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Make traits / trait methods detected by the dead code lint!
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@mu001999
mu001999 authored Jan 15, 2024
1 parent 1ead476 commit 999a162
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Showing 3 changed files with 136 additions and 20 deletions.
91 changes: 71 additions & 20 deletions compiler/rustc_passes/src/dead.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
// is dead.

use hir::def_id::{LocalDefIdMap, LocalDefIdSet};
use hir::ItemKind;
use rustc_data_structures::unord::UnordSet;
use rustc_errors::MultiSpan;
use rustc_hir as hir;
Expand All @@ -14,7 +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, TyCtxt, Visibility};
use rustc_session::lint;
use rustc_session::lint::builtin::DEAD_CODE;
use rustc_span::symbol::{sym, Symbol};
Expand Down Expand Up @@ -376,9 +377,46 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
intravisit::walk_item(self, item)
}
hir::ItemKind::ForeignMod { .. } => {}
hir::ItemKind::Trait(..) => {
for impl_def_id in self.tcx.all_impls(item.owner_id.to_def_id()) {
if let Some(local_def_id) = impl_def_id.as_local()
&& let ItemKind::Impl(impl_ref) =
self.tcx.hir().expect_item(local_def_id).kind
{
// skip items
// mark dependent traits live
intravisit::walk_generics(self, impl_ref.generics);
// mark dependent parameters live
intravisit::walk_path(self, impl_ref.of_trait.unwrap().path);
}
}

intravisit::walk_item(self, item)
}
_ => intravisit::walk_item(self, item),
},
Node::TraitItem(trait_item) => {
// mark corresponing ImplTerm live
let trait_item_id = trait_item.owner_id.to_def_id();
if let Some(trait_id) = self.tcx.trait_of_item(trait_item_id) {
// mark the trait live
self.check_def_id(trait_id);

for impl_id in self.tcx.all_impls(trait_id) {
if let Some(local_impl_id) = impl_id.as_local()
&& let ItemKind::Impl(impl_ref) =
self.tcx.hir().expect_item(local_impl_id).kind
{
// mark self_ty live
intravisit::walk_ty(self, impl_ref.self_ty);
if let Some(&impl_item_id) =
self.tcx.impl_item_implementor_ids(impl_id).get(&trait_item_id)
{
self.check_def_id(impl_item_id);
}
}
}
}
intravisit::walk_trait_item(self, trait_item);
}
Node::ImplItem(impl_item) => {
Expand Down Expand Up @@ -627,10 +665,6 @@ fn check_item<'tcx>(
}
}
DefKind::Impl { of_trait } => {
if of_trait {
worklist.push((id.owner_id.def_id, ComesFromAllowExpect::No));
}

// get DefIds from another query
let local_def_ids = tcx
.associated_item_def_ids(id.owner_id)
Expand All @@ -639,7 +673,11 @@ fn check_item<'tcx>(

// And we access the Map here to get HirId from LocalDefId
for id in local_def_ids {
if of_trait {
// for impl trait blocks, mark associate functions live if the trait is public
if of_trait
&& (!matches!(tcx.def_kind(id), DefKind::AssocFn)
|| tcx.local_visibility(id) == Visibility::Public)
{
worklist.push((id, ComesFromAllowExpect::No));
} else if let Some(comes_from_allow) = has_allow_dead_code_or_lang_attr(tcx, id) {
worklist.push((id, comes_from_allow));
Expand Down Expand Up @@ -670,7 +708,7 @@ fn check_trait_item(
use hir::TraitItemKind::{Const, Fn};
if matches!(tcx.def_kind(id.owner_id), DefKind::AssocConst | DefKind::AssocFn) {
let trait_item = tcx.hir().trait_item(id);
if matches!(trait_item.kind, Const(_, Some(_)) | Fn(_, hir::TraitFn::Provided(_)))
if matches!(trait_item.kind, Const(_, Some(_)) | Fn(..))
&& let Some(comes_from_allow) =
has_allow_dead_code_or_lang_attr(tcx, trait_item.owner_id.def_id)
{
Expand Down Expand Up @@ -939,7 +977,8 @@ impl<'tcx> DeadVisitor<'tcx> {
| DefKind::TyAlias
| DefKind::Enum
| DefKind::Union
| DefKind::ForeignTy => self.warn_dead_code(def_id, "used"),
| DefKind::ForeignTy
| DefKind::Trait => self.warn_dead_code(def_id, "used"),
DefKind::Struct => self.warn_dead_code(def_id, "constructed"),
DefKind::Variant | DefKind::Field => bug!("should be handled specially"),
_ => {}
Expand All @@ -964,18 +1003,33 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
let module_items = tcx.hir_module_items(module);

