[FE] Prohibit expect external and expect tailrec

^KT-58536 Fixed

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

@@ -790,6 +790,8 @@ public interface Errors {
     DiagnosticFactory0<PsiElement> EXPECTED_LATEINIT_PROPERTY = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<PsiElement> SUPERTYPE_INITIALIZED_IN_EXPECTED_CLASS = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<PsiElement> EXPECTED_PRIVATE_DECLARATION = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> EXPECTED_EXTERNAL_DECLARATION = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> EXPECTED_TAILREC_FUNCTION = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<KtDelegatedSuperTypeEntry> IMPLEMENTATION_BY_DELEGATION_IN_EXPECT_CLASS = DiagnosticFactory0.create(ERROR);
 
     DiagnosticFactory0<KtTypeAlias> ACTUAL_TYPE_ALIAS_NOT_TO_CLASS = DiagnosticFactory0.create(ERROR, DECLARATION_SIGNATURE);

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

@@ -352,6 +352,8 @@ public class DefaultErrorMessages {
         MAP.put(EXPECTED_LATEINIT_PROPERTY, "Expected property cannot be lateinit");
         MAP.put(SUPERTYPE_INITIALIZED_IN_EXPECTED_CLASS, "Expected classes cannot initialize supertypes");
         MAP.put(EXPECTED_PRIVATE_DECLARATION, "Expected declaration cannot be private");
+        MAP.put(EXPECTED_EXTERNAL_DECLARATION, "Expected declaration cannot be external");
+        MAP.put(EXPECTED_TAILREC_FUNCTION, "Expected function cannot have 'tailrec' modifier");
 
         MAP.put(IMPLEMENTATION_BY_DELEGATION_IN_EXPECT_CLASS, "Implementation by delegation in expected classes is prohibited");
 

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

@@ -343,7 +343,7 @@ class DeclarationsChecker(
 
         checkPrimaryConstructor(classOrObject, classDescriptor)
 
-        checkPrivateExpectedDeclaration(classOrObject, classDescriptor)
+        checkExpectDeclarationModifiers(classOrObject, classDescriptor)
     }
 
     private fun checkLocalAnnotation(classDescriptor: ClassDescriptor, classOrObject: KtClassOrObject) {
@@ -618,14 +618,29 @@ class DeclarationsChecker(
         shadowedExtensionChecker.checkDeclaration(property, propertyDescriptor)
         checkPropertyTypeParametersAreUsedInReceiverType(propertyDescriptor)
         checkImplicitCallableType(property, propertyDescriptor)
-        checkPrivateExpectedDeclaration(property, propertyDescriptor)
+        checkExpectDeclarationModifiers(property, propertyDescriptor)
         checkBackingField(property)
     }
 
-    private fun checkPrivateExpectedDeclaration(declaration: KtDeclaration, descriptor: MemberDescriptor) {
-        if (descriptor.isExpect && DescriptorVisibilities.isPrivate(descriptor.visibility)) {
+    private fun checkExpectDeclarationModifiers(declaration: KtDeclaration, descriptor: MemberDescriptor) {
+        if (!descriptor.isExpect) return
+
+        if (DescriptorVisibilities.isPrivate(descriptor.visibility)) {
             trace.report(EXPECTED_PRIVATE_DECLARATION.on(declaration.modifierList?.getModifier(KtTokens.PRIVATE_KEYWORD) ?: declaration))
         }
+
+        checkExpectDeclarationHasNoExternalModifier(declaration)
+        if (declaration is KtFunction) {
+            declaration.modifierList?.getModifier(KtTokens.TAILREC_KEYWORD)?.let {
+                trace.report(EXPECTED_TAILREC_FUNCTION.on(it))
+            }
+        }
+    }
+
+    private fun checkExpectDeclarationHasNoExternalModifier(declaration: KtDeclaration) {
+        declaration.modifierList?.getModifier(KtTokens.EXTERNAL_KEYWORD)?.let {
+            trace.report(EXPECTED_EXTERNAL_DECLARATION.on(it))
+        }
     }
 
     private fun checkPropertyTypeParametersAreUsedInReceiverType(descriptor: PropertyDescriptor) {
@@ -925,7 +940,7 @@ class DeclarationsChecker(
             trace.report(EXPECTED_DECLARATION_WITH_BODY.on(function))
         }
 
-        checkPrivateExpectedDeclaration(function, functionDescriptor)
+        checkExpectDeclarationModifiers(function, functionDescriptor)
     }
 
     private fun checkActualFunction(element: KtDeclaration, functionDescriptor: FunctionDescriptor) {
@@ -1022,6 +1037,9 @@ class DeclarationsChecker(
                 }
             }
         }
+        if (propertyDescriptor.isExpect) {
+            checkExpectDeclarationHasNoExternalModifier(accessor)
+        }
     }
 
     private fun checkEnumEntry(enumEntry: KtEnumEntry, enumEntryClass: ClassDescriptor) {