Diagnose if lifetime dependence specifier is present on Escapable type

Author: meg-gupta

include/swift/AST/DiagnosticsSema.def

@@ -7807,8 +7807,7 @@ ERROR(pack_iteration_where_clause_not_supported, none,
        "functions, methods, initializers",
        ())
  ERROR(lifetime_dependence_invalid_return_type, none,
-       "lifetime dependence specifiers can only be specifier on ~Escapable "
-       "results", ())
+       "lifetime dependence can only be specified on ~Escapable results", ())
  ERROR(lifetime_dependence_missing_ownership_modifier, none,
        "lifetime dependence can only be specified on parameters with ownership "
        "modifiers (borrowing, consuming, inout)", ())

lib/Sema/TypeCheckDecl.cpp

@@ -2592,14 +2592,11 @@ llvm::Optional<LifetimeDependenceInfo> validateLifetimeDependenceInfo(
     auto loc = specifier.getLoc();
     auto kind = specifier.getLifetimeDependenceKind();
 
-    /* TODO: Enable this
-    if (TypeChecker::conformsToKnownProtocol(resultTy,
-                                             InvertibleProtocolKind::Escapable,
-                                             dc->getParentModule())) {
+    if (resultTy->isEscapable()) {
       diags.diagnose(loc, diag::lifetime_dependence_invalid_return_type);
       return true;
     }
-    */
+
     if (ownership == ValueOwnership::Default) {
       diags.diagnose(loc, diag::lifetime_dependence_missing_ownership_modifier);
       return true;

test/Sema/explicit_lifetime_dependence_specifiers.swift

@@ -22,7 +22,7 @@ struct WrapperStruct {
   let k: Klass
 }
 
-func invalidLifetimeDependenceOnEscapable(_ w: borrowing WrapperStruct) -> Klass {
+func invalidLifetimeDependenceOnEscapableResult(_ w: borrowing WrapperStruct) -> _borrow(w) Klass { // expected-error{{lifetime dependence can only be specified on ~Escapable results}}
   return w.k
 }