bjoernager/rust
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On object safety error, mention new enum as alternative

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When we encounter a `dyn Trait` that isn't object safe, look for its
implementors. If there's one, mention using it directly If there are
less than 9, mention the possibility of creating a new enum and using
that instead.

Account for object unsafe `impl Trait on dyn Trait {}`.  Make a
distinction between public and sealed traits.

Fix #80194.
This commit is contained in:
Esteban Küber 2023-10-24 16:45:04 +00:00
parent 608e9682f0
commit 8c04999226
25 changed files with 130 additions and 1 deletions
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64
compiler/rustc_infer/src/traits/error_reporting/mod.rs
View file

@ -5,7 +5,8 @@ use rustc_data_structures::fx::FxIndexSet;
use rustc_errors::{struct_span_err, DiagnosticBuilder, ErrorGuaranteed, MultiSpan};
use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_middle::ty::TyCtxt;
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::{self, TyCtxt};
use rustc_span::Span;
use std::fmt;
use std::iter;
@ -108,5 +109,66 @@ pub fn report_object_safety_error<'tcx>(
violation.solution(&mut err);
}
}
let impls_of = tcx.trait_impls_of(trait_def_id);
let impls = if impls_of.blanket_impls().is_empty() {
impls_of
.non_blanket_impls()
.values()
.flatten()
.filter(|def_id| {
!matches!(tcx.type_of(*def_id).instantiate_identity().kind(), ty::Dynamic(..))
})
.collect::<Vec<_>>()
} else {
vec![]
};
let externally_visible = if !impls.is_empty()
&& let Some(def_id) = trait_def_id.as_local()
&& tcx.effective_visibilities(()).is_exported(def_id)
{
true
} else {
false
};
match &impls[..] {
[] => {}
_ if impls.len() > 9 => {}
[only] if externally_visible => {
err.help(with_no_trimmed_paths!(format!(
"only type `{}` is seen to implement the trait in this crate, consider using it \
directly instead",
tcx.type_of(*only).instantiate_identity(),
)));
}
[only] => {
err.help(with_no_trimmed_paths!(format!(
"only type `{}` implements the trait, consider using it directly instead",
tcx.type_of(*only).instantiate_identity(),
)));
}
impls => {
let types = impls
.iter()
.map(|t| {
with_no_trimmed_paths!(format!(" {}", tcx.type_of(*t).instantiate_identity(),))
})
.collect::<Vec<_>>();
err.help(format!(
"the following types implement the trait, consider defining an enum where each \
variant holds one of these types, implementing `{}` for this new enum and using \
it instead:\n{}",
trait_str,
types.join("\n"),
));
}
}
if externally_visible {
err.note(format!(
"`{trait_str}` can be implemented in other crates; if you want to support your users \
passing their own types here, you can't refer to a specific type",
));
}
err
}