[groovy] prefer empty vararg over implicit null (IDEA-178858)

plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/resolve/GrDefaultMethodComparator.java

@@ -69,6 +69,11 @@ public class GrDefaultMethodComparator extends GrMethodComparator {
 
     PsiParameter[] params1 = method1.getParameterList().getParameters();
     PsiParameter[] params2 = method2.getParameterList().getParameters();
+
+    if (argTypes != null && argTypes.length == 0) {
+      if (params2.length == 1 && params2[0].getType() instanceof PsiArrayType) return true;
+    }
+
     if (argTypes == null && params1.length != params2.length) return false;
 
     if (params1.length < params2.length) {

plugins/groovy/test/org/jetbrains/plugins/groovy/lang/resolve/ResolveMethodTest.groovy

@@ -19,6 +19,7 @@ package org.jetbrains.plugins.groovy.lang.resolve
 import com.intellij.psi.*
 import com.intellij.psi.util.PropertyUtil
 import org.jetbrains.plugins.groovy.codeInspection.assignment.GroovyAssignabilityCheckInspection
+import org.jetbrains.plugins.groovy.lang.psi.GroovyFile
 import org.jetbrains.plugins.groovy.lang.psi.api.statements.GrVariable
 import org.jetbrains.plugins.groovy.lang.psi.api.statements.expressions.GrBinaryExpression
 import org.jetbrains.plugins.groovy.lang.psi.api.statements.expressions.GrNewExpression
@@ -2292,4 +2293,19 @@ new SomeClass().si<caret>ze()
 ''', GrMethodImpl
 
   }
+
+  void 'test prefer varargs in no-arg call'() {
+    def file = fixture.configureByText('_.groovy', '''\
+class A {
+  A(String... a) { println "varargs" }
+  A(A a) { println "single" }
+}
+
+new A()
+''') as GroovyFile
+    def expression = file.statements.last() as GrNewExpression
+    def resolved = expression.resolveMethod()
+    assert resolved instanceof GrMethod
+    assert resolved.isVarArgs()
+  }
 }