tree 6643a49147add264fb50ba1da2b1975d9876e134
parent 68c7b62bc34d7b827dceb4e248f7527f93e4d6d4
author Devin Jeanpierre <jeanpierreda@google.com> 1678487187 -0800
committer Copybara-Service <copybara-worker@google.com> 1678487224 -0800

Use `#[serde(deny_unknown_fields)]` for IR.

https://serde.rs/container-attrs.html#deny_unknown_fields

Unknown fields are always a bug, since we control both serialization and deserialization and they both come from the same version of the codebase. (Unlike traditional deserialization code, we don't need to deal with data that was generated a long time ago.)

This is a common, and potentially confusing, source of bugs. As an example, during recent feature work I accidentally forgot to rename a field in `ir.rs` when renaming it in `ir.h`, and the result was that everything compiled and ran but did a subtly incorrect thing, which took time to debug. `deny_unknown_fields` would have prevented this.

(We don't need to stop using `default`, because a mismatch in name will show up as both an unknown field and a defaulted field -- it's never a major or confusing bug to just have a defaulted field with no corresponding unknown field.)

Note that the attribute isn't necessary for enums. [Fieldless enums](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=aeedbefac83cb6e73eb459927dcc3682) fail as one might expect even without the attribute, but so do [fieldful enums](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=b752164835f2b9d853f2ed1e669d1a36).

PiperOrigin-RevId: 515738803