Prohibit using kotlin.Result as a return type in most cases

#KT-26659 In Progress

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

@@ -334,6 +334,10 @@ public interface Errors {
     DiagnosticFactory1<PsiElement, String> RESERVED_MEMBER_INSIDE_INLINE_CLASS = DiagnosticFactory1.create(ERROR);
     DiagnosticFactory0<PsiElement> SECONDARY_CONSTRUCTOR_WITH_BODY_INSIDE_INLINE_CLASS = DiagnosticFactory0.create(ERROR);
 
+    // Result class
+
+    DiagnosticFactory0<PsiElement> RESULT_CLASS_IN_RETURN_TYPE = DiagnosticFactory0.create(ERROR);
+
     // Secondary constructors
 
     DiagnosticFactory0<KtConstructorDelegationReferenceExpression> CYCLIC_CONSTRUCTOR_DELEGATION_CALL = DiagnosticFactory0.create(ERROR);

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

@@ -665,6 +665,8 @@ public class DefaultErrorMessages {
         MAP.put(RESERVED_MEMBER_INSIDE_INLINE_CLASS, "Member with the name ''{0}'' is reserved for future releases", STRING);
         MAP.put(SECONDARY_CONSTRUCTOR_WITH_BODY_INSIDE_INLINE_CLASS, "Secondary constructors with bodies are reserved for for future releases");
 
+        MAP.put(RESULT_CLASS_IN_RETURN_TYPE, "'kotlin.Result' cannot be used as a return type");
+
         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/TargetPlatform.kt

@@ -120,7 +120,8 @@ private val DEFAULT_DECLARATION_CHECKERS = listOf(
     InlineClassDeclarationChecker,
     PropertiesWithBackingFieldsInsideInlineClass(),
     AnnotationClassTargetAndRetentionChecker(),
-    ReservedMembersAndConstructsForInlineClass()
+    ReservedMembersAndConstructsForInlineClass(),
+    ResultClassInReturnTypeChecker()
 )
 
 private val DEFAULT_CALL_CHECKERS = listOf(

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

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. 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.resolve.checkers
+
+import org.jetbrains.kotlin.builtins.KotlinBuiltIns
+import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.diagnostics.reportDiagnosticOnce
+import org.jetbrains.kotlin.psi.KtCallableDeclaration
+import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.types.KotlinType
+
+class ResultClassInReturnTypeChecker : DeclarationChecker {
+    companion object {
+        private const val RESULT_NAME = "Result"
+    }
+
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+        if (declaration !is KtCallableDeclaration || descriptor !is CallableMemberDescriptor) return
+
+        val returnType = descriptor.returnType ?: return
+        if (isForbiddenReturnType(returnType, descriptor)) {
+            val typeReferenceOrDeclarationName = declaration.typeReference ?: declaration.nameIdentifier ?: return
+            context.trace.reportDiagnosticOnce(Errors.RESULT_CLASS_IN_RETURN_TYPE.on(typeReferenceOrDeclarationName))
+        }
+    }
+
+    private fun isForbiddenReturnType(returnType: KotlinType, declarationDescriptor: DeclarationDescriptor): Boolean {
+        val descriptor = returnType.constructor.declarationDescriptor ?: return false
+        if (!descriptor.isResultClass()) return false
+
+        if (declarationDescriptor is PropertyDescriptor || declarationDescriptor is PropertyGetterDescriptor) {
+            val visibility = (declarationDescriptor as DeclarationDescriptorWithVisibility).effectiveVisibility()
+            return when (visibility) {
+                is EffectiveVisibility.Private, is EffectiveVisibility.Local,
+                is EffectiveVisibility.InternalOrPackage, is EffectiveVisibility.InternalProtected,
+                is EffectiveVisibility.InternalProtectedBound -> false
+
+                is EffectiveVisibility.Public, is EffectiveVisibility.Protected,
+                is EffectiveVisibility.ProtectedBound -> true
+            }
+        }
+
+        return true
+    }
+
+    private fun DeclarationDescriptor.isResultClass(): Boolean {
+        val container = containingDeclaration ?: return false
+        return container is PackageFragmentDescriptor &&
+                container.fqName == KotlinBuiltIns.BUILT_INS_PACKAGE_FQ_NAME &&
+                name.asString() == RESULT_NAME
+    }
+}

compiler/testData/diagnostics/testsWithStdLib/coroutines/usageOfResultTypeInReturnType.kt

