From d4418d5686de513a2ac1a5e9d6c4bdd6b1dbc6b4 Mon Sep 17 00:00:00 2001
From: Denis Zharkov <denis.zharkov@jetbrains.com>
Date: Thu, 29 Sep 2016 15:55:28 +0300
Subject: [PATCH] Prohibit not-Unit suspend functions

 #KT-13560 Fixed
---
 .../org/jetbrains/kotlin/resolve/SuspendModifierChecker.kt    | 4 ++++
 .../diagnostics/tests/coroutines/suspendApplicability.kt      | 3 +++
 .../diagnostics/tests/coroutines/suspendApplicability.txt     | 2 ++
 idea/testData/checker/infos/suspendApplicability.kt           | 2 ++
 4 files changed, 11 insertions(+)

diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/SuspendModifierChecker.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/SuspendModifierChecker.kt
index 1dd7bc6e243..0b0bf8819c8 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/SuspendModifierChecker.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/SuspendModifierChecker.kt
@@ -80,6 +80,10 @@ object SuspendModifierChecker : SimpleDeclarationChecker {
         if (continuationParameterType?.arguments?.firstOrNull()?.isStarProjection == true) {
             report("Continuation<*> is prohibited as a last parameter of suspend function")
         }
+
+        if (functionDescriptor.returnType?.isUnit() != true) {
+            report("return type of suspension function must be a kotlin.Unit, but ${functionDescriptor.returnType} was found")
+        }
     }
 }
 
diff --git a/compiler/testData/diagnostics/tests/coroutines/suspendApplicability.kt b/compiler/testData/diagnostics/tests/coroutines/suspendApplicability.kt
index 45d81fb151b..0861e54a892 100644
--- a/compiler/testData/diagnostics/tests/coroutines/suspendApplicability.kt
+++ b/compiler/testData/diagnostics/tests/coroutines/suspendApplicability.kt
@@ -38,4 +38,7 @@ class Controller {
     suspend fun String.memberExtension(x: Continuation<Int>) {
 
     }
+
+    suspend fun returnsUnit(x: Continuation<Int>) = Unit
+    <!INAPPLICABLE_MODIFIER!>suspend<!> fun returnsNotUnit(x: Continuation<Int>) = 1
 }
diff --git a/compiler/testData/diagnostics/tests/coroutines/suspendApplicability.txt b/compiler/testData/diagnostics/tests/coroutines/suspendApplicability.txt
index 69b97159f46..f50c3555f93 100644
--- a/compiler/testData/diagnostics/tests/coroutines/suspendApplicability.txt
+++ b/compiler/testData/diagnostics/tests/coroutines/suspendApplicability.txt
@@ -10,6 +10,8 @@ public suspend fun kotlin.String.wrongExtension(/*0*/ x: kotlin.coroutines.Conti
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public final inline suspend fun inlineFun(/*0*/ x: kotlin.coroutines.Continuation<kotlin.Int>): kotlin.Unit
     public final suspend fun noParams(): kotlin.Unit
+    public final suspend fun returnsNotUnit(/*0*/ x: kotlin.coroutines.Continuation<kotlin.Int>): kotlin.Int
+    public final suspend fun returnsUnit(/*0*/ x: kotlin.coroutines.Continuation<kotlin.Int>): kotlin.Unit
     public final suspend fun starProjection(/*0*/ x: kotlin.coroutines.Continuation<*>): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
     public final suspend fun valid(/*0*/ x: kotlin.coroutines.Continuation<kotlin.Int>): kotlin.Unit
diff --git a/idea/testData/checker/infos/suspendApplicability.kt b/idea/testData/checker/infos/suspendApplicability.kt
index 232fae1fe61..987145420cf 100644
--- a/idea/testData/checker/infos/suspendApplicability.kt
+++ b/idea/testData/checker/infos/suspendApplicability.kt
@@ -38,4 +38,6 @@ class Controller {
     <info descr="null">suspend</info> fun String.memberExtension(<warning descr="[UNUSED_PARAMETER] Parameter 'x' is never used">x</warning>: Continuation<Int>) {
 
     }
+
+    <error descr="[INAPPLICABLE_MODIFIER] 'suspend' modifier is inapplicable. The reason is that return type of suspension function must be a kotlin.Unit, but Int was found"><info descr="null">suspend</info></error> fun returnsNotUnit(<warning descr="[UNUSED_PARAMETER] Parameter 'x' is never used">x</warning>: Continuation<Int>) = 1
 }