Add -experimental-feature NonEscapableTypes

Author: atrick

include/swift/AST/DiagnosticsSema.def

@@ -7536,6 +7536,9 @@ ERROR(noncopyable_cannot_have_read_set_accessor,none,
       "noncopyable %select{variable|subscript}0 cannot provide a read and set accessor",
       (unsigned))
 
+ERROR(nonescapable_types_attr_disabled,none,
+      "attribute requires '-enable-experimental-feature NonEscapableTypes'", ())
+
 //------------------------------------------------------------------------------
 // MARK: Init accessors
 //------------------------------------------------------------------------------

include/swift/Basic/Features.def

@@ -252,6 +252,10 @@ EXPERIMENTAL_FEATURE(TypedThrows, true)
 /// Allow destructuring stored `let` bindings in structs.
 EXPERIMENTAL_FEATURE(StructLetDestructuring, true)
 
+/// Enable non-escapable type attributes and function attributes that support
+/// lifetime-dependent results.
+EXPERIMENTAL_FEATURE(NonEscapableTypes, false)
+
 #undef EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE

lib/AST/ASTPrinter.cpp

@@ -3512,6 +3512,11 @@ static bool usesFeatureStructLetDestructuring(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureNonEscapableTypes(Decl *decl) {
+  return decl->getAttrs().hasAttribute<NonEscapableAttr>()
+    || decl->getAttrs().hasAttribute<UnsafeNonEscapableResultAttr>();
+}
+
 static bool hasParameterPacks(Decl *decl) {
   if (auto genericContext = decl->getAsGenericContext()) {
     auto sig = genericContext->getGenericSignature();

lib/Sema/TypeCheckAttr.cpp

@@ -161,8 +161,6 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   IGNORED_ATTR(BackDeployed)
   IGNORED_ATTR(Documentation)
   IGNORED_ATTR(LexicalLifetimes)
-  IGNORED_ATTR(NonEscapable)
-  IGNORED_ATTR(UnsafeNonEscapableResult)
 #undef IGNORED_ATTR
 
   void visitAlignmentAttr(AlignmentAttr *attr) {
@@ -349,6 +347,9 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   void visitMacroRoleAttr(MacroRoleAttr *attr);
 
   void visitRawLayoutAttr(RawLayoutAttr *attr);
+
+  void visitNonEscapableAttr(NonEscapableAttr *attr);
+  void visitUnsafeNonEscapableResultAttr(UnsafeNonEscapableResultAttr *attr);
 };
 
 } // end anonymous namespace
@@ -7060,6 +7061,19 @@ void AttributeChecker::visitRawLayoutAttr(RawLayoutAttr *attr) {
   sd->setHasUnreferenceableStorage(true);
 }
 
+void AttributeChecker::visitNonEscapableAttr(NonEscapableAttr *attr) {
+  if (!Ctx.LangOpts.hasFeature(Feature::NonEscapableTypes)) {
+    diagnoseAndRemoveAttr(attr, diag::nonescapable_types_attr_disabled);
+  }
+}
+
+void AttributeChecker::visitUnsafeNonEscapableResultAttr(
+  UnsafeNonEscapableResultAttr *attr) {
+  if (!Ctx.LangOpts.hasFeature(Feature::NonEscapableTypes)) {
+    diagnoseAndRemoveAttr(attr, diag::nonescapable_types_attr_disabled);
+  }
+}
+
 namespace {
 
 class ClosureAttributeChecker

test/attr/attr_nonEscapable.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift
+// RUN: %target-typecheck-verify-swift -enable-experimental-feature NonEscapableTypes
 
 @_nonEscapable public struct NES {
   let x: Int