From 9deef9a01fa1166b06a5d6bd686b23900349ef71 Mon Sep 17 00:00:00 2001
From: Tim te Beek <tim@moderne.io>
Date: Wed, 23 Oct 2024 12:02:50 +0200
Subject: [PATCH] Allow removal of unused local variables with side effects in
 initializer

For https://github.com/openrewrite/rewrite-feature-flags/pull/35
---
 .../RemoveUnusedLocalVariables.java           | 10 ++++-
 .../RemoveUnusedLocalVariablesTest.java       | 43 ++++++++++++++++---
 2 files changed, 45 insertions(+), 8 deletions(-)

diff --git a/src/main/java/org/openrewrite/staticanalysis/RemoveUnusedLocalVariables.java b/src/main/java/org/openrewrite/staticanalysis/RemoveUnusedLocalVariables.java
index 49296fb04..dc08fde4c 100644
--- a/src/main/java/org/openrewrite/staticanalysis/RemoveUnusedLocalVariables.java
+++ b/src/main/java/org/openrewrite/staticanalysis/RemoveUnusedLocalVariables.java
@@ -43,6 +43,12 @@ public class RemoveUnusedLocalVariables extends Recipe {
             example = "[unused, notUsed, IGNORE_ME]")
     String @Nullable [] ignoreVariablesNamed;
 
+    @Option(displayName = "Remove unused local variables with side effects in initializer",
+            description = "Whether to remove unused local variables despite side effects in the initializer. Default false.",
+            required = false)
+    @Nullable
+    Boolean withSideEffects;
+
     @Override
     public String getDisplayName() {
         return "Remove unused local variables";
@@ -177,7 +183,9 @@ public J.MethodInvocation visitMethodInvocation(J.MethodInvocation methodInvocat
                         if (SAFE_GETTER_METHODS.matches(methodInvocation)) {
                             return methodInvocation;
                         }
-                        result.set(true);
+                        if (withSideEffects == null || Boolean.FALSE.equals(withSideEffects)) {
+                            result.set(true);
+                        }
                         return methodInvocation;
                     }
 
diff --git a/src/test/java/org/openrewrite/staticanalysis/RemoveUnusedLocalVariablesTest.java b/src/test/java/org/openrewrite/staticanalysis/RemoveUnusedLocalVariablesTest.java
index 54c3616ff..9aa093a2a 100644
--- a/src/test/java/org/openrewrite/staticanalysis/RemoveUnusedLocalVariablesTest.java
+++ b/src/test/java/org/openrewrite/staticanalysis/RemoveUnusedLocalVariablesTest.java
@@ -46,7 +46,7 @@ class RemoveUnusedLocalVariablesTest implements RewriteTest {
 
     @Override
     public void defaults(RecipeSpec spec) {
-        spec.recipe(new RemoveUnusedLocalVariables(new String[0]));
+        spec.recipe(new RemoveUnusedLocalVariables(new String[0], null));
     }
 
     @Test
@@ -73,18 +73,21 @@ static int method(int x) {
     @SuppressWarnings("MethodMayBeStatic")
     void ignoreVariablesNamed() {
         rewriteRun(
-          spec -> spec.recipe(new RemoveUnusedLocalVariables(new String[]{"unused", "ignoreMe"})),
+          spec -> spec.recipe(new RemoveUnusedLocalVariables(new String[]{"unused"}, null)),
           //language=java
           java(
             """
               class Test {
                   void method(Object someData) {
-                      int unused = writeDataToTheDB(someData);
-                      int ignoreMe = writeDataToTheDB(someData);
+                      int unused = 123;
+                      int removed = 123;
                   }
-
-                  int writeDataToTheDB(Object save) {
-                      return 1;
+              }
+              """,
+            """
+              class Test {
+                  void method(Object someData) {
+                      int unused = 123;
                   }
               }
               """
@@ -1066,6 +1069,32 @@ static void method() {
         );
     }
 
+    @Test
+    @Issue("https://github.com/openrewrite/rewrite-feature-flags/pull/35")
+    void removeDespiteSideEffects() {
+        rewriteRun(
+          spec -> spec.recipe(new RemoveUnusedLocalVariables(null, true)),
+          //language=java
+          java(
+            """
+              class Test {
+                  int sideEffect() { return 123; }
+                  void method(Object someData) {
+                      int unused = sideEffect();
+                  }
+              }
+              """,
+            """
+              class Test {
+                  int sideEffect() { return 123; }
+                  void method(Object someData) {
+                  }
+              }
+              """
+          )
+        );
+    }
+
     @Nested
     class Kotlin {