[GR-17457] Ensure toArray(TYPE::new) is not used as it's less efficient than toArray(TYPE.EMPTY_ARRAY)

PullRequest: truffleruby/3927

Author: eregon

src/main/.checkstyle_checks.xml

@@ -195,15 +195,19 @@
     </module>
     <module name="RegexpSinglelineJava">
       <property name="format" value='\.toArray\(new \w+\[\w+\.size\(\)\]\)'/>
-      <property name="message" value='Use toArray(new Type[0]) instead.'/>
+      <property name="message" value='Use toArray(Type.EMPTY_ARRAY) instead.'/>
     </module>
     <module name="RegexpSinglelineJava">
       <property name="format" value='new\s+\w+\[\]\s*\{\s*\}'/>
-      <property name="message" value='Use new Type[0] instead.'/>
+      <property name="message" value='Use EMPTY_ARRAY = new Type[0] instead.'/>
     </module>
     <module name="RegexpSinglelineJava">
       <property name="format" value='(?!=)\S\s*new\s+\w+\[0\]'/>
-      <property name="message" value='Use a EMPTY_type_ARRAY constant instead.'/>
+      <property name="message" value='Use a Type.EMPTY_ARRAY or EMPTY_type_ARRAY constant instead.'/>
+    </module>
+    <module name="RegexpSinglelineJava">
+      <property name="format" value='.toArray\(.+\[\]::new\)'/>
+      <property name="message" value='Use .toArray(Type.EMPTY_ARRAY) instead, because this avoids extra allocations.'/>
     </module>
     <module name="RegexpSinglelineJava">
       <property name="format" value="transferToInterpreterOnException"/>

src/main/java/org/truffleruby/parser/ast/ArgsParseNode.java

@@ -38,6 +38,7 @@
 import java.util.Arrays;
 import java.util.List;
 
+import org.truffleruby.core.string.StringUtils;
 import org.truffleruby.language.SourceIndexLength;
 import org.truffleruby.language.methods.Arity;
 import org.truffleruby.parser.Helpers;
@@ -153,7 +154,7 @@ private Arity createArity() {
             final List<String> keywords = new ArrayList<>(requiredKeywords);
             keywords.addAll(optionalKeywords);
 
-            keywordArguments = keywords.toArray(String[]::new);
+            keywordArguments = keywords.toArray(StringUtils.EMPTY_STRING_ARRAY);
             requiredKeywordArgumentsCount = requiredKeywords.size();
         } else {
             keywordArguments = Arity.NO_KEYWORDS;