33 lines
1.1 KiB
Rust
33 lines
1.1 KiB
Rust
use darling::FromMeta;
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/// This usage of `from_expr` is VALID because there are no unit variants that should conflict with the
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/// implementation.
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#[derive(FromMeta)]
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#[darling(from_expr = |expr| Ok(HasNoUnits::Variant2 { other: format!("{:?}", expr) }))]
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enum HasNoUnits {
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Variant1 { field: String },
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Variant2 { other: String },
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}
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/// This usage of `from_expr` is invalid because unit variants already generate a from_expr
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/// method, and we don't allow using the from_expr override when it conflicts with the macro's
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/// "normal" operation.
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#[derive(FromMeta)]
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#[darling(from_expr = |expr| Ok(HasUnits::Variant2))]
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enum HasUnits {
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Variant1 { field: String },
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Variant2,
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}
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fn newtype_from_expr(_expr: &syn::Expr) -> darling::Result<Newtype> {
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Ok(Newtype(true))
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}
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// This usage of `from_expr` is invalid because newtype structs call the inner type's `from_meta`
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// directly from their `from_meta`, so the custom `from_expr` will never be called in normal usage.
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#[derive(FromMeta)]
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#[darling(from_expr = newtype_from_expr)]
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struct Newtype(bool);
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fn main() {}
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