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Suggest impl Trait for References to Bare Trait in Function Header

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This commit is contained in:
Veera 2024-07-13 12:05:16 -04:00
parent 102997a939
commit 12de141df2
4 changed files with 92 additions and 52 deletions
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78
compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs
View file

@ -120,9 +120,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
return;
};
let sugg = self.add_generic_param_suggestion(generics, self_ty.span, &impl_trait_name);
if sugg.is_empty() {
return;
};
diag.multipart_suggestion(
format!(
"alternatively use a blanket implementation to implement `{of_trait_name}` for \
@ -157,6 +154,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
let parent_id = tcx.hir().get_parent_item(self_ty.hir_id).def_id;
// FIXME: If `type_alias_impl_trait` is enabled, also look for `Trait0<Ty = Trait1>`
// and suggest `Trait0<Ty = impl Trait1>`.
// Functions are found in three different contexts.
// 1. Independent functions
// 2. Functions inside trait blocks
// 3. Functions inside impl blocks
let (sig, generics, owner) = match tcx.hir_node_by_def_id(parent_id) {
hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, generics, _), .. }) => {
(sig, generics, None)
@ -167,6 +168,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
owner_id,
..
}) => (sig, generics, Some(tcx.parent(owner_id.to_def_id()))),
hir::Node::ImplItem(hir::ImplItem {
kind: hir::ImplItemKind::Fn(sig, _),
generics,
owner_id,
..
}) => (sig, generics, Some(tcx.parent(owner_id.to_def_id()))),
_ => return false,
};
let Ok(trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else {
@ -174,6 +181,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
};
let impl_sugg = vec![(self_ty.span.shrink_to_lo(), "impl ".to_string())];
let mut is_downgradable = true;
// Check if trait object is safe for suggesting dynamic dispatch.
let is_object_safe = match self_ty.kind {
hir::TyKind::TraitObject(objects, ..) => {
objects.iter().all(|o| match o.trait_ref.path.res {
@ -189,8 +198,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
}
_ => false,
};
let borrowed = matches!(
tcx.parent_hir_node(self_ty.hir_id),
hir::Node::Ty(hir::Ty { kind: hir::TyKind::Ref(..), .. })
);
// Suggestions for function return type.
if let hir::FnRetTy::Return(ty) = sig.decl.output
&& ty.hir_id == self_ty.hir_id
&& ty.peel_refs().hir_id == self_ty.hir_id
{
let pre = if !is_object_safe {
format!("`{trait_name}` is not object safe, ")
@ -201,14 +217,26 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
"{pre}use `impl {trait_name}` to return an opaque type, as long as you return a \
single underlying type",
);
diag.multipart_suggestion_verbose(msg, impl_sugg, Applicability::MachineApplicable);
// Suggest `Box<dyn Trait>` for return type
if is_object_safe {
diag.multipart_suggestion_verbose(
"alternatively, you can return an owned trait object",
// If the return type is `&Trait`, we don't want
// the ampersand to be displayed in the `Box<dyn Trait>`
// suggestion.
let suggestion = if borrowed {
vec![(ty.span, format!("Box<dyn {trait_name}>"))]
} else {
vec![
(ty.span.shrink_to_lo(), "Box<dyn ".to_string()),
(ty.span.shrink_to_hi(), ">".to_string()),
],
]
};
diag.multipart_suggestion_verbose(
"alternatively, you can return an owned trait object",
suggestion,
Applicability::MachineApplicable,
);
} else if is_downgradable {
@ -217,24 +245,24 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
}
return true;
}
// Suggestions for function parameters.
for ty in sig.decl.inputs {
if ty.hir_id != self_ty.hir_id {
if ty.peel_refs().hir_id != self_ty.hir_id {
continue;
}
let sugg = self.add_generic_param_suggestion(generics, self_ty.span, &trait_name);
if !sugg.is_empty() {
diag.multipart_suggestion_verbose(
format!("use a new generic type parameter, constrained by `{trait_name}`"),
sugg,
Applicability::MachineApplicable,
);
diag.multipart_suggestion_verbose(
"you can also use an opaque type, but users won't be able to specify the type \
parameter when calling the `fn`, having to rely exclusively on type inference",
impl_sugg,
Applicability::MachineApplicable,
);
}
diag.multipart_suggestion_verbose(
format!("use a new generic type parameter, constrained by `{trait_name}`"),
sugg,
Applicability::MachineApplicable,
);
diag.multipart_suggestion_verbose(
"you can also use an opaque type, but users won't be able to specify the type \
parameter when calling the `fn`, having to rely exclusively on type inference",
impl_sugg,
Applicability::MachineApplicable,
);
if !is_object_safe {
diag.note(format!("`{trait_name}` it is not object safe, so it can't be `dyn`"));
if is_downgradable {
@ -242,14 +270,18 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
diag.downgrade_to_delayed_bug();
}
} else {
// No ampersand in suggestion if it's borrowed already
let (dyn_str, paren_dyn_str) =
if borrowed { ("dyn ", "(dyn ") } else { ("&dyn ", "&(dyn ") };
let sugg = if let hir::TyKind::TraitObject([_, _, ..], _, _) = self_ty.kind {
// There are more than one trait bound, we need surrounding parentheses.
vec![
(self_ty.span.shrink_to_lo(), "&(dyn ".to_string()),
(self_ty.span.shrink_to_lo(), paren_dyn_str.to_string()),
(self_ty.span.shrink_to_hi(), ")".to_string()),
]
} else {
vec![(self_ty.span.shrink_to_lo(), "&dyn ".to_string())]
vec![(self_ty.span.shrink_to_lo(), dyn_str.to_string())]
};
diag.multipart_suggestion_verbose(
format!(