[JVM IR] Support Suspend Main

This adds supports for (parameterless) suspend main entry points for
the JVM IR backend.

In case main is a suspend function, it gains a continuation during
lowering, so we simply generate a plain old `public static void
main(String[] args)`. This entry point invokes `suspend main` via
`kotlin.coroutines.jvm.internal.RunSuspendKt#runSuspend`.

This PR introduces `runSuspend` as a built-in, and generates the
following `main`, passing `args` as appropriate:

```
fun main(args: Array<String>) {
  runSuspend { main(args) }
}
```

The phase ordering has been reshuffled countrary to previous
discussion on #2780, as the MainMethodGeneration pass now introduces lambdas in
the IR. Hence, it has to run before InventNamesForLocalClasses, yet
still after JvmOverloadsAnnotations.

Some dead code was discovered in AddContinuationLowering

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/DeclarationOrigins.kt

@@ -32,7 +32,8 @@ interface JvmLoweredDeclarationOrigin : IrDeclarationOrigin {
     object INLINE_CLASS_GENERATED_IMPL_METHOD : IrDeclarationOriginImpl("INLINE_CLASS_GENERATED_IMPL_METHOD")
     object STATIC_INLINE_CLASS_REPLACEMENT : IrDeclarationOriginImpl("STATIC_INLINE_CLASS_REPLACEMENT")
     object GENERATED_ASSERTION_ENABLED_FIELD : IrDeclarationOriginImpl("GENERATED_ASSERTION_ENABLED_FIELD", isSynthetic = true)
-    object GENERATED_MAIN_FOR_PARAMETERLESS_MAIN_METHOD : IrDeclarationOriginImpl("GENERATED_MAIN_FOR_PARAMETERLESS_MAIN_METHOD", isSynthetic = true)
+    object GENERATED_EXTENDED_MAIN : IrDeclarationOriginImpl("GENERATED_EXTENDED_MAIN", isSynthetic = true)
+    object SUSPEND_FUNCTION_VIEW : IrDeclarationOriginImpl("SUSPEND_FUNCTION_VIEW")
     object SUSPEND_IMPL_STATIC_FUNCTION : IrDeclarationOriginImpl("SUSPEND_IMPL_STATIC_FUNCTION", isSynthetic = true)
     object INTERFACE_COMPANION_PRIVATE_INSTANCE : IrDeclarationOriginImpl("INTERFACE_COMPANION_PRIVATE_INSTANCE", isSynthetic = true)
     object POLYMORPHIC_SIGNATURE_INSTANTIATION : IrDeclarationOriginImpl("POLYMORPHIC_SIGNATURE_INSTANTIATION", isSynthetic = true)

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmLower.kt

@@ -260,6 +260,10 @@ private val jvmFilePhases =
         typeAliasAnnotationMethodsPhase then
         stripTypeAliasDeclarationsPhase then
         provisionalFunctionExpressionPhase then
+
+        jvmOverloadsAnnotationPhase then
+        mainMethodGenerationPhase then
+
         inventNamesForLocalClassesPhase then
         kCallableNamePropertyPhase then
         annotationPhase then
@@ -298,7 +302,6 @@ private val jvmFilePhases =
         localDeclarationsPhase then
         jvmLocalClassExtractionPhase then
 
-        jvmOverloadsAnnotationPhase then
         jvmDefaultConstructorPhase then
 
         forLoopsPhase then
@@ -347,7 +350,6 @@ private val jvmFilePhases =
 
         checkLocalNamesWithOldBackendPhase then
 
-        mainMethodGenerationPhase then
         renameFieldsPhase then
         fakeInliningLocalVariablesLowering then
 

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmSymbols.kt

@@ -19,10 +19,9 @@ import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.descriptors.impl.EmptyPackageFragmentDescriptor
 import org.jetbrains.kotlin.ir.builders.declarations.*
-import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.*
-import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
-import org.jetbrains.kotlin.ir.declarations.IrPackageFragment
 import org.jetbrains.kotlin.ir.declarations.impl.IrExternalPackageFragmentImpl
+import org.jetbrains.kotlin.ir.declarations.impl.IrFunctionImpl
 import org.jetbrains.kotlin.ir.symbols.*
 import org.jetbrains.kotlin.ir.symbols.impl.IrExternalPackageFragmentSymbolImpl
 import org.jetbrains.kotlin.ir.types.*
@@ -607,6 +606,16 @@ class JvmSymbols(
 
     val enumValueOfFunction: IrSimpleFunctionSymbol =
         javaLangEnum.functionByName("valueOf")
+
+    val runSuspendFunction: IrSimpleFunctionSymbol =
+        buildFun {
+            name = Name.identifier("runSuspend")
+            origin = IrDeclarationOrigin.IR_EXTERNAL_DECLARATION_STUB
+        }.apply {
+            parent = kotlinCoroutinesJvmInternalPackage
+            returnType = irBuiltIns.unitType
+            addValueParameter("block", getJvmSuspendFunctionClass(0).typeWith(continuationClass.typeWith(irBuiltIns.unitType), irBuiltIns.anyNType))
+        }.symbol
 }
 
 private fun IrClassSymbol.functionByName(name: String): IrSimpleFunctionSymbol =

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/intrinsics/IrIntrinsicMethods.kt

