[embedded] Diagnose usage of weak and unowned variables in embedded Swift

Author: kubamracek

include/swift/AST/DiagnosticsSema.def

@@ -2032,6 +2032,9 @@ ERROR(attr_only_at_non_generic_scope, none,
 ERROR(attr_only_on_static_properties, none,
       "properties with attribute '_section' must be static", (StringRef))
 
+ERROR(weak_unowned_in_embedded_swift, none,
+      "attribute %0 cannot be used in embedded Swift", (ReferenceOwnership))
+
 ERROR(access_control_in_protocol,none,
       "%0 modifier cannot be used in protocols", (DeclAttribute))
 NOTE(access_control_in_protocol_detail,none,

lib/Parse/ParseDecl.cpp

@@ -3055,6 +3055,14 @@ ParserStatus Parser::parseNewDeclAttribute(DeclAttributes &Attributes,
       AttrRange = SourceRange(Loc);
     }
 
+    // Embedded Swift prohibits weak/unowned but allows unowned(unsafe).
+    if (Context.LangOpts.hasFeature(Feature::Embedded)) {
+      if (Kind == ReferenceOwnership::Weak ||
+          Kind == ReferenceOwnership::Unowned) {
+        diagnose(Loc, diag::weak_unowned_in_embedded_swift, Kind);
+      }
+    }
+
     if (!DiscardAttribute)
       Attributes.add(
           new (Context) ReferenceOwnershipAttr(AttrRange, Kind));

test/embedded/weak-unowned.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swift-emit-ir %s -wmo
+// RUN: %target-swift-emit-ir %s -enable-experimental-feature Embedded -verify
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: optimized_stdlib
+// REQUIRES: OS=macosx || OS=linux-gnu
+
+public class MyClass { }
+
+public struct MyStruct {
+  var normalVar: MyClass
+  weak var weakVar: MyClass? // expected-error {{attribute 'weak' cannot be used in embedded Swift}}
+  unowned var unownedVar: MyClass // expected-error {{attribute 'unowned' cannot be used in embedded Swift}}
+  unowned(unsafe) var unownedUnsafe: MyClass
+}