516 lines
17 KiB
Rust
516 lines
17 KiB
Rust
use clippy_utils::diagnostics::span_lint;
|
|
use clippy_utils::{in_macro, trait_ref_of_method};
|
|
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
|
|
use rustc_hir::intravisit::{
|
|
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::{
|
|
BareFnTy, BodyId, FnDecl, GenericArg, GenericBound, GenericParam, GenericParamKind, Generics, ImplItem,
|
|
ImplItemKind, Item, ItemKind, LangItem, 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};
|
|
|
|
declare_clippy_lint! {
|
|
/// **What it does:** Checks for lifetime annotations which can be removed by
|
|
/// relying on lifetime elision.
|
|
///
|
|
/// **Why is this bad?** The additional lifetimes make the code look more
|
|
/// complicated, while there is nothing out of the ordinary going on. Removing
|
|
/// them leads to more readable code.
|
|
///
|
|
/// **Known problems:**
|
|
/// - We bail out if the function has a `where` clause where lifetimes
|
|
/// are mentioned due to potenial false positives.
|
|
/// - Lifetime bounds such as `impl Foo + 'a` and `T: 'a` must be elided with the
|
|
/// placeholder notation `'_` because the fully elided notation leaves the type bound to `'static`.
|
|
///
|
|
/// **Example:**
|
|
/// ```rust
|
|
/// // Bad: unnecessary lifetime annotations
|
|
/// fn in_and_out<'a>(x: &'a u8, y: u8) -> &'a u8 {
|
|
/// x
|
|
/// }
|
|
///
|
|
/// // Good
|
|
/// fn elided(x: &u8, y: u8) -> &u8 {
|
|
/// x
|
|
/// }
|
|
/// ```
|
|
pub NEEDLESS_LIFETIMES,
|
|
complexity,
|
|
"using explicit lifetimes for references in function arguments when elision rules \
|
|
would allow omitting them"
|
|
}
|
|
|
|
declare_clippy_lint! {
|
|
/// **What it does:** Checks for lifetimes in generics that are never used
|
|
/// anywhere else.
|
|
///
|
|
/// **Why is this bad?** The additional lifetimes make the code look more
|
|
/// complicated, while there is nothing out of the ordinary going on. Removing
|
|
/// them leads to more readable code.
|
|
///
|
|
/// **Known problems:** None.
|
|
///
|
|
/// **Example:**
|
|
/// ```rust
|
|
/// // Bad: unnecessary lifetimes
|
|
/// fn unused_lifetime<'a>(x: u8) {
|
|
/// // ..
|
|
/// }
|
|
///
|
|
/// // Good
|
|
/// fn no_lifetime(x: u8) {
|
|
/// // ...
|
|
/// }
|
|
/// ```
|
|
pub EXTRA_UNUSED_LIFETIMES,
|
|
complexity,
|
|
"unused lifetimes in function definitions"
|
|
}
|
|
|
|
declare_lint_pass!(Lifetimes => [NEEDLESS_LIFETIMES, EXTRA_UNUSED_LIFETIMES]);
|
|
|
|
impl<'tcx> LateLintPass<'tcx> for Lifetimes {
|
|
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
|
|
if let ItemKind::Fn(ref sig, ref generics, id) = item.kind {
|
|
check_fn_inner(cx, sig.decl, Some(id), generics, item.span, true);
|
|
}
|
|
}
|
|
|
|
fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
|
|
if let ImplItemKind::Fn(ref sig, id) = item.kind {
|
|
let report_extra_lifetimes = trait_ref_of_method(cx, item.hir_id()).is_none();
|
|
check_fn_inner(
|
|
cx,
|
|
sig.decl,
|
|
Some(id),
|
|
&item.generics,
|
|
item.span,
|
|
report_extra_lifetimes,
|
|
);
|
|
}
|
|
}
|
|
|
|
fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
|
|
if let TraitItemKind::Fn(ref sig, ref body) = item.kind {
|
|
let body = match *body {
|
|
TraitFn::Required(_) => None,
|
|
TraitFn::Provided(id) => Some(id),
|
|
};
|
|
check_fn_inner(cx, sig.decl, body, &item.generics, item.span, true);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// The lifetime of a &-reference.
