Check Sizedness of return type in WF #136274
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rustbot
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compiler-errors
commented
Jan 30, 2025
| ObligationCauseCode::SizedReturnType, | ||
| ); | ||
| // We checked the root's signature during wfcheck, but not the child. | ||
| // We checked the root's ret ty during wfcheck, but not the child. | ||
| if fcx.tcx.is_typeck_child(fn_def_id.to_def_id()) { |
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I have no idea why I duplicated this sized check... we were checking Sized twice here for typeck children.
| @@ -186,8 +186,6 @@ fn typeck_with_inspect<'tcx>( | |||
| let wf_code = ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(def_id))); | |||
| fcx.register_wf_obligation(expected_type.into(), body.value.span, wf_code); | |||
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| fcx.require_type_is_sized(expected_type, body.value.span, ObligationCauseCode::ConstSized); | |||
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This is redundant. We already check sizedness in wfcheck for statics and consts!
| @@ -1789,25 +1789,13 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> { | |||
| } else { | |||
| ("dyn ", span.shrink_to_lo()) | |||
| }; | |||
| let alternatively = if visitor | |||
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This logic only exists to avoid suggesting turning -> dyn Trait into -> impl Trait if there are multiple returns with different types.... but it didn't even erase regions so:
fn test() -> dyn Any {
if false {
return &2;
}
&1
}
Currently says:
= help: if there were a single returned type, you could use `impl Trait` instead
😭
| let ty = self.resolve_vars_if_possible(returned_ty); | ||
| if ty.references_error() { | ||
| // don't print out the [type error] here | ||
| err.downgrade_to_delayed_bug(); |
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This downgrade was very much not useful.
| // don't print out the [type error] here | ||
| err.downgrade_to_delayed_bug(); | ||
| } else { | ||
| err.span_label(expr.span, format!("this returned value is of type `{ty}`")); |
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We don't really need this span. The fact that the return type is not sized is not a result of the return exprs...
| @@ -26,6 +26,26 @@ help: alternatively, consider constraining `foo` so it does not apply to trait o | |||
| LL | fn foo() -> Self where Self: Sized; | |||
| | +++++++++++++++++ | |||
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| error[E0746]: return type cannot have an unboxed trait object | |||
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TODO: I should change this to be "cannot be a trait object without pointer indirection"... or something.
| --> $DIR/opaque-type-unsatisfied-bound.rs:15:16 | ||
| | | ||
| LL | fn weird0() -> impl Sized + !Sized {} | ||
| | ^^^^^^^^^^^^^^^^^^^ the trait bound `(): !Sized` is not satisfied | ||
| | ^^^^^^^^^^^^^^^^^^^ types differ |
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Absolutely no idea why this error message changed...
| @@ -3,6 +3,6 @@ | |||
| #![feature(negative_bounds, unboxed_closures)] | |||
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| fn produce() -> impl !Fn<(u32,)> {} | |||
| //~^ ERROR the trait bound `(): !Fn(u32)` is not satisfied | |||
| //~^ ERROR type mismatch resolving | |||
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The job Click to see the possible cause of the failure (guessed by this bot) |
lcnr
reviewed
Jan 30, 2025
| ObligationCause::new(span, def_id, traits::ObligationCauseCode::SizedReturnType), | ||
| wfcx.param_env, | ||
| ty, | ||
| tcx.require_lang_item(LangItem::Sized, None), |
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Suggested change
| tcx.require_lang_item(LangItem::Sized, None), | |
| tcx.require_lang_item(LangItem::Sized, Some(span)), |
?
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Still need to clean this up a bit. This should fix rust-lang/trait-system-refactor-initiative#150.
r? lcnr