numbers = []
+                if (true) {
+                    numbers = strings.collect { string ->
+                        if (!string.isNumber()) return
+                        (Number) Integer.parseInt(string)
+                    }
+                }
+                numbers
+            }
+            assert test(['1','2','3','x']) == [1,2,3,null]
+        '''
+    }
+
     void testWithIntReturnType() {
         assertScript '''
             class Test {