PSI Unifier: Unify references which correspond to the same declaration

#KT-5996 Fixed

idea/src/org/jetbrains/kotlin/idea/util/psi/patternMatching/JetPsiUnifier.kt

@@ -160,6 +160,7 @@ public class JetPsiUnifier(
             val decl1 = DescriptorToSourceUtils.descriptorToDeclaration(d1) as? JetDeclaration
             val decl2 = DescriptorToSourceUtils.descriptorToDeclaration(d2) as? JetDeclaration
             if (decl1 == null || decl2 == null) return false
+            if (decl1 == decl2) return true
 
             if ((decl1 in originalTarget && decl2 in originalPattern) || (decl2 in originalTarget && decl1 in originalPattern)) {
                 return matchDeclarations(decl1, decl2, d1, d2) == MATCHED

idea/testData/refactoring/introduceVariable/callUnderSmartCast.kt

@@ -0,0 +1,11 @@
+trait T {
+    fun foo(): Int
+}
+
+trait U: T
+
+fun test(t: T): Int {
+    return if (t is U)
+        <selection>t.foo()</selection> + 1
+    else t.foo()
+}

idea/testData/refactoring/introduceVariable/callUnderSmartCast.kt.after

@@ -0,0 +1,12 @@
+trait T {
+    fun foo(): Int
+}
+
+trait U: T
+
+fun test(t: T): Int {
+    val i = t.foo()
+    return if (t is U)
+        i + 1
+    else i
+}

idea/testData/unifier/equivalence/expressions/calls/callUnderSmartCast.kt

@@ -0,0 +1,11 @@
+trait T {
+    fun foo(): Int
+}
+
+trait U: T
+
+fun test(t: T): Int {
+    return if (t is U)
+        <selection>t.foo()</selection> + 1
+    else t.foo()
+}

idea/testData/unifier/equivalence/expressions/calls/callUnderSmartCast.kt.match

@@ -0,0 +1,3 @@
+t.foo()
+
+t.foo()

idea/tests/org/jetbrains/kotlin/idea/refactoring/introduce/JetExtractionTestGenerated.java

@@ -49,6 +49,12 @@ public class JetExtractionTestGenerated extends AbstractJetExtractionTest {
             doIntroduceVariableTest(fileName);
         }
 
+        @TestMetadata("callUnderSmartCast.kt")
+        public void testCallUnderSmartCast() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/testData/refactoring/introduceVariable/callUnderSmartCast.kt");
+            doIntroduceVariableTest(fileName);
+        }
+
         @TestMetadata("ClassBody.kt")
         public void testClassBody() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("idea/testData/refactoring/introduceVariable/ClassBody.kt");

idea/tests/org/jetbrains/kotlin/psi/patternMatching/JetPsiUnifierTestGenerated.java

@@ -425,6 +425,12 @@ public class JetPsiUnifierTestGenerated extends AbstractJetPsiUnifierTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("callUnderSmartCast.kt")
+                public void testCallUnderSmartCast() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("idea/testData/unifier/equivalence/expressions/calls/callUnderSmartCast.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("externalArgumentsRuntime.kt")
                 public void testExternalArgumentsRuntime() throws Exception {
                     String fileName = JetTestUtils.navigationMetadata("idea/testData/unifier/equivalence/expressions/calls/externalArgumentsRuntime.kt");