New lint: pub enum tuple variant adds or removes field (i.e. tuple arity changed)

[obi1kenobi]

pub enum Example {
    Variant(a: i64, /* b: i64 */),
}

Both adding and removing the commented-out portion is a breaking change, and I don't believe we currently would catch that.

[me-diru]

Hey!

I was checking out this issue. The adds and removes field cases in a pub enum are already checked with separate lints

• pub enum struct variant adds field: Add lint for exhaustive struct variants gaining new fields. #238
• pub enum struct variant removes field: New lint - detecting field removals from a struct variant in enum #156

Do they both cover the case of tuple arity being changed, or are we looking for something different here? thanks

[obi1kenobi]

I think those lints only cover changes enums' struct variants, not changes in tuple variants. More info on different enum variant kinds: https://doc.rust-lang.org/std/keyword.enum.html

For tuple variants, we can probably have just a single lint that checks that "the tuple contains a different number of elements."

As a query, this can make use of the @fold @transform(op: "count") combination of directives to count how many fields each tuple has, and then use @tag, @filter, and @output accordingly to output the old and new counts and establish they are different. I believe one can find examples of that combination of directives in other lints' queries already.

[me-diru]

Thanks for the quick response!

I have written a lint query for the same. However, the enum tuple variant field changes are already covered in the following lints.

• https://github.com/obi1kenobi/cargo-semver-checks/blob/main/test_crates/enum_tuple_variant_field_added/old/src/lib.rs#L3
• https://github.com/obi1kenobi/cargo-semver-checks/blob/main/test_crates/enum_tuple_variant_field_missing/old/src/lib.rs#L3

Please let me know if I am misinterpreting it; it was interesting to understand how the querying works, though; writing a lint itself is pretty intuitive

[obi1kenobi]

Ah darn, I did a pass through the lints to see if those were implemented, and yet somehow I missed them anyway. Sorry about my sloppiness that ended up wasting your time here.

You're right, this issue is completed with no further action needed. If you'd like, I can find and suggest other opportunities to write lints or otherwise contribute to the project — it would be much appreciated!

[obi1kenobi]

Some relatively easy high-impact lints here, for example: #633