@@ -104,7 +104,8 @@ class IrIntrinsicMethods(val irBuiltIns: IrBuiltIns, val symbols: JvmSymbols) {
                 irBuiltIns.dataClassArrayMemberToStringSymbol.toKey()!! to IrDataClassArrayMemberToString,
                 symbols.unsafeCoerceIntrinsic.toKey()!! to UnsafeCoerce,
                 symbols.signatureStringIntrinsic.toKey()!! to SignatureString,
-                symbols.reassignParameterIntrinsic.toKey()!! to ReassignParameter
+                symbols.reassignParameterIntrinsic.toKey()!! to ReassignParameter,
+                symbols.runSuspendFunction.toKey()!! to RunSuspend
             ) +
                     numberConversionMethods() +
                     unaryFunForPrimitives("plus", UnaryPlus) +

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/intrinsics/RunSuspend.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.jvm.intrinsics
+
+import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
+import org.jetbrains.kotlin.ir.expressions.IrFunctionAccessExpression
+import org.jetbrains.kotlin.resolve.jvm.jvmSignature.JvmMethodSignature
+
+object RunSuspend : IntrinsicMethod() {
+    override fun toCallable(
+        expression: IrFunctionAccessExpression,
+        signature: JvmMethodSignature,
+        context: JvmBackendContext
+    ): IrIntrinsicFunction {
+        return IrIntrinsicFunction.create(expression, signature, context) {
+            it.invokestatic("kotlin/coroutines/jvm/internal/RunSuspendKt", "runSuspend", "(Lkotlin/jvm/functions/Function1;)V", false)
+        }
+    }
+}

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/InventNamesForLocalClasses.kt

@@ -24,7 +24,9 @@ import org.jetbrains.org.objectweb.asm.Type
 val inventNamesForLocalClassesPhase = makeIrFilePhase<JvmBackendContext>(
     { context -> InventNamesForLocalClasses(context) },
     name = "InventNamesForLocalClasses",
-    description = "Invent names for local classes and anonymous objects"
+    description = "Invent names for local classes and anonymous objects",
+    // MainMethodGeneration introduces lambdas, needing names for their local classes.
+    prerequisite = setOf(mainMethodGenerationPhase)
 )
 
 class InventNamesForLocalClasses(private val context: JvmBackendContext) : FileLoweringPass {

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/MainMethodGenerationLowering.kt

@@ -11,19 +11,24 @@ import org.jetbrains.kotlin.backend.common.lower.createIrBuilder
 import org.jetbrains.kotlin.backend.common.phaser.makeIrFilePhase
 import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
 import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
+import org.jetbrains.kotlin.backend.jvm.ir.createJvmIrBuilder
 import org.jetbrains.kotlin.backend.jvm.ir.getJvmNameFromAnnotation
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.config.languageVersionSettings
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.descriptors.Visibilities
+import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
+import org.jetbrains.kotlin.ir.builders.*
 import org.jetbrains.kotlin.ir.builders.declarations.addFunction
 import org.jetbrains.kotlin.ir.builders.declarations.addValueParameter
-import org.jetbrains.kotlin.ir.builders.irBlockBody
+import org.jetbrains.kotlin.ir.builders.declarations.buildFun
-import org.jetbrains.kotlin.ir.builders.irCall
-import org.jetbrains.kotlin.ir.builders.irReturn
 import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
+import org.jetbrains.kotlin.ir.declarations.IrValueParameter
+import org.jetbrains.kotlin.ir.declarations.impl.IrFunctionImpl
+import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
+import org.jetbrains.kotlin.ir.expressions.impl.IrFunctionReferenceImpl
 import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.util.functions
 import org.jetbrains.kotlin.ir.util.isFileClass
@@ -33,37 +38,69 @@ import org.jetbrains.kotlin.types.Variance
 internal val mainMethodGenerationPhase = makeIrFilePhase(
     ::MainMethodGenerationLowering,
     name = "MainMethodGeneration",
-    description = "Identify parameterless main methods and generate bridge main-methods",
+    description = "Generate main bridges to parameterless mains, and wrappers for suspend mains.",
     prerequisite = setOf(jvmOverloadsAnnotationPhase)
 )
 
