FIR checker: check TOPLEVEL_TYPEALIASES_ONLY

compiler/fir/analysis-tests/testData/resolve/visibility/exposedTypeAlias.kt

@@ -2,12 +2,12 @@ class A {
     private inner class Inner
 }
 class B {
-    typealias <!EXPOSED_TYPEALIAS_EXPANDED_TYPE!>AInner<!> = A.Inner
+    <!TOPLEVEL_TYPEALIASES_ONLY!>typealias <!EXPOSED_TYPEALIAS_EXPANDED_TYPE!>AInner<!> = A.Inner<!>
     inner class Inner
 }
 
 class C {
-    typealias BInner = B.Inner
+    <!TOPLEVEL_TYPEALIASES_ONLY!>typealias BInner = B.Inner<!>
 }
 
 typealias <!EXPOSED_TYPEALIAS_EXPANDED_TYPE!>AInner0<!> = A.Inner
@@ -15,4 +15,4 @@ typealias BInner0 = B.Inner
 
 private typealias MyString = String
 
-fun foo(): MyString = ""
+fun foo(): MyString = ""

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt

@@ -10,7 +10,6 @@ import com.intellij.psi.PsiTypeElement
 import org.jetbrains.kotlin.contracts.description.EventOccurrencesRange
 import org.jetbrains.kotlin.descriptors.Visibility
 import org.jetbrains.kotlin.diagnostics.WhenMissingCase
-import org.jetbrains.kotlin.resolve.ForbiddenNamedArgumentsTarget
 import org.jetbrains.kotlin.fir.FirEffectiveVisibility
 import org.jetbrains.kotlin.fir.FirSourceElement
 import org.jetbrains.kotlin.fir.PrivateForInline
@@ -26,6 +25,7 @@ import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.resolve.ForbiddenNamedArgumentsTarget
 import kotlin.properties.PropertyDelegateProvider
 import kotlin.properties.ReadOnlyProperty
 
@@ -523,6 +523,10 @@ object DIAGNOSTICS_LIST : DiagnosticList() {
         val NO_SET_METHOD by error<FirSourceElement, KtArrayAccessExpression>(PositioningStrategy.ARRAY_ACCESS)
     }
 
+    val TYPE_ALIAS by object : DiagnosticGroup("Type alias") {
+        val TOPLEVEL_TYPEALIASES_ONLY by error<FirSourceElement, KtTypeAlias>()
+    }
+
     val EXTENDED_CHECKERS by object : DiagnosticGroup("Extended checkers") {
         val REDUNDANT_VISIBILITY_MODIFIER by warning<FirSourceElement, KtModifierListOwner>(PositioningStrategy.VISIBILITY_MODIFIER)
         val REDUNDANT_MODALITY_MODIFIER by warning<FirSourceElement, KtModifierListOwner>(PositioningStrategy.MODALITY_MODIFIER)

compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -41,6 +41,7 @@ import org.jetbrains.kotlin.psi.KtProperty
 import org.jetbrains.kotlin.psi.KtPropertyAccessor
 import org.jetbrains.kotlin.psi.KtPropertyDelegate
 import org.jetbrains.kotlin.psi.KtSimpleNameExpression
+import org.jetbrains.kotlin.psi.KtTypeAlias
 import org.jetbrains.kotlin.psi.KtTypeParameter
 import org.jetbrains.kotlin.psi.KtTypeParameterList
 import org.jetbrains.kotlin.psi.KtTypeReference
@@ -313,6 +314,9 @@ object FirErrors {
     val NO_GET_METHOD by error0<FirSourceElement, KtArrayAccessExpression>(SourceElementPositioningStrategies.ARRAY_ACCESS)
     val NO_SET_METHOD by error0<FirSourceElement, KtArrayAccessExpression>(SourceElementPositioningStrategies.ARRAY_ACCESS)
 