|
|
#[derive(PartialEq, Eq, Hash, Debug, Clone)]
|
|
enum RefLt {
|
|
Unnamed,
|
|
Static,
|
|
Named(Symbol),
|
|
}
|
|
|
|
fn check_fn_inner<'tcx>(
|
|
cx: &LateContext<'tcx>,
|
|
decl: &'tcx FnDecl<'_>,
|
|
body: Option<BodyId>,
|
|
generics: &'tcx Generics<'_>,
|
|
span: Span,
|
|
report_extra_lifetimes: bool,
|
|
) {
|
|
if in_macro(span) || has_where_lifetimes(cx, &generics.where_clause) {
|
|
return;
|
|
}
|
|
|
|
let types = generics
|
|
.params
|
|
.iter()
|
|
.filter(|param| matches!(param.kind, GenericParamKind::Type { .. }));
|
|
for typ in types {
|
|
for bound in typ.bounds {
|
|
let mut visitor = RefVisitor::new(cx);
|
|
walk_param_bound(&mut visitor, bound);
|
|
if visitor.lts.iter().any(|lt| matches!(lt, RefLt::Named(_))) {
|
|
return;
|
|
}
|
|
if let GenericBound::Trait(ref trait_ref, _) = *bound {
|
|
let params = &trait_ref
|
|
.trait_ref
|
|
.path
|
|
.segments
|
|
.last()
|
|
.expect("a path must have at least one segment")
|
|
.args;
|
|
if let Some(params) = *params {
|
|
let lifetimes = params.args.iter().filter_map(|arg| match arg {
|
|
GenericArg::Lifetime(lt) => Some(lt),
|
|
_ => None,
|
|
});
|
|
for bound in lifetimes {
|
|
if bound.name != LifetimeName::Static && !bound.is_elided() {
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
if could_use_elision(cx, decl, body, generics.params) {
|
|
span_lint(
|
|
cx,
|
|
NEEDLESS_LIFETIMES,
|
|
span.with_hi(decl.output.span().hi()),
|
|
"explicit lifetimes given in parameter types where they could be elided \
|
|
(or replaced with `'_` if needed by type declaration)",
|
|
);
|
|
}
|
|
if report_extra_lifetimes {
|
|
self::report_extra_lifetimes(cx, decl, generics);
|
|
}
|
|
}
|
|
|
|
fn could_use_elision<'tcx>(
|
|
cx: &LateContext<'tcx>,
|
|
func: &'tcx FnDecl<'_>,
|
|
body: Option<BodyId>,
|
|
named_generics: &'tcx [GenericParam<'_>],
|
|
) -> bool {
|
|
// There are two scenarios where elision works:
|
|
// * no output references, all input references have different LT
|
|
// * output references, exactly one input reference with same LT
|
|
// All lifetimes must be unnamed, 'static or defined without bounds on the
|
|
// level of the current item.
|
|
|
|
// check named LTs
|
|
let allowed_lts = allowed_lts_from(named_generics);
|
|
|
|
// these will collect all the lifetimes for references in arg/return types
|
|
let mut input_visitor = RefVisitor::new(cx);
|
|
let mut output_visitor = RefVisitor::new(cx);
|
|
|
|
// extract lifetimes in input argument types
|
|
for arg in func.inputs {
|
|
input_visitor.visit_ty(arg);
|
|
}
|
|
// extract lifetimes in output type
|
|
if let Return(ty) = func.output {
|
|
output_visitor.visit_ty(ty);
|
|
}
|
|
for lt in named_generics {
|
|
input_visitor.visit_generic_param(lt);
|
|
}
|
|
|
|
if input_visitor.abort() || output_visitor.abort() {
|
|
return false;
|
|
}
|
|
|
|
if allowed_lts
|
|
.intersection(
|
|
&input_visitor
|
|
.nested_elision_site_lts
|
|
.iter()
|
|
.chain(output_visitor.nested_elision_site_lts.iter())
|
|
.cloned()
|
|
.filter(|v| matches!(v, RefLt::Named(_)))
|
|
.collect(),
|
|
)
|
|
.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 {
|
|
lifetimes_used_in_body: false,
|
|
};
|
|
checker.visit_expr(&cx.tcx.hir().body(body_id).value);
|
|
if checker.lifetimes_used_in_body {
|
|
return false;
|
|
}
|
|
}
|
|
|
|
// check for lifetimes from higher scopes
|
|
for lt in input_lts.iter().chain(output_lts.iter()) {
|
|
if !allowed_lts.contains(lt) {
|
|
return false;
|
|
}
|
|
}
|
|
|
|
// no input lifetimes? easy case!
