Standardize "use parentheses to call" suggestions between typeck and trait selection #102863
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| @@ -11,6 +11,10 @@ note: required by a bound in `take_const_owned` | |||
| | | |||
| LL | fn take_const_owned<F>(_: F) where F: FnOnce() + Sync + Send { | |||
| | ^^^^ required by this bound in `take_const_owned` | |||
| help: use parentheses to call this type parameter | |||
| | | |||
| LL | take_const_owned(f()); | |||
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This is, unfortunately, an erroneous suggestion that is uncovered by the generalizations I made in the last commit in the stack. However, this is not really the fault of the changes I made. For example, a similarly erroneous suggestion already triggers on nightly with this code:
struct Foo;
fn foo() -> Foo {
todo!()
}
trait Bar {}
impl Bar for Foo {}
fn needs_foo_and_callable<T>(_: impl Bar + Fn() -> T) { }
fn main() {
needs_foo_and_callable(foo);
}Results in:
error[E0277]: the trait bound `fn() -> Foo {foo}: Bar` is not satisfied
--> src/main.rs:14:15
|
3 | fn foo() -> Foo {
| --- consider calling this function
...
14 | needs_foo_and_callable(foo);
| ---------------------- ^^^ the trait `Bar` is not implemented for fn item `fn() -> Foo {foo}`
| |
| required by a bound introduced by this call
|
note: required by a bound in `needs_foo_and_callable`
--> src/main.rs:11:25
|
11 | fn needs_foo_and_callable<T>(_: impl Bar + Fn() -> T) { }
| ^^^ required by this bound in `needs_foo`
help: use parentheses to call the function
|
14 | needs_foo_and_callable(foo());
| ++
But adding those parentheses causes:
error[E0277]: expected a `Fn<()>` closure, found `Foo`
--> src/main.rs:14:15
|
14 | needs_foo_and_callable(foo());
| ---------------------- ^^^^^ expected an `Fn<()>` closure, found `Foo`
| |
| required by a bound introduced by this call
|
= help: the trait `Fn<()>` is not implemented for `Foo`
= note: wrap the `Foo` in a closure with no arguments: `|| { /* code */ }`
note: required by a bound in `needs_foo_and_callable`
--> src/main.rs:11:31
|
11 | fn needs_foo_and_callable<T>(_: impl Bar + Fn() -> T) { }
| ^^^^^^^^^ required by this bound in `needs_foo`
For more information about this error, try `rustc --explain E0277`.
This is a fundamental limitation to the suggestion being implemented here in trait selection -- I'm happy to brainstorm ways of suppressing this, but I'm happy with keeping it as is and filing a follow-up bug.
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| | | ||
| LL | fn insert_resource<R: Resource>(resource: R) {} | ||
| | ^^^^^^^^ required by this bound in `insert_resource` | ||
| help: use parentheses to instantiate this tuple struct |
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I’m not entirely sure about using “instantiate” here, due to the parallels with OOP. I think we typically tend towards using “construct”.
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Rollup of 6 pull requests Successful merges: - rust-lang#102863 (Standardize "use parentheses to call" suggestions between typeck and trait selection) - rust-lang#103034 (Let expressions on RHS shouldn't be terminating scopes) - rust-lang#103127 (Make transpose const and inline) - rust-lang#103153 (Allow `Vec::leak` when using `no_global_oom_handling`) - rust-lang#103182 (Clean up query descriptions) - rust-lang#103216 (Consider patterns in fn params in an `Elided(Infer)` lifetime rib.) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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FnDefs but they have a different def kind and hir representation, so we were leaving them out./* Ty */as the placeholder for an arg, and not the parameter's name, which is less helpful.predicate_must_hold_modulo_regionsinstead of matching onEvaluationResult-- this might cause some suggestions to be filtered out, but we really shouldn't be suggesting a call if it "may" hold, only when it "must" hold.extract_callable_infoto generalize this suggestion to fn pointers, type parameters, and opaque types.Fixes #102852