Rename variables if the name matches class name

Author: radoslaw-panuszewski

rewrite-core/src/main/java/org/openrewrite/internal/StringUtils.java

@@ -732,4 +732,14 @@ public static boolean containsWhitespace(String s) {
 
         return false;
     }
+
+    /**
+     * @return string with first character changed to lowercase (or empty string)
+     */
+    public static String decapitalize(@Nullable String string) {
+        if (string != null && !string.isEmpty()) {
+            return Character.toLowerCase(string.charAt(0)) + string.substring(1);
+        }
+        return "";
+    }
 }

rewrite-java-test/src/test/java/org/openrewrite/java/ChangeTypeTest.java

@@ -1592,8 +1592,8 @@ public A1 method(A1 a1) {
               import a.A2;
               
               public class Example {
-                  public A2 method(A2 a1) {
-                      return a1;
+                  public A2 method(A2 a2) {
+                      return a2;
                   }
               }
               """

rewrite-java/src/main/java/org/openrewrite/java/ChangeType.java

@@ -32,6 +32,7 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import static java.util.Objects.requireNonNull;
+import static org.openrewrite.internal.StringUtils.decapitalize;
 
 @Value
 @EqualsAndHashCode(callSuper = false)
@@ -368,6 +369,19 @@ public J visitIdentifier(J.Identifier ident, ExecutionContext ctx) {
                     }
                 }
 
+                // Rename variable if it matches class name (starting with a lowercase character)
+                if (ident.getSimpleName().equals(decapitalize(className))) {
+                    if (targetType instanceof JavaType.FullyQualified) {
+                        String newName = decapitalize(((JavaType.FullyQualified) targetType).getClassName());
+
+                        ident = ident.withSimpleName(newName);
+
+                        if (ident.getFieldType() != null) {
+                            ident = ident.withFieldType(ident.getFieldType().withName(newName));
+                        }
+                    }
+                }
+
                 // Recreate any static imports as needed
                 if (sf != null) {
                     for (J.Import anImport : sf.getImports()) {
@@ -387,6 +401,15 @@ public J visitIdentifier(J.Identifier ident, ExecutionContext ctx) {
             return visitAndCast(ident, ctx, super::visitIdentifier);
         }
 
+        @Override
+        public J.VariableDeclarations.NamedVariable visitVariable(J.VariableDeclarations.NamedVariable variable, ExecutionContext executionContext) {
+            J.VariableDeclarations.NamedVariable v = (J.VariableDeclarations.NamedVariable) super.visitVariable(variable, executionContext);
+            if (v.getVariableType() != null && !v.getSimpleName().equals(v.getVariableType().getName())) {
+                return v.withVariableType(v.getVariableType().withName(v.getSimpleName()));
+            }
+            return v;
+        }
+
         @Override
         public J visitMethodInvocation(J.MethodInvocation method, ExecutionContext ctx) {
             if (method.getMethodType() != null && method.getMethodType().hasFlags(Flag.Static)) {