serde_derive: fix ser/de inconsistency with skipped enum variants #2952
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When serde_derive generates Serialize/Deserialize implementations for an enum with #[serde(skipped)] variants, it leaves a gap in the assigned `variant_index`es for the variants (i.e., includes skipped variants in the count) in the Serialize impl, but excludes skipped variants in the count in the Deserialize impl. This means that non-self-describing data formats that rely on variant indices instead of variant names cannot correctly serialize+deserialize enums with skipped variants. This changes the generated Serialize impl to match the deserialize impl by excluding skipped variants from the count. This is also consistent with how #[serde(skip)] affects field indices in structs. Fixes serde-rs#2614
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When serde_derive generates Serialize/Deserialize implementations for an enum with #[serde(skipped)] variants, it leaves a gap in the assigned
variant_indexes for the variants (i.e., includes skipped variants in the count) in the Serialize impl, but excludes skipped variants in the count in the Deserialize impl. This means that non-self-describing data formats that rely on variant indices instead of variant names cannot correctly serialize+deserialize enums with skipped variants.This changes the generated Serialize impl to match the deserialize impl by excluding skipped variants from the count. This is also consistent with how #[serde(skip)] affects field indices in structs.
Fixes #2614
This is not covered by existing tests because the test suite only covers variant names, not variant indices (serde-deprecated/test#21). As such, I'm not sure the best way to add test coverage for this particular case.