From 6776930881e74bf0e12aa253445b9e29df41e0f7 Mon Sep 17 00:00:00 2001
From: Nikolay Lunyak <lunyak.kolya@mail.ru>
Date: Tue, 17 Aug 2021 18:11:27 +0300
Subject: [PATCH] [FIR] Forbid explicit backing fields for FE 1.0

---
 .../src/org/jetbrains/kotlin/diagnostics/Errors.java       | 2 ++
 .../kotlin/diagnostics/rendering/DefaultErrorMessages.java | 2 ++
 .../org/jetbrains/kotlin/resolve/DeclarationsChecker.kt    | 7 +++++++
 3 files changed, 11 insertions(+)

diff --git a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java
index c24265d768d..33696758ccc 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java
@@ -71,6 +71,8 @@ public interface Errors {
     DiagnosticFactory1<PsiElement, Pair<LanguageFeature, LanguageVersionSettings>> EXPERIMENTAL_FEATURE_WARNING = DiagnosticFactory1.create(WARNING);
     DiagnosticFactory1<PsiElement, Pair<LanguageFeature, LanguageVersionSettings>> EXPERIMENTAL_FEATURE_ERROR = DiagnosticFactory1.create(ERROR);
 
+    DiagnosticFactory0<KtElement> EXPLICIT_BACKING_FIELDS_UNSUPPORTED = DiagnosticFactory0.create(ERROR);
+
     ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
     // Generic errors/warnings: applicable in many contexts
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java
index 8af252ce3d3..c39764f14c2 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java
@@ -712,6 +712,8 @@ public class DefaultErrorMessages {
         MAP.put(EXPERIMENTAL_FEATURE_WARNING, "{0}", new LanguageFeatureMessageRenderer(LanguageFeatureMessageRenderer.Type.WARNING));
         MAP.put(EXPERIMENTAL_FEATURE_ERROR, "{0}", new LanguageFeatureMessageRenderer(LanguageFeatureMessageRenderer.Type.ERROR));
 
+        MAP.put(EXPLICIT_BACKING_FIELDS_UNSUPPORTED, "Explicit backing field declarations are not supported in FE 1.0");
+
         MAP.put(EXCEPTION_FROM_ANALYZER, "Internal Error occurred while analyzing this expression:\n{0}", THROWABLE);
         MAP.put(MISSING_STDLIB, "{0}. Ensure you have the standard Kotlin library in dependencies", STRING);
         MAP.put(UNNECESSARY_SAFE_CALL, "Unnecessary safe call on a non-null receiver of type {0}. This expression will have nullable type in future releases", RENDER_TYPE);
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/DeclarationsChecker.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/DeclarationsChecker.kt
index c9586d17109..1c9927433c6 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/DeclarationsChecker.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/DeclarationsChecker.kt
@@ -591,6 +591,12 @@ class DeclarationsChecker(
         }
     }
 
+    private fun checkBackingField(property: KtProperty) {
+        property.fieldDeclaration?.let {
+            trace.report(EXPLICIT_BACKING_FIELDS_UNSUPPORTED.on(it))
+        }
+    }
+
     private fun checkProperty(property: KtProperty, propertyDescriptor: PropertyDescriptor) {
         val containingDeclaration = propertyDescriptor.containingDeclaration
         if (containingDeclaration is ClassDescriptor) {
@@ -605,6 +611,7 @@ class DeclarationsChecker(
         checkPropertyTypeParametersAreUsedInReceiverType(propertyDescriptor)
         checkImplicitCallableType(property, propertyDescriptor)
         checkPrivateExpectedDeclaration(property, propertyDescriptor)
+        checkBackingField(property)
     }
 
     private fun checkPrivateExpectedDeclaration(declaration: KtDeclaration, descriptor: MemberDescriptor) {