Prohibit 'expect' lateinit member properties

#KT-20319 Fixed

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

@@ -563,6 +563,7 @@ public interface Errors {
     DiagnosticFactory0<KtEnumEntry> EXPECTED_ENUM_ENTRY_WITH_BODY = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<KtExpression> EXPECTED_PROPERTY_INITIALIZER = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<KtPropertyDelegate> EXPECTED_DELEGATED_PROPERTY = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> EXPECTED_LATEINIT_PROPERTY = DiagnosticFactory0.create(ERROR);
 
     DiagnosticFactory0<KtTypeAlias> ACTUAL_TYPE_ALIAS_NOT_TO_CLASS = DiagnosticFactory0.create(ERROR, DECLARATION_SIGNATURE);
     DiagnosticFactory0<KtTypeAlias>

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

@@ -271,6 +271,7 @@ public class DefaultErrorMessages {
         MAP.put(EXPECTED_ENUM_ENTRY_WITH_BODY, "Expected enum entry cannot have a body");
         MAP.put(EXPECTED_PROPERTY_INITIALIZER, "Expected property cannot have an initializer");
         MAP.put(EXPECTED_DELEGATED_PROPERTY, "Expected property cannot be delegated");
+        MAP.put(EXPECTED_LATEINIT_PROPERTY, "Expected property cannot be lateinit");
 
         MAP.put(ACTUAL_TYPE_ALIAS_NOT_TO_CLASS, "Right-hand side of actual type alias should be a class, not another type alias");
         MAP.put(ACTUAL_TYPE_ALIAS_TO_CLASS_WITH_DECLARATION_SITE_VARIANCE, "Aliased class should not have type parameters with declaration-site variance");

compiler/frontend/src/org/jetbrains/kotlin/resolve/DeclarationsChecker.kt

@@ -670,9 +670,14 @@ class DeclarationsChecker(
             else if (noExplicitTypeOrGetterType(property)) {
                 trace.report(PROPERTY_WITH_NO_TYPE_NO_INITIALIZER.on(property))
             }
-            if (backingFieldRequired && !inInterface && propertyDescriptor.isLateInit && !isUninitialized &&
-                trace[MUST_BE_LATEINIT, propertyDescriptor] != true) {
-                trace.report(UNNECESSARY_LATEINIT.on(property))
+
+            if (propertyDescriptor.isLateInit) {
+                if (propertyDescriptor.isExpect) {
+                    trace.report(EXPECTED_LATEINIT_PROPERTY.on(property.modifierList?.getModifier(KtTokens.LATEINIT_KEYWORD) ?: property))
+                }
+                if (backingFieldRequired && !inInterface && !isUninitialized && trace[MUST_BE_LATEINIT, propertyDescriptor] != true) {
+                    trace.report(UNNECESSARY_LATEINIT.on(property))
+                }
             }
         }
     }

compiler/frontend/src/org/jetbrains/kotlin/resolve/ModifiersChecker.kt

@@ -191,9 +191,6 @@ object ModifierCheckerCore {
         // (see the KEEP https://github.com/Kotlin/KEEP/blob/master/proposals/sealed-class-inheritance.md)
         result += incompatibilityRegister(SEALED_KEYWORD, INNER_KEYWORD)
 
-        // lateinit is incompatible with header / expect
-        result += incompatibilityRegister(LATEINIT_KEYWORD, HEADER_KEYWORD, EXPECT_KEYWORD)
-
         // header / expect / impl / actual are all incompatible
         result += incompatibilityRegister(HEADER_KEYWORD, EXPECT_KEYWORD, IMPL_KEYWORD, ACTUAL_KEYWORD)
 

compiler/testData/diagnostics/tests/multiplatform/headerClass/memberPropertyKinds.kt

@@ -23,6 +23,8 @@ expect class Foo {
     <!EXPECTED_DECLARATION_WITH_BODY!>get()<!> = "no"
     <!EXPECTED_DECLARATION_WITH_BODY!>set(value)<!> {}
 
+    <!EXPECTED_LATEINIT_PROPERTY!>lateinit<!> var lateinitVar: String
+
     val delegated: String <!EXPECTED_DELEGATED_PROPERTY!>by Delegate<!>
 }
 

compiler/testData/diagnostics/tests/multiplatform/headerClass/memberPropertyKinds.txt

@@ -17,6 +17,7 @@ public final expect class Foo {
     public expect final val delegated: kotlin.String
     public expect final val justVal: kotlin.String
     public expect final var justVar: kotlin.String
+    public expect final lateinit var lateinitVar: kotlin.String
     public expect final val valWithGet: kotlin.String
     public expect final var varWithGetSet: kotlin.String
     public expect final val kotlin.String.extensionVal: kotlin.Unit

compiler/testData/diagnostics/tests/multiplatform/topLevelProperty/differentKindsOfProperties.kt

@@ -1,4 +1,4 @@
-// !LANGUAGE: +MultiPlatformProjects
+// !LANGUAGE: +MultiPlatformProjects +LateinitTopLevelProperties
 // MODULE: m1-common
 // FILE: common.kt
 
@@ -28,7 +28,7 @@ expect var customAccessorVar: String
 
 expect <!CONST_VAL_WITHOUT_INITIALIZER!>const<!> val constVal: Int
 
-<!INCOMPATIBLE_MODIFIERS!>expect<!> <!INCOMPATIBLE_MODIFIERS!>lateinit<!> var lateinitVar: String
+expect <!EXPECTED_LATEINIT_PROPERTY!>lateinit<!> var lateinitVar: String
 
 expect val delegated: String <!EXPECTED_DELEGATED_PROPERTY!>by Delegate<!>
 object Delegate { operator fun getValue(x: Any?, y: Any?): String = "" }