Introduced "Unused receiver parameter" inspection.

idea/testData/inspections/unusedReceiverParameter/calledInFunction.kt

@@ -0,0 +1,3 @@
+fun String.foo() {
+    println(length())
+}

idea/testData/inspections/unusedReceiverParameter/implicitReceiverOfExtensionFunction.kt

@@ -0,0 +1,5 @@
+private fun String.foo() {
+    otherExt()
+}
+
+fun String.otherExt() = length()

idea/testData/inspections/unusedReceiverParameter/inspectionData/expected.xml

@@ -0,0 +1,34 @@
+<problems>
+    <problem>
+        <file>unusedInProperty.kt</file>
+        <line>1</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/unusedInProperty.kt" />
+        <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Unused receiver parameter</problem_class>
+        <description>Receiver parameter is never used</description>
+    </problem>
+    <problem>
+        <file>unusedInFunction.kt</file>
+        <line>1</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/unusedInFunction.kt" />
+        <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Unused receiver parameter</problem_class>
+        <description>Receiver parameter is never used</description>
+    </problem>
+    <problem>
+        <file>irrelevantThisInFunction.kt</file>
+        <line>1</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/irrelevantThisInFunction.kt" />
+        <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Unused receiver parameter</problem_class>
+        <description>Receiver parameter is never used</description>
+    </problem>
+    <problem>
+        <file>irrelevantCallInFunction.kt</file>
+        <line>1</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/irrelevantCallInFunction.kt" />
+        <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Unused receiver parameter</problem_class>
+        <description>Receiver parameter is never used</description>
+    </problem>
+</problems>

idea/testData/inspections/unusedReceiverParameter/inspectionData/inspections.test

@@ -0,0 +1 @@
+// INSPECTION_CLASS: org.jetbrains.kotlin.idea.inspections.UnusedReceiverParameterInspection

idea/testData/inspections/unusedReceiverParameter/irrelevantCallInFunction.kt

@@ -0,0 +1,5 @@
+fun String.foo() {
+    fun String.local() {
+        println(length())
+    }
+}

idea/testData/inspections/unusedReceiverParameter/irrelevantThisInFunction.kt

@@ -0,0 +1,5 @@
+fun Any.foo() {
+    fun Any.local() {
+        println(this)
+    }
+}

idea/testData/inspections/unusedReceiverParameter/unusedButOverride.kt

@@ -0,0 +1,11 @@
+open class Foo {
+    open fun Any.foo() {
+
+    }
+}
+
+class Bar: Foo() {
+    override fun Any.foo() {
+
+    }
+}

idea/testData/inspections/unusedReceiverParameter/unusedInFunction.kt

@@ -0,0 +1,3 @@
+fun String.foo() {
+    println()
+}

idea/testData/inspections/unusedReceiverParameter/unusedInProperty.kt

@@ -0,0 +1,6 @@
+val String.something: Int
+    get() = 42
+
+fun main(args: Array<String>) {
+    "".something
+}

idea/testData/inspections/unusedReceiverParameter/usedExplicitlyInFunction.kt

@@ -0,0 +1,3 @@
+fun String.foo() {
+    println(this)
+}

idea/testData/inspections/unusedReceiverParameter/usedInProperty.kt

@@ -0,0 +1,6 @@
+val String.doubleLength: Int
+    get() = length() * 2
+
+fun main(args: Array<String>) {
+    "".doubleLength
+}