Prohibit using suspend functions as SAM in fun interfaces

#KT-40978 Fixed

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -376,6 +376,7 @@ public interface Errors {
     DiagnosticFactory0<PsiElement> FUN_INTERFACE_ABSTRACT_METHOD_WITH_TYPE_PARAMETERS = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<PsiElement> FUN_INTERFACE_ABSTRACT_METHOD_WITH_DEFAULT_VALUE = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<PsiElement> FUN_INTERFACE_CONSTRUCTOR_REFERENCE = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> FUN_INTERFACE_WITH_SUSPEND_FUNCTION = DiagnosticFactory0.create(ERROR);
 
     // Secondary constructors
 

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -718,6 +718,7 @@ public class DefaultErrorMessages {
         MAP.put(FUN_INTERFACE_ABSTRACT_METHOD_WITH_TYPE_PARAMETERS, "Single abstract member cannot declare type parameters");
         MAP.put(FUN_INTERFACE_ABSTRACT_METHOD_WITH_DEFAULT_VALUE, "Single abstract member cannot declare default values");
         MAP.put(FUN_INTERFACE_CONSTRUCTOR_REFERENCE, "Functional interface constructor references are prohibited");
+        MAP.put(FUN_INTERFACE_WITH_SUSPEND_FUNCTION, "'suspend' modifier is not allowed on a single abstract member");
 
         MAP.put(VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED, "Variance annotations are only allowed for type parameters of classes and interfaces");
         MAP.put(BOUND_ON_TYPE_ALIAS_PARAMETER_NOT_ALLOWED, "Bounds are not allowed on type alias parameters");

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/FunInterfaceDeclarationChecker.kt

@@ -6,9 +6,16 @@
 package org.jetbrains.kotlin.resolve.checkers
 
 import com.intellij.psi.PsiElement
-import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.descriptors.FunctionDescriptor
+import org.jetbrains.kotlin.descriptors.PropertyDescriptor
 import org.jetbrains.kotlin.diagnostics.Errors
-import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.lexer.KtTokens
+import org.jetbrains.kotlin.psi.KtClass
+import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.psi.KtNamedFunction
+import org.jetbrains.kotlin.psi.KtProperty
 import org.jetbrains.kotlin.resolve.calls.components.hasDefaultValue
 import org.jetbrains.kotlin.resolve.sam.getAbstractMembers
 import org.jetbrains.kotlin.resolve.source.getPsi
@@ -52,6 +59,13 @@ class FunInterfaceDeclarationChecker : DeclarationChecker {
         context: DeclarationCheckerContext,
     ) {
         val ktFunction = abstractMember.source.getPsi() as? KtNamedFunction
+
+        if (abstractMember.isSuspend) {
+            val reportOn = ktFunction?.modifierList?.getModifier(KtTokens.SUSPEND_KEYWORD) ?: funInterfaceKeyword
+            context.trace.report(Errors.FUN_INTERFACE_WITH_SUSPEND_FUNCTION.on(reportOn))
+            return
+        }
+
         if (abstractMember.typeParameters.isNotEmpty()) {
             val reportOn = ktFunction?.typeParameterList ?: ktFunction?.funKeyword ?: funInterfaceKeyword
             context.trace.report(Errors.FUN_INTERFACE_ABSTRACT_METHOD_WITH_TYPE_PARAMETERS.on(reportOn))

compiler/testData/codegen/box/funInterface/suspendFunInterfaceConversionCodegen.kt

@@ -6,6 +6,7 @@ import helpers.*
 import kotlin.coroutines.*
 
 fun interface SuspendRunnable {
+    @Suppress("FUN_INTERFACE_WITH_SUSPEND_FUNCTION")
     suspend fun invoke()
 }
 

compiler/testData/diagnostics/tests/funInterface/funInterfaceDeclarationCheck.kt

@@ -71,7 +71,7 @@ interface BaseWithGeneric {
 fun interface GoodExtensionGeneric : GoodGeneric<String>
 
 fun interface GoodSuspend {
-    suspend fun invoke()
+    <!FUN_INTERFACE_WITH_SUSPEND_FUNCTION!>suspend<!> fun invoke()
 }
 
 class WithNestedFun<K> {

compiler/testData/diagnostics/tests/funInterface/suspendFunInterfaceConversion.fir.kt

