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needless-lifetime / nested elision sites / PR remarks
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@tnielens
tnielens committed Sep 8, 2020
1 parent 390a13b commit a60e5de
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Showing 4 changed files with 102 additions and 152 deletions.
222 changes: 71 additions & 151 deletions clippy_lints/src/lifetimes.rs
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Original file line number Diff line number Diff line change
@@ -1,23 +1,22 @@
use crate::utils::paths;
use crate::utils::{get_trait_def_id, in_macro, span_lint, trait_ref_of_method};
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir::def::{DefKind, Res};
use rustc_hir::intravisit::{
walk_fn_decl, walk_generic_param, walk_generics, walk_param_bound, walk_trait_ref, walk_ty, NestedVisitorMap,
Visitor,
walk_fn_decl, walk_generic_param, walk_generics, walk_item, walk_param_bound, walk_poly_trait_ref, walk_ty,
NestedVisitorMap, Visitor,
};
use rustc_hir::FnRetTy::Return;
use rustc_hir::{
BodyId, FnDecl, GenericArg, GenericBound, GenericParam, GenericParamKind, Generics, ImplItem, ImplItemKind, Item,
ItemKind, Lifetime, LifetimeName, ParamName, QPath, TraitBoundModifier, TraitFn, TraitItem, TraitItemKind,
TraitRef, Ty, TyKind, WhereClause, WherePredicate,
BareFnTy, BodyId, FnDecl, GenericArg, GenericBound, GenericParam, GenericParamKind, Generics, ImplItem,
ImplItemKind, Item, ItemKind, Lifetime, LifetimeName, ParamName, PolyTraitRef, TraitBoundModifier, TraitFn,
TraitItem, TraitItemKind, Ty, TyKind, WhereClause, WherePredicate,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::hir::map::Map;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use rustc_span::symbol::{kw, Symbol};

use crate::utils::paths;
use crate::utils::{get_trait_def_id, in_macro, last_path_segment, span_lint, trait_ref_of_method};
use std::iter::FromIterator;

declare_clippy_lint! {
/// **What it does:** Checks for lifetime annotations which can be removed by
Expand Down Expand Up @@ -110,7 +109,7 @@ impl<'tcx> LateLintPass<'tcx> for Lifetimes {
}

/// The lifetime of a &-reference.
#[derive(PartialEq, Eq, Hash, Debug)]
#[derive(PartialEq, Eq, Hash, Debug, Clone)]
enum RefLt {
Unnamed,
Static,
Expand All @@ -129,15 +128,6 @@ fn check_fn_inner<'tcx>(
return;
}

// fn pointers and closure trait bounds are also lifetime elision sites. This lint does not
// support nested elision sites in a fn item.
if FnPointerOrClosureTraitBoundFinder::find_in_generics(cx, generics)
|| FnPointerOrClosureTraitBoundFinder::find_in_fn_decl(cx, decl)
{
return;
}

let mut bounds_lts = Vec::new();
let types = generics
.params
.iter()
Expand Down Expand Up @@ -166,13 +156,12 @@ fn check_fn_inner<'tcx>(
if bound.name != LifetimeName::Static && !bound.is_elided() {
return;
}
bounds_lts.push(bound);
}
}
}
}
}
if could_use_elision(cx, decl, body, &generics.params, bounds_lts) {
if could_use_elision(cx, decl, body, &generics.params) {
span_lint(
cx,
NEEDLESS_LIFETIMES,
Expand All @@ -191,7 +180,6 @@ fn could_use_elision<'tcx>(
func: &'tcx FnDecl<'_>,
body: Option<BodyId>,
named_generics: &'tcx [GenericParam<'_>],
bounds_lts: Vec<&'tcx Lifetime>,
) -> bool {
// There are two scenarios where elision works:
// * no output references, all input references have different LT
Expand All @@ -214,15 +202,31 @@ fn could_use_elision<'tcx>(
if let Return(ref ty) = func.output {
output_visitor.visit_ty(ty);
}
for lt in named_generics {
input_visitor.visit_generic_param(lt)
}

let input_lts = match input_visitor.into_vec() {
Some(lts) => lts_from_bounds(lts, bounds_lts.into_iter()),
None => return false,
};
let output_lts = match output_visitor.into_vec() {
Some(val) => val,
None => return false,
};
if input_visitor.abort() || output_visitor.abort() {
return false;
}

