[FIR] Add PLATFORM_CLASS_MAPPED_TO_KOTLIN

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

@@ -657,6 +657,10 @@ object DIAGNOSTICS_LIST : DiagnosticList("FirErrors") {
         }
 
         val REDUNDANT_NULLABLE by warning<KtTypeReference>(PositioningStrategy.REDUNDANT_NULLABLE)
+
+        val PLATFORM_CLASS_MAPPED_TO_KOTLIN by warning<PsiElement>(PositioningStrategy.REFERENCED_NAME_BY_QUALIFIED) {
+            parameter<FqName>("kotlinClass")
+        }
     }
 
     val REFLECTION by object : DiagnosticGroup("Reflection") {

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

@@ -396,6 +396,7 @@ object FirErrors {
     val TYPE_VARIANCE_CONFLICT_IN_EXPANDED_TYPE by error4<PsiElement, FirTypeParameterSymbol, Variance, Variance, ConeKotlinType>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE_OR_DEFAULT)
     val SMARTCAST_IMPOSSIBLE by error4<KtExpression, ConeKotlinType, FirExpression, String, Boolean>()
     val REDUNDANT_NULLABLE by warning0<KtTypeReference>(SourceElementPositioningStrategies.REDUNDANT_NULLABLE)
+    val PLATFORM_CLASS_MAPPED_TO_KOTLIN by warning1<PsiElement, FqName>(SourceElementPositioningStrategies.REFERENCED_NAME_BY_QUALIFIED)
 
     // Reflection
     val EXTENSION_IN_CLASS_REFERENCE_NOT_ALLOWED by error1<KtExpression, FirCallableSymbol<*>>(SourceElementPositioningStrategies.REFERENCE_BY_QUALIFIED)

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/ExtendedDeclarationCheckers.kt

@@ -11,6 +11,11 @@ import org.jetbrains.kotlin.fir.analysis.checkers.declaration.*
 import org.jetbrains.kotlin.fir.analysis.checkers.extended.*
 
 object ExtendedDeclarationCheckers : DeclarationCheckers() {
+    override val fileCheckers: Set<FirFileChecker>
+        get() = setOf(
+            PlatformClassMappedToKotlinImportsChecker
+        )
+
     override val basicDeclarationCheckers: Set<FirBasicDeclarationChecker>
         get() = setOf(
             RedundantVisibilityModifierSyntaxChecker,

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/ExtendedTypeCheckers.kt

@@ -5,11 +5,13 @@
 
 package org.jetbrains.kotlin.fir.analysis.checkers
 
+import org.jetbrains.kotlin.fir.analysis.checkers.extended.PlatformClassMappedToKotlinTypeRefChecker
 import org.jetbrains.kotlin.fir.analysis.checkers.extended.RedundantNullableChecker
 import org.jetbrains.kotlin.fir.analysis.checkers.type.*
 
 object ExtendedTypeCheckers : TypeCheckers() {
     override val typeRefCheckers: Set<FirTypeRefChecker> = setOf(
-        RedundantNullableChecker
+        RedundantNullableChecker,
+        PlatformClassMappedToKotlinTypeRefChecker
     )
 }

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/PlatformClassMappedToKotlinImportsChecker.kt

@@ -0,0 +1,34 @@
+/*
+ * 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.extended
+
+import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirFileChecker
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
+import org.jetbrains.kotlin.fir.declarations.FirFile
+import org.jetbrains.kotlin.fir.declarations.FirResolvedImport
+import org.jetbrains.kotlin.fir.scopes.platformClassMapper
+import org.jetbrains.kotlin.name.ClassId
+
+object PlatformClassMappedToKotlinImportsChecker : FirFileChecker() {
+    override fun check(declaration: FirFile, context: CheckerContext, reporter: DiagnosticReporter) {
+        declaration.imports.forEach { import ->
+            val importedFqName = import.importedFqName ?: return
+            if (importedFqName.isRoot || importedFqName.shortName().asString().isEmpty()) return
+            val classId = (import as? FirResolvedImport)?.resolvedParentClassId ?: ClassId.topLevel(importedFqName)
+            if (classId.asSingleFqName() != importedFqName) {
+                return
+            }
+
+            val kotlinClass = context.session.platformClassMapper.getCorrespondingKotlinClass(classId)
+            if (kotlinClass != null) {
+                reporter.reportOn(import.source, FirErrors.PLATFORM_CLASS_MAPPED_TO_KOTLIN, importedFqName, context)
+            }
+        }
+    }
+}

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/PlatformClassMappedToKotlinTypeRefChecker.kt

@@ -0,0 +1,27 @@
+/*
+ * 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.extended
+
+import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.type.FirTypeRefChecker
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
+import org.jetbrains.kotlin.fir.scopes.platformClassMapper
+import org.jetbrains.kotlin.fir.types.FirResolvedTypeRef
+import org.jetbrains.kotlin.fir.types.FirTypeRef
+import org.jetbrains.kotlin.fir.types.classId
+
+object PlatformClassMappedToKotlinTypeRefChecker : FirTypeRefChecker() {
+    override fun check(typeRef: FirTypeRef, context: CheckerContext, reporter: DiagnosticReporter) {
+        if (typeRef is FirResolvedTypeRef) {
+            val kotlinClass = context.session.platformClassMapper.getCorrespondingKotlinClass(typeRef.type.classId)
+            if (kotlinClass != null) {
+                reporter.reportOn(typeRef.source, FirErrors.PLATFORM_CLASS_MAPPED_TO_KOTLIN, kotlinClass.asSingleFqName(), context)
+            }
+        }
+    }
+}

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

@@ -349,6 +349,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.OVERRIDE_BY_INLIN
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.OVERRIDE_DEPRECATION
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.OVERRIDING_FINAL_MEMBER
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.PACKAGE_CANNOT_BE_IMPORTED
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.PLATFORM_CLASS_MAPPED_TO_KOTLIN
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.PRIMARY_CONSTRUCTOR_DELEGATION_CALL_EXPECTED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.PRIMARY_CONSTRUCTOR_REQUIRED_FOR_DATA_CLASS
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.PRIVATE_CLASS_MEMBER_FROM_INLINE
@@ -624,6 +625,7 @@ object FirErrorsDefaultMessages : BaseDiagnosticRendererFactory() {
         map.put(SINGLETON_IN_SUPERTYPE, "Cannot inherit from a singleton")
         map.put(NULLABLE_SUPERTYPE, "A supertype cannot be nullable")
         map.put(REDUNDANT_NULLABLE, "Redundant '?'")
+        map.put(PLATFORM_CLASS_MAPPED_TO_KOTLIN, "This class shouldn't be used in Kotlin. Use {0} instead.", TO_STRING)
         map.put(MANY_CLASSES_IN_SUPERTYPE_LIST, "Only one class may appear in a supertype list")
         map.put(SUPERTYPE_APPEARS_TWICE, "A supertype appears twice")
         map.put(CLASS_IN_SUPERTYPE_FOR_ENUM, "Enum class cannot inherit from classes")