Make variable naming conventions skip unnamed variables

Fix pmd#4954

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/ASTVariableId.java

@@ -127,6 +127,15 @@ private ModifierOwner getModifierOwnerParent() {
  return (ModifierOwner) parent;
  }
 
+ /**
+ * Return true if this variable has no name. The name is then equal to {@code "_"}.
+ * A variable declaration with this name does not actually declare a variable in
+ * the current scope.
+ */
+ public boolean isUnnamed() {
+ return "_".equals(name);
+ }
+
  /** Returns the name of the variable. */
  public String getName() {
  return name;

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/codestyle/FormalParameterNamingConventionsRule.java

@@ -39,6 +39,10 @@ public FormalParameterNamingConventionsRule() {
 
  @Override
  public Object visit(ASTVariableId node, Object data) {
+ if (node.isUnnamed()) {
+ // unnamed variables do not have to match the regexes.
+ return null;
+ }
 
  if (node.isLambdaParameter()) {
  checkMatches(node, node.isTypeInferred() ? lambdaParamRegex : explicitLambdaParamRegex, data);

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/codestyle/LocalVariableNamingConventionsRule.java

@@ -38,6 +38,10 @@ public LocalVariableNamingConventionsRule() {
 
  @Override
  public Object visit(ASTVariableId node, Object data) {
+ if (node.isUnnamed()) {
+ // unnamed variables do not have to match the regexes.
+ return null;
+ }
 
  if (node.isExceptionBlockParameter()) {
  checkMatches(node, exceptionBlockParameterRegex, data);