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Inference failure sometimes results in things being considered functions. #89995
Description
Given the following code (playground):
use std::collections::HashSet;
use std::rc::Rc;
fn intern(cache: &mut HashSet<Rc<str>>, data: &str) -> Rc<str> {
match cache.get(data) {
Some(s) => s.clone(),
None => {
let d = Rc::from(data);
cache.insert(d.clone());
d
}
}
}The current output is:
error[E0282]: type annotations needed
--> src/lib.rs:9:28
|
9 | cache.insert(d.clone());
| ^^^^^ cannot infer type
|
= note: type must be known at this point
error[E0599]: no method named `clone` found for struct `Rc<_>` in the current scope
--> src/lib.rs:9:28
|
9 | cache.insert(d.clone());
| ^^^^^ method not found in `Rc<_>`
|
= note: `d` is a function, perhaps you wish to call it
I'm surprised it can't infer the type of d correctly, considering there are multiple indications it must be Rc<str> (and R-A does so). Maybe it's confused by Rc<&str> being a thing?
The final note is straight up perplexing, however: where on earth is it getting the idea that that's a function from? That should probably be squashed.
Edit: even shorter reproduction (playground):
use std::rc::Rc;
fn intern(data: &str) -> Rc<str> {
Rc::from(data).clone()
}
Activity
cuviper commentedon Oct 18, 2021
In the smaller reproducer, the return type does solve the inference when you take out the
.clone(), but that method call interrupts the link. It works if you writeRc::clone(&...)though.For a coarse bisect, that note first appeared on stable in Rust 1.33.0. Just looking at the release notes, I'll make a wild guess that it's related to #56805, and I can indeed reproduce the note with
ArcandPinas well.estebank commentedon Aug 14, 2023
Current output: