Stop hiding '@Frozen' from code completion (#26942)

And print it explicitly on imported NS_CLOSED_ENUMs.

Author: jrose-apple

include/swift/AST/Attr.def

@@ -362,8 +362,7 @@ SIMPLE_DECL_ATTR(_weakLinked, WeakLinked,
   OnSubscript | OnConstructor | OnEnumElement | OnExtension | UserInaccessible,
   75)
 SIMPLE_DECL_ATTR(frozen, Frozen,
-  OnEnum | OnStruct |
-  UserInaccessible,
+  OnEnum | OnStruct,
   76)
 DECL_ATTR_ALIAS(_frozen, Frozen)
 SIMPLE_DECL_ATTR(_forbidSerializingReference, ForbidSerializingReference,

lib/ClangImporter/ImportDecl.cpp

@@ -2873,12 +2873,8 @@ namespace {
         enumDecl->computeType();
 
         // Annotate as 'frozen' if appropriate.
-        assert((DeclAttribute::getOptions(DAK_Frozen) &
-                DeclAttribute::UserInaccessible) &&
-               "Once 'frozen' is supported, the attribute should not be "
-               "implicit (below)");
         if (enumKind == EnumKind::FrozenEnum)
-          enumDecl->getAttrs().add(new (C) FrozenAttr(/*implicit*/true));
+          enumDecl->getAttrs().add(new (C) FrozenAttr(/*implicit*/false));
 
         // Set up the C underlying type as its Swift raw type.
         enumDecl->setRawType(underlyingType);

test/ClangImporter/enum-exhaustivity.swift

@@ -7,8 +7,7 @@
 // CHECK-NEXT: case B
 // CHECK-NEXT: {{^}$}}
 
-// Note that we don't print '@frozen' here yet.
-// CHECK-LABEL: {{^}}enum ExhaustiveEnum : {{.+}} {
+// CHECK-LABEL: {{^}}@frozen enum ExhaustiveEnum : {{.+}} {
 // CHECK:      case A
 // CHECK-NEXT: case B
 // CHECK-NEXT: {{^}$}}

test/IDE/complete_decl_attribute.swift

@@ -94,6 +94,7 @@ struct MyStruct {}
 // KEYWORD4-NEXT:             Keyword/None:                       dynamicCallable[#Enum Attribute#]; name=dynamicCallable
 // KEYWORD4-NEXT:             Keyword/None:                       dynamicMemberLookup[#Enum Attribute#]; name=dynamicMemberLookup
 // KEYWORD4-NEXT:             Keyword/None:                       usableFromInline[#Enum Attribute#]; name=usableFromInline
+// KEYWORD4-NEXT:             Keyword/None:                       frozen[#Enum Attribute#]; name=frozen
 // KEYWORD4-NEXT:             Keyword/None:                       propertyWrapper[#Enum Attribute#]; name=propertyWrapper
 // KEYWORD4-NEXT:             Keyword/None:                       _functionBuilder[#Enum Attribute#]; name=_functionBuilder
 // KEYWORD4-NEXT:             End completions
@@ -105,6 +106,7 @@ struct MyStruct {}
 // KEYWORD5-NEXT:             Keyword/None:                       dynamicCallable[#Struct Attribute#]; name=dynamicCallable
 // KEYWORD5-NEXT:             Keyword/None:                       dynamicMemberLookup[#Struct Attribute#]; name=dynamicMemberLookup
 // KEYWORD5-NEXT:             Keyword/None:                       usableFromInline[#Struct Attribute#]; name=usableFromInline
+// KEYWORD5-NEXT:             Keyword/None:                       frozen[#Struct Attribute#]; name=frozen
 // KEYWORD5-NEXT:             Keyword/None:                       propertyWrapper[#Struct Attribute#]; name=propertyWrapper
 // KEYWORD5-NEXT:             Keyword/None:                       _functionBuilder[#Struct Attribute#]; name=_functionBuilder
 // KEYWORD5-NEXT:             End completions
@@ -263,6 +265,7 @@ func dummy2() {}
 // KEYWORD_LAST-NEXT:             Keyword/None:                       usableFromInline[#Declaration Attribute#]; name=usableFromInline{{$}}
 // KEYWORD_LAST-NEXT:             Keyword/None:                       discardableResult[#Declaration Attribute#]; name=discardableResult
 // KEYWORD_LAST-NEXT:             Keyword/None:                       GKInspectable[#Declaration Attribute#]; name=GKInspectable{{$}}
+// KEYWORD_LAST-NEXT:             Keyword/None:                       frozen[#Declaration Attribute#]; name=frozen
 // KEYWORD_LAST-NEXT:             Keyword/None:                       propertyWrapper[#Declaration Attribute#]; name=propertyWrapper
 // KEYWORD_LAST-NEXT:             Keyword/None:                       _functionBuilder[#Declaration Attribute#]; name=_functionBuilder{{$}}
 // KEYWORD_LAST-NEXT:             Keyword/None:                       IBSegueAction[#Declaration Attribute#]; name=IBSegueAction{{$}}