@@ -0,0 +1,116 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER, -UNUSED_EXPRESSION, -UNUSED_VARIABLE
+// !LANGUAGE: +InlineClasses
+
+typealias ResultAlias<T> = Result<T>
+
+inline class InlineResult<out T>(private val r: Result<T>)
+
+fun params(
+    r1: Result<Int>,
+    r2: Result<Int>?,
+    r3: ResultAlias<String>,
+    r4: List<Result<Int>>,
+    r5: InlineResult<Int>,
+    <!FORBIDDEN_VARARG_PARAMETER_TYPE!>vararg<!> r6: Result<Int>
+) {}
+
+class CtorParams(r1: Result<Int>)
+
+fun returnTypePublic(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+internal fun returnTypeInternal(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+private fun returnTypePrivate(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+fun returnTypeNullable(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int>?<!> = TODO()
+fun returnTypeAlias(): <!RESULT_CLASS_IN_RETURN_TYPE!>ResultAlias<Int><!> = TODO()
+fun <!RESULT_CLASS_IN_RETURN_TYPE!>returnInferred<!>(r1: Result<Int>, r2: ResultAlias<Int>, b: Boolean) = if (b) r1 else r2
+
+fun returnTypeInline(): InlineResult<Int> = TODO()
+fun returnContainer(): List<Result<Int>> = TODO()
+
+val topLevelP: <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+val <!RESULT_CLASS_IN_RETURN_TYPE!>topLevelPInferred<!> = topLevelP
+internal val topLevelPInternal: Result<Int> = TODO()
+private val topLevelPPrivate: Result<Int> = TODO()
+private val topLevelPPrivateInferred = topLevelP
+
+val asFunctional: () -> Result<Int> = TODO()
+
+open class PublicCls(
+    val r1: <!RESULT_CLASS_IN_RETURN_TYPE!>Result<String><!>,
+    val r2: <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int>?<!>,
+    val r3: <!RESULT_CLASS_IN_RETURN_TYPE!>ResultAlias<Int><!>,
+    val r4: <!RESULT_CLASS_IN_RETURN_TYPE!>ResultAlias<Int>?<!>,
+
+    val r5: InlineResult<Int>,
+    internal val r6: Result<Int>,
+    private val r7: Result<Int>,
+    val r8: List<Result<Int>>
+) {
+    val p1: <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+    var p2: <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+    val p3: <!RESULT_CLASS_IN_RETURN_TYPE!>ResultAlias<Int>?<!> = TODO()
+
+    val <!RESULT_CLASS_IN_RETURN_TYPE!>p4<!> = p1
+
+    internal val p5: Result<Int> = TODO()
+    private var p6: Result<Int> = TODO()
+
+    internal val p7 = p1
+
+    protected val <!RESULT_CLASS_IN_RETURN_TYPE!>p8<!> = p1
+
+    fun returnInCls(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+    protected fun returnInClsProtected(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+    private fun returnInClsPrivate(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+}
+
+internal open class InternalCls(
+    val r1: Result<Int>,
+    val r2: ResultAlias<Int>?,
+    val r3: List<Result<Int>>
+) {
+    companion object {
+        val cr1: Result<Int> = TODO()
+        private val cr2: Result<Int> = TODO()
+    }
+
+    val p1 = r1
+    val p2: Result<String> = TODO()
+
+    protected val p3 = p1
+
+    fun returnInInternal(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+    protected fun returnInClsProtected(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+}
+
+private class PrivateCls(
+    val r1: Result<Int>,
+    val r2: ResultAlias<Int>?,
+    val r3: List<Result<Int>>
+) {
+    companion object {
+        val cr1: Result<Int> = TODO()
+        private val cr2: Result<Int> = TODO()
+    }
+
+    val p1 = r1
+    val p2: Result<String> = TODO()
+
+    fun returnInPrivate(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+}
+
+fun local(r: Result<Int>) {
+    val l1: Result<Int>? = null
+    val l2 = r
+
+    fun localFun(): <!RESULT_CLASS_IN_RETURN_TYPE!>Result<Int><!> = TODO()
+
+    class F {
+        val p1: Result<Int> = r
+        val p2 = r
+    }
+}
+
+fun <T> resultInGenericFun(r: Result<Int>): T = r <!UNCHECKED_CAST!>as T<!>
+
+val asFunPublic: () -> Result<Int> = TODO()
+private val asFun: () -> Result<Int>? = TODO()

compiler/testData/diagnostics/testsWithStdLib/coroutines/usageOfResultTypeInReturnType.txt

