Check access control for the generic requirements of subscripts

Oops.

Author: jrose-apple

lib/Sema/TypeCheckAccess.cpp

@@ -365,9 +365,16 @@ void AccessControlCheckerBase::checkGenericParamAccess(
   if (minAccessScope.isPublic())
     return;
 
+  // FIXME: Promote this to an error in the next -swift-version break.
+  if (isa<SubscriptDecl>(owner))
+    downgradeToWarning = DowngradeToWarning::Yes;
+
   if (checkUsableFromInline) {
-    auto diagID = diag::generic_param_usable_from_inline;
     if (!TC.Context.isSwiftVersionAtLeast(5))
+      downgradeToWarning = DowngradeToWarning::Yes;
+
+    auto diagID = diag::generic_param_usable_from_inline;
+    if (downgradeToWarning == DowngradeToWarning::Yes)
       diagID = diag::generic_param_usable_from_inline_warn;
     auto diag = TC.diagnose(owner,
                             diagID,
@@ -802,6 +809,8 @@ class AccessControlChecker : public AccessControlCheckerBase,
   }
 
   void visitSubscriptDecl(SubscriptDecl *SD) {
+    checkGenericParamAccess(SD->getGenericParams(), SD);
+
     auto minAccessScope = AccessScope::getPublic();
     const TypeRepr *complainRepr = nullptr;
     auto downgradeToWarning = DowngradeToWarning::No;
@@ -1294,6 +1303,8 @@ class UsableFromInlineChecker : public AccessControlCheckerBase,
   }
 
   void visitSubscriptDecl(SubscriptDecl *SD) {
+    checkGenericParamAccess(SD->getGenericParams(), SD);
+
     for (auto &P : *SD->getIndices()) {
       checkTypeAccess(P->getTypeLoc(), SD, /*mayBeInferred*/false,
                       [&](AccessScope typeAccessScope,

test/Sema/accessibility.swift

@@ -869,3 +869,10 @@ public extension ObjCSub {
     set {}
   }
 }
+
+public struct TestGenericSubscripts {
+  // We'd like these to be errors in a future version of Swift, but they weren't
+  // in Swift 5.0.
+  public subscript<T: PrivateProto>(_: T) -> Int { return 0 } // expected-warning {{subscript should not be declared public because its generic parameter uses a private type}} {{none}}
+  public subscript<T>(where _: T) -> Int where T: PrivateProto { return 0 } // expected-warning {{subscript should not be declared public because its generic requirement uses a private type}} {{none}}
+}

test/attr/attr_usableFromInline.swift

@@ -87,7 +87,7 @@ internal struct InternalStruct {}
 // expected-error@-1 {{type referenced from the underlying type of a '@usableFromInline' type alias must be '@usableFromInline' or public}}
 
 protocol InternalProtocol {
-  // expected-note@-1 4{{type declared here}}
+  // expected-note@-1 * {{type declared here}}
   associatedtype T
 }
 
@@ -147,3 +147,8 @@ enum BadEnum {
 @usableFromInline
 class BadClass : InternalClass {}
 // expected-error@-1 {{type referenced from the superclass of a '@usableFromInline' class must be '@usableFromInline' or public}}
+
+public struct TestGenericSubscripts {
+  @usableFromInline subscript<T: InternalProtocol>(_: T) -> Int { return 0 } // expected-warning {{type referenced from a generic parameter of a '@usableFromInline' subscript should be '@usableFromInline' or public}}
+  @usableFromInline subscript<T>(where _: T) -> Int where T: InternalProtocol { return 0 } // expected-warning {{type referenced from a generic requirement of a '@usableFromInline' subscript should be '@usableFromInline' or public}}
+}