feat: normalize effective getter methods

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

@@ -70,7 +70,25 @@ 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) {
+        boolean takesNoParameters = method.getParameters().get(0) instanceof J.Empty;
+        boolean singularReturn = method.getBody() != null //abstract methods can be null
+                && method.getBody().getStatements().size() == 1 //
+                && method.getBody().getStatements().get(0) instanceof J.Return;
+
+        if (takesNoParameters && singularReturn) {
+            Expression returnExpression = ((J.Return) method.getBody().getStatements().get(0)).getExpression();
+            //returns just an identifier
+            if (returnExpression instanceof J.Identifier) {
+                J.Identifier identifier = (J.Identifier) returnExpression;
+                JavaType.Variable fieldType = identifier.getFieldType();
+                return method.getType().equals(fieldType.getType()); //type match
+            }
+        }
+        return false;
+    }
+
+    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 +1,147 @@
+/*
+ * 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.tree.J;
+
+import java.util.ArrayList;
+import java.util.List;
+
+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() {
+        //language=markdown
+        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." +
+                " - If the correct name for a method is already taken by another method then the name will not be corrected." +
+                " - Method name swaps or circular renaming within a class cannot be performed because the names block each other. " +
+                "E.g. `int getFoo() { return ba; } int getBa() { return foo; }` stays as it is."
+                ;
+    }
+
+    @Value
+    public static class RenameRecord {
+        String pathToClass_;
+        String methodName_;
+        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.ClassDeclaration visitClassDeclaration(J.ClassDeclaration classDecl, ExecutionContext ctx) {
+                List<String> doNotRename = classDecl.getBody().getStatements().stream()
+                        .filter(s -> s instanceof J.MethodDeclaration)
+                        .map(s -> (J.MethodDeclaration) s)
+                        .map(J.MethodDeclaration::getSimpleName)
+                        .collect(toList());
+                getCursor().putMessage(DO_NOT_RENAME, doNotRename);
+
+                return super.visitClassDeclaration(classDecl, ctx);
+            }
+
+            @Override
+            public J.MethodDeclaration visitMethodDeclaration(J.MethodDeclaration method, ExecutionContext ctx) {
+                assert method.getMethodType() != null;
+
+                if (!LombokUtils.isEffectivelyGetter(method)) {
+                    return method;
+                }
+
+                //return early if the method overrides another
+                //if the project defined both the original and the overridden method,
+                // then the renaming of the "original" in the base class will cover the override
+                if (method.getLeadingAnnotations().stream().anyMatch(a -> "Override".equals(a.getSimpleName()))) {
+                    return method;
+                }
+
+                J.Return return_ = (J.Return) method.getBody().getStatements().get(0);
+                J.Identifier returnExpression = (J.Identifier) return_.getExpression();
+
+                String expectedMethodName = LombokUtils.deriveGetterMethodName(returnExpression.getType(), returnExpression.getSimpleName());
+                String actualMethodName = method.getSimpleName();
+
+                //if method already has the name it should have, then nothing to be done
+                if (expectedMethodName.equals(actualMethodName)) {
+                    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;
+                }
+                //WON'T DO: there is a rare edge case, that is not addressed yet.
+                // If `getFoo()` returns `ba` and `getBa()` returns `foo` then neither will be renamed.
+                // This could be fixed by compiling a list of planned changes and doing a soundness check (and not renaming sequentially, or rather introducing temporary method names)
+                // At this point I don't think it's worth the effort.
+
+
+                String pathToClass = method.getMethodType().getDeclaringType().getFullyQualifiedName().replace('$', '.');
+                //todo write separate recipe for merging effective getters
+                renameRecords.add(new RenameRecord(pathToClass, actualMethodName, expectedMethodName));
+                doNotRename.remove(actualMethodName); //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) {
+                    String methodPattern = String.format("%s %s()", rr.pathToClass_, rr.methodName_);
+                    tree = new ChangeMethodName(methodPattern, rr.newMethodName_, true, null)
+                            .getVisitor().visit(tree, ctx);
+                }
+                return tree;
+            }
+        };
+    }
+}