Merge pull request swiftlang#22800 from slavapestov/witness-access-check-crash

Sema: Fix crashes in witness access control checking

Author: slavapestov

lib/Sema/TypeCheckProtocol.cpp

@@ -2463,16 +2463,19 @@ void ConformanceChecker::recordTypeWitness(AssociatedTypeDecl *assocType,
     if (checkWitnessAccess(assocType, typeDecl, &isSetter)) {
       assert(!isSetter);
 
-      // Avoid relying on the lifetime of 'this'.
+      // Note: you must not capture 'this' in the below closure.
       const DeclContext *DC = this->DC;
+      auto requiredAccessScope = getRequiredAccessScope();
+
       diagnoseOrDefer(assocType, false,
-          [this, DC, typeDecl](NormalProtocolConformance *conformance) {
+          [DC, requiredAccessScope, typeDecl](
+            NormalProtocolConformance *conformance) {
         AccessLevel requiredAccess =
-            getRequiredAccessScope().requiredAccessForDiagnostics();
+            requiredAccessScope.requiredAccessForDiagnostics();
         auto proto = conformance->getProtocol();
         auto protoAccessScope = proto->getFormalAccessScope(DC);
         bool protoForcesAccess =
-            getRequiredAccessScope().hasEqualDeclContextWith(protoAccessScope);
+            requiredAccessScope.hasEqualDeclContextWith(protoAccessScope);
         auto diagKind = protoForcesAccess
                           ? diag::type_witness_not_accessible_proto
                           : diag::type_witness_not_accessible_type;
@@ -2546,11 +2549,6 @@ void ConformanceChecker::recordTypeWitness(AssociatedTypeDecl *assocType,
         aliasDecl->getAttrs().add(attr);
       }
 
-      bool unused;
-      assert(TC.Context.hadError() ||
-             !checkWitnessAccess(assocType, aliasDecl, &unused));
-      (void)unused;
-
       if (nominal == DC) {
         nominal->addMember(aliasDecl);
       } else {

test/Compatibility/attr_escaping.swift

@@ -0,0 +1,7 @@
+// RUN: not %target-swift-frontend -typecheck %s -swift-version 4
+// RUN: not %target-swift-frontend -typecheck %s -swift-version 5
+
+public struct Horse : OptionSet {
+  typealias Element = Horse // this was not public...
+  public static let horse = Horse()
+}