-internal class MainMethodGenerationLowering(val context: JvmBackendContext) : ClassLoweringPass {
+private class MainMethodGenerationLowering(private val context: JvmBackendContext) : ClassLoweringPass {
 
+    /**
+     * This pass finds extended main methods and introduces a regular
+     * `public static void main(String[] args)` entry point, as appropriate:
+     *   - invocation via [kotlin.coroutines.jvm.internal.runSuspend] suspend main methods.
+     *   - a simple delegating wrapper for parameterless main methods
+     *
+     * There are three cases that must be handled, in order of precedence:
+     *
+     * 1. `suspend fun main(args: Array<String>) { .. }` for which we generate
+     *    ```
+     *    fun main(args: Array<String>) {
+     *      runSuspend { main(args) }
+     *    }
+     *    ```
+     *
+     * 2. `suspend fun main() { .. }` for which we generate
+     *    ```
+     *    fun main(args: Array<String>) {
+     *      runSuspend { main() }
+     *    }
+     *    ```
+     *
+     * 3. `fun main() { .. }` for which we generate
+     *    ```
+     *    fun main(args: Array<String>) {
+     *      main()
+     *    }
+     *    ```
+     */
     override fun lower(irClass: IrClass) {
         if (!context.configuration.languageVersionSettings.supportsFeature(LanguageFeature.ExtendedMainConvention)) return
         if (!irClass.isFileClass) return
 
-        val parameterlessMain = irClass.functions.find { it.isParameterlessMainMethod() } ?: return
+        irClass.functions.find { it.isMainMethod() }?.let { mainMethod ->
-
+            if (mainMethod.isSuspend) {
-        if (irClass.functions.any { it.isMainMethod() }) return
+                generateMainMethod(irClass) { args ->
-
+                    body = buildRunSuspendWrapper {
-        generateMainMethod(irClass, parameterlessMain)
+                        +irCall(mainMethod).apply {
-    }
+                            putValueArgument(0, irGet(args))
-
+                        }
-    private fun generateMainMethod(irClass: IrClass, parameterlessMain: IrSimpleFunction) {
+                    }
-        irClass.addFunction {
+                }
-            name = Name.identifier("main")
-            visibility = Visibilities.PUBLIC
-            returnType = context.irBuiltIns.unitType
-            modality = Modality.FINAL
-            origin = JvmLoweredDeclarationOrigin.GENERATED_MAIN_FOR_PARAMETERLESS_MAIN_METHOD
-        }.apply {
-            addValueParameter {
-                name = Name.identifier("args")
-                type = context.irBuiltIns.arrayClass.typeWith(context.irBuiltIns.stringType)
             }
-            body = context.createIrBuilder(this.symbol).irBlockBody {
+            return
-                +irReturn(this.irCall(parameterlessMain))
+        }
+
+        irClass.functions.find { it.isParameterlessMainMethod() }?.let { parameterlessMainMethod ->
+            generateMainMethod(irClass) {
+                body = if (parameterlessMainMethod.isSuspend) {
+                    buildRunSuspendWrapper {
+                        +irCall(parameterlessMainMethod)
+                    }
+                } else {
+                    context.createIrBuilder(symbol).irBlockBody {
+                        +irCall(parameterlessMainMethod)
+                    }
+                }
             }
         }
     }
@@ -75,7 +112,6 @@ internal class MainMethodGenerationLowering(val context: JvmBackendContext) : Cl
                 returnType.isUnit() &&
                 name.asString() == "main"
 
