Skip to content

Commit

Permalink
Rollup merge of rust-lang#125572 - mu001999-contrib:dead/enhance, r=p…
Browse files Browse the repository at this point in the history
…nkfelix

Detect pub structs never constructed and unused associated constants

<!--
If this PR is related to an unstable feature or an otherwise tracked effort,
please link to the relevant tracking issue here. If you don't know of a related
tracking issue or there are none, feel free to ignore this.

This PR will get automatically assigned to a reviewer. In case you would like
a specific user to review your work, you can assign it to them by using

    r​? <reviewer name>
-->

Lints never constructed public structs.

If we don't provide public methods to construct public structs with private fields, and don't construct them in the local crate. They would be never constructed. So that we can detect such public structs.

---
Update:

Also lints unused associated constants in traits.
  • Loading branch information
matthiaskrgr authored Jun 7, 2024
2 parents 6e534c7 + 35130d7 commit 13314df
Show file tree
Hide file tree
Showing 32 changed files with 272 additions and 88 deletions.
121 changes: 93 additions & 28 deletions compiler/rustc_passes/src/dead.rs
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ use rustc_hir::{Node, PatKind, TyKind};
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
use rustc_middle::middle::privacy::Level;
use rustc_middle::query::Providers;
use rustc_middle::ty::{self, TyCtxt};
use rustc_middle::ty::{self, AssocItemContainer, TyCtxt};
use rustc_middle::{bug, span_bug};
use rustc_session::lint;
use rustc_session::lint::builtin::DEAD_CODE;
Expand Down Expand Up @@ -44,16 +44,63 @@ fn should_explore(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
)
}

fn ty_ref_to_pub_struct(tcx: TyCtxt<'_>, ty: &hir::Ty<'_>) -> bool {
struct Publicness {
ty_is_public: bool,
ty_and_all_fields_are_public: bool,
}

impl Publicness {
fn new(ty_is_public: bool, ty_and_all_fields_are_public: bool) -> Self {
Self { ty_is_public, ty_and_all_fields_are_public }
}
}

fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: DefId) -> 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
tcx.adt_def(id).all_fields().all(|field| {
let field_type = tcx.type_of(field.did).instantiate_identity();
if field_type.is_phantom_data() {
return true;
}
let is_positional = field.name.as_str().starts_with(|c: char| c.is_ascii_digit());
if is_positional
&& tcx
.layout_of(tcx.param_env(field.did).and(field_type))
.map_or(true, |layout| layout.is_zst())
{
return true;
}
field.vis.is_public()
})
}

/// check struct and its fields are public or not,
/// 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()
&& matches!(def_kind, DefKind::Struct | DefKind::Enum | DefKind::Union)
{
tcx.visibility(def_id).is_public()
} else {
true
return match def_kind {
DefKind::Enum | DefKind::Union => {
let ty_is_public = tcx.visibility(def_id).is_public();
Publicness::new(ty_is_public, ty_is_public)
}
DefKind::Struct => {
let ty_is_public = tcx.visibility(def_id).is_public();
Publicness::new(
ty_is_public,
ty_is_public && struct_all_fields_are_public(tcx, def_id),
)
}
_ => Publicness::new(true, true),
};
}

Publicness::new(true, true)
}

/// Determine if a work from the worklist is coming from the a `#[allow]`
Expand Down Expand Up @@ -427,9 +474,11 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
{
if matches!(trait_item.kind, hir::TraitItemKind::Fn(..))
&& !ty_ref_to_pub_struct(self.tcx, impl_ref.self_ty)
.ty_and_all_fields_are_public
{
// skip methods of private ty,
// they would be solved in `solve_rest_impl_items`
// skip impl-items of non pure pub ty,
// cause we don't know the ty is constructed or not,
// check these later in `solve_rest_impl_items`
continue;
}