if allowed_lts
.intersection(&FxHashSet::from_iter(
input_visitor
.nested_elision_site_lts
.iter()
.chain(output_visitor.nested_elision_site_lts.iter())
.cloned()
.filter(|v| matches!(v, RefLt::Named(_))),
))
.next()
.is_some()
{
return false;
}

let input_lts = input_visitor.lts;
let output_lts = output_visitor.lts;

if let Some(body_id) = body {
let mut checker = BodyLifetimeChecker {
Expand Down Expand Up @@ -287,35 +291,29 @@ fn allowed_lts_from(named_generics: &[GenericParam<'_>]) -> FxHashSet<RefLt> {
allowed_lts
}

fn lts_from_bounds<'a, T: Iterator<Item = &'a Lifetime>>(mut vec: Vec<RefLt>, bounds_lts: T) -> Vec<RefLt> {
for lt in bounds_lts {
if lt.name != LifetimeName::Static {
vec.push(RefLt::Named(lt.name.ident().name));
}
}

vec
}

/// Number of unique lifetimes in the given vector.
#[must_use]
fn unique_lifetimes(lts: &[RefLt]) -> usize {
lts.iter().collect::<FxHashSet<_>>().len()
}

const CLOSURE_TRAIT_BOUNDS: [&[&str]; 3] = [&paths::FN, &paths::FN_MUT, &paths::FN_ONCE];

/// A visitor usable for `rustc_front::visit::walk_ty()`.
struct RefVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
lts: Vec<RefLt>,
abort: bool,
nested_elision_site_lts: Vec<RefLt>,
unelided_trait_object_lifetime: bool,
}

impl<'a, 'tcx> RefVisitor<'a, 'tcx> {
fn new(cx: &'a LateContext<'tcx>) -> Self {
Self {
cx,
lts: Vec::new(),
abort: false,
nested_elision_site_lts: Vec::new(),
unelided_trait_object_lifetime: false,
}
}

Expand All @@ -335,40 +333,16 @@ impl<'a, 'tcx> RefVisitor<'a, 'tcx> {
}
}

fn into_vec(self) -> Option<Vec<RefLt>> {
if self.abort {
None
} else {
Some(self.lts)
}
fn all_lts(&self) -> Vec<RefLt> {
self.lts
.iter()
.chain(self.nested_elision_site_lts.iter())
.cloned()
.collect::<Vec<_>>()
}

fn collect_anonymous_lifetimes(&mut self, qpath: &QPath<'_>, ty: &Ty<'_>) {
if let Some(ref last_path_segment) = last_path_segment(qpath).args {
if !last_path_segment.parenthesized
&& !last_path_segment
.args
.iter()
.any(|arg| matches!(arg, GenericArg::Lifetime(_)))
{
let hir_id = ty.hir_id;
match self.cx.qpath_res(qpath, hir_id) {
Res::Def(DefKind::TyAlias | DefKind::Struct, def_id) => {
let generics = self.cx.tcx.generics_of(def_id);
for _ in generics.params.as_slice() {
self.record(&None);
}
},
Res::Def(DefKind::Trait, def_id) => {
let trait_def = self.cx.tcx.trait_def(def_id);
for _ in &self.cx.tcx.generics_of(trait_def.def_id).params {
self.record(&None);
}
},
_ => (),
}
}
}
fn abort(&self) -> bool {
self.unelided_trait_object_lifetime
}
}

Expand All @@ -380,30 +354,36 @@ impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
self.record(&Some(*lifetime));
}

fn visit_poly_trait_ref(&mut self, poly_tref: &'tcx PolyTraitRef<'tcx>, tbm: TraitBoundModifier) {
let trait_ref = &poly_tref.trait_ref;
if CLOSURE_TRAIT_BOUNDS
.iter()
.any(|trait_path| trait_ref.trait_def_id() == get_trait_def_id(self.cx, trait_path))
{
let mut sub_visitor = RefVisitor::new(self.cx);
sub_visitor.visit_trait_ref(trait_ref);
self.nested_elision_site_lts.append(&mut sub_visitor.all_lts());
} else {
walk_poly_trait_ref(self, poly_tref, tbm);
}
}

