Lint non-Rusty trait names

[kpreid]

What it does

Detects prefixes and suffixes on the names of trait-like entities that are idiomatic in other languages but not in Rust, such as:

• Prefix “I”, followed by another uppercase letter.

  In this case, the help should give a hint that trait names can often avoid conflict with type names by naming the operation, likely a verb, rather than the kind of thing that implements it, likely a noun.

• Suffix “able”.

  In this case, removing the suffix to produce a verb should be suggested. (The trait’s methods could sometimes be used to improve the spelling of the verb without needing a complete English dictionary.) If removing the suffix would collide with an existing type name, the suggestion should not be emitted.

Advantage

• Introduces new users to Rust-specific naming conventions.
• Will typically result in more concise code without any loss in clarity.

Drawbacks

• As with any naming lint, will have false positives on bindings crates that are intentionally using existing foreign names. Traits are an uncommon sort of item to map directly, though.
• Could have false positives in cases like trait Table.
• A perfect implementation of the suggestion would need an English stemmer and dictionary of irregular cases.
• While I’m a big fan of naming traits with verbs whenever possible, that’s not actually part of the Rust style guide or API guide.

Example

trait Flippable {
    fn flip(self) -> Self;
}

Could be written as:

trait Flip {
    fn flip(self) -> Self;
}

The lint message could be:

warning: trait names should not have `-able` suffixes
 --> src/lib.rs:1:7
  |
1 | trait Flippable {
  |       ^^^^^^^^^^ help: consider naming the trait using a verb instead of an adjective: `trait Flip`

Comparison with existing lints

It’s not completely clear whether Clippy should have this much opinion about naming, but I think that it is worth considering given existing naming lints such as:

• enum_variant_names
• self_named_constructors (another other-language-conventions lint)
• upper_case_acronyms

I do not know of any lints that overlap with this one or lint nearby cases, except that upper_case_acronyms might trigger in code with “I” prefixes where it would not otherwise.

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@rustbot label +L-style