Introduce Rewrite & PMD covering S1144: Unused "private" methods should be removed

Vincent Potucek · Vincent Potucek · commit 297f424fc04d · 2025-08-31T20:38:41.000+02:00
Signed-off-by: Vincent Potucek &lt;vpotucek@me.com&gt;
diff --git a/.github/workflows/precommit.yml b/.github/workflows/precommit.yml
@@ -26,3 +26,8 @@ jobs:
         shell: bash
         run: |
           ./gradlew javadoc precommit --parallel
+      - name: Run Gradle (rewrite)
+        continue-on-error: ${{ matrix.experimental }}
+        shell: bash
+        run: ./gradlew rewriteDryRun -Dorg.gradle.jvmargs=-Xmx8G
+        timeout-minutes: 90 # dependency lookup takes 15 mins
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -14,6 +14,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Use S3CrtClient for higher throughput while uploading files to S3 ([#18800](https://github.com/opensearch-project/OpenSearch/pull/18800))
 - Add a dynamic setting to change skip_cache_factor and min_frequency for querycache ([#18351](https://github.com/opensearch-project/OpenSearch/issues/18351))
 - Add overload constructor for Translog to accept Channel Factory as a parameter ([#18918](https://github.com/opensearch-project/OpenSearch/pull/18918))
+- Introduce `Rewrite & PMD` covering S1144: Unused "private" methods should be removed ([#18791](https://github.com/opensearch-project/OpenSearch/pull/18791))
 
 ### Changed
 - Add CompletionStage variants to methods in the Client Interface and default to ActionListener impl ([#18998](https://github.com/opensearch-project/OpenSearch/pull/18998))
diff --git a/DEVELOPER_GUIDE.md b/DEVELOPER_GUIDE.md
@@ -76,9 +76,9 @@ Fork [opensearch-project/OpenSearch](https://github.com/opensearch-project/OpenS
 
 #### JDK
 
-OpenSearch recommends building with the [Temurin/Adoptium](https://adoptium.net/temurin/releases/) distribution. JDK 11 is the minimum supported, and JDK-24 is the newest supported. You must have a supported JDK installed with the environment variable `JAVA_HOME` referencing the path to Java home for your JDK installation, e.g. `JAVA_HOME=/usr/lib/jvm/jdk-21`. 
+OpenSearch recommends building with the [Temurin/Adoptium](https://adoptium.net/temurin/releases/) distribution. JDK 11 is the minimum supported, and JDK-24 is the newest supported. You must have a supported JDK installed with the environment variable `JAVA_HOME` referencing the path to Java home for your JDK installation, e.g. `JAVA_HOME=/usr/lib/jvm/jdk-21`.
 
-Download Java 11 from [here](https://adoptium.net/releases.html?variant=openjdk11). 
+Download Java 11 from [here](https://adoptium.net/releases.html?variant=openjdk11).
 
 
 In addition, certain backward compatibility tests check out and compile the previous major version of OpenSearch, and therefore require installing [JDK 11](https://adoptium.net/temurin/releases/?version=11) and [JDK 17](https://adoptium.net/temurin/releases/?version=17) and setting the `JAVA11_HOME` and `JAVA17_HOME` environment variables. More to that, since 8.10 release, Gradle has deprecated the usage of the any JDKs below JDK-16. For smooth development experience, the recommendation is to install at least [JDK 17](https://adoptium.net/temurin/releases/?version=17) or [JDK 21](https://adoptium.net/temurin/releases/?version=21). If you still want to build with JDK-11 only, please add `-Dorg.gradle.warning.mode=none` when invoking any Gradle build task from command line, for example:
@@ -341,6 +341,60 @@ Please follow these formatting guidelines:
 * Note that JavaDoc and block comments i.e. `/* ... */` are not formatted, but line comments i.e `// ...` are.
 * There is an implicit rule that negative boolean expressions should use the form `foo == false` instead of `!foo` for better readability of the code. While this isn't strictly enforced, it might get called out in PR reviews as something to change.
 
