2 use rustc::hir::def::{DefKind, Res};
3 use rustc::hir::intravisit::*;
5 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
6 use rustc::{declare_lint_pass, declare_tool_lint};
7 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
8 use syntax::source_map::Span;
9 use syntax::symbol::kw;
11 use crate::reexport::*;
12 use crate::utils::{last_path_segment, span_lint, trait_ref_of_method};
14 declare_clippy_lint! {
15 /// **What it does:** Checks for lifetime annotations which can be removed by
16 /// relying on lifetime elision.
18 /// **Why is this bad?** The additional lifetimes make the code look more
19 /// complicated, while there is nothing out of the ordinary going on. Removing
20 /// them leads to more readable code.
22 /// **Known problems:** Potential false negatives: we bail out if the function
23 /// has a `where` clause where lifetimes are mentioned.
27 /// fn in_and_out<'a>(x: &'a u8, y: u8) -> &'a u8 {
31 pub NEEDLESS_LIFETIMES,
33 "using explicit lifetimes for references in function arguments when elision rules \
34 would allow omitting them"
37 declare_clippy_lint! {
38 /// **What it does:** Checks for lifetimes in generics that are never used
41 /// **Why is this bad?** The additional lifetimes make the code look more
42 /// complicated, while there is nothing out of the ordinary going on. Removing
43 /// them leads to more readable code.
45 /// **Known problems:** None.
49 /// fn unused_lifetime<'a>(x: u8) {
53 pub EXTRA_UNUSED_LIFETIMES,
55 "unused lifetimes in function definitions"
58 declare_lint_pass!(Lifetimes => [NEEDLESS_LIFETIMES, EXTRA_UNUSED_LIFETIMES]);
60 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Lifetimes {
61 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
62 if let ItemKind::Fn(ref sig, ref generics, id) = item.kind {
63 check_fn_inner(cx, &sig.decl, Some(id), generics, item.span, true);
67 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
68 if let ImplItemKind::Method(ref sig, id) = item.kind {
69 let report_extra_lifetimes = trait_ref_of_method(cx, item.hir_id).is_none();
76 report_extra_lifetimes,
81 fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
82 if let TraitItemKind::Method(ref sig, ref body) = item.kind {
83 let body = match *body {
84 TraitMethod::Required(_) => None,
85 TraitMethod::Provided(id) => Some(id),
87 check_fn_inner(cx, &sig.decl, body, &item.generics, item.span, true);
92 /// The lifetime of a &-reference.
93 #[derive(PartialEq, Eq, Hash, Debug)]
100 fn check_fn_inner<'a, 'tcx>(
101 cx: &LateContext<'a, 'tcx>,
103 body: Option<BodyId>,
104 generics: &'tcx Generics,
106 report_extra_lifetimes: bool,
108 if in_external_macro(cx.sess(), span) || has_where_lifetimes(cx, &generics.where_clause) {
112 let mut bounds_lts = Vec::new();
113 let types = generics.params.iter().filter(|param| match param.kind {
114 GenericParamKind::Type { .. } => true,
118 for bound in &typ.bounds {
119 let mut visitor = RefVisitor::new(cx);
120 walk_param_bound(&mut visitor, bound);
121 if visitor.lts.iter().any(|lt| matches!(lt, RefLt::Named(_))) {
124 if let GenericBound::Trait(ref trait_ref, _) = *bound {
125 let params = &trait_ref
130 .expect("a path must have at least one segment")
132 if let Some(ref params) = *params {
133 let lifetimes = params.args.iter().filter_map(|arg| match arg {
134 GenericArg::Lifetime(lt) => Some(lt),
137 for bound in lifetimes {
138 if bound.name != LifetimeName::Static && !bound.is_elided() {
141 bounds_lts.push(bound);
147 if could_use_elision(cx, decl, body, &generics.params, bounds_lts) {
152 "explicit lifetimes given in parameter types where they could be elided \
153 (or replaced with `'_` if needed by type declaration)",
156 if report_extra_lifetimes {
157 self::report_extra_lifetimes(cx, decl, generics);
161 fn could_use_elision<'a, 'tcx>(
162 cx: &LateContext<'a, 'tcx>,
164 body: Option<BodyId>,
165 named_generics: &'tcx [GenericParam],
166 bounds_lts: Vec<&'tcx Lifetime>,
168 // There are two scenarios where elision works:
169 // * no output references, all input references have different LT
170 // * output references, exactly one input reference with same LT
171 // All lifetimes must be unnamed, 'static or defined without bounds on the
172 // level of the current item.