-
     private fun IrSimpleFunction.isMainMethod(): Boolean {
         if (getJvmNameFromAnnotation() ?: name.asString() != "main") return false
         if (!returnType.isUnit()) return false
@@ -91,4 +127,57 @@ internal class MainMethodGenerationLowering(val context: JvmBackendContext) : Cl
             else -> false
         }
     }
+
+    private fun generateMainMethod(
+        irClass: IrClass,
+        makeBody: IrFunctionImpl.(IrValueParameter) -> Unit
+    ) {
+        irClass.addFunction {
+            name = Name.identifier("main")
+            visibility = Visibilities.PUBLIC
+            returnType = context.irBuiltIns.unitType
+            modality = Modality.FINAL
+            this.origin = JvmLoweredDeclarationOrigin.GENERATED_EXTENDED_MAIN
+        }.apply {
+            val args = addValueParameter {
+                name = Name.identifier("args")
+                type = context.irBuiltIns.arrayClass.typeWith(context.irBuiltIns.stringType)
+            }
+            makeBody(args)
+        }
+    }
+
+    private fun IrFunctionImpl.buildRunSuspendWrapper(buildMainInvocation: IrBlockBodyBuilder.() -> Unit) =
+        context.createJvmIrBuilder(symbol).irBlockBody {
+            val lambda = irBlock(UNDEFINED_OFFSET, UNDEFINED_OFFSET, IrStatementOrigin.LAMBDA) {
+                val function = buildFun {
+                    origin = IrDeclarationOrigin.LOCAL_FUNCTION_FOR_LAMBDA
+                    name = Name.identifier("wrapper_for_suspend_main")
+                    visibility = Visibilities.LOCAL
+                    returnType = context.irBuiltIns.unitType
+                }.apply {
+                    addValueParameter("k", context.irBuiltIns.anyNType)
+                    parent = this
+                    body = irBlockBody {
+                        buildMainInvocation()
+                    }
+                }
+                +function
+                +IrFunctionReferenceImpl(
+                    UNDEFINED_OFFSET,
+                    UNDEFINED_OFFSET,
+                    context.irBuiltIns.function1.typeWith(
+                        context.irBuiltIns.anyNType,
+                        context.irBuiltIns.unitType
+                    ),
+                    function.symbol,
+                    typeArgumentsCount = 0,
+                    origin = IrStatementOrigin.LAMBDA,
+                    reflectionTarget = null
+                )
+            }
+            +irCall(this@MainMethodGenerationLowering.context.ir.symbols.runSuspendFunction).apply {
+                putValueArgument(0, lambda)
+            }
+        }
 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/descriptors/IrBuiltIns.kt

@@ -318,4 +318,6 @@ class IrBuiltIns(
         const val ANDAND = "ANDAND"
         const val OROR = "OROR"
     }
+
+    val function1: IrClassSymbol = builtIns.getFunction(1).toIrSymbol()
 }

compiler/testData/writeSignature/suspendMain/parameterlessSuspendMain.kt

@@ -0,0 +1,12 @@
+// WITH_RUNTIME
+suspend fun main() {
+
+}
+
+// method: ParameterlessSuspendMainKt::main
+// jvm signature:     (Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+// generic signature: (Lkotlin/coroutines/Continuation<-Lkotlin/Unit;>;)Ljava/lang/Object;
+
+// method: ParameterlessSuspendMainKt::main
+// jvm signature:     ([Ljava/lang/String;)V
+// generic signature: null

compiler/testData/writeSignature/suspendMain/suspendMain.kt

@@ -0,0 +1,17 @@
+// WITH_RUNTIME
+suspend fun f(): Int {
+  return 4
+}
+
+suspend fun main(args: Array<String>) {
+  f()
+}
+
+// method: SuspendMainKt::main
+// jvm signature:     ([Ljava/lang/String;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+// generic signature: ([Ljava/lang/String;Lkotlin/coroutines/Continuation<-Lkotlin/Unit;>;)Ljava/lang/Object;
+
+// method: SuspendMainKt::main
+// jvm signature:     ([Ljava/lang/String;)V
+// generic signature: null
+

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrWriteSignatureTestGenerated.java

@@ -656,4 +656,27 @@ public class IrWriteSignatureTestGenerated extends AbstractIrWriteSignatureTest
             runTest("compiler/testData/writeSignature/parameterlessMain/simple.kt");
         }
     }
+
+    @TestMetadata("compiler/testData/writeSignature/suspendMain")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class SuspendMain extends AbstractIrWriteSignatureTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, TargetBackend.JVM_IR, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInSuspendMain() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/writeSignature/suspendMain"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM_IR, true);
+        }
+
+        @TestMetadata("parameterlessSuspendMain.kt")
+        public void testParameterlessSuspendMain() throws Exception {
+            runTest("compiler/testData/writeSignature/suspendMain/parameterlessSuspendMain.kt");
+        }
+
+        @TestMetadata("suspendMain.kt")
+        public void testSuspendMain() throws Exception {
+            runTest("compiler/testData/writeSignature/suspendMain/suspendMain.kt");
+        }
+    }
 }

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

@@ -655,4 +655,27 @@ public class WriteSignatureTestGenerated extends AbstractWriteSignatureTest {
             runTest("compiler/testData/writeSignature/parameterlessMain/simple.kt");
         }
     }
+
+    @TestMetadata("compiler/testData/writeSignature/suspendMain")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class SuspendMain extends AbstractWriteSignatureTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, this, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInSuspendMain() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/writeSignature/suspendMain"), Pattern.compile("^(.+)\\.kt$"), true);
+        }
+
+        @TestMetadata("parameterlessSuspendMain.kt")
+        public void testParameterlessSuspendMain() throws Exception {
+            runTest("compiler/testData/writeSignature/suspendMain/parameterlessSuspendMain.kt");
+        }
+
+        @TestMetadata("suspendMain.kt")
+        public void testSuspendMain() throws Exception {
+            runTest("compiler/testData/writeSignature/suspendMain/suspendMain.kt");
+        }
+    }
 }