Bug 2068188 - Use a string-literal wrapper type for simple payload marker field names. r=bas,profiler-reviewers,canova

This avoids the need to create the `defined_name_##arg` constants which will
let us add support for named arguments using string literals. It's also
simpler.

Differential Revision: https://phabricator.services.mozilla.com/D322682

tools/profiler/public/ProfilerMarkers.h

@@ -265,11 +265,24 @@ MarkerSchema::getDefaultFormatForType<nsCString>() {
 }  // namespace mozilla
 
 namespace geckoprofiler::markers {
+// Wraps a string literal so that it can be used as a non-type template
+// parameter.
+template <size_t N>
+struct MarkerFieldName {
+  char mName[N];
+
+  constexpr MOZ_IMPLICIT MarkerFieldName(const char (&aName)[N]) {
+    for (size_t i = 0; i < N; ++i) {
+      mName[i] = aName[i];
+    }
+  }
+};
+
 // This allows us to bundle the argument name and its type into a single class
 // so they may be passed to the SimplePayloadMarkerTemplate class.
-template <const char* ArgName, typename ArgType>
+template <MarkerFieldName ArgName, typename ArgType>
 struct FieldDescription {
-  static constexpr const char* name = ArgName;
+  static constexpr const char* name = ArgName.mName;
   using type = ArgType;
 };
 
@@ -299,17 +312,8 @@ struct SimplePayloadMarkerTemplate
 };
 }  // namespace geckoprofiler::markers
 
-// This defines the classes needed for the template class.
-#define DEFINE_FIELD_STRUCT(arg)                                   \
-  static constexpr char defined_name_##arg[] = #arg;               \
-  using FieldDescription##arg =                                    \
-      geckoprofiler::markers::FieldDescription<defined_name_##arg, \
-                                               decltype(arg)>;
-
-#define DEFINE_FIELD_STRUCTS(...) \
-  MOZ_FOR_EACH(DEFINE_FIELD_STRUCT, (), (__VA_ARGS__))
-
-#define MARKER_GET_ARG_TYPE(arg) FieldDescription##arg
+#define MARKER_GET_ARG_TYPE(arg) \
+  ::geckoprofiler::markers::FieldDescription<#arg, decltype(arg)>
 
 // This adds a profiler marker with a schema for payload based on the arguments
 // passed. Note that each marker must have a unique name so you can only use
@@ -330,7 +334,6 @@ struct SimplePayloadMarkerTemplate
   do {                                                                       \
     static constexpr char marker_name[] = markerName;                        \
     static constexpr char table_label[] = label;                             \
-    DEFINE_FIELD_STRUCTS(__VA_ARGS__)                                        \
     using SimplePayloadMarkerImpl =                                          \
         geckoprofiler::markers::SimplePayloadMarkerTemplate<                 \
             marker_name, table_label,                                        \