175 let allowed_lts = allowed_lts_from(named_generics);
177 // these will collect all the lifetimes for references in arg/return types
178 let mut input_visitor = RefVisitor::new(cx);
179 let mut output_visitor = RefVisitor::new(cx);
181 // extract lifetimes in input argument types
182 for arg in &func.inputs {
183 input_visitor.visit_ty(arg);
185 // extract lifetimes in output type
186 if let Return(ref ty) = func.output {
187 output_visitor.visit_ty(ty);
190 let input_lts = match input_visitor.into_vec() {
191 Some(lts) => lts_from_bounds(lts, bounds_lts.into_iter()),
192 None => return false,
194 let output_lts = match output_visitor.into_vec() {
196 None => return false,
199 if let Some(body_id) = body {
200 let mut checker = BodyLifetimeChecker {
201 lifetimes_used_in_body: false,
203 checker.visit_expr(&cx.tcx.hir().body(body_id).value);
204 if checker.lifetimes_used_in_body {
209 // check for lifetimes from higher scopes
210 for lt in input_lts.iter().chain(output_lts.iter()) {
211 if !allowed_lts.contains(lt) {
216 // no input lifetimes? easy case!
217 if input_lts.is_empty() {
219 } else if output_lts.is_empty() {
220 // no output lifetimes, check distinctness of input lifetimes
222 // only unnamed and static, ok
223 let unnamed_and_static = input_lts.iter().all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static);
224 if unnamed_and_static {
227 // we have no output reference, so we only need all distinct lifetimes
228 input_lts.len() == unique_lifetimes(&input_lts)
230 // we have output references, so we need one input reference,
231 // and all output lifetimes must be the same
232 if unique_lifetimes(&output_lts) > 1 {
235 if input_lts.len() == 1 {
236 match (&input_lts[0], &output_lts[0]) {
237 (&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
238 (&RefLt::Named(_), &RefLt::Unnamed) => true,
239 _ => false, /* already elided, different named lifetimes
240 * or something static going on */
248 fn allowed_lts_from(named_generics: &[GenericParam]) -> FxHashSet<RefLt> {
249 let mut allowed_lts = FxHashSet::default();
250 for par in named_generics.iter() {
251 if let GenericParamKind::Lifetime { .. } = par.kind {
252 if par.bounds.is_empty() {
253 allowed_lts.insert(RefLt::Named(par.name.ident().name));
257 allowed_lts.insert(RefLt::Unnamed);
258 allowed_lts.insert(RefLt::Static);
262 fn lts_from_bounds<'a, T: Iterator<Item = &'a Lifetime>>(mut vec: Vec<RefLt>, bounds_lts: T) -> Vec<RefLt> {
263 for lt in bounds_lts {
264 if lt.name != LifetimeName::Static {
265 vec.push(RefLt::Named(lt.name.ident().name));
272 /// Number of unique lifetimes in the given vector.
274 fn unique_lifetimes(lts: &[RefLt]) -> usize {
275 lts.iter().collect::<FxHashSet<_>>().len()
278 /// A visitor usable for `rustc_front::visit::walk_ty()`.
