feat: normalize effective getter methods

src/main/java/org/openrewrite/java/migrate/lombok/LombokUtils.java

@@ -85,7 +85,25 @@ private static boolean hasMatchingTypeAndGetterName(J.MethodDeclaration method,
         return false;
     }
 
-    private static String deriveGetterMethodName(@Nullable JavaType type, String fieldName) {
+    public static boolean isEffectivelyGetter(J.MethodDeclaration method) {
+        if (!method.getParameters().isEmpty() && !(method.getParameters().get(0) instanceof J.Empty)) {
+            return false;
+        }
+        if (method.getBody() == null ||
+                method.getBody().getStatements().size() != 1 ||
+                !(method.getBody().getStatements().get(0) instanceof J.Return)) {
+            return false;
+        }
+        Expression returnExpression = ((J.Return) method.getBody().getStatements().get(0)).getExpression();
+        if (!(returnExpression instanceof J.Identifier) && !(returnExpression instanceof J.FieldAccess)) {
+            return false;
+        }
+        // compiler already guarantees that the returned variable is a subtype of the method type, but we want an exact match
+        return method.getType() == returnExpression.getType();
+    }
+
+    public static String deriveGetterMethodName(@Nullable JavaType type, String fieldName) {
+
         if (type == JavaType.Primitive.Boolean) {
             boolean alreadyStartsWithIs = fieldName.length() >= 3 &&
                     fieldName.substring(0, 3).matches("is[A-Z]");

src/main/java/org/openrewrite/java/migrate/lombok/NormalizeGetter.java

@@ -0,0 +1,139 @@
+/*
+ * 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.migrate.lombok;
+
+import lombok.EqualsAndHashCode;
+import lombok.Value;
+import org.jspecify.annotations.Nullable;
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.ScanningRecipe;
+import org.openrewrite.Tree;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.java.ChangeMethodName;
+import org.openrewrite.java.JavaIsoVisitor;
+import org.openrewrite.java.MethodMatcher;
+import org.openrewrite.java.tree.Expression;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.JavaType;
+import org.openrewrite.java.tree.TypeUtils;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+
+import static java.util.stream.Collectors.toList;
+
+@Value
+@EqualsAndHashCode(callSuper = false)
+public class NormalizeGetter extends ScanningRecipe<List<NormalizeGetter.RenameRecord>> {
+
+    private final static String DO_NOT_RENAME = "DO_NOT_RENAME";
+
+    @Override
+    public String getDisplayName() {
+        return "Rename getter methods to fit Lombok";
+    }
+
+    @Override
+    public String getDescription() {
+        return "Rename methods that are effectively getter to the name Lombok would give them.\n\n" +
+                "Limitations:\n" +
+                " - If two methods in a class are effectively the same getter then one's name will be corrected and the others name will be left as it is.\n" +
+                " - If the correct name for a method is already taken by another method then the name will not be corrected.\n" +
+                " - Method name swaps or circular renaming within a class cannot be performed because the names block each other.\n" +
+                "E.g. `int getFoo() { return ba; } int getBa() { return foo; }` stays as it is."
+                ;
+    }
+
+    @Value
+    public static class RenameRecord {
+        String methodPattern;
+        String newMethodName;
+    }
+
+    @Override
+    public List<RenameRecord> getInitialValue(ExecutionContext ctx) {
+        return new ArrayList<>();
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getScanner(List<RenameRecord> renameRecords) {
+        return new JavaIsoVisitor<ExecutionContext>() {
+            @Override
+            public J.CompilationUnit visitCompilationUnit(J.CompilationUnit cu, ExecutionContext ctx) {
+                // Cheaply collect all declared methods; this also means we do not support clashing nested class methods
+                Set<JavaType.Method> declaredMethods = cu.getTypesInUse().getDeclaredMethods();
+                List<String> existingMethodNames = new ArrayList<>();
+                for (JavaType.Method method : declaredMethods) {
+                    existingMethodNames.add(method.getName());
+                }
+                getCursor().putMessage(DO_NOT_RENAME, existingMethodNames);
+                return super.visitCompilationUnit(cu, ctx);
+            }
+
+            @Override
+            public J.MethodDeclaration visitMethodDeclaration(J.MethodDeclaration method, ExecutionContext ctx) {
+                if (method.getMethodType() == null || method.getBody() == null ||
+                        !LombokUtils.isEffectivelyGetter(method) ||
+                        TypeUtils.isOverride(method.getMethodType())) {
+                    return method;
+                }
+
+                String simpleName;
+                Expression returnExpression = ((J.Return) method.getBody().getStatements().get(0)).getExpression();
+                if (returnExpression instanceof J.Identifier) {
+                    simpleName = ((J.Identifier) returnExpression).getSimpleName();
+                } else if (returnExpression instanceof J.FieldAccess) {
+                    simpleName = ((J.FieldAccess) returnExpression).getSimpleName();
+                } else {
+                    return method;
+                }
+
+                // If method already has the name it should have, then nothing to be done
+                String expectedMethodName = LombokUtils.deriveGetterMethodName(returnExpression.getType(), simpleName);
+                if (expectedMethodName.equals(method.getSimpleName())) {
+                    return method;
+                }
+
+                // If the desired method name is already taken by an existing method, the current method cannot be renamed
+                List<String> doNotRename = getCursor().getNearestMessage(DO_NOT_RENAME);
+                assert doNotRename != null;
+                if (doNotRename.contains(expectedMethodName)) {
+                    return method;
+                }
+
+                renameRecords.add(new RenameRecord(MethodMatcher.methodPattern(method), expectedMethodName));
+                doNotRename.remove(method.getSimpleName()); //actual method name becomes available again
+                doNotRename.add(expectedMethodName); //expected method name now blocked
+                return method;
+            }
+        };
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor(List<RenameRecord> renameRecords) {
+        return new TreeVisitor<Tree, ExecutionContext>() {
+            @Override
+            public @Nullable Tree visit(@Nullable Tree tree, ExecutionContext ctx) {
+                for (RenameRecord rr : renameRecords) {
+                    tree = new ChangeMethodName(rr.methodPattern, rr.newMethodName, true, null)
+                            .getVisitor().visit(tree, ctx);
+                }
+                return tree;
+            }
+        };
+    }
+}