Avoiding Name Clashes with WIT Keywords

[adrian-javid]

According to the WIT documentation, an identifier must be proceeded by a single % sign if the identifier would otherwise be a WIT keyword.

Suppose someone makes a user-defined type called struct, and they do not prefix it with % because struct is not a keyword.

Suppose later, in a newer version of WIT, struct becomes a keyword. Then, their WIT code breaks because their user-defined type struct is not prefixed with %.

Perhaps, keywords and primitive types in WIT should be prefixed with some character that is not allowed in user-defined identifiers. That would allow addition of keywords and primitive types in the future without breaking old WIT code that uses those keywords as identifiers. Otherwise, I feel technically incentivized to add % to every user-defined identifier, but that does not feel good.

[lukewagner]

That's a good question; thanks for filing!

One nice thing about WIT is that its persistent package representation is a component binary (.wasm) which, along with the WAT text format, allows identifiers to be WIT keywords (WIT keywords end up turning into opcodes in the binary format). Thus, if you generate a WIT package with a struct identifier at point in time when there is no struct WIT keyword and then at a later time struct becomes a WIT keyword, the WIT package is still valid and when you view it as WIT text, an updated WIT tool will render %struct as necessary. Thus, long-lived, versioned WIT packages (e.g., the recent wasi:http@0.3.0) should be safe against the addition of WIT keywords. Additionally, components and wasm runtime embeddings built against the original WIT package won't have to be updated since they only operate on the component binary/text format.

That still means WIT text files may have to be updated when WIT tooling is updated, but given the above, this seems about par for the course for source code and not too onerous. In particular, I think this means you can safely omit % from your WIT files without painting yourself into a corner.