Expand Down Expand Up @@ -510,22 +559,21 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
&& let Some(local_def_id) = def_id.as_local()
&& matches!(def_kind, DefKind::Struct | DefKind::Enum | DefKind::Union)
{
if self.tcx.visibility(impl_item_id).is_public() {
// for the public method, we don't know the trait item is used or not,
// so we mark the method live if the self is used
return self.live_symbols.contains(&local_def_id);
}

if let Some(trait_item_id) = self.tcx.associated_item(impl_item_id).trait_item_def_id
&& let Some(local_id) = trait_item_id.as_local()
{
// for the private method, we can know the trait item is used or not,
// for the local impl item, we can know the trait item is used or not,
// so we mark the method live if the self is used and the trait item is used
return self.live_symbols.contains(&local_id)
&& self.live_symbols.contains(&local_def_id);
self.live_symbols.contains(&local_id) && self.live_symbols.contains(&local_def_id)
} else {
// for the foreign method and inherent pub method,
// we don't know the trait item or the method is used or not,
// so we mark the method live if the self is used
self.live_symbols.contains(&local_def_id)
}
} else {
false
}
false
}
}

Expand Down Expand Up @@ -747,7 +795,9 @@ fn check_item<'tcx>(
.iter()
.filter_map(|def_id| def_id.as_local());

let ty_is_pub = ty_ref_to_pub_struct(tcx, tcx.hir().item(id).expect_impl().self_ty);
let self_ty = tcx.hir().item(id).expect_impl().self_ty;
let Publicness { ty_is_public, ty_and_all_fields_are_public } =
ty_ref_to_pub_struct(tcx, self_ty);

// And we access the Map here to get HirId from LocalDefId
for local_def_id in local_def_ids {
Expand All @@ -763,18 +813,20 @@ fn check_item<'tcx>(
// for trait impl blocks,
// mark the method live if the self_ty is public,
// or the method is public and may construct self
if of_trait
&& (!matches!(tcx.def_kind(local_def_id), DefKind::AssocFn)
|| tcx.visibility(local_def_id).is_public()
&& (ty_is_pub || may_construct_self))
if of_trait && matches!(tcx.def_kind(local_def_id), DefKind::AssocTy)
|| tcx.visibility(local_def_id).is_public()
&& (ty_and_all_fields_are_public || may_construct_self)
{
// if the impl item is public,
// and the ty may be constructed or can be constructed in foreign crates,
// mark the impl item live
worklist.push((local_def_id, ComesFromAllowExpect::No));
} else if let Some(comes_from_allow) =
has_allow_dead_code_or_lang_attr(tcx, local_def_id)
{
worklist.push((local_def_id, comes_from_allow));
} else if of_trait {
// private method || public method not constructs self
} else if of_trait || tcx.visibility(local_def_id).is_public() && ty_is_public {
// private impl items of traits || public impl items not constructs self
unsolved_impl_items.push((id, local_def_id));
}
}
Expand Down Expand Up @@ -841,6 +893,14 @@ fn create_and_seed_worklist(
effective_vis
.is_public_at_level(Level::Reachable)
.then_some(id)
.filter(|&id|
// checks impls, impl-items and pub structs with all public fields later
match tcx.def_kind(id) {
DefKind::Impl { .. } => false,
DefKind::AssocConst | DefKind::AssocFn => !matches!(tcx.associated_item(id).container, AssocItemContainer::ImplContainer),
DefKind::Struct => struct_all_fields_are_public(tcx, id.to_def_id()),
_ => true
})
.map(|id| (id, ComesFromAllowExpect::No))
})
// Seed entry point
Expand Down Expand Up @@ -1113,10 +1173,15 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
|| (def_kind == DefKind::Trait && live_symbols.contains(&item.owner_id.def_id))
{
for &def_id in tcx.associated_item_def_ids(item.owner_id.def_id) {
// We have diagnosed unused methods in traits
// We have diagnosed unused assoc consts and fns in traits
if matches!(def_kind, DefKind::Impl { of_trait: true })
&& tcx.def_kind(def_id) == DefKind::AssocFn
|| def_kind == DefKind::Trait && tcx.def_kind(def_id) != DefKind::AssocFn
&& matches!(tcx.def_kind(def_id), DefKind::AssocConst | DefKind::AssocFn)
// skip unused public inherent methods,
// cause we have diagnosed unconstructed struct
|| matches!(def_kind, DefKind::Impl { of_trait: false })
&& tcx.visibility(def_id).is_public()
&& ty_ref_to_pub_struct(tcx, tcx.hir().item(item).expect_impl().self_ty).ty_is_public
|| def_kind == DefKind::Trait && tcx.def_kind(def_id) == DefKind::AssocTy
{
continue;
}
Expand Down
10 changes: 5 additions & 5 deletions tests/codegen-units/item-collection/generic-impl.rs
Original file line number Diff line number Diff line change
Expand Up @@ -22,16 +22,16 @@ impl<T> Struct<T> {
}
}

