'SuspendFunction$n' should not be visible in member scopes (should be unresolved).

'SuspendFunction$n' class descriptors are created on demand by KotlinBuiltIns (and cached).
On serialization, types constructed with 'SuspendFunction$n' are written as 'Function$n' with extra flag (SUSPEND_TYPE).
On deserialization, corresponding 'SuspendFunction$n' classes are used.

compiler/serialization/src/org/jetbrains/kotlin/serialization/DescriptorSerializer.kt

@@ -17,6 +17,8 @@
 package org.jetbrains.kotlin.serialization
 
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
+import org.jetbrains.kotlin.builtins.functions.FunctionClassDescriptor
+import org.jetbrains.kotlin.builtins.getFunctionalClassKind
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.annotations.Annotated
 import org.jetbrains.kotlin.name.Name
@@ -25,6 +27,7 @@ import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.DescriptorUtils.isEnumEntry
 import org.jetbrains.kotlin.resolve.MemberComparator
 import org.jetbrains.kotlin.resolve.constants.NullValue
+import org.jetbrains.kotlin.resolve.descriptorUtil.builtIns
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.utils.Interner
 import java.io.ByteArrayOutputStream
@@ -455,12 +458,25 @@ class DescriptorSerializer private constructor(
     }
 
     private fun fillFromPossiblyInnerType(builder: ProtoBuf.Type.Builder, type: PossiblyInnerType) {
-        val classifierDescriptor = type.classifierDescriptor
+        val classifierDescriptor: ClassifierDescriptorWithTypeParameters
+        val isSuspendType: Boolean
+
+        val originalClassifierDescriptor = type.classifierDescriptor
+        if (originalClassifierDescriptor.getFunctionalClassKind() == FunctionClassDescriptor.Kind.SuspendFunction) {
+            classifierDescriptor = originalClassifierDescriptor.builtIns.getFunction(originalClassifierDescriptor.declaredTypeParameters.size)
+            isSuspendType = true
+        }
+        else {
+            classifierDescriptor = originalClassifierDescriptor
+            isSuspendType = false
+        }
+
         val classifierId = getClassifierId(classifierDescriptor)
         when (classifierDescriptor) {
             is ClassDescriptor -> builder.className = classifierId
             is TypeAliasDescriptor -> builder.typeAliasName = classifierId
         }
+        builder.flags = Flags.getTypeFlags(isSuspendType)
 
         for (projection in type.arguments) {
             builder.addArgument(typeArgument(projection))

compiler/testData/diagnostics/tests/coroutines/suspendFunctionType/modifierApplicability.kt

@@ -11,7 +11,7 @@ typealias Test4 = <!WRONG_MODIFIER_TARGET!>suspend<!> Action
 typealias Test5 = List<suspend () -> Unit>
 typealias Test6 = <!WRONG_MODIFIER_TARGET!>suspend<!> List<() -> Unit>
 typealias Test7 = <!WRONG_MODIFIER_TARGET!>suspend<!> SAM
-typealias Test8 = SuspendFunction0<Unit>
+typealias Test8 = <!WRONG_MODIFIER_TARGET!>suspend<!> <!UNRESOLVED_REFERENCE!>SuspendFunction0<!><Unit>
 typealias Test9 = suspend (() -> Unit) -> Unit
 typealias Test10 = suspend (suspend () -> Unit) -> Unit
 typealias Test11 = suspend () -> (suspend () -> Unit)

compiler/testData/diagnostics/tests/coroutines/suspendFunctionType/modifierApplicability.txt

@@ -17,5 +17,5 @@ public typealias Test4 = Action
 public typealias Test5 = kotlin.collections.List<suspend () -> kotlin.Unit>
 public typealias Test6 = kotlin.collections.List<() -> kotlin.Unit>
 public typealias Test7 = SAM
-public typealias Test8 = suspend () -> kotlin.Unit
+public typealias Test8 = [ERROR : SuspendFunction0<Unit>]<kotlin.Unit>
 public typealias Test9 = suspend (() -> kotlin.Unit) -> kotlin.Unit

compiler/testData/diagnostics/tests/coroutines/suspendFunctionType/suspendFunctionNIsUnresolved.kt

