Fix sporadic false-positive "Receiver parameter is never used" for local functions (KT-26481)

idea/src/org/jetbrains/kotlin/idea/inspections/UnusedReceiverParameterInspection.kt

@@ -76,7 +76,7 @@ class UnusedReceiverParameterInspection : AbstractKotlinInspection() {
                 val receiverTypeDeclaration = receiverType.constructor.declarationDescriptor
                 if (DescriptorUtils.isCompanionObject(receiverTypeDeclaration)) return
 
-                val callable = callableDeclaration.descriptor ?: return
+                val callable = context[BindingContext.DECLARATION_TO_DESCRIPTOR, callableDeclaration] ?: return
 
                 if (callableDeclaration.isMainFunction(callable)) return
 

idea/testData/inspections/unusedReceiverParameter/kt26481.kt

@@ -0,0 +1,20 @@
+class My(val x: Int)
+class Your(val x: Int)
+
+fun Your.foo(): Int {
+    println(x)
+    fun My.bar(): Int {
+        return x
+    }
+    return My(0).bar() + x
+}
+
+fun bar() {
+    fun String.foo() = this.length
+    "".foo()
+}
+
+fun baz() {
+    fun String.foo() = length
+    "".foo()
+}