UseVar must not modify fields of anonymous subclasses

Fixes: #241

Author: knutwannheden

src/main/java/org/openrewrite/java/migrate/lang/var/DeclarationCheck.java

@@ -15,11 +15,11 @@
  */
 package org.openrewrite.java.migrate.lang.var;
 
-import static java.util.Objects.requireNonNull;
-
 import org.openrewrite.Cursor;
 import org.openrewrite.java.tree.*;
 
+import static java.util.Objects.requireNonNull;
+
 final class DeclarationCheck {
 
     private DeclarationCheck() {
@@ -37,14 +37,11 @@ private DeclarationCheck() {
      * @return true if var is applicable in general
      */
     public static boolean isVarApplicable(Cursor cursor, J.VariableDeclarations vd) {
-        boolean isMethodParameter = DeclarationCheck.isMethodParameter(vd, cursor);
-        boolean isMultiVarDefinition = !DeclarationCheck.isSingleVariableDefinition(vd);
-        boolean useTernary = DeclarationCheck.initializedByTernary(vd);
-        if (isMethodParameter || isMultiVarDefinition || useTernary) return false;
-
-        boolean isInsideMethod = DeclarationCheck.isInsideMethod(cursor);
-        boolean isInsideInitializer = DeclarationCheck.isInsideInitializer(cursor, 0);
-        return isInsideMethod || isInsideInitializer;
+        if (isField(vd, cursor) || isMethodParameter(vd, cursor) || !isSingleVariableDefinition(vd) || initializedByTernary(vd)) {
+            return false;
+        }
+
+        return isInsideMethod(cursor) || isInsideInitializer(cursor, 0);
     }
 
     /**
@@ -140,6 +137,15 @@ private static boolean isInsideMethod(Cursor cursor) {
         return isNotRoot && isNotClassDeclaration && isMethodDeclaration;
     }
 
+    private static boolean isField(J.VariableDeclarations vd, Cursor cursor) {
+        Cursor parent = cursor.getParentTreeCursor();
+        if (parent.getParent() == null) {
+            return false;
+        }
+        Cursor grandparent = parent.getParentTreeCursor();
+        return parent.getValue() instanceof J.Block && (grandparent.getValue() instanceof J.ClassDeclaration || grandparent.getValue() instanceof J.NewClass);
+    }
+
     /**
      * Determine if the variable declaration at hand is part of a method declaration
      *

src/main/java/org/openrewrite/java/migrate/lang/var/UseVarForObject.java

@@ -64,7 +64,7 @@ static final class UseVarForObjectVisitor extends JavaIsoVisitor<ExecutionContex
         public J.VariableDeclarations visitVariableDeclarations(J.VariableDeclarations vd, ExecutionContext ctx) {
             vd = super.visitVariableDeclarations(vd, ctx);
 
-            boolean isGeneralApplicable = DeclarationCheck.isVarApplicable(this.getCursor(), vd);
+            boolean isGeneralApplicable = DeclarationCheck.isVarApplicable(getCursor(), vd);
             if (!isGeneralApplicable) return vd;
 
             boolean isPrimitive = DeclarationCheck.isPrimitive(vd);

src/test/java/org/openrewrite/java/migrate/lang/var/UseVarForObjectsTest.java

@@ -21,7 +21,8 @@
 import org.openrewrite.DocumentExample;
 import org.openrewrite.test.RecipeSpec;
 
-import static org.openrewrite.java.Assertions.*;
+import static org.openrewrite.java.Assertions.java;
+import static org.openrewrite.java.Assertions.javaVersion;
 
 class UseVarForObjectsTest extends VarBaseTest {
 
@@ -184,6 +185,23 @@ class A {
 
     @Nested
     class NotApplicable {
+        @Test
+        void fieldInAnonymousSubclass() {
+            //language=java
+            rewriteRun(
+              java("""
+                class A {
+                    void m() {
+                        new Object() {
+                            private final Object o1 = new Object();
+                        };
+                    }
+                }
+                """
+              )
+            );
+        }
+
         @Test
         void asParameter() {
             //language=java