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Add async_fn_in_trait lint

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This commit is contained in:
Michael Goulet 2023-09-26 20:20:21 +00:00
parent 2e5a9dd6c9
commit ec79720c1e
7 changed files with 186 additions and 53 deletions
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122
compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
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@ -4000,14 +4000,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
// ... whose signature is `async` (i.e. this is an AFIT)
let (sig, body) = item.expect_fn();
let hir::IsAsync::Async(async_span) = sig.header.asyncness else {
return;
};
let Ok(async_span) =
self.tcx.sess.source_map().span_extend_while(async_span, |c| c.is_whitespace())
else {
return;
};
let hir::FnRetTy::Return(hir::Ty { kind: hir::TyKind::OpaqueDef(def, ..), .. }) =
sig.decl.output
else {
@ -4021,55 +4013,17 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
return;
}
let future = self.tcx.hir().item(*def).expect_opaque_ty();
let Some(hir::GenericBound::LangItemTrait(_, _, _, generics)) = future.bounds.get(0) else {
// `async fn` should always lower to a lang item bound... but don't ICE.
return;
};
let Some(hir::TypeBindingKind::Equality { term: hir::Term::Ty(future_output_ty) }) =
generics.bindings.get(0).map(|binding| binding.kind)
else {
// Also should never happen.
let Some(sugg) = suggest_desugaring_async_fn_to_impl_future_in_trait(
self.tcx,
*sig,
*body,
opaque_def_id.expect_local(),
&format!(" + {auto_trait}"),
) else {
return;
};
let function_name = self.tcx.def_path_str(fn_def_id);
let mut sugg = if future_output_ty.span.is_empty() {
vec![
(async_span, String::new()),
(
future_output_ty.span,
format!(" -> impl std::future::Future<Output = ()> + {auto_trait}"),
),
]
} else {
vec![
(
future_output_ty.span.shrink_to_lo(),
"impl std::future::Future<Output = ".to_owned(),
),
(future_output_ty.span.shrink_to_hi(), format!("> + {auto_trait}")),
(async_span, String::new()),
]
};
// If there's a body, we also need to wrap it in `async {}`
if let hir::TraitFn::Provided(body) = body {
let body = self.tcx.hir().body(*body);
let body_span = body.value.span;
let body_span_without_braces =
body_span.with_lo(body_span.lo() + BytePos(1)).with_hi(body_span.hi() - BytePos(1));
if body_span_without_braces.is_empty() {
sugg.push((body_span_without_braces, " async {} ".to_owned()));
} else {
sugg.extend([
(body_span_without_braces.shrink_to_lo(), "async {".to_owned()),
(body_span_without_braces.shrink_to_hi(), "} ".to_owned()),
]);
}
}
err.multipart_suggestion(
format!(
"`{auto_trait}` can be made part of the associated future's \
@ -4321,3 +4275,65 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ReplaceImplTraitFolder<'tcx> {
self.tcx
}
}
pub fn suggest_desugaring_async_fn_to_impl_future_in_trait<'tcx>(
tcx: TyCtxt<'tcx>,
sig: hir::FnSig<'tcx>,
body: hir::TraitFn<'tcx>,
opaque_def_id: LocalDefId,
add_bounds: &str,
) -> Option<Vec<(Span, String)>> {
let hir::IsAsync::Async(async_span) = sig.header.asyncness else {
return None;
};
let Ok(async_span) = tcx.sess.source_map().span_extend_while(async_span, |c| c.is_whitespace())
else {
return None;
};
let future = tcx.hir().get_by_def_id(opaque_def_id).expect_item().expect_opaque_ty();
let Some(hir::GenericBound::LangItemTrait(_, _, _, generics)) = future.bounds.get(0) else {
// `async fn` should always lower to a lang item bound... but don't ICE.
return None;
};
let Some(hir::TypeBindingKind::Equality { term: hir::Term::Ty(future_output_ty) }) =
generics.bindings.get(0).map(|binding| binding.kind)
else {
// Also should never happen.
return None;
};
let mut sugg = if future_output_ty.span.is_empty() {
vec![
(async_span, String::new()),
(
future_output_ty.span,
format!(" -> impl std::future::Future<Output = ()>{add_bounds}"),
),
]
} else {
vec![
(future_output_ty.span.shrink_to_lo(), "impl std::future::Future<Output = ".to_owned()),
(future_output_ty.span.shrink_to_hi(), format!(">{add_bounds}")),
(async_span, String::new()),
]
};
// If there's a body, we also need to wrap it in `async {}`
if let hir::TraitFn::Provided(body) = body {
let body = tcx.hir().body(body);
let body_span = body.value.span;
let body_span_without_braces =
body_span.with_lo(body_span.lo() + BytePos(1)).with_hi(body_span.hi() - BytePos(1));
if body_span_without_braces.is_empty() {
sugg.push((body_span_without_braces, " async {} ".to_owned()));
} else {
sugg.extend([
(body_span_without_braces.shrink_to_lo(), "async {".to_owned()),
(body_span_without_braces.shrink_to_hi(), "} ".to_owned()),
]);
}
}
Some(sugg)
}