Sonar codemod for removing unused local variable (#261)

Codemod to remove unused local variables which expression is a variable
(`NameExpr`) or just a Literal expression like a single boolean, char,
double, integer, long, null, string or a text block string. We are not
considering create object expression, method call expressions, condition
expressions, etc. because all of them have an expression node and that
expression node could result in a method call expression where a process
could be performed and deleting it could result on some unexpected
behaviors.

Examples of unused `LiteralExpr` : 
* String msg = "my message"
* char myChar = 'c';
* int ten = 10;
* etc

sonar cloud report example:
https://sonarcloud.io/project/issues?fileUuids=AYvtrjqJLCzGLicz7Abq&resolved=false&types=CODE_SMELL&id=nahsra_WebGoat_10_23

reference: https://rules.sonarsource.com/java/RSPEC-1481/

Author: carlosu7

core-codemods/src/main/java/io/codemodder/codemods/AddMissingOverrideCodemod.java

@@ -22,7 +22,7 @@ public final class AddMissingOverrideCodemod extends SonarPluginJavaParserChange
   @Inject
   public AddMissingOverrideCodemod(
       @ProvidedSonarScan(ruleId = "java:S1161") final RuleIssues issues) {
-    super(issues, SimpleName.class, RegionNodeMatcher.MATCHES_START);
+    super(issues, SimpleName.class);
   }
 
   @Override

core-codemods/src/main/java/io/codemodder/codemods/AvoidImplicitPublicConstructorCodemod.java

@@ -27,7 +27,7 @@ public final class AvoidImplicitPublicConstructorCodemod
   @Inject
   public AvoidImplicitPublicConstructorCodemod(
       @ProvidedSonarScan(ruleId = "java:S1118") final RuleIssues issues) {
-    super(issues, SimpleName.class, RegionNodeMatcher.MATCHES_START);
+    super(issues, SimpleName.class);
   }
 
   @Override

core-codemods/src/main/java/io/codemodder/codemods/FixRedundantStaticOnEnumCodemod.java

@@ -20,7 +20,7 @@ public final class FixRedundantStaticOnEnumCodemod
   @Inject
   public FixRedundantStaticOnEnumCodemod(
       @ProvidedSonarScan(ruleId = "java:S2786") final RuleIssues issues) {
-    super(issues, EnumDeclaration.class, RegionNodeMatcher.MATCHES_START);
+    super(issues, EnumDeclaration.class);
   }
 
   @Override

core-codemods/src/main/java/io/codemodder/codemods/RemoveRedundantVariableCreationCodemod.java

@@ -22,7 +22,7 @@ public final class RemoveRedundantVariableCreationCodemod
   @Inject
   public RemoveRedundantVariableCreationCodemod(
       @ProvidedSonarScan(ruleId = "java:S1488") final RuleIssues issues) {
-    super(issues, ObjectCreationExpr.class, RegionNodeMatcher.MATCHES_START);
+    super(issues, ObjectCreationExpr.class);
   }
 
   @Override

core-codemods/src/main/java/io/codemodder/codemods/RemoveUnusedLocalVariableCodemod.java

