Allow contracts on final non-override members since 1.4

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

@@ -23,7 +23,6 @@ import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.builtins.getReceiverTypeFromFunctionType
 import org.jetbrains.kotlin.builtins.getValueParameterTypesFromFunctionType
 import org.jetbrains.kotlin.builtins.isBuiltinFunctionalType
-import org.jetbrains.kotlin.config.AnalysisFlags
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.contracts.description.ContractProviderKey
@@ -259,8 +258,9 @@ class FunctionDescriptorResolver(
         if (function !is KtNamedFunction) return null
 
         val isContractsEnabled = languageVersionSettings.supportsFeature(LanguageFeature.AllowContractsForCustomFunctions)
+        val isAllowedOnMembers = languageVersionSettings.supportsFeature(LanguageFeature.AllowContractsForNonOverridableMembers)
 
-        if (!isContractsEnabled || !function.mayHaveContract()) return null
+        if (!isContractsEnabled || !function.mayHaveContract(isAllowedOnMembers)) return null
 
         return LazyContractProvider(storageManager) {
             AstLoadingFilter.forceAllowTreeLoading(function.containingFile, ThrowableComputable {

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/ContractNotAllowedCallChecker.kt

@@ -6,11 +6,9 @@
 package org.jetbrains.kotlin.resolve.calls.checkers
 
 import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.contracts.parsing.isContractCallDescriptor
-import org.jetbrains.kotlin.descriptors.FunctionDescriptor
-import org.jetbrains.kotlin.descriptors.PackageFragmentDescriptor
-import org.jetbrains.kotlin.descriptors.PropertyAccessorDescriptor
-import org.jetbrains.kotlin.descriptors.isOverridable
+import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.diagnostics.Errors
 import org.jetbrains.kotlin.psi.KtElement
 import org.jetbrains.kotlin.psi.psiUtil.isFirstStatement
@@ -25,6 +23,8 @@ object ContractNotAllowedCallChecker : CallChecker {
         val descriptor = resolvedCall.resultingDescriptor as? FunctionDescriptor ?: return
         if (!descriptor.isContractCallDescriptor()) return
 
+        val allowedOnMembers = context.languageVersionSettings.supportsFeature(LanguageFeature.AllowContractsForNonOverridableMembers)
+
         val callElement = resolvedCall.call.callElement
         var hasErrors = false
 
@@ -40,7 +40,24 @@ object ContractNotAllowedCallChecker : CallChecker {
             contractNotAllowed("Contracts are allowed only for functions")
 
         var inFunctionBodyBlock = true
-        if (scope.ownerDescriptor.containingDeclaration !is PackageFragmentDescriptor
+
+        val declarationOwner = scope.ownerDescriptor.containingDeclaration
+        val acceptableParent = if (allowedOnMembers) {
+            var owner = declarationOwner
+            var result = true
+            while (owner !is PackageFragmentDescriptor) {
+                if (owner !is ClassDescriptor) {
+                    result = false
+                    break
+                }
+                owner = owner.containingDeclaration
+            }
+            result
+        } else {
+            declarationOwner is PackageFragmentDescriptor
+        }
+
+        if (!acceptableParent
             || scope.kind != LexicalScopeKind.CODE_BLOCK
             || (scope.parent as? LexicalScope)?.kind != LexicalScopeKind.FUNCTION_INNER_SCOPE
         ) {
@@ -48,13 +65,23 @@ object ContractNotAllowedCallChecker : CallChecker {
                 contractNotAllowed("Contracts are allowed only in function body block")
                 inFunctionBodyBlock = false
             } else {
-                contractNotAllowed("Contracts are allowed only for top-level functions")
+                val message = if (allowedOnMembers)
+                    "Contracts are allowed only for functions"
+                else
+                    "Contracts are allowed only for top-level functions"
+                contractNotAllowed(message)
             }
         }
 
         if (functionDescriptor?.isOperator == true) contractNotAllowed("Contracts are not allowed for operator functions")
 
-        if (functionDescriptor?.isOverridable == true) contractNotAllowed("Contracts are not allowed for open functions")
+
+        if (!allowedOnMembers && functionDescriptor?.isOverridable == true) {
+            contractNotAllowed("Contracts are not allowed for open functions")
+        }
+        if (allowedOnMembers && functionDescriptor?.isOverridableOrOverrides == true) {
+            contractNotAllowed("Contracts are not allowed for open or override functions")
+        }
 
         if (!callElement.isFirstStatement() && inFunctionBodyBlock) {
             contractNotAllowed("Contract should be the first statement")