@@ -0,0 +1,109 @@
+package
+
+private val asFun: () -> kotlin.Result<kotlin.Int>?
+public val asFunPublic: () -> kotlin.Result<kotlin.Int>
+public val asFunctional: () -> kotlin.Result<kotlin.Int>
+public val topLevelP: kotlin.Result<kotlin.Int>
+public val topLevelPInferred: kotlin.Result<kotlin.Int>
+internal val topLevelPInternal: kotlin.Result<kotlin.Int>
+private val topLevelPPrivate: kotlin.Result<kotlin.Int>
+private val topLevelPPrivateInferred: kotlin.Result<kotlin.Int>
+public fun local(/*0*/ r: kotlin.Result<kotlin.Int>): kotlin.Unit
+public fun params(/*0*/ r1: kotlin.Result<kotlin.Int>, /*1*/ r2: kotlin.Result<kotlin.Int>?, /*2*/ r3: ResultAlias<kotlin.String> /* = kotlin.Result<kotlin.String> */, /*3*/ r4: kotlin.collections.List<kotlin.Result<kotlin.Int>>, /*4*/ r5: InlineResult<kotlin.Int>, /*5*/ vararg r6: kotlin.Result<kotlin.Int> /*kotlin.Array<out kotlin.Result<kotlin.Int>>*/): kotlin.Unit
+public fun </*0*/ T> resultInGenericFun(/*0*/ r: kotlin.Result<kotlin.Int>): T
+public fun returnContainer(): kotlin.collections.List<kotlin.Result<kotlin.Int>>
+public fun returnInferred(/*0*/ r1: kotlin.Result<kotlin.Int>, /*1*/ r2: ResultAlias<kotlin.Int> /* = kotlin.Result<kotlin.Int> */, /*2*/ b: kotlin.Boolean): kotlin.Result<kotlin.Int>
+public fun returnTypeAlias(): ResultAlias<kotlin.Int> /* = kotlin.Result<kotlin.Int> */
+public fun returnTypeInline(): InlineResult<kotlin.Int>
+internal fun returnTypeInternal(): kotlin.Result<kotlin.Int>
+public fun returnTypeNullable(): kotlin.Result<kotlin.Int>?
+private fun returnTypePrivate(): kotlin.Result<kotlin.Int>
+public fun returnTypePublic(): kotlin.Result<kotlin.Int>
+
+public final class CtorParams {
+    public constructor CtorParams(/*0*/ r1: kotlin.Result<kotlin.Int>)
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final inline class InlineResult</*0*/ out T> {
+    public constructor InlineResult</*0*/ out T>(/*0*/ r: kotlin.Result<T>)
+    private final val r: kotlin.Result<T>
+    public open override /*1*/ /*synthesized*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*synthesized*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*synthesized*/ fun toString(): kotlin.String
+}
+
+internal open class InternalCls {
+    public constructor InternalCls(/*0*/ r1: kotlin.Result<kotlin.Int>, /*1*/ r2: ResultAlias<kotlin.Int>? /* = kotlin.Result<kotlin.Int>? */, /*2*/ r3: kotlin.collections.List<kotlin.Result<kotlin.Int>>)
+    public final val p1: kotlin.Result<kotlin.Int>
+    public final val p2: kotlin.Result<kotlin.String>
+    protected final val p3: kotlin.Result<kotlin.Int>
+    public final val r1: kotlin.Result<kotlin.Int>
+    public final val r2: ResultAlias<kotlin.Int>? /* = kotlin.Result<kotlin.Int>? */
+    public final val r3: kotlin.collections.List<kotlin.Result<kotlin.Int>>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    protected final fun returnInClsProtected(): kotlin.Result<kotlin.Int>
+    public final fun returnInInternal(): kotlin.Result<kotlin.Int>
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public companion object Companion {
+        private constructor Companion()
+        public final val cr1: kotlin.Result<kotlin.Int>
+        private final val cr2: kotlin.Result<kotlin.Int>
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}
+
+private final class PrivateCls {
+    public constructor PrivateCls(/*0*/ r1: kotlin.Result<kotlin.Int>, /*1*/ r2: ResultAlias<kotlin.Int>? /* = kotlin.Result<kotlin.Int>? */, /*2*/ r3: kotlin.collections.List<kotlin.Result<kotlin.Int>>)
+    public final val p1: kotlin.Result<kotlin.Int>
+    public final val p2: kotlin.Result<kotlin.String>
+    public final val r1: kotlin.Result<kotlin.Int>
+    public final val r2: ResultAlias<kotlin.Int>? /* = kotlin.Result<kotlin.Int>? */
+    public final val r3: kotlin.collections.List<kotlin.Result<kotlin.Int>>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final fun returnInPrivate(): kotlin.Result<kotlin.Int>
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public companion object Companion {
+        private constructor Companion()
+        public final val cr1: kotlin.Result<kotlin.Int>
+        private final val cr2: kotlin.Result<kotlin.Int>
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}
+
+public open class PublicCls {
+    public constructor PublicCls(/*0*/ r1: kotlin.Result<kotlin.String>, /*1*/ r2: kotlin.Result<kotlin.Int>?, /*2*/ r3: ResultAlias<kotlin.Int> /* = kotlin.Result<kotlin.Int> */, /*3*/ r4: ResultAlias<kotlin.Int>? /* = kotlin.Result<kotlin.Int>? */, /*4*/ r5: InlineResult<kotlin.Int>, /*5*/ r6: kotlin.Result<kotlin.Int>, /*6*/ r7: kotlin.Result<kotlin.Int>, /*7*/ r8: kotlin.collections.List<kotlin.Result<kotlin.Int>>)
+    public final val p1: kotlin.Result<kotlin.Int>
+    public final var p2: kotlin.Result<kotlin.Int>
+    public final val p3: ResultAlias<kotlin.Int>? /* = kotlin.Result<kotlin.Int>? */
+    public final val p4: kotlin.Result<kotlin.Int>
+    internal final val p5: kotlin.Result<kotlin.Int>
+    private final var p6: kotlin.Result<kotlin.Int>
+    internal final val p7: kotlin.Result<kotlin.Int>
+    protected final val p8: kotlin.Result<kotlin.Int>
+    public final val r1: kotlin.Result<kotlin.String>
+    public final val r2: kotlin.Result<kotlin.Int>?
+    public final val r3: ResultAlias<kotlin.Int> /* = kotlin.Result<kotlin.Int> */
+    public final val r4: ResultAlias<kotlin.Int>? /* = kotlin.Result<kotlin.Int>? */
+    public final val r5: InlineResult<kotlin.Int>
+    internal final val r6: kotlin.Result<kotlin.Int>
+    private final val r7: kotlin.Result<kotlin.Int>
+    public final val r8: kotlin.collections.List<kotlin.Result<kotlin.Int>>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final fun returnInCls(): kotlin.Result<kotlin.Int>
+    private final fun returnInClsPrivate(): kotlin.Result<kotlin.Int>
+    protected final fun returnInClsProtected(): kotlin.Result<kotlin.Int>
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+public typealias ResultAlias</*0*/ T> = kotlin.Result<T>