pub struct LifeTimeOnly<'a> {
pub struct _LifeTimeOnly<'a> {
_a: &'a u32,
}

impl<'a> LifeTimeOnly<'a> {
//~ MONO_ITEM fn LifeTimeOnly::<'_>::foo
impl<'a> _LifeTimeOnly<'a> {
//~ MONO_ITEM fn _LifeTimeOnly::<'_>::foo
pub fn foo(&self) {}
//~ MONO_ITEM fn LifeTimeOnly::<'_>::bar
//~ MONO_ITEM fn _LifeTimeOnly::<'_>::bar
pub fn bar(&'a self) {}
//~ MONO_ITEM fn LifeTimeOnly::<'_>::baz
//~ MONO_ITEM fn _LifeTimeOnly::<'_>::baz
pub fn baz<'b>(&'b self) {}

pub fn non_instantiated<T>(&self) {}
Expand Down
24 changes: 12 additions & 12 deletions tests/codegen-units/item-collection/overloaded-operators.rs
Original file line number Diff line number Diff line change
Expand Up @@ -5,44 +5,44 @@

use std::ops::{Add, Deref, Index, IndexMut};

pub struct Indexable {
pub struct _Indexable {
data: [u8; 3],
}

impl Index<usize> for Indexable {
impl Index<usize> for _Indexable {
type Output = u8;

//~ MONO_ITEM fn <Indexable as std::ops::Index<usize>>::index
//~ MONO_ITEM fn <_Indexable as std::ops::Index<usize>>::index
fn index(&self, index: usize) -> &Self::Output {
if index >= 3 { &self.data[0] } else { &self.data[index] }
}
}

impl IndexMut<usize> for Indexable {
//~ MONO_ITEM fn <Indexable as std::ops::IndexMut<usize>>::index_mut
impl IndexMut<usize> for _Indexable {
//~ MONO_ITEM fn <_Indexable as std::ops::IndexMut<usize>>::index_mut
fn index_mut(&mut self, index: usize) -> &mut Self::Output {
if index >= 3 { &mut self.data[0] } else { &mut self.data[index] }
}
}

//~ MONO_ITEM fn <Equatable as std::cmp::PartialEq>::eq
//~ MONO_ITEM fn <Equatable as std::cmp::PartialEq>::ne
//~ MONO_ITEM fn <_Equatable as std::cmp::PartialEq>::eq
//~ MONO_ITEM fn <_Equatable as std::cmp::PartialEq>::ne
#[derive(PartialEq)]
pub struct Equatable(u32);
pub struct _Equatable(u32);

impl Add<u32> for Equatable {
impl Add<u32> for _Equatable {
type Output = u32;

//~ MONO_ITEM fn <Equatable as std::ops::Add<u32>>::add
//~ MONO_ITEM fn <_Equatable as std::ops::Add<u32>>::add
fn add(self, rhs: u32) -> u32 {
self.0 + rhs
}
}

impl Deref for Equatable {
impl Deref for _Equatable {
type Target = u32;

