Don't report unused symbol if secondary constructor used

#KT-6997 Fixed

idea/idea-analysis/src/org/jetbrains/kotlin/idea/references/referenceUtil.kt

@@ -50,7 +50,7 @@ public fun PsiReference.matchesTarget(candidateTarget: PsiElement): Boolean {
 
     if (this is JetReference) {
         return targets.any {
-            it is PsiMethod && it.isConstructor() && it.getContainingClass() == unwrappedCandidate
+            it.isConstructorOf(unwrappedCandidate)
             || it is JetObjectDeclaration && it.isCompanion() && it.getNonStrictParentOfType<JetClass>() == unwrappedCandidate
         }
     }
@@ -68,6 +68,12 @@ public fun PsiReference.matchesTarget(candidateTarget: PsiElement): Boolean {
     return false
 }
 
+private fun PsiElement.isConstructorOf(unwrappedCandidate: PsiElement) =
+    // call to Java constructor
+    (this is PsiMethod && isConstructor() && getContainingClass() == unwrappedCandidate) ||
+    // call to Kotlin constructor
+    (this is JetSecondaryConstructor && getStrictParentOfType<JetClass>() == unwrappedCandidate)
+
 fun AbstractJetReference<out JetExpression>.renameImplicitConventionalCall(newName: String?): JetExpression {
     if (newName == null) return expression
 

idea/testData/findUsages/kotlin/findClassUsages/javaClassSecondaryCtrUsages.0.kt

@@ -0,0 +1,5 @@
+// PSI_ELEMENT: org.jetbrains.kotlin.psi.JetClass
+// OPTIONS: usages, constructorUsages
+open class <caret>A {
+    constructor() {}
+}

idea/testData/findUsages/kotlin/findClassUsages/javaClassSecondaryCtrUsages.1.java

@@ -0,0 +1,5 @@
+class B {
+    public static void foo() {
+        new A()
+    }
+}

idea/testData/findUsages/kotlin/findClassUsages/javaClassSecondaryCtrUsages.results.txt

@@ -0,0 +1 @@
+New instance creation (3: 13) new A()

idea/testData/findUsages/kotlin/findClassUsages/kotlinClassSecondaryCtorUsages.0.kt

@@ -0,0 +1,5 @@
+// PSI_ELEMENT: org.jetbrains.kotlin.psi.JetClass
+// OPTIONS: usages, constructorUsages
+open class <caret>A {
+    constructor() {}
+}

idea/testData/findUsages/kotlin/findClassUsages/kotlinClassSecondaryCtorUsages.1.kt

@@ -0,0 +1,3 @@
+fun foo() {
+    A()
+}

idea/testData/findUsages/kotlin/findClassUsages/kotlinClassSecondaryCtorUsages.results.txt

@@ -0,0 +1 @@
+New instance creation (2: 5) A()

idea/testData/inspections/unusedSymbol/class/constructorUsage.kt

@@ -0,0 +1,7 @@
+fun main(args: Array<String>) {
+    A()
+}
+
+class A {
+    constructor() {}
+}

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

@@ -257,6 +257,12 @@ public class JetFindUsagesTestGenerated extends AbstractJetFindUsagesTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("javaClassSecondaryCtrUsages.0.kt")
+            public void testJavaClassSecondaryCtrUsages() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("idea/testData/findUsages/kotlin/findClassUsages/javaClassSecondaryCtrUsages.0.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("javaDerivedClassUsages1.0.kt")
             public void testJavaDerivedClassUsages1() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("idea/testData/findUsages/kotlin/findClassUsages/javaDerivedClassUsages1.0.kt");
@@ -395,6 +401,12 @@ public class JetFindUsagesTestGenerated extends AbstractJetFindUsagesTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("kotlinClassSecondaryCtorUsages.0.kt")
+            public void testKotlinClassSecondaryCtorUsages() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("idea/testData/findUsages/kotlin/findClassUsages/kotlinClassSecondaryCtorUsages.0.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("kotlinDeeplyNestedClassAllUsages.0.kt")
             public void testKotlinDeeplyNestedClassAllUsages() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("idea/testData/findUsages/kotlin/findClassUsages/kotlinDeeplyNestedClassAllUsages.0.kt");