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

@@ -1658,6 +1658,11 @@ public class DiagnosticsTestWithStdLibGenerated extends AbstractDiagnosticsTestW
             runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/unsupported.kt");
         }
 
+        @TestMetadata("usageOfResultTypeInReturnType.kt")
+        public void testUsageOfResultTypeInReturnType() throws Exception {
+            runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/usageOfResultTypeInReturnType.kt");
+        }
+
         @TestMetadata("compiler/testData/diagnostics/testsWithStdLib/coroutines/callableReference")
         @TestDataPath("$PROJECT_ROOT")
         @RunWith(JUnit3RunnerWithInners.class)

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsTestWithStdLibUsingJavacGenerated.java

@@ -1658,6 +1658,11 @@ public class DiagnosticsTestWithStdLibUsingJavacGenerated extends AbstractDiagno
             runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/unsupported.kt");
         }
 
+        @TestMetadata("usageOfResultTypeInReturnType.kt")
+        public void testUsageOfResultTypeInReturnType() throws Exception {
+            runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/usageOfResultTypeInReturnType.kt");
+        }
+
         @TestMetadata("compiler/testData/diagnostics/testsWithStdLib/coroutines/callableReference")
         @TestDataPath("$PROJECT_ROOT")
         @RunWith(JUnit3RunnerWithInners.class)