+    // Type alias
+    val TOPLEVEL_TYPEALIASES_ONLY by error0<FirSourceElement, KtTypeAlias>()
+
     // Extended checkers
     val REDUNDANT_VISIBILITY_MODIFIER by warning0<FirSourceElement, KtModifierListOwner>(SourceElementPositioningStrategies.VISIBILITY_MODIFIER)
     val REDUNDANT_MODALITY_MODIFIER by warning0<FirSourceElement, KtModifierListOwner>(SourceElementPositioningStrategies.MODALITY_MODIFIER)

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirTypeAliasChecker.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2021 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.fir.analysis.checkers.declaration
+
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
+import org.jetbrains.kotlin.fir.analysis.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.declarations.FirFile
+import org.jetbrains.kotlin.fir.declarations.FirMemberDeclaration
+import org.jetbrains.kotlin.fir.declarations.FirTypeAlias
+
+object FirTypeAliasChecker : FirMemberDeclarationChecker() {
+    override fun check(declaration: FirMemberDeclaration, context: CheckerContext, reporter: DiagnosticReporter) {
+        if (declaration !is FirTypeAlias) return
+        if (context.containingDeclarations.lastOrNull() !is FirFile) {
+            reporter.reportOn(declaration.source, FirErrors.TOPLEVEL_TYPEALIASES_ONLY, context)
+        }
+    }
+}

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt

@@ -189,6 +189,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SUPERTYPE_NOT_INI
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SUPER_IS_NOT_AN_EXPRESSION
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SUPER_NOT_AVAILABLE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SYNTAX
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TOPLEVEL_TYPEALIASES_ONLY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_ARGUMENTS_NOT_ALLOWED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_MISMATCH
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETERS_IN_ENUM
@@ -691,6 +692,9 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
             map.put(NO_GET_METHOD, "No get method providing array access")
             map.put(NO_SET_METHOD, "No set method providing array access")
 
+            // Type alias
+            map.put(TOPLEVEL_TYPEALIASES_ONLY, "Nested and local type aliases are not supported")
+
             // Extended checkers group
             map.put(REDUNDANT_VISIBILITY_MODIFIER, "Redundant visibility modifier")
             map.put(REDUNDANT_MODALITY_MODIFIER, "Redundant modality modifier")

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/checkers/CommonDeclarationCheckers.kt

@@ -24,6 +24,7 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
         FirInfixFunctionDeclarationChecker,
         FirExposedVisibilityDeclarationChecker,
         FirSealedSupertypeChecker,
+        FirTypeAliasChecker,
     )
 
     override val functionCheckers: Set<FirFunctionChecker> = setOf(

compiler/testData/diagnostics/tests/classLiteral/typealiases.fir.kt

@@ -9,7 +9,7 @@ typealias TTNullableTString = TNullableTString
 fun f3() = TTNullableTString::class
 
 inline fun <reified T> f4(b: Boolean): Any {
-    typealias X = T
-    typealias Y = T?
+    <!TOPLEVEL_TYPEALIASES_ONLY!>typealias X = T<!>
+    <!TOPLEVEL_TYPEALIASES_ONLY!>typealias Y = T?<!>
     return if (b) <!UNRESOLVED_REFERENCE!>X<!>::class else <!UNRESOLVED_REFERENCE!>Y<!>::class
 }

compiler/testData/diagnostics/tests/typealias/topLevelTypeAliasesOnly.fir.kt

@@ -1,19 +0,0 @@
-typealias TopLevel = Any
-
-interface A {
-    typealias Nested = Any
-}
-
-class C {
-    typealias Nested = Any
-    class D {
-        typealias Nested = Any
-        fun foo() {
-            typealias LocalInMember = Any
-        }
-    }
-}
-
-fun foo() {
-    typealias Local = Any
-}

compiler/testData/diagnostics/tests/typealias/topLevelTypeAliasesOnly.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 typealias TopLevel = Any
 
 interface A {