remove #[derive(TryFromU32)]

[fee1-dead]

seems like it could just be replaced with a declarative macro

cc @Zalathar

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cc @Zalathar

[jieyouxu]

r? @Zalathar

[Zalathar]

Is there some reason to do this? I don’t understand the motivation for wanting to make these enums considerably harder to maintain.

[fee1-dead]

procedural macros hurt build times because it feeds tokens to a parser for each procedural macro called for each type. There's no point in using a procedural macro for something this trivial.

There are alternatives to this, if you don't like maintaining two lists (is that really hard? just two lists, and you get compiler errors if one doesn't match the other).

One is to wrap the whole thing in the declarative macro, doable but I don't like how it looks.

The other is to use the upcoming macro-attr to write attributes as declarative macros. That will have to wait until beta bumps and it's an item in my todo list.

On the other hand, one additional procedural macro in rustc_macro, with ui-fulldeps tests seem like a lot of weight.