@@ -0,0 +1,74 @@
+package io.codemodder.codemods;
+
+import com.github.javaparser.ast.CompilationUnit;
+import com.github.javaparser.ast.Node;
+import com.github.javaparser.ast.NodeList;
+import com.github.javaparser.ast.body.VariableDeclarator;
+import com.github.javaparser.ast.expr.*;
+import io.codemodder.*;
+import io.codemodder.providers.sonar.ProvidedSonarScan;
+import io.codemodder.providers.sonar.RuleIssues;
+import io.codemodder.providers.sonar.SonarPluginJavaParserChanger;
+import io.codemodder.providers.sonar.api.Issue;
+import java.util.Optional;
+import java.util.stream.Collectors;
+import javax.inject.Inject;
+
+/**
+ * Codemod to remove unused local variables which expression is a variable or just a Literal
+ * expression like a single boolean, char, double, integer, long, null, string or a text block
+ * string. We are not considering create object expression, method call expressions, condition
+ * expressions, etc. because all of them have an expression node and that expression node could
+ * result in a method call expression where a process could be performed and deleting it could
+ * result on some unexpected behaviors.
+ */
+@Codemod(
+    id = "sonar:java/remove-unused-local-variable-s1481",
+    reviewGuidance = ReviewGuidance.MERGE_WITHOUT_REVIEW,
+    executionPriority = CodemodExecutionPriority.HIGH)
+public final class RemoveUnusedLocalVariableCodemod
+    extends SonarPluginJavaParserChanger<VariableDeclarator> {
+
+  @Inject
+  public RemoveUnusedLocalVariableCodemod(
+      @ProvidedSonarScan(ruleId = "java:S1481") final RuleIssues issues) {
+    super(issues, VariableDeclarator.class);
+  }
+
+  @Override
+  public boolean onIssueFound(
+      final CodemodInvocationContext context,
+      final CompilationUnit cu,
+      final VariableDeclarator variableDeclarator,
+      final Issue issue) {
+
+    final Optional<Expression> initializer = variableDeclarator.getInitializer();
+
+    if (initializer.isPresent()) {
+      final Expression initializerExpr = initializer.get();
+
+      if (initializerExpr instanceof LiteralExpr || initializerExpr instanceof NameExpr) {
+        final Optional<Node> variableDeclarationExprOptional = variableDeclarator.getParentNode();
+
+        if (variableDeclarationExprOptional.isPresent()) {
+          final VariableDeclarationExpr variableDeclarationExpr =
+              (VariableDeclarationExpr) variableDeclarationExprOptional.get();
+
+          if (1 == variableDeclarationExpr.getVariables().size()) {
+            variableDeclarationExpr.removeForced();
+          } else {
+            final NodeList<VariableDeclarator> variables =
+                variableDeclarationExpr.getVariables().stream()
+                    .filter(variable -> !variable.equals(variableDeclarator))
+                    .collect(Collectors.toCollection(NodeList::new));
+            variableDeclarationExpr.setVariables(variables);
+          }
+
+          return true;
+        }
+      }
+    }
+
+    return false;
+  }
+}

core-codemods/src/main/java/io/codemodder/codemods/SimplifyRestControllerAnnotationsCodemod.java

@@ -30,7 +30,7 @@ public final class SimplifyRestControllerAnnotationsCodemod
   @Inject
   public SimplifyRestControllerAnnotationsCodemod(
       @ProvidedSonarScan(ruleId = "java:S6833") final RuleIssues issues) {
-    super(issues, ClassOrInterfaceDeclaration.class, RegionNodeMatcher.MATCHES_START);
+    super(issues, ClassOrInterfaceDeclaration.class);
   }
 
   @Override

core-codemods/src/main/java/io/codemodder/codemods/SubstituteReplaceAllCodemod.java

@@ -19,7 +19,7 @@ public final class SubstituteReplaceAllCodemod extends SonarPluginJavaParserChan
   @Inject
   public SubstituteReplaceAllCodemod(
       @ProvidedSonarScan(ruleId = "java:S5361") final RuleIssues issues) {
-    super(issues, SimpleName.class, RegionNodeMatcher.MATCHES_START);
+    super(issues, SimpleName.class);
   }
 
   @Override

core-codemods/src/main/resources/io/codemodder/codemods/RemoveUnusedLocalVariableCodemod/description.md

@@ -0,0 +1,11 @@
+This change removes unused variables. Unused variables make the code harder to read, which will lead to confusion and bugs. We only remove variables that have no state-changing effects.
+
+Our changes look something like this:
+
+```diff
+     catch (final UnsolvedSymbolException e) {
+-      String errorMessage = "An unexpected exception happened";
+       LOG.error("Problem resolving type of : {}", expr, e);
+       return false;
+     }
+```

core-codemods/src/main/resources/io/codemodder/codemods/RemoveUnusedLocalVariableCodemod/report.json

@@ -0,0 +1,7 @@
+{
+  "summary" : "Removed unused local variable (Sonar)",
+  "change" : "Removed unused local variable",
+  "references" : [
+    "https://rules.sonarsource.com/java/RSPEC-1481/"
+  ]
+}

core-codemods/src/test/java/io/codemodder/codemods/RemoveUnusedLocalVariableCodemodTest.java

@@ -0,0 +1,12 @@
+package io.codemodder.codemods;
+
+import io.codemodder.testutils.CodemodTestMixin;
+import io.codemodder.testutils.Metadata;
+
+@Metadata(
+    codemodType = RemoveUnusedLocalVariableCodemod.class,
+    testResourceDir = "remove-unused-local-variable-s1481",
+    renameTestFile =
+        "src/main/java/org/owasp/webgoat/container/assignments/AssignmentEndpoint.java",
+    dependencies = {})
+final class RemoveUnusedLocalVariableCodemodTest implements CodemodTestMixin {}