@@ -0,0 +1,3 @@
+typealias Test1 = <!UNRESOLVED_REFERENCE!>SuspendFunction0<!><Unit>
+typealias Test2 = kotlin.<!UNRESOLVED_REFERENCE!>SuspendFunction0<!><Unit>
+typealias Test3 = kotlin.coroutines.<!UNRESOLVED_REFERENCE!>SuspendFunction0<!><Unit>

compiler/testData/diagnostics/tests/coroutines/suspendFunctionType/suspendFunctionNIsUnresolved.txt

@@ -0,0 +1,5 @@
+package
+
+public typealias Test1 = [ERROR : SuspendFunction0<Unit>]<kotlin.Unit>
+public typealias Test2 = [ERROR : kotlin.SuspendFunction0<Unit>]<kotlin.Unit>
+public typealias Test3 = [ERROR : kotlin.coroutines.SuspendFunction0<Unit>]<kotlin.Unit>

compiler/testData/loadJava/compiledKotlin/type/SuspendFunction.kt

@@ -0,0 +1,7 @@
+package test
+
+fun test1(): suspend () -> Unit = null!!
+fun test2(): suspend (Int, String) -> Int = null!!
+fun test3(): suspend Int.(String) -> Int = null!!
+fun test4(): List<suspend () -> Unit> = null!!
+fun test5(): suspend (suspend () -> Unit) -> Unit = null!!

compiler/testData/loadJava/compiledKotlin/type/SuspendFunction.txt

@@ -0,0 +1,7 @@
+package test
+
+public fun test1(): suspend () -> kotlin.Unit
+public fun test2(): suspend (kotlin.Int, kotlin.String) -> kotlin.Int
+public fun test3(): suspend kotlin.Int.(kotlin.String) -> kotlin.Int
+public fun test4(): kotlin.collections.List<suspend () -> kotlin.Unit>
+public fun test5(): suspend (suspend () -> kotlin.Unit) -> kotlin.Unit

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -4466,6 +4466,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/coroutines/suspendFunctionType/noInvokeForSuspendFunction.kt");
                     doTest(fileName);
                 }
+
+                @TestMetadata("suspendFunctionNIsUnresolved.kt")
+                public void testSuspendFunctionNIsUnresolved() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/coroutines/suspendFunctionType/suspendFunctionNIsUnresolved.kt");
+                    doTest(fileName);
+                }
             }
 
             @TestMetadata("compiler/testData/diagnostics/tests/coroutines/tailCalls")

compiler/tests/org/jetbrains/kotlin/jvm/compiler/LoadJavaTestGenerated.java

@@ -4805,6 +4805,12 @@ public class LoadJavaTestGenerated extends AbstractLoadJavaTest {
                 doTestCompiledKotlin(fileName);
             }
 
+            @TestMetadata("SuspendFunction.kt")
+            public void testSuspendFunction() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/loadJava/compiledKotlin/type/SuspendFunction.kt");
+                doTestCompiledKotlin(fileName);
+            }
+
             @TestMetadata("Unit.kt")
             public void testUnit() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/loadJava/compiledKotlin/type/Unit.kt");

compiler/tests/org/jetbrains/kotlin/jvm/compiler/LoadKotlinWithTypeTableTestGenerated.java

@@ -3038,6 +3038,12 @@ public class LoadKotlinWithTypeTableTestGenerated extends AbstractLoadKotlinWith
             doTest(fileName);
         }
 
+        @TestMetadata("SuspendFunction.kt")
+        public void testSuspendFunction() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/loadJava/compiledKotlin/type/SuspendFunction.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("Unit.kt")
         public void testUnit() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/loadJava/compiledKotlin/type/Unit.kt");

compiler/tests/org/jetbrains/kotlin/jvm/runtime/JvmRuntimeDescriptorLoaderTestGenerated.java

@@ -3040,6 +3040,12 @@ public class JvmRuntimeDescriptorLoaderTestGenerated extends AbstractJvmRuntimeD
                 doTest(fileName);
             }
 
+            @TestMetadata("SuspendFunction.kt")
+            public void testSuspendFunction() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/loadJava/compiledKotlin/type/SuspendFunction.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("Unit.kt")
             public void testUnit() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/loadJava/compiledKotlin/type/Unit.kt");