fn visit_ty(&mut self, ty: &'tcx Ty<'_>) {
match ty.kind {
TyKind::Rptr(ref lt, _) if lt.is_elided() => {
self.record(&None);
},
TyKind::Path(ref path) => {
self.collect_anonymous_lifetimes(path, ty);
},
TyKind::OpaqueDef(item, _) => {
let map = self.cx.tcx.hir();
if let ItemKind::OpaqueTy(ref exist_ty) = map.expect_item(item.id).kind {
for bound in exist_ty.bounds {
if let GenericBound::Outlives(_) = *bound {
self.record(&None);
}
}
} else {
unreachable!()
}
let item = map.expect_item(item.id);
walk_item(self, item);
walk_ty(self, ty);
},
TyKind::BareFn(&BareFnTy { decl, .. }) => {
let mut sub_visitor = RefVisitor::new(self.cx);
sub_visitor.visit_fn_decl(decl);
self.nested_elision_site_lts.append(&mut sub_visitor.all_lts());
},
TyKind::TraitObject(bounds, ref lt) => {
if !lt.is_elided() {
self.abort = true;
self.unelided_trait_object_lifetime = true;
}
for bound in bounds {
self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
Expand Down Expand Up @@ -440,16 +420,7 @@ fn has_where_lifetimes<'tcx>(cx: &LateContext<'tcx>, where_clause: &'tcx WhereCl
walk_param_bound(&mut visitor, bound);
}
// and check that all lifetimes are allowed
match visitor.into_vec() {
None => return false,
Some(lts) => {
for lt in lts {
if !allowed_lts.contains(&lt) {
return true;
}
}
},
}
return visitor.all_lts().iter().any(|it| !allowed_lts.contains(it));
},
WherePredicate::EqPredicate(ref pred) => {
let mut visitor = RefVisitor::new(cx);
Expand Down Expand Up @@ -533,54 +504,3 @@ impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
NestedVisitorMap::None
}
}

const CLOSURE_TRAIT_BOUNDS: [&[&str]; 3] = [&paths::FN, &paths::FN_MUT, &paths::FN_ONCE];

struct FnPointerOrClosureTraitBoundFinder<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
found: bool,
}

impl<'a, 'tcx> FnPointerOrClosureTraitBoundFinder<'a, 'tcx> {
fn find_in_generics(cx: &'a LateContext<'tcx>, generics: &'tcx Generics<'tcx>) -> bool {
let mut finder = Self { cx, found: false };
finder.visit_generics(generics);
finder.found
}

fn find_in_fn_decl(cx: &'a LateContext<'tcx>, generics: &'tcx FnDecl<'tcx>) -> bool {
let mut finder = Self { cx, found: false };
finder.visit_fn_decl(generics);
finder.found
}
}

impl<'a, 'tcx> Visitor<'tcx> for FnPointerOrClosureTraitBoundFinder<'a, 'tcx> {
type Map = Map<'tcx>;
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}

fn visit_trait_ref(&mut self, tref: &'tcx TraitRef<'tcx>) {
if CLOSURE_TRAIT_BOUNDS
.iter()
.any(|trait_path| tref.trait_def_id() == get_trait_def_id(self.cx, trait_path))
{
self.found = true;
}
walk_trait_ref(self, tref);
}

fn visit_ty(&mut self, ty: &'tcx Ty<'tcx>) {
match ty.kind {
TyKind::BareFn(..) => self.found = true,
TyKind::OpaqueDef(item_id, _) => {
let map = self.cx.tcx.hir();
let item = map.expect_item(item_id.id);
self.visit_item(item);
},
_ => (),
}
walk_ty(self, ty);
}
}
10 changes: 10 additions & 0 deletions tests/ui/crashes/ice-2774.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/ice-2774.rs:17:1
|
LL | pub fn add_barfoos_to_foos<'a>(bars: &HashSet<&'a Bar>) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `-D clippy::needless-lifetimes` implied by `-D warnings`

error: aborting due to previous error

14 changes: 14 additions & 0 deletions tests/ui/crashes/needless_lifetimes_impl_trait.stderr
View file
Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes_impl_trait.rs:17:5
|
LL | fn baz<'a>(&'a self) -> impl Foo + 'a {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: the lint level is defined here
--> $DIR/needless_lifetimes_impl_trait.rs:3:9
|
LL | #![deny(clippy::needless_lifetimes)]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

8 changes: 7 additions & 1 deletion tests/ui/needless_lifetimes.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,12 @@ error: explicit lifetimes given in parameter types where they could be elided (o
LL | fn lifetime_param_2<'a, 'b>(_x: Ref<'a>, _y: &'b u8) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:86:1
|
LL | fn fn_bound_2<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:120:5
|
Expand Down Expand Up @@ -96,5 +102,5 @@ error: explicit lifetimes given in parameter types where they could be elided (o
LL | fn needless_lt<'a>(_x: &'a u8) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 16 previous errors
error: aborting due to 17 previous errors

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