279 struct RefVisitor<'a, 'tcx> {
280 cx: &'a LateContext<'a, 'tcx>,
285 impl<'v, 't> RefVisitor<'v, 't> {
286 fn new(cx: &'v LateContext<'v, 't>) -> Self {
294 fn record(&mut self, lifetime: &Option<Lifetime>) {
295 if let Some(ref lt) = *lifetime {
296 if lt.name == LifetimeName::Static {
297 self.lts.push(RefLt::Static);
298 } else if let LifetimeName::Param(ParamName::Fresh(_)) = lt.name {
299 // Fresh lifetimes generated should be ignored.
300 } else if lt.is_elided() {
301 self.lts.push(RefLt::Unnamed);
303 self.lts.push(RefLt::Named(lt.name.ident().name));
306 self.lts.push(RefLt::Unnamed);
310 fn into_vec(self) -> Option<Vec<RefLt>> {
318 fn collect_anonymous_lifetimes(&mut self, qpath: &QPath, ty: &Ty) {
319 if let Some(ref last_path_segment) = last_path_segment(qpath).args {
320 if !last_path_segment.parenthesized
321 && !last_path_segment.args.iter().any(|arg| match arg {
322 GenericArg::Lifetime(_) => true,
326 let hir_id = ty.hir_id;
327 match self.cx.tables.qpath_res(qpath, hir_id) {
328 Res::Def(DefKind::TyAlias, def_id) | Res::Def(DefKind::Struct, def_id) => {
329 let generics = self.cx.tcx.generics_of(def_id);
330 for _ in generics.params.as_slice() {
334 Res::Def(DefKind::Trait, def_id) => {
335 let trait_def = self.cx.tcx.trait_def(def_id);
336 for _ in &self.cx.tcx.generics_of(trait_def.def_id).params {
347 impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
348 // for lifetimes as parameters of generics
349 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
350 self.record(&Some(*lifetime));
353 fn visit_ty(&mut self, ty: &'tcx Ty) {
355 TyKind::Rptr(ref lt, _) if lt.is_elided() => {
358 TyKind::Path(ref path) => {
359 self.collect_anonymous_lifetimes(path, ty);
361 TyKind::Def(item, _) => {
362 let map = self.cx.tcx.hir();
363 if let ItemKind::OpaqueTy(ref exist_ty) = map.expect_item(item.id).kind {
364 for bound in &exist_ty.bounds {
365 if let GenericBound::Outlives(_) = *bound {
374 TyKind::TraitObject(ref bounds, ref lt) => {
378 for bound in bounds {
379 self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
387 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
388 NestedVisitorMap::None
392 /// Are any lifetimes mentioned in the `where` clause? If so, we don't try to
393 /// reason about elision.
394 fn has_where_lifetimes<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, where_clause: &'tcx WhereClause) -> bool {
395 for predicate in &where_clause.predicates {
397 WherePredicate::RegionPredicate(..) => return true,
398 WherePredicate::BoundPredicate(ref pred) => {
399 // a predicate like F: Trait or F: for<'a> Trait<'a>
400 let mut visitor = RefVisitor::new(cx);
401 // walk the type F, it may not contain LT refs
402 walk_ty(&mut visitor, &pred.bounded_ty);
403 if !visitor.lts.is_empty() {
406 // if the bounds define new lifetimes, they are fine to occur
407 let allowed_lts = allowed_lts_from(&pred.bound_generic_params);
408 // now walk the bounds
409 for bound in pred.bounds.iter() {
410 walk_param_bound(&mut visitor, bound);
412 // and check that all lifetimes are allowed
413 match visitor.into_vec() {
414 None => return false,
417 if !allowed_lts.contains(<) {
424 WherePredicate::EqPredicate(ref pred) => {
425 let mut visitor = RefVisitor::new(cx);
426 walk_ty(&mut visitor, &pred.lhs_ty);
427 walk_ty(&mut visitor, &pred.rhs_ty);
428 if !visitor.lts.is_empty() {
437 struct LifetimeChecker {
438 map: FxHashMap<Name, Span>,
441 impl<'tcx> Visitor<'tcx> for LifetimeChecker {
442 // for lifetimes as parameters