Give a friendly error for enums with fields #45
Conversation
Right now we generate invalid code, and the error message is pretty inscrutable. Instead, generate a nice descriptive user-facing error.
illicitonion
force-pushed
the
error-on-fields
branch
from
fb4f0a6
to
581303d
Compare
| let fields = variant.fields; | ||
|
|
||
| match fields { | ||
| Fields::Named(_) | Fields::Unnamed(_) => { |
There was a problem hiding this comment.
Tiny nit: since tuple variants don't really have fields / or rather, it may not be seen as such by some users, I'd replace the fields mention for Fields::Unnamed with something else. Maybe something like associated data / payloads, or even simpler: "only unit variants are supported". Since this is subjective, feel free to disregard this 🙂
There was a problem hiding this comment.
Great feedback - thanks!
num_enum_derive/src/lib.rs
Outdated
| let mut span = variant.span(); | ||
| // Sadly `Span::join` is a nightly-only API at the moment - see https://github.com/rust-lang/rust/issues/54725 | ||
| if let Some(span_with_fields) = span.join(variant.fields.span()) { | ||
| span = span_with_fields; | ||
| } |
There was a problem hiding this comment.
FWIW, if we were to use Error::new_spanned(variant over Error::new(variant.span() (the die! macro currently leads us to the latter; maybe we could try to feature a die_spanned_at variant for the former), then we'd have a correctly spanned error message, even on stable Rust. Indeed, new_spanned uses a hack to achieve this:
// imbued with the _start_ of the span
// vvvvvvvvvvvvvv
compile_error! { "…" }
// ^^^^^^^
// imbued with the _end_ of the spaneffectively yielding an error which does span over the whole range. Demo using new_spanned(variant vs. new(variant.span():
There was a problem hiding this comment.
Ooh, TIL! This is amazing - done - thanks for the suggestion!
Right now we generate invalid code, and the error message is pretty
inscrutable. Instead, generate a nice descriptive user-facing error.