Fix search usages for invoke() with vararg parameter (KT-18479)

#KT-18479 Fixed

idea/idea-analysis/src/org/jetbrains/kotlin/idea/search/usagesSearch/operators/InvokeOperatorReferenceSearcher.kt

@@ -47,7 +47,7 @@ class InvokeOperatorReferenceSearcher(
         val uMethod = uastContext.convertOpt<UMethod>(targetDeclaration, null)
         val uastParameters = uMethod?.uastParameters
 
-        val isStableNumberOfArguments = uastParameters != null && uastParameters.none { it.uastInitializer != null }
+        val isStableNumberOfArguments = uastParameters != null && uastParameters.none { it.uastInitializer != null || it.isVarArgs }
         callArgumentsSize = if (isStableNumberOfArguments) {
             val numberOfArguments = uastParameters!!.size
             when {

idea/testData/findUsages/kotlin/conventions/invokeWithVarArg.0.kt

@@ -0,0 +1,15 @@
+// PSI_ELEMENT: org.jetbrains.kotlin.psi.KtNamedFunction
+// OPTIONS: usages
+package pack
+
+class P {
+    operator fun <caret>invoke(vararg i: Int) = 1
+}
+
+fun f(p: P) {
+    p()
+    p(1, 2)
+    p(1)
+    p.invoke()
+    p.invoke(1, 2, 3)
+}

idea/testData/findUsages/kotlin/conventions/invokeWithVarArg.log

@@ -0,0 +1,7 @@
+Resolved p()
+Resolved p(1)
+Resolved p(1, 2)
+Searched references to pack.P
+Searched references to parameter p of pack.f(p: P) in non-Java files
+Used plain search of pack.P.invoke(vararg i: Int) in LocalSearchScope:
+    CLASS:P

idea/testData/findUsages/kotlin/conventions/invokeWithVarArg.results.txt

@@ -0,0 +1,5 @@
+Function call 13 p.invoke()
+Function call 14 p.invoke(1, 2, 3)
+Implicit 'invoke' 10 p()
+Implicit 'invoke' 11 p(1, 2)
+Implicit 'invoke' 12 p(1)

idea/tests/org/jetbrains/kotlin/findUsages/FindUsagesTestGenerated.java

@@ -139,6 +139,12 @@ public class FindUsagesTestGenerated extends AbstractFindUsagesTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("invokeWithVarArg.0.kt")
+            public void testInvokeWithVarArg() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("idea/testData/findUsages/kotlin/conventions/invokeWithVarArg.0.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("plus.0.kt")
             public void testPlus() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("idea/testData/findUsages/kotlin/conventions/plus.0.kt");