Swift: describe TrapTagTraits API and implementation

Author: AlexDenisov

swift/codegen/templates/trap_traps.mustache

@@ -29,12 +29,5 @@ inline std::ostream &operator<<(std::ostream &out, const {{name}}{{trap_affix}}
       << {{#get_streamer}}e.{{field_name}}{{/get_streamer}}{{/fields}} << ")";
   return out;
 }
-{{#id}}
-
-template <>
-struct TagToBindingTrapFunctor<typename {{type}}::Tag> {
-  using type = {{name}}{{trap_affix}};
-};
-{{/id}}
 {{/traps}}
 }

swift/extractor/SwiftTagTraits.h

@@ -1,6 +1,8 @@
 #pragma once
 
+// This file implements the mapping needed by the API defined in the TrapTagTraits.h
 #include <swift/AST/ASTVisitor.h>
+#include "swift/extractor/trap/TrapTagTraits.h"
 #include "swift/extractor/trap/generated/TrapTags.h"
 
 namespace codeql {
@@ -12,22 +14,22 @@ using SILBoxTypeTag = SilBoxTypeTag;
 using SILFunctionTypeTag = SilFunctionTypeTag;
 using SILTokenTypeTag = SilTokenTypeTag;
 
-#define MAP_TYPE_TO_TAG(TYPE, TAG)   \
-  template <>                        \
-  struct ToTagFunctor<swift::TYPE> { \
-    using type = TAG;                \
+#define MAP_TYPE_TO_TAG(TYPE, TAG)           \
+  template <>                                \
+  struct detail::ToTagFunctor<swift::TYPE> { \
+    using type = TAG;                        \
   }
 #define MAP_TAG(TYPE) MAP_TYPE_TO_TAG(TYPE, TYPE##Tag)
 #define MAP_SUBTAG(TYPE, PARENT)                           \
   MAP_TAG(TYPE);                                           \
   static_assert(std::is_base_of_v<PARENT##Tag, TYPE##Tag>, \
                 #PARENT "Tag must be a base of " #TYPE "Tag");
 
-#define OVERRIDE_TAG(TYPE, TAG)       \
-  template <>                         \
-  struct ToTagOverride<swift::TYPE> { \
-    using type = TAG;                 \
-  };                                  \
+#define OVERRIDE_TAG(TYPE, TAG)               \
+  template <>                                 \
+  struct detail::ToTagOverride<swift::TYPE> { \
+    using type = TAG;                         \
+  };                                          \
   static_assert(std::is_base_of_v<TYPE##Tag, TAG>, "override is not a subtag");
 
 MAP_TAG(Stmt);

swift/extractor/trap/TrapTagTraits.h

@@ -1,21 +1,21 @@
 #pragma once
 
+// This file defines functors that can be specialized to define a mapping from arbitrary types to
+// label tags
+
 #include <type_traits>
 
 namespace codeql {
 
+namespace detail {
 template <typename T>
 struct ToTagFunctor;
 template <typename T>
 struct ToTagOverride : ToTagFunctor<T> {};
 
-template <typename T>
-using ToTag = typename ToTagOverride<std::remove_const_t<T>>::type;
+}  // namespace detail
 
 template <typename T>
-struct TagToBindingTrapFunctor;
-
-template <typename Tag>
-using TagToBindingTrap = typename TagToBindingTrapFunctor<Tag>::type;
+using ToTag = typename detail::ToTagOverride<std::remove_const_t<T>>::type;
 
 }  // namespace codeql