+## PMD
+
+As a quick alternative to rewrite, it's quick scanning locally. Build being part of pre-commit executed (optionally) locally but definitely on CI.
+
+### ⚙️ Usage
+
+- **pmdMain (check for compliance):**
+    - Full project:
+        - `./gradlew pmdMain`
+    - Subproject (e.g., `server`):
+        - `./gradlew server:pmdMain`
+- **Apply needed transformations by leveraging rewrite, please see below**
+
+## Rewrite
+*(Advanced Refactoring, Modernization, and Bulk Code Changes)*
+
+The OpenSearch build system supports **automated, large-scale code transformations** using [Moderne](https://moderne.io/) and OpenRewrite. These tools enable:
+
+- **Safe Refactoring** (e.g., renaming methods, migrating deprecated APIs)
+- **Modernization** (e.g., adopting Java 17 features like `var`, `records`, or `switch` expressions)
+- **Anti-Pattern Fixes** (e.g., replacing `Vector` with `ArrayList`, removing redundant `StringBuilder`)
+- **Convention Enforcement** (e.g., consistent JUnit test naming, `final` keyword usage)
+- **Dependency Upgrades** (e.g., automatic migration when updating library versions)
+
+### ⚙️ Usage
+
+- **Dry-run (check for changes):**
+    - Full project:
+      - `./gradlew rewriteDryRun -Dorg.gradle.jvmargs=-Xmx8G`
+    - Subproject (e.g., `server`):
+      - `./gradlew server:rewriteDryRun -Dorg.gradle.jvmargs=-Xmx8G`
+---
+
+- **Apply transformations:**
+    - Full project:
+      - `./gradlew rewriteRun -Dorg.gradle.jvmargs=-Xmx8G`
+    - Subproject:
+      - `./gradlew server:rewriteRun -Dorg.gradle.jvmargs=-Xmx8G`
+---
+### 🛠️ Example Transformations
+
+| **Before**                     | **After**                          | **Rule**                          |
+|--------------------------------|------------------------------------|-----------------------------------|
+| `new ArrayList<String>()`      | `new ArrayList<>()`                | Diamond Operator (Java 7+)        |
+| `if (x == false)`              | `if (!x)`                          | Boolean Simplification            |
+| `@Test public void testFoo()`  | `@Test void foo()`                 | JUnit 5 Convention                |
+
+### ⚠️ Notes
+
+- **Custom Rules**: Add project-specific rewrites in `code-convention.yml`.
+- **Exclusions**: Use `// rewrite:off` and `// rewrite:on` to opt out of transformations for specific code blocks.
+- **PR Reviews**: Automated rewrites are flagged in CI. Verify changes match intent before merging.
+- **javalangoutofmemoryerror**: https://docs.openrewrite.org/reference/faq#im-getting-javalangoutofmemoryerror-java-heap-space-when-running-openrewrite
+
 ## Adding Dependencies
 
 When adding a new dependency or removing an existing dependency via any `build.gradle` (that are not in the test scope), update the dependency LICENSE and library SHAs.
diff --git a/build.gradle b/build.gradle
@@ -56,6 +56,8 @@ plugins {
   id 'opensearch.global-build-info'
   id "com.diffplug.spotless" version "6.25.0" apply false
   id "org.gradle.test-retry" version "1.6.2" apply false
+  id "org.openrewrite.rewrite" version "7.15.0" apply false
+  id "pmd"
   id "test-report-aggregation"
   id 'jacoco-report-aggregation'
 }
@@ -65,6 +67,8 @@ apply from: 'gradle/runtime-jdk-provision.gradle'
 apply from: 'gradle/ide.gradle'
 apply from: 'gradle/forbidden-dependencies.gradle'
 apply from: 'gradle/formatting.gradle'
+apply from: 'gradle/pmd.gradle'
+apply from: 'gradle/rewrite.gradle'
 apply from: 'gradle/local-distribution.gradle'
 apply from: 'gradle/run.gradle'
 apply from: 'gradle/missing-javadoc.gradle'
diff --git a/gradle/pmd.gradle b/gradle/pmd.gradle
@@ -0,0 +1,45 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ *
+ * Modifications Copyright OpenSearch Contributors. See
+ * GitHub history for details.
+ */
+
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.
+ */
+
+import org.opensearch.gradle.BuildPlugin
+
+allprojects {
+  plugins.withType(BuildPlugin).whenPluginAdded {
+    project.apply plugin: "pmd"
+
+    pmd {
+      consoleOutput = true
+      ruleSetFiles = files("${rootDir}/pmd.xml")
+      toolVersion = "7.16.0"
+    }
+
+    precommit.dependsOn('pmdMain')
+  }
+}
diff --git a/gradle/rewrite.gradle b/gradle/rewrite.gradle
@@ -0,0 +1,43 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ *
+ * Modifications Copyright OpenSearch Contributors. See
+ * GitHub history for details.
+ */
+
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.
+ */
+
+project.apply plugin: "org.openrewrite.rewrite"
+
+rewrite {
+  activeRecipe("DefinitionOfDone")
+  exclusion("**SearchAfterIT.java")
+  exclusion("**StarTreeMapper.java")
+  setExportDatatables(true)
+  setFailOnDryRunResults(true)
+}
+
+dependencies {
+  rewrite("org.openrewrite.recipe:rewrite-static-analysis:2.15.0")
+}
diff --git a/pmd.xml b/pmd.xml
@@ -0,0 +1,11 @@
+<?xml version="1.0"?>
+<ruleset name="DefinitionOfDone"
+         xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 https://pmd.sourceforge.net/ruleset_2_0_0.xsd">
+    <description>DefinitionOfDone</description>
+    <exclude-pattern>.*/sfBugs/.*</exclude-pattern>
+    <exclude-pattern>.*/spotbugsTestCases/.*</exclude-pattern>
+    <rule ref="category/java/bestpractices.xml/UnusedPrivateMethod"/>
+    <!--<rule ref="category/java/codestyle.xml/UnnecessaryImport"/>-->
+</ruleset>
diff --git a/rewrite.yml b/rewrite.yml
@@ -0,0 +1,7 @@
+type: specs.openrewrite.org/v1beta/recipe
+name: DefinitionOfDone
+displayName: Definition of Done
+description: Automatically cleanup code to apply coding convention.
+recipeList:
+  - org.openrewrite.staticanalysis.RemoveUnusedPrivateMethods
+  #- org.openrewrite.java.RemoveUnusedImports