for item in module_items.items() {
if let hir::ItemKind::Impl(impl_item) = tcx.hir().item(item).kind {
let mut dead_items = Vec::new();
for item in impl_item.items {
let def_id = item.id.owner_id.def_id;
if !visitor.is_live_code(def_id) {
let name = tcx.item_name(def_id.to_def_id());
let level = visitor.def_lint_level(def_id);
let def_kind = tcx.def_kind(item.owner_id);

dead_items.push(DeadItem { def_id, name, level })
let mut dead_codes = Vec::new();
// if we have diagnosed the trait, do not diagnose unused methods
if matches!(def_kind, DefKind::Impl { .. })
|| (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
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
{
continue;
}

if let Some(local_def_id) = def_id.as_local()
&& !visitor.is_live_code(local_def_id)
{
let name = tcx.item_name(def_id);
let level = visitor.def_lint_level(local_def_id);
dead_codes.push(DeadItem { def_id: local_def_id, name, level });
}
}
visitor.warn_multiple(item.owner_id.def_id, "used", dead_items, ReportOn::NamedField);
}
if !dead_codes.is_empty() {
visitor.warn_multiple(item.owner_id.def_id, "used", dead_codes, ReportOn::NamedField);
}

if !live_symbols.contains(&item.owner_id.def_id) {
Expand All @@ -988,7 +1042,6 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
continue;
}

let def_kind = tcx.def_kind(item.owner_id);
if let DefKind::Struct | DefKind::Union | DefKind::Enum = def_kind {
let adt = tcx.adt_def(item.owner_id);
let mut dead_variants = Vec::new();
Expand Down Expand Up @@ -1035,8 +1088,6 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
for foreign_item in module_items.foreign_items() {
visitor.check_definition(foreign_item.owner_id.def_id);
}

// We do not warn trait items.
}

pub(crate) fn provide(providers: &mut Providers) {
Expand Down
29 changes: 29 additions & 0 deletions tests/ui/lint/dead-code/issue-41883.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
#![deny(dead_code)]

enum Category {
Dead, //~ ERROR variant `Dead` is never constructed
Used,
}

trait UnusedTrait { //~ ERROR trait `UnusedTrait` is never used
fn this_is_unused(&self) -> Category {
Category::Dead
}
}

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

impl UnusedTrait for UnusedStruct {
fn this_is_unused(&self) -> Category {
Category::Used
}
}

mod private {
#[derive(Debug)]
struct UnusedStruct; //~ ERROR struct `UnusedStruct` is never constructed
}

fn main() {
let _c = Category::Used;
}
36 changes: 36 additions & 0 deletions tests/ui/lint/dead-code/issue-41883.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
error: variant `Dead` is never constructed
--> $DIR/issue-41883.rs:4:5
|
LL | enum Category {
| -------- variant in this enum
LL | Dead,
| ^^^^
|
note: the lint level is defined here
--> $DIR/issue-41883.rs:1:9
|
LL | #![deny(dead_code)]
| ^^^^^^^^^

error: trait `UnusedTrait` is never used
--> $DIR/issue-41883.rs:8:7
|
LL | trait UnusedTrait {
| ^^^^^^^^^^^

error: struct `UnusedStruct` is never constructed
--> $DIR/issue-41883.rs:14:8
|
LL | struct UnusedStruct;
| ^^^^^^^^^^^^

error: struct `UnusedStruct` is never constructed
--> $DIR/issue-41883.rs:24:12
|
LL | struct UnusedStruct;
| ^^^^^^^^^^^^
|
= note: `UnusedStruct` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis

error: aborting due to 4 previous errors

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