Feedback for adding zyn to a work in progress macro crate

[antonWetzel]

Good morning ^^

I added zyn to a personal project and wanted to share my feedback.

Source: https://github.com/antonWetzel/wgsl-gpu/tree/main/wgsl-gpu-macros/src

These are mostly my notes what did not work at first, so this is a lot more negative than my experience. Overall zyn feels better as pure syn + quote macro crates.

Good

• Interpolation with {{ <rust> }} feels very nice, especially using {{ value.member }}
• Nesting @for or other @nodes reduces code for simple cases
• Documentation helped a lot

Hiccups

• @for only allows identifiers, not patterns (@for (index, value) in ...)
• zyn::derive expects <derive_name>, <arguments>
  • A derive name must be specified if arguments are used
• Missing annotations for free standing proc-macros ([Feature]: Create "freestanding" macros using zyn #23)

[element]

• The arguments are changed from value to ref ([Bug]: Parameters in element are passed by reference #22)
• I have a lot of @element(name = name, value = value, ...)
  • If possible a shorthand value initialization if names match might be useful
• The return type of the function is ignored
  • The docs use zyn::TokenStream
  • I think the correct type is zyn::Output
  • I can write whatever I want (SomeNotExistingType works)

Pipes

• Pipes may be shorter, but I prefer to use normal rust to avoid special syntax
• Pipes only accept strings as arguments
  • I wanted to use a pipe for usize -> Index, which would introduce some conversions

Error handling

• Be default I used functions which return zyn::Output
  • This can contain Diagnostic, so using Result feels wrong
  • I would like to use ?, but this would require Result at the moment
• What is the correct way to replace a panic!
  • I used syn::Error as zyn::Diagnostic as zyn::Output

Arg/Args handling

• I wanted to use zyn::Attribute to parse the attributes for every member in a struct
  • I could not find a easy way to use attributes from a Vec<syn::Attribute>

Design questions

• A lot of syn and quote is available in zyn::<name>, but also as zyn::syn::<name>
  • I don't like multiple available input paths for the same items
  • Replacing syn or quote with zyn (syn/quote just for internals) seems infeasible
• I don't like the implicit context, which is passed to nested arguments
  • I would like to change the context from maybe a StructItem to a Field in a nested element

[aacebo]

Hello @antonWetzel and thanks for the feedback, I have similar feelings on almost all fronts and am working on a v1 that will be a more complete version of this api, it will add support for more rust syntax, work with references/values interchangeably, and yes also the context issue.

One thing to note is your question on panic!, the diagnostics equivalent (return early unrecoverable failure) is bail and is documented here https://aacebo.github.io/zyn/03-elements/diagnostics.html#bail--early-return-on-errors .

Once I have something to share for the v1, which should likely be in the next month or two, ill let you know here! Please also share any more feedback you have if you continue using zyn and think of anything in the meantime, feedback is a critical part of the process as we all know!