Add recipe to remove mutable static fields from Recipes (#4557)

* Add recipe to remove mutable static fields from Recipes

* Update NoMutableStaticFieldsInRecipes.java

rewrite-java/src/main/java/org/openrewrite/java/recipes/NoMutableStaticFieldsInRecipes.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2024 the original author or authors.
+ * <p>
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.java.recipes;
+
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.Preconditions;
+import org.openrewrite.Recipe;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.internal.ListUtils;
+import org.openrewrite.java.JavaIsoVisitor;
+import org.openrewrite.java.search.UsesType;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.TypeUtils;
+
+public class NoMutableStaticFieldsInRecipes extends Recipe {
+    @Override
+    public String getDisplayName() {
+        return "Recipe classes should not have mutable `static` fields";
+    }
+
+    @Override
+    public String getDescription() {
+        return "Remove mutable static fields from Recipe classes to discourage their use.";
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        return Preconditions.check(
+                new UsesType<>("org.openrewrite.Recipe", true),
+                new JavaIsoVisitor<ExecutionContext>() {
+                    @Override
+                    public J.ClassDeclaration visitClassDeclaration(J.ClassDeclaration classDecl, ExecutionContext ctx) {
+                        J.ClassDeclaration cd = super.visitClassDeclaration(classDecl, ctx);
+                        if (TypeUtils.isAssignableTo("org.openrewrite.Recipe", cd.getType())) {
+                            return cd.withBody(cd.getBody().withStatements(ListUtils.map(cd.getBody().getStatements(), stmt -> {
+                                        if (stmt instanceof J.VariableDeclarations) {
+                                            J.VariableDeclarations field = (J.VariableDeclarations) stmt;
+                                            if (field.hasModifier(J.Modifier.Type.Static) && !field.hasModifier(J.Modifier.Type.Final)) {
+                                                // We want to discourage the use of mutable static fields in recipes,
+                                                // so rather than make them immutable, we'll just remove the field.
+                                                // Any fields that were intended as constants should be made final.
+                                                return null;
+                                            }
+                                        }
+                                        return stmt;
+                                    })
+                            ));
+                        }
+                        return cd;
+                    }
+                }
+        );
+    }
+}

rewrite-java/src/test/java/org/openrewrite/java/recipes/NoMutableStaticFieldsInRecipesTest.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2024 the original author or authors.
+ * <p>
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.java.recipes;
+
+import org.junit.jupiter.api.Test;
+import org.openrewrite.DocumentExample;
+import org.openrewrite.java.JavaParser;
+import org.openrewrite.test.RecipeSpec;
+import org.openrewrite.test.RewriteTest;
+
+import static org.openrewrite.java.Assertions.java;
+
+class NoMutableStaticFieldsInRecipesTest implements RewriteTest {
+
+    @Override
+    public void defaults(RecipeSpec spec) {
+        spec
+          .recipe(new NoMutableStaticFieldsInRecipes())
+          .parser(JavaParser.fromJavaVersion().classpath(JavaParser.runtimeClasspath()));
+    }
+
+    @Test
+    @DocumentExample
+    void removeNonFinalStaticFields() {
+        rewriteRun(
+          java(
+            """
+              import org.openrewrite.Recipe;
+              
+              public class A extends Recipe {
+                  static final int immutable = 0;
+                  static int mutable = 0;
+              }
+              """,
+            """
+              import org.openrewrite.Recipe;
+              
+              public class A extends Recipe {
+                  static final int immutable = 0;
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void retainFieldsOutsideRecipes() {
+        rewriteRun(
+          java(
+            """
+              import org.openrewrite.Recipe;
+              
+              public class A {
+                  static final int immutable = 0;
+                  static int mutable = 0;
+              }
+              """
+          )
+        );
+    }
+}