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Rollup merge of rust-lang#127017 - mu001999-contrib:dead/enhance, r=p…
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…nkfelix

Extend rules of dead code analysis for impls for adts to impls for types refer to adts

The rules of dead code analysis for impl blocks can be extended to self types which refer to adts.

So that we can lint the following unused struct and trait:
```rust
struct Foo; //~ ERROR struct `Foo` is never constructed

trait Trait { //~ ERROR trait `Trait` is never used
    fn foo(&self) {}
}

impl Trait for &Foo {}
```

r? `@pnkfelix`
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tgross35 authored Jul 26, 2024
2 parents ceae371 + 8449d10 commit a70dc29
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Showing 3 changed files with 87 additions and 10 deletions.
32 changes: 22 additions & 10 deletions compiler/rustc_passes/src/dead.rs
Original file line number Diff line number Diff line change
Expand Up @@ -54,7 +54,24 @@ impl Publicness {
}
}

fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: DefId) -> bool {
fn adt_of<'tcx>(ty: &hir::Ty<'tcx>) -> Option<(LocalDefId, DefKind)> {
match ty.kind {
TyKind::Path(hir::QPath::Resolved(_, path)) => {
if let Res::Def(def_kind, def_id) = path.res
&& let Some(local_def_id) = def_id.as_local()
{
Some((local_def_id, def_kind))
} else {
None
}
}
TyKind::Slice(ty) | TyKind::Array(ty, _) => adt_of(ty),
TyKind::Ptr(ty) | TyKind::Ref(_, ty) => adt_of(ty.ty),
_ => None,
}
}

fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: LocalDefId) -> bool {
// treat PhantomData and positional ZST as public,
// we don't want to lint types which only have them,
// cause it's a common way to use such types to check things like well-formedness
Expand All @@ -79,10 +96,7 @@ fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: DefId) -> bool {
/// for enum and union, just check they are public,
/// and doesn't solve types like &T for now, just skip them
fn ty_ref_to_pub_struct(tcx: TyCtxt<'_>, ty: &hir::Ty<'_>) -> Publicness {
if let TyKind::Path(hir::QPath::Resolved(_, path)) = ty.kind
&& let Res::Def(def_kind, def_id) = path.res
&& def_id.is_local()
{
if let Some((def_id, def_kind)) = adt_of(ty) {
return match def_kind {
DefKind::Enum | DefKind::Union => {
let ty_is_public = tcx.visibility(def_id).is_public();
Expand Down Expand Up @@ -565,10 +579,8 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
}

fn impl_item_with_used_self(&mut self, impl_id: hir::ItemId, impl_item_id: LocalDefId) -> bool {
if let TyKind::Path(hir::QPath::Resolved(_, path)) =
self.tcx.hir().item(impl_id).expect_impl().self_ty.kind
&& let Res::Def(def_kind, def_id) = path.res
&& let Some(local_def_id) = def_id.as_local()
if let Some((local_def_id, def_kind)) =
adt_of(self.tcx.hir().item(impl_id).expect_impl().self_ty)
&& matches!(def_kind, DefKind::Struct | DefKind::Enum | DefKind::Union)
{
if let Some(trait_item_id) = self.tcx.associated_item(impl_item_id).trait_item_def_id
Expand Down Expand Up @@ -915,7 +927,7 @@ fn create_and_seed_worklist(
match tcx.def_kind(id) {
DefKind::Impl { .. } => false,
DefKind::AssocConst | DefKind::AssocTy | DefKind::AssocFn => !matches!(tcx.associated_item(id).container, AssocItemContainer::ImplContainer),
DefKind::Struct => struct_all_fields_are_public(tcx, id.to_def_id()) || has_allow_dead_code_or_lang_attr(tcx, id).is_some(),
DefKind::Struct => struct_all_fields_are_public(tcx, id) || has_allow_dead_code_or_lang_attr(tcx, id).is_some(),
_ => true
})
.map(|id| (id, ComesFromAllowExpect::No))
Expand Down
45 changes: 45 additions & 0 deletions tests/ui/lint/dead-code/unused-impl-for-non-adts.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
#![deny(dead_code)]

struct Foo; //~ ERROR struct `Foo` is never constructed

trait Trait { //~ ERROR trait `Trait` is never used
fn foo(&self) {}
}

impl Trait for Foo {}

impl Trait for [Foo] {}
impl<const N: usize> Trait for [Foo; N] {}

impl Trait for *const Foo {}
impl Trait for *mut Foo {}

impl Trait for &Foo {}
impl Trait for &&Foo {}
impl Trait for &mut Foo {}

impl Trait for [&Foo] {}
impl Trait for &[Foo] {}
impl Trait for &*const Foo {}

pub trait Trait2 {
fn foo(&self) {}
}

impl Trait2 for Foo {}

impl Trait2 for [Foo] {}
impl<const N: usize> Trait2 for [Foo; N] {}

impl Trait2 for *const Foo {}
impl Trait2 for *mut Foo {}

impl Trait2 for &Foo {}
impl Trait2 for &&Foo {}
impl Trait2 for &mut Foo {}

impl Trait2 for [&Foo] {}
impl Trait2 for &[Foo] {}
impl Trait2 for &*const Foo {}

fn main() {}
20 changes: 20 additions & 0 deletions tests/ui/lint/dead-code/unused-impl-for-non-adts.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
error: struct `Foo` is never constructed
--> $DIR/unused-impl-for-non-adts.rs:3:8
|
LL | struct Foo;
| ^^^
|
note: the lint level is defined here
--> $DIR/unused-impl-for-non-adts.rs:1:9
|
LL | #![deny(dead_code)]
| ^^^^^^^^^

error: trait `Trait` is never used
--> $DIR/unused-impl-for-non-adts.rs:5:7
|
LL | trait Trait {
| ^^^^^

error: aborting due to 2 previous errors

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