[CodeCompletion] Suggest freestanding after @

rdar://108163121

Author: ahoppen

include/swift/IDE/CompletionLookup.h

@@ -581,7 +581,7 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
 
   static bool canUseAttributeOnDecl(DeclAttrKind DAK, bool IsInSil,
                                     bool IsConcurrencyEnabled,
-                                    Optional<DeclKind> DK);
+                                    Optional<DeclKind> DK, StringRef Name);
 
   void getAttributeDeclCompletions(bool IsInSil, Optional<DeclKind> DK);
 

lib/IDE/CompletionLookup.cpp

@@ -2966,7 +2966,8 @@ void CompletionLookup::getGenericRequirementCompletions(
 
 bool CompletionLookup::canUseAttributeOnDecl(DeclAttrKind DAK, bool IsInSil,
                                              bool IsConcurrencyEnabled,
-                                             Optional<DeclKind> DK) {
+                                             Optional<DeclKind> DK,
+                                             StringRef Name) {
   if (DeclAttribute::isUserInaccessible(DAK))
     return false;
   if (DeclAttribute::isDeclModifier(DAK))
@@ -2979,6 +2980,11 @@ bool CompletionLookup::canUseAttributeOnDecl(DeclAttrKind DAK, bool IsInSil,
     return false;
   if (!DK.has_value())
     return true;
+  // Hide underscored attributes even if they are not marked as user
+  // inaccessible. This can happen for attributes that are an underscored
+  // variant of a user-accessible attribute (like @_backDeployed)
+  if (Name.empty() || Name[0] == '_')
+    return false;
   return DeclAttribute::canAttributeAppearOnDeclKind(DAK, DK.value());
 }
 
@@ -2997,9 +3003,10 @@ void CompletionLookup::getAttributeDeclCompletions(bool IsInSil,
   }
   bool IsConcurrencyEnabled = Ctx.LangOpts.EnableExperimentalConcurrency;
   std::string Description = TargetName.str() + " Attribute";
+#define DECL_ATTR_ALIAS(KEYWORD, NAME) DECL_ATTR(KEYWORD, NAME, 0, 0)
 #define DECL_ATTR(KEYWORD, NAME, ...)                                          \
-  if (canUseAttributeOnDecl(DAK_##NAME, IsInSil, IsConcurrencyEnabled,         \
-                            DK))                         \
+  if (canUseAttributeOnDecl(DAK_##NAME, IsInSil, IsConcurrencyEnabled, DK,     \
+                            #KEYWORD))                                         \
     addDeclAttrKeyword(#KEYWORD, Description);
 #include "swift/AST/Attr.def"
 }

test/IDE/complete_decl_attribute.swift

@@ -323,6 +323,7 @@ struct _S {
 // ON_MEMBER_LAST-DAG: Keyword/None:                       preconcurrency[#Declaration Attribute#]; name=preconcurrency
 // ON_MEMBER_LAST-DAG: Keyword/None:                       runtimeMetadata[#Declaration Attribute#]; name=runtimeMetadata
 // ON_MEMBER_LAST-DAG: Keyword/None:                       attached[#Declaration Attribute#]; name=attached
+// ON_MEMBER_LAST-DAG: Keyword/None:                       freestanding[#Declaration Attribute#]; name=freestanding
 // ON_MEMBER_LAST-NOT: Keyword
 // ON_MEMBER_LAST-DAG: Decl[Struct]/CurrModule:            MyStruct[#MyStruct#]; name=MyStruct
 // ON_MEMBER_LAST-DAG: Decl[Struct]/CurrModule/TypeRelation[Convertible]: MyPropertyWrapper[#MyPropertyWrapper#]; name=MyPropertyWrapper
@@ -358,6 +359,7 @@ func dummy2() {}
 @#^KEYWORD_LAST^#
 
 // KEYWORD_LAST-DAG: Keyword/None:                       available[#Declaration Attribute#]; name=available{{$}}
+// KEYWORD_LAST-DAG: Keyword/None:                       freestanding[#Declaration Attribute#]; name=freestanding{{$}}
 // KEYWORD_LAST-DAG: Keyword/None:                       objc[#Declaration Attribute#]; name=objc{{$}}
 // KEYWORD_LAST-DAG: Keyword/None:                       dynamicCallable[#Declaration Attribute#]; name=dynamicCallable
 // KEYWORD_LAST-DAG: Keyword/None:                       main[#Declaration Attribute#]; name=main