[groovy] dfa: check reassigned type in @CompileStatic (IDEA-186753)

plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/expressions/GrReferenceExpressionImpl.java

@@ -310,7 +310,19 @@ public class GrReferenceExpressionImpl extends GrReferenceElementImpl<GrExpressi
 
     Boolean reassigned = GrReassignedLocalVarsChecker.isReassignedVar(refExpr);
     if (reassigned != null && reassigned.booleanValue()) {
-      return GrReassignedLocalVarsChecker.getReassignedVarType(refExpr, true);
+      PsiType reassignedType = GrReassignedLocalVarsChecker.getReassignedVarType(refExpr, true);
+      if (reassignedType == null) {
+        return nominal;
+      }
+      else if (nominal == null) {
+        return reassignedType;
+      }
+      else if (TypeConversionUtil.isAssignable(TypeConversionUtil.erasure(nominal), reassignedType, false)) {
+        return reassignedType;
+      }
+      else {
+        return nominal;
+      }
     }
 
     final PsiType inferred = getInferredTypes(refExpr, resolved);

plugins/groovy/test/org/jetbrains/plugins/groovy/lang/resolve/TypeInferenceTest.groovy

@@ -1091,4 +1091,17 @@ while (condition) {
 <caret>prevParent
 ''', 'java.lang.String'
   }
+
+  void 'test String variable assigned with GString inside closure @CS'() {
+    doTest '''\
+@groovy.transform.CompileStatic
+def test() {
+    String key
+    return {
+        key = "hi ${"there"}"
+        <caret>key
+    }
+}
+''', JAVA_LANG_STRING
+  }
 }