refactor(eventsub): use variants for sum types (#5930)

lib/twitch-eventsub-ws/ast/lib/templates/field-variant.tmpl

@@ -0,0 +1,49 @@
+{% if not field.tag -%}
+static_assert(false, "{{field.name}} doesn't have a json_tag");
+{%- endif %}
+const auto *jv{{field.name}}Tag = root.if_contains("{{field.tag}}");
+if (jv{{field.name}}Tag == nullptr)
+{
+    EVENTSUB_BAIL_HERE(error::Kind::FieldMissing);
+}
+
+auto {{field.name}}TagRes = boost::json::try_value_to<boost::json::string>(*jv{{field.name}}Tag);
+if ({{field.name}}TagRes.has_error())
+{
+    return {{field.name}}TagRes.error();
+}
+std::string_view {{field.name}}Tag = *{{field.name}}TagRes;
+decltype(std::declval<{{struct.full_name}}>().{{field.name}}) {{field.name}};
+{%- for type in field.variant_types %}
+
+{%- if not loop.first %}else{% endif %} if ({{field.name}}Tag == {{type.name}}::TAG)
+{
+{%- if type.empty -%}
+    {{field.name}}.emplace<{{type.name}}>();
+{%- else -%}
+    const auto *{{field.name}}Val = root.if_contains(detail::fieldFor<{{type.name}}>());
+    if (!{{field.name}}Val)
+    {
+        EVENTSUB_BAIL_HERE(error::Kind::FieldMissing);
+    }
+    auto {{field.name}}{{type.name}} = boost::json::try_value_to<{{type.name}}>(*{{field.name}}Val);
+    if ({{field.name}}{{type.name}}.has_error())
+    {
+        return {{field.name}}{{type.name}}.error();
+    }
+    {% if type.trivial -%}
+    {{field.name}}.emplace<{{type.name}}>({{field.name}}{{type.name}}.value());
+    {%- else -%}
+    {{field.name}}.emplace<{{type.name}}>(std::move({{field.name}}{{type.name}}.value()));
+    {%- endif %}
+{%- endif -%}
+}
+{%- endfor -%}
+else
+{
+{%- if field.variant_fallback -%}
+    {{field.name}}.emplace<{{field.variant_fallback}}>({{field.name}}Tag);
+{%- else -%}
+    EVENTSUB_BAIL_HERE(error::Kind::UnknownVariant);
+{%- endif -%}
+}

lib/twitch-eventsub-ws/ast/lib/templates/initializer-variant.tmpl

@@ -0,0 +1 @@
+.{{field.name}} = std::move({{field.name}}),

lib/twitch-eventsub-ws/ast/lib/templates/struct-implementation.tmpl

@@ -1,5 +1,5 @@
 boost::json::result_for<{{struct.full_name}}, boost::json::value>::type tag_invoke(
-    boost::json::try_value_to_tag<{{struct.full_name}}> /* tag */, const boost::json::value &jvRoot)
+    boost::json::try_value_to_tag<{{struct.full_name}}> /* tag */, const boost::json::value &{%- if struct.members|length -%}jvRoot{%- else -%}/* jvRoot */{%- endif -%})
 {
     {% if struct.inner_root %}
     if (!jvRoot.is_object())
@@ -38,6 +38,8 @@ boost::json::result_for<{{struct.full_name}}, boost::json::value>::type tag_invo
     {% include 'field-optional.tmpl' indent content %}
     {%- elif field.member_type == MemberType.OPTIONAL_VECTOR -%}
     {% include 'field-optional-vector.tmpl' indent content %}
+    {%- elif field.member_type == MemberType.VARIANT -%}
+    {% include 'field-variant.tmpl' indent content %}
     {%- endif -%}
 {% endfor %}
 
@@ -51,6 +53,8 @@ boost::json::result_for<{{struct.full_name}}, boost::json::value>::type tag_invo
         {% include 'initializer-optional.tmpl' indent content %}
         {%- elif field.member_type == MemberType.OPTIONAL_VECTOR -%}
         {% include 'initializer-optional-vector.tmpl' indent content %}
+        {%- elif field.member_type == MemberType.VARIANT -%}
+        {% include 'initializer-variant.tmpl' indent content %}
         {%- endif -%}
 {% endfor %}
     };