Unused symbol: handle functions with inline class parameters correctly

#KT-27357 Fixed

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

@@ -67,6 +67,7 @@ import org.jetbrains.kotlin.psi.psiUtil.*
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameSafe
+import org.jetbrains.kotlin.resolve.isInlineClassType
 import org.jetbrains.kotlin.util.findCallableMemberBySignature
 import java.awt.GridBagConstraints
 import java.awt.GridBagLayout
@@ -309,7 +310,7 @@ class UnusedSymbolInspection : AbstractKotlinInspection() {
             if (referenceUsed) return true
         }
 
-        if (declaration is KtCallableDeclaration && !declaration.hasModifier(KtTokens.INTERNAL_KEYWORD)) {
+        if (declaration is KtCallableDeclaration && declaration.canBeHandledByLightMethods(descriptor)) {
             val lightMethods = declaration.toLightMethods()
             if (lightMethods.isNotEmpty()) {
                 val lightMethodsUsed = lightMethods.any { method ->
@@ -323,6 +324,24 @@ class UnusedSymbolInspection : AbstractKotlinInspection() {
         return referenceUsed
     }
 
+    private fun KtCallableDeclaration.canBeHandledByLightMethods(descriptor: DeclarationDescriptor?): Boolean {
+        return when {
+            hasModifier(KtTokens.INTERNAL_KEYWORD) -> false
+            this !is KtNamedFunction -> true
+            descriptor !is FunctionDescriptor -> true
+            else -> !descriptor.hasInlineClassParameters()
+        }
+
+    }
+
+    private fun FunctionDescriptor.hasInlineClassParameters(): Boolean {
+        return when {
+            dispatchReceiverParameter?.type?.isInlineClassType() == true -> true
+            extensionReceiverParameter?.type?.isInlineClassType() == true -> true
+            else -> valueParameters.any { it.type.isInlineClassType() }
+        }
+    }
+
     private fun hasOverrides(declaration: KtNamedDeclaration, useScope: SearchScope): Boolean =
         DefinitionsScopedSearch.search(declaration, useScope).findFirst() != null
 

idea/testData/inspections/unusedSymbol/function/functionWithInlineClassParam.kt

@@ -0,0 +1,6 @@
+inline class InlineClass(val x: Int)
+
+// Unused
+fun foo(arg: InlineClass) {
+    arg.x.hashCode()
+}

idea/testData/inspections/unusedSymbol/function/inspectionData/expected.xml

@@ -78,4 +78,13 @@
     <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Unused symbol</problem_class>
     <description>Constructor is never used</description>
   </problem>
+
+  <problem>
+    <file>functionWithInlineClassParam.kt</file>
+    <line>4</line>
+    <module>light_idea_test_case</module>
+    <entry_point TYPE="file" FQNAME="temp:///src/functionWithInlineClassParam.kt" />
+    <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Unused symbol</problem_class>
+    <description>Function &quot;foo&quot; is never used</description>
+  </problem>
 </problems>

idea/testData/inspectionsLocal/unusedSymbol/functionWithInlineClass.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+
+inline class InlineClass(val x: Int)
+
+fun <caret>takeInline(inlineClass: InlineClass) = 1
+
+val call = takeInline(InlineClass(1))

idea/testData/inspectionsLocal/unusedSymbol/functionWithInlineClassReceiver.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+
+inline class InlineClass(val x: Int)
+
+fun InlineClass.<caret>takeInline() = 1
+
+val call = InlineClass(1).takeInline()

idea/testData/inspectionsLocal/unusedSymbol/inlineClassMemberFunction.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+
+inline class InlineClass(val x: Int) {
+    fun <caret>takeInline() = 1
+}
+
+val call = InlineClass(1).takeInline()

idea/tests/org/jetbrains/kotlin/idea/inspections/LocalInspectionTestGenerated.java

@@ -6377,6 +6377,16 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
             runTest("idea/testData/inspectionsLocal/unusedSymbol/dataInlineClassDeclaration.kt");
         }
 
+        @TestMetadata("functionWithInlineClass.kt")
+        public void testFunctionWithInlineClass() throws Exception {
+            runTest("idea/testData/inspectionsLocal/unusedSymbol/functionWithInlineClass.kt");
+        }
+
+        @TestMetadata("functionWithInlineClassReceiver.kt")
+        public void testFunctionWithInlineClassReceiver() throws Exception {
+            runTest("idea/testData/inspectionsLocal/unusedSymbol/functionWithInlineClassReceiver.kt");
+        }
+
         @TestMetadata("inAnonymous.kt")
         public void testInAnonymous() throws Exception {
             runTest("idea/testData/inspectionsLocal/unusedSymbol/inAnonymous.kt");
@@ -6392,6 +6402,11 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
             runTest("idea/testData/inspectionsLocal/unusedSymbol/inAnonymousRunWrapped.kt");
         }
 
+        @TestMetadata("inlineClassMemberFunction.kt")
+        public void testInlineClassMemberFunction() throws Exception {
+            runTest("idea/testData/inspectionsLocal/unusedSymbol/inlineClassMemberFunction.kt");
+        }
+
         @TestMetadata("internal.kt")
         public void testInternal() throws Exception {
             runTest("idea/testData/inspectionsLocal/unusedSymbol/internal.kt");