Do not remove private fields with missing types

Fixes #524

Author: timtebeek

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedPrivateFields.java

@@ -18,13 +18,11 @@
 import lombok.EqualsAndHashCode;
 import lombok.Value;
 import org.jspecify.annotations.Nullable;
-import org.openrewrite.Cursor;
-import org.openrewrite.ExecutionContext;
-import org.openrewrite.Recipe;
-import org.openrewrite.TreeVisitor;
+import org.openrewrite.*;
 import org.openrewrite.java.AnnotationMatcher;
 import org.openrewrite.java.JavaIsoVisitor;
 import org.openrewrite.java.JavaVisitor;
+import org.openrewrite.java.NoMissingTypes;
 import org.openrewrite.java.service.AnnotationService;
 import org.openrewrite.java.tree.J;
 import org.openrewrite.java.tree.Space;
@@ -62,7 +60,7 @@ public Duration getEstimatedEffortPerOccurrence() {
 
     @Override
     public TreeVisitor<?, ExecutionContext> getVisitor() {
-        return new JavaIsoVisitor<ExecutionContext>() {
+        JavaIsoVisitor<ExecutionContext> visitor = new JavaIsoVisitor<ExecutionContext>() {
             @Value
             class CheckField {
                 J.VariableDeclarations declarations;
@@ -147,6 +145,7 @@ private boolean isSerialVersionUid(J.VariableDeclarations vd) {
                        vd.getVariables().stream().anyMatch(it -> "serialVersionUID".equals(it.getSimpleName()));
             }
         };
+        return Preconditions.check(new NoMissingTypes(), Repeat.repeatUntilStable(visitor));
     }
 
     private static class VariableUses {

src/test/java/org/openrewrite/staticanalysis/RemoveUnusedPrivateFieldsTest.java

@@ -23,6 +23,7 @@
 import org.openrewrite.java.JavaParser;
 import org.openrewrite.test.RecipeSpec;
 import org.openrewrite.test.RewriteTest;
+import org.openrewrite.test.TypeValidation;
 
 import static org.openrewrite.java.Assertions.java;
 
@@ -446,4 +447,42 @@ class A {
           )
         );
     }
+
+    @Issue("https://github.com/openrewrite/rewrite-static-analysis/issues/524")
+    @Test
+    void removeUntilStable() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+              public class Test {
+                  private String a = "a";
+                  private String ab = a + "b";
+                  private String abc = ab + "c";
+              }
+              """,
+            """
+              public class Test {
+              }
+              """
+          )
+        );
+    }
+
+    @Issue("https://github.com/openrewrite/rewrite-static-analysis/issues/524")
+    @Test
+    void doNotRemoveWhenThereAreMissingTypes() {
+        rewriteRun(
+          spec -> spec.typeValidationOptions(TypeValidation.all().identifiers(false)),
+          //language=java
+          java(
+            """
+              import can.not.be.Found;
+              public class Test {
+                  private Found notUsed;
+              }
+              """
+          )
+        );
+    }
 }