self: &Box<Self> produces confusing error due to failure to spot elided lifetime #117715
Closed
Description
Code
struct Concrete(u32);
impl Concrete {
fn m(self: &std::boxed::Box<Self>) -> &u32 {
&self.0
}
}Current output
error[E0106]: missing lifetime specifier
--> src/lib.rs:4:43
|
4 | fn m(self: &std::boxed::Box<Self>) -> &u32 {
| ---------------------- ^ expected named lifetime parameter
|
= help: this function's return type contains a borrowed value, but the signature does not say which `self` it is borrowed from
help: consider introducing a named lifetime parameter
|
4 | fn m<'a>(self: &'a std::boxed::Box<Self>) -> &'a u32 {
| ++++ ++ ++
For more information about this error, try `rustc --explain E0106`.
error: could not compile `playground` (lib) due to previous errorDesired output
Ideally, rustc recognizes the elided lifetime in the `self` parameter and uses that.
Alternatively, "the signature does not say which `self` it is borrowed from" is reworded to more accurately describe the error.Rationale and extra context
No response
Other cases
No response
Anything else?
fn n(self: &std::boxed::Box<Self>, _other: &u32) -> &u32 {
&self.0
}results in an error where rustc assumes we're returning the _other parameter, which presumably results from the same failure to spot a lifetime attached to self.
This issue was identified during discussion about a new Rust RFC, here.
I suspect this is caused by something within find_lifetime_for_self which isn't aware of the need to support things like Box as a self type: I haven't spotted the bug yet, I thought it was more important to get it reported properly first.