"field" reassignment: fix and test

compiler/frontend/src/org/jetbrains/kotlin/cfg/JetFlowInformationProvider.java

@@ -47,6 +47,7 @@ import org.jetbrains.kotlin.cfg.pseudocodeTraverser.Edges;
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.PseudocodeTraverserPackage;
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.TraversalOrder;
 import org.jetbrains.kotlin.descriptors.*;
+import org.jetbrains.kotlin.descriptors.impl.SyntheticFieldDescriptor;
 import org.jetbrains.kotlin.diagnostics.Diagnostic;
 import org.jetbrains.kotlin.diagnostics.DiagnosticFactory;
 import org.jetbrains.kotlin.diagnostics.Errors;
@@ -400,8 +401,11 @@ public class JetFlowInformationProvider {
             @NotNull Collection<VariableDescriptor> varWithValReassignErrorGenerated
     ) {
         VariableDescriptor variableDescriptor = ctxt.variableDescriptor;
-        if (JetPsiUtil.isBackingFieldReference(expression) && variableDescriptor instanceof PropertyDescriptor) {
+        if (variableDescriptor instanceof SyntheticFieldDescriptor
-            PropertyDescriptor propertyDescriptor = (PropertyDescriptor) variableDescriptor;
+            || (JetPsiUtil.isBackingFieldReference(expression) && variableDescriptor instanceof PropertyDescriptor)) {
+            PropertyDescriptor propertyDescriptor = variableDescriptor instanceof SyntheticFieldDescriptor
+                                                    ? ((SyntheticFieldDescriptor) variableDescriptor).getPropertyDescriptor()
+                                                    : (PropertyDescriptor) variableDescriptor;
             JetPropertyAccessor accessor = PsiTreeUtil.getParentOfType(expression, JetPropertyAccessor.class);
             if (accessor != null) {
                 DeclarationDescriptor accessorDescriptor = trace.get(BindingContext.DECLARATION_TO_DESCRIPTOR, accessor);

compiler/testData/diagnostics/tests/backingField/FieldReassignment.kt

@@ -0,0 +1,5 @@
+val my: Int = 1
+    get() {
+        field++
+        return field
+    }

compiler/testData/diagnostics/tests/backingField/FieldReassignment.txt

@@ -0,0 +1,3 @@
+package
+
+public val my: kotlin.Int = 1

compiler/tests/org/jetbrains/kotlin/checkers/JetDiagnosticsTestGenerated.java

@@ -1362,6 +1362,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("FieldReassignment.kt")
+            public void testFieldReassignment() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/backingField/FieldReassignment.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("FieldShadow.kt")
             public void testFieldShadow() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/backingField/FieldShadow.kt");