Add synthetic flag to generated private suspend functions

Private suspend functions need to be generated as package-local, since
they are called from their continuations.
However, this means that they can be called from Java, which breaks
their private visibility.
Adding synthetic to them fixes the issue.
 #KT-17584: Fixed

compiler/backend/src/org/jetbrains/kotlin/codegen/AsmUtil.java

@@ -244,7 +244,8 @@ public class AsmUtil {
         int flags = getVisibilityAccessFlag(functionDescriptor);
         flags |= getVarargsFlag(functionDescriptor);
         flags |= getDeprecatedAccessFlag(functionDescriptor);
-        if (state.getDeprecationProvider().isDeprecatedHidden(functionDescriptor)) {
+        if (state.getDeprecationProvider().isDeprecatedHidden(functionDescriptor) ||
+            (functionDescriptor.isSuspend()) && functionDescriptor.getVisibility().equals(Visibilities.PRIVATE)) {
             flags |= ACC_SYNTHETIC;
         }
         return flags;

compiler/testData/codegen/bytecodeListing/privateSuspendFun.kt

@@ -0,0 +1,5 @@
+private suspend fun foo() {}
+
+class A {
+    private suspend fun foo() {}
+}

compiler/testData/codegen/bytecodeListing/privateSuspendFun.txt

@@ -0,0 +1,10 @@
+@kotlin.Metadata
+public final class A {
+    public method <init>(): void
+    synthetic final @org.jetbrains.annotations.Nullable method foo(@org.jetbrains.annotations.Nullable p0: java.lang.Object): java.lang.Object
+}
+
+@kotlin.Metadata
+public final class PrivateSuspendFunKt {
+    synthetic final static @org.jetbrains.annotations.Nullable method foo(@org.jetbrains.annotations.Nullable p0: java.lang.Object): java.lang.Object
+}

compiler/testData/codegen/bytecodeListing/tailcall/tailCallIntrinsics.txt

@@ -15,6 +15,6 @@ public final class TailCallIntrinsicsKt {
     static method <clinit>(): void
     public final static method getP(): int
     public final static method setP(p0: int): void
-    final static @org.jetbrains.annotations.Nullable method withInline(@org.jetbrains.annotations.NotNull p0: kotlin.coroutines.experimental.Continuation): java.lang.Object
+    synthetic final static @org.jetbrains.annotations.Nullable method withInline(@org.jetbrains.annotations.NotNull p0: kotlin.coroutines.experimental.Continuation): java.lang.Object
-    final static @org.jetbrains.annotations.Nullable method withoutInline(@org.jetbrains.annotations.NotNull p0: kotlin.coroutines.experimental.Continuation): java.lang.Object
+    synthetic final static @org.jetbrains.annotations.Nullable method withoutInline(@org.jetbrains.annotations.NotNull p0: kotlin.coroutines.experimental.Continuation): java.lang.Object
 }

compiler/tests/org/jetbrains/kotlin/codegen/BytecodeListingTestGenerated.java

@@ -145,6 +145,12 @@ public class BytecodeListingTestGenerated extends AbstractBytecodeListingTest {
         doTest(fileName);
     }
 
+    @TestMetadata("privateSuspendFun.kt")
+    public void testPrivateSuspendFun() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeListing/privateSuspendFun.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("samAdapterAndInlinedOne.kt")
     public void testSamAdapterAndInlinedOne() throws Exception {
         String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeListing/samAdapterAndInlinedOne.kt");