prevent uses of Escapable in general

include/swift/AST/DiagnosticsSema.def

@@ -7708,7 +7708,7 @@ NOTE(add_explicit_protocol_for_conformance,none,
      "consider making %kind0 explicitly conform to the '%1' protocol",
      (const ValueDecl *, StringRef))
 ERROR(escapable_requires_feature_flag,none,
-      "type '~Escapable' requires -enable-experimental-feature NonescapableTypes",
+      "type 'Escapable' requires -enable-experimental-feature NonescapableTypes",
       ())
 ERROR(non_bitwise_copyable_type_class,none,
       "class cannot conform to 'BitwiseCopyable'", ())

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -124,10 +124,9 @@ class CheckRepressions {
     auto ipk = getInvertibleProtocolKind(*kp);
     if (ipk) {
       // Gate the '~Escapable' type behind a specific flag for now.
+      // Uses of 'Escapable' itself are already diagnosed; return ErrorType.
       if (*ipk == InvertibleProtocolKind::Escapable &&
           !ctx.LangOpts.hasFeature(Feature::NonescapableTypes)) {
-        diagnoseInvalid(repr, repr.getLoc(),
-                        diag::escapable_requires_feature_flag);
         return ErrorType::get(ctx);
       }
 

lib/Sema/TypeCheckType.cpp

@@ -4770,6 +4770,21 @@ TypeResolver::resolveDeclRefTypeRepr(DeclRefTypeRepr *repr,
     auto *dc = getDeclContext();
     auto &ctx = getASTContext();
 
+    // Gate the 'Escapable' type behind a specific flag for now.
+    //
+    // NOTE: we do not return an ErrorType, though! We're just artificially
+    // preventing people from referring to the type without the feature.
+    if (auto proto = result->getAs<ProtocolType>()) {
+      if (auto known = proto->getKnownProtocol()) {
+        if (*known == KnownProtocolKind::Escapable
+            && !isSILSourceFile()
+            && !ctx.LangOpts.hasFeature(Feature::NonescapableTypes)) {
+          diagnoseInvalid(repr, repr->getLoc(),
+                          diag::escapable_requires_feature_flag);
+        }
+      }
+    }
+
     if (ctx.LangOpts.hasFeature(Feature::ImplicitSome) &&
         options.isConstraintImplicitExistential()) {
       // Check whether this type is an implicit opaque result type.
@@ -5774,10 +5789,9 @@ NeverNullType TypeResolver::resolveInverseType(InverseTypeRepr *repr,
     if (auto kind = getInvertibleProtocolKind(*kp)) {
 
       // Gate the '~Escapable' type behind a specific flag for now.
+      // Uses of 'Escapable' itself are already diagnosed; return ErrorType.
       if (*kind == InvertibleProtocolKind::Escapable &&
           !getASTContext().LangOpts.hasFeature(Feature::NonescapableTypes)) {
-        diagnoseInvalid(repr, repr->getLoc(),
-                        diag::escapable_requires_feature_flag);
         return wrapInExistential(ErrorType::get(getASTContext()));
       }
 

stdlib/public/core/Misc.swift

@@ -171,6 +171,7 @@ func _rethrowsViaClosure(_ fn: () throws -> ()) rethrows {
 
 @_marker public protocol Copyable {}
 
+@_documentation(visibility: internal)
 @_marker public protocol Escapable {}
 
 #if $NoncopyableGenerics && $NonescapableTypes

test/Parse/inverse_escapable_feature.swift

@@ -2,4 +2,8 @@
 
 
 
-struct S: ~Escapable {} // expected-error {{type '~Escapable' requires -enable-experimental-feature NonescapableTypes}}
+struct S: ~Escapable {} // expected-error {{type 'Escapable' requires -enable-experimental-feature NonescapableTypes}}
+
+func hello(_ t: some Escapable, _ u: any Escapable) {} // expected-error 2{{type 'Escapable' requires -enable-experimental-feature NonescapableTypes}}
+
+protocol Whatever: Escapable {} // expected-error {{type 'Escapable' requires -enable-experimental-feature NonescapableTypes}}

test/Sema/invertible_no_stdlib.swift

@@ -14,7 +14,7 @@ func reqCopy2<T: Builtin.Copyable>(_ t: T) {} // expected-note {{generic paramet
 
 protocol P {}
 
-struct DataType: P, Builtin.Escapable {}
+struct DataType: P, Builtin.Escapable {} // expected-error {{type 'Escapable' requires -enable-experimental-feature NonescapableTypes}}
 struct DataTypeNC: ~Builtin.Copyable {}
 
 func main() {

test/decl/ext/extensions.swift

@@ -398,6 +398,7 @@ extension B4 {
 extension Sendable {} // expected-error {{cannot extend protocol 'Sendable'}}
 extension Copyable {} // expected-error {{cannot extend protocol 'Copyable'}}
 extension Escapable {} // expected-error {{cannot extend protocol 'Escapable'}}
+// expected-error@-1 {{type 'Escapable' requires -enable-experimental-feature NonescapableTypes}}
 extension _BitwiseCopyable {} // expected-error {{cannot extend protocol '_BitwiseCopyable'}}
 
 @_marker protocol MyMarkerProto {}