@@ -0,0 +1,14 @@
+// !LANGUAGE: +NewInference +SamConversionForKotlinFunctions +SamConversionPerArgument +FunctionalInterfaceConversion
+// !DIAGNOSTICS: -UNUSED_PARAMETER -NOTHING_TO_INLINE
+
+fun interface SuspendRunnable {
+    suspend fun invoke()
+}
+
+fun run(r: SuspendRunnable) {}
+
+suspend fun bar() {}
+
+fun test() {
+    run(::bar)
+}

compiler/testData/diagnostics/tests/funInterface/suspendFunInterfaceConversion.kt

@@ -1,9 +1,8 @@
-// FIR_IDENTICAL
 // !LANGUAGE: +NewInference +SamConversionForKotlinFunctions +SamConversionPerArgument +FunctionalInterfaceConversion
 // !DIAGNOSTICS: -UNUSED_PARAMETER -NOTHING_TO_INLINE
 
 fun interface SuspendRunnable {
-    suspend fun invoke()
+    <!FUN_INTERFACE_WITH_SUSPEND_FUNCTION!>suspend<!> fun invoke()
 }
 
 fun run(r: SuspendRunnable) {}

compiler/testData/diagnostics/tests/suspendConversion/chainedFunSuspendConversionForSimpleExpression.kt

@@ -2,7 +2,7 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 fun interface SuspendRunnable {
-    suspend fun invoke()
+    <!FUN_INTERFACE_WITH_SUSPEND_FUNCTION!>suspend<!> fun invoke()
 }
 
 fun foo(s: SuspendRunnable) {}

compiler/testData/diagnostics/tests/suspendConversion/suspendAndFunConversionInDisabledMode.kt

@@ -2,7 +2,7 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_EXPRESSION
 
 fun interface SuspendRunnable {
-    suspend fun run()
+    <!FUN_INTERFACE_WITH_SUSPEND_FUNCTION!>suspend<!> fun run()
 }
 
 object Test1 {

compiler/testData/diagnostics/tests/suspendConversion/suspendConversionWithFunInterfaces.fir.kt

@@ -0,0 +1,21 @@
+// !LANGUAGE: +SuspendConversion
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+fun interface SuspendRunnable {
+    suspend fun invoke()
+}
+
+fun foo1(s: SuspendRunnable) {}
+fun bar1() {}
+
+fun bar2(s: String = ""): Int = 0
+
+fun bar3() {}
+suspend fun bar3(s: String = ""): Int = 0
+
+fun test() {
+    foo1(::bar1)
+    foo1(::bar2)
+
+    foo1(::bar3) // Should be ambiguity
+}

compiler/testData/diagnostics/tests/suspendConversion/suspendConversionWithFunInterfaces.kt

@@ -1,9 +1,8 @@
-// FIR_IDENTICAL
 // !LANGUAGE: +SuspendConversion
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 fun interface SuspendRunnable {
-    suspend fun invoke()
+    <!FUN_INTERFACE_WITH_SUSPEND_FUNCTION!>suspend<!> fun invoke()
 }
 
 fun foo1(s: SuspendRunnable) {}

compiler/testData/diagnostics/tests/unitConversion/chainedFunSuspendUnitConversion.kt

@@ -2,7 +2,7 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_EXPRESSION
 
 fun interface SuspendRunnable {
-    suspend fun run()
+    <!FUN_INTERFACE_WITH_SUSPEND_FUNCTION!>suspend<!> fun run()
 }
 
 fun foo(r: SuspendRunnable) {}