rust-lang / rust-lang/rust-clippy
`clippy::type_complexity` has become more sensitive
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Description
Summary
The following code (an excerpt from my actual code) produces a clippy::type_complexity warning on nightly, but not on stable 1.62.1. I think this should be considered a regression, because the type does not really have very much nesting to it, and would not be made clearer by introducing a type alias — it's “just” a boxed function.
Lint Name
type_complexity
Reproducer
use std::{error::Error, rc::Rc};
type PredicateRes = Result<(), Box<dyn Error>>;
struct TransactionAndPredicate<'a, Tr, Ta> {
transaction: Tr,
predicate: Rc<dyn Fn(&Ta, &Ta) -> PredicateRes + 'a>,
}
I saw this happen:
warning: very complex type used. Consider factoring parts into `type` definitions
--> src/lib.rs:6:16
|
6 | predicate: Rc<dyn Fn(&Ta, &Ta) -> PredicateRes + 'a>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `#[warn(clippy::type_complexity)]` on by default
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#type_complexity
I expected to see this happen: No warning.
Version
rustc 1.64.0-nightly (affe0d3a0 2022-08-05)
binary: rustc
commit-hash: affe0d3a00e92fa7885e3f5d2c5073fde432d154
commit-date: 2022-08-05
host: x86_64-apple-darwin
release: 1.64.0-nightly
LLVM version: 14.0.6
Additional Labels
No response
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the supplied Rust reproducer with the type_complexity lint enabled, then inspect how the lint handles the shown Rc<dyn Fn...> field. Done means the reproducer no longer emits the warning while the lint remains available for genuinely complex types.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 28/100