Implement feature(precise_capturing_of_types) by compiler-errors · Pull Request #138473 · rust-lang/rust (original) (raw)
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- Set uncaptured ty/ct substs as bivariant. I'm almost certain is still quite broken, and I'll come up with a follow-up PR hopefully soon exercising some of the ways that it doesn't work today (related to the fact that "invariant xform bivariant = invariant").
- Validate that uncaptured ty/ct substs don't show up in the hidden type. I also reworked uncaptured ty/ct errors for TAITs. That diagnostic could also be improved tbh.
- Add a couple simple tests.
r? lcnr or reassign if you're not interested in reviewing feature work
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Status: Awaiting review from the assignee but also interested parties.
Relevant to the compiler team, which will review and decide on the PR/issue.
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how does this avoid unconstrained type variables when doing something like
fn foo() -> impl Sized + use<> {}
fn main() { let x = foo(); // opaque; let y = x; // opaque<?unconstrained> }
it doesn't afaict :> this feature is still pretty broken, that's why it's incomplete
Comment on lines +228 to +245
| let guar = if self.uncaptured_args.contains(&ct.into()) { |
|---|
| // FIXME(precise_capturing_of_types): Mention `use<>` list |
| // and add an structured suggestion. |
| self.tcx.dcx().struct_span_err( |
| self.span, |
| format!("hidden type mentions uncaptured const parameter `{ct}`"), |
| ) |
| } else { |
| self.tcx.dcx().struct_span_err( |
| self.span, |
| format!( |
| "const parameter `{ct}` is mentioned in hidden type of \ |
| type alias impl trait, but is not declared in its generic \ |
| args" |
| ), |
| ) |
| } |
| .emit_unless(self.ignore_errors); |
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also extract this into a subfn?
it doesn't afaict :> this feature is still pretty broken, that's why it's incomplete
do you have a plan for how to fix this? I feel like the feature as is doesn't have much value and worry that we likely can't stabilize it without large changes
however, I don't think the cost of supporting this is meaningfully large, so r=me after nits
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Status: Awaiting review from the assignee but also interested parties.
Relevant to the compiler team, which will review and decide on the PR/issue.