|
|
if input_lts.is_empty() {
|
|
false
|
|
} else if output_lts.is_empty() {
|
|
// no output lifetimes, check distinctness of input lifetimes
|
|
|
|
// only unnamed and static, ok
|
|
let unnamed_and_static = input_lts.iter().all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static);
|
|
if unnamed_and_static {
|
|
return false;
|
|
}
|
|
// we have no output reference, so we only need all distinct lifetimes
|
|
input_lts.len() == unique_lifetimes(&input_lts)
|
|
} else {
|
|
// we have output references, so we need one input reference,
|
|
// and all output lifetimes must be the same
|
|
if unique_lifetimes(&output_lts) > 1 {
|
|
return false;
|
|
}
|
|
if input_lts.len() == 1 {
|
|
match (&input_lts[0], &output_lts[0]) {
|
|
(&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
|
|
(&RefLt::Named(_), &RefLt::Unnamed) => true,
|
|
_ => false, /* already elided, different named lifetimes
|
|
* or something static going on */
|
|
}
|
|
} else {
|
|
false
|
|
}
|
|
}
|
|
}
|
|
|
|
fn allowed_lts_from(named_generics: &[GenericParam<'_>]) -> FxHashSet<RefLt> {
|
|
let mut allowed_lts = FxHashSet::default();
|
|
for par in named_generics.iter() {
|
|
if let GenericParamKind::Lifetime { .. } = par.kind {
|
|
if par.bounds.is_empty() {
|
|
allowed_lts.insert(RefLt::Named(par.name.ident().name));
|
|
}
|
|
}
|
|
}
|
|
allowed_lts.insert(RefLt::Unnamed);
|
|
allowed_lts.insert(RefLt::Static);
|
|
allowed_lts
|
|
}
|
|
|
|
/// 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: [LangItem; 3] = [LangItem::Fn, LangItem::FnMut, LangItem::FnOnce];
|
|
|
|
/// A visitor usable for `rustc_front::visit::walk_ty()`.
|
|
struct RefVisitor<'a, 'tcx> {
|
|
cx: &'a LateContext<'tcx>,
|
|
lts: Vec<RefLt>,
|
|
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(),
|
|
nested_elision_site_lts: Vec::new(),
|
|
unelided_trait_object_lifetime: false,
|
|
}
|
|
}
|
|
|
|
fn record(&mut self, lifetime: &Option<Lifetime>) {
|
|
if let Some(ref lt) = *lifetime {
|
|
if lt.name == LifetimeName::Static {
|
|
self.lts.push(RefLt::Static);
|
|
} else if let LifetimeName::Param(ParamName::Fresh(_)) = lt.name {
|
|
// Fresh lifetimes generated should be ignored.
|
|
} else if lt.is_elided() {
|
|
self.lts.push(RefLt::Unnamed);
|
|
} else {
|
|
self.lts.push(RefLt::Named(lt.name.ident().name));
|
|
}
|
|
} else {
|
|
self.lts.push(RefLt::Unnamed);
|
|
}
|
|
}
|
|
|
|
fn all_lts(&self) -> Vec<RefLt> {
|
|
self.lts
|
|
.iter()
|
|
.chain(self.nested_elision_site_lts.iter())
|
|
.cloned()
|
|
.collect::<Vec<_>>()
|
|
}
|
|
|
|
fn abort(&self) -> bool {
|
|
self.unelided_trait_object_lifetime
|
|
}
|
|
}
|
|
|
|
impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
|
|
type Map = Map<'tcx>;
|
|
|
|
// for lifetimes as parameters of generics
|
|
fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
|
|
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(|&item| {
|
|
self.cx
|
|
.tcx
|
|
.lang_items()
|
|
.require(item)
|
|
.map_or(false, |id| Some(id) == trait_ref.trait_def_id())
|
|
}) {
|
|
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::OpaqueDef(item, _) => {
|
|
let map = self.cx.tcx.hir();
|
|
let item = map.item(item);
|
|
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());
|
|
return;
|
|
},
|
|
TyKind::TraitObject(bounds, ref lt, _) => {
|
|
if !lt.is_elided() {
|
|
self.unelided_trait_object_lifetime = true;
|
|
}
|
|
for bound in bounds {
|
|
self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
|
|
}
|
|
return;
|
|
},
|
|
_ => (),
|
|
}
|
|
walk_ty(self, ty);
|
|
}
|
|
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
|
|
NestedVisitorMap::None
|
|
}
|
|
}
|
|
|
|
/// Are any lifetimes mentioned in the `where` clause? If so, we don't try to
|
|
/// reason about elision.