//~ MONO_ITEM fn <Equatable as std::ops::Deref>::deref
//~ MONO_ITEM fn <_Equatable as std::ops::Deref>::deref
fn deref(&self) -> &Self::Target {
&self.0
}
Expand Down
1 change: 1 addition & 0 deletions tests/ui/coherence/re-rebalance-coherence.rs
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
extern crate re_rebalance_coherence_lib as lib;
use lib::*;

#[allow(dead_code)]
struct Oracle;
impl Backend for Oracle {}
impl<'a, T:'a, Tab> QueryFragment<Oracle> for BatchInsert<'a, T, Tab> {}
Expand Down
1 change: 1 addition & 0 deletions tests/ui/const-generics/defaults/repr-c-issue-82792.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

//@ run-pass

#[allow(dead_code)]
#[repr(C)]
pub struct Loaf<T: Sized, const N: usize = 1> {
head: [T; N],
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,8 @@ impl BlockCipher for BarCipher {
const BLOCK_SIZE: usize = 32;
}

pub struct Block<C>(#[allow(dead_code)] C);
#[allow(dead_code)]
pub struct Block<C>(C);

pub fn test<C: BlockCipher, const M: usize>()
where
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@

use std::mem::MaybeUninit;

#[allow(dead_code)]
#[repr(transparent)]
pub struct MaybeUninitWrapper<const N: usize>(MaybeUninit<[u64; N]>);

Expand Down
4 changes: 2 additions & 2 deletions tests/ui/derives/clone-debug-dead-code-in-the-same-struct.rs
Original file line number Diff line number Diff line change
@@ -1,9 +1,9 @@
#![forbid(dead_code)]

#[derive(Debug)]
pub struct Whatever {
pub struct Whatever { //~ ERROR struct `Whatever` is never constructed
pub field0: (),
field1: (), //~ ERROR fields `field1`, `field2`, `field3`, and `field4` are never read
field1: (),
field2: (),
field3: (),
field4: (),
Expand Down
16 changes: 3 additions & 13 deletions tests/ui/derives/clone-debug-dead-code-in-the-same-struct.stderr
Original file line number Diff line number Diff line change
@@ -1,19 +1,9 @@
error: fields `field1`, `field2`, `field3`, and `field4` are never read
--> $DIR/clone-debug-dead-code-in-the-same-struct.rs:6:5
error: struct `Whatever` is never constructed
--> $DIR/clone-debug-dead-code-in-the-same-struct.rs:4:12
|
LL | pub struct Whatever {
| -------- fields in this struct
LL | pub field0: (),
LL | field1: (),
| ^^^^^^
LL | field2: (),
| ^^^^^^
LL | field3: (),
| ^^^^^^
LL | field4: (),
| ^^^^^^
| ^^^^^^^^
|
= note: `Whatever` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis
note: the lint level is defined here
--> $DIR/clone-debug-dead-code-in-the-same-struct.rs:1:11
|
Expand Down
1 change: 1 addition & 0 deletions tests/ui/issues/issue-5708.rs
Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,7 @@ pub trait MyTrait<T> {
fn dummy(&self, t: T) -> T { panic!() }
}

#[allow(dead_code)]
pub struct MyContainer<'a, T:'a> {
foos: Vec<&'a (dyn MyTrait<T>+'a)> ,
}
Expand Down
5 changes: 2 additions & 3 deletions tests/ui/lint/dead-code/lint-dead-code-1.rs
Original file line number Diff line number Diff line change
Expand Up @@ -46,11 +46,10 @@ struct SemiUsedStruct;
impl SemiUsedStruct {
fn la_la_la() {}
}
struct StructUsedAsField;
struct StructUsedAsField; //~ ERROR struct `StructUsedAsField` is never constructed
pub struct StructUsedInEnum;
struct StructUsedInGeneric;
pub struct PubStruct2 {
#[allow(dead_code)]
pub struct PubStruct2 { //~ ERROR struct `PubStruct2` is never constructed
struct_used_as_field: *const StructUsedAsField
}

Expand Down
Loading

0 comments on commit 13314df

Please sign in to comment.