|
|
fn has_where_lifetimes<'tcx>(cx: &LateContext<'tcx>, where_clause: &'tcx WhereClause<'_>) -> bool {
|
|
for predicate in where_clause.predicates {
|
|
match *predicate {
|
|
WherePredicate::RegionPredicate(..) => return true,
|
|
WherePredicate::BoundPredicate(ref pred) => {
|
|
// a predicate like F: Trait or F: for<'a> Trait<'a>
|
|
let mut visitor = RefVisitor::new(cx);
|
|
// walk the type F, it may not contain LT refs
|
|
walk_ty(&mut visitor, pred.bounded_ty);
|
|
if !visitor.all_lts().is_empty() {
|
|
return true;
|
|
}
|
|
// if the bounds define new lifetimes, they are fine to occur
|
|
let allowed_lts = allowed_lts_from(pred.bound_generic_params);
|
|
// now walk the bounds
|
|
for bound in pred.bounds.iter() {
|
|
walk_param_bound(&mut visitor, bound);
|
|
}
|
|
// and check that all lifetimes are allowed
|
|
if visitor.all_lts().iter().any(|it| !allowed_lts.contains(it)) {
|
|
return true;
|
|
}
|
|
},
|
|
WherePredicate::EqPredicate(ref pred) => {
|
|
let mut visitor = RefVisitor::new(cx);
|
|
walk_ty(&mut visitor, pred.lhs_ty);
|
|
walk_ty(&mut visitor, pred.rhs_ty);
|
|
if !visitor.lts.is_empty() {
|
|
return true;
|
|
}
|
|
},
|
|
}
|
|
}
|
|
false
|
|
}
|
|
|
|
struct LifetimeChecker {
|
|
map: FxHashMap<Symbol, Span>,
|
|
}
|
|
|
|
impl<'tcx> Visitor<'tcx> for LifetimeChecker {
|
|
type Map = Map<'tcx>;
|
|
|
|
// for lifetimes as parameters of generics
|
|
fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
|
|
self.map.remove(&lifetime.name.ident().name);
|
|
}
|
|
|
|
fn visit_generic_param(&mut self, param: &'tcx GenericParam<'_>) {
|
|
// don't actually visit `<'a>` or `<'a: 'b>`
|
|
// we've already visited the `'a` declarations and
|
|
// don't want to spuriously remove them
|
|
// `'b` in `'a: 'b` is useless unless used elsewhere in
|
|
// a non-lifetime bound
|
|
if let GenericParamKind::Type { .. } = param.kind {
|
|
walk_generic_param(self, param);
|
|
}
|
|
}
|
|
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
|
|
NestedVisitorMap::None
|
|
}
|
|
}
|
|
|
|
fn report_extra_lifetimes<'tcx>(cx: &LateContext<'tcx>, func: &'tcx FnDecl<'_>, generics: &'tcx Generics<'_>) {
|
|
let hs = generics
|
|
.params
|
|
.iter()
|
|
.filter_map(|par| match par.kind {
|
|
GenericParamKind::Lifetime { .. } => Some((par.name.ident().name, par.span)),
|
|
_ => None,
|
|
})
|
|
.collect();
|
|
let mut checker = LifetimeChecker { map: hs };
|
|
|
|
walk_generics(&mut checker, generics);
|
|
walk_fn_decl(&mut checker, func);
|
|
|
|
for &v in checker.map.values() {
|
|
span_lint(
|
|
cx,
|
|
EXTRA_UNUSED_LIFETIMES,
|
|
v,
|
|
"this lifetime isn't used in the function definition",
|
|
);
|
|
}
|
|
}
|
|
|
|
struct BodyLifetimeChecker {
|
|
lifetimes_used_in_body: bool,
|
|
}
|
|
|
|
impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
|
|
type Map = Map<'tcx>;
|
|
|
|
// for lifetimes as parameters of generics
|
|
fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
|
|
if lifetime.name.ident().name != kw::Empty && lifetime.name.ident().name != kw::StaticLifetime {
|
|
self.lifetimes_used_in_body = true;
|
|
}
|
|
}
|
|
|
|
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
|
|
NestedVisitorMap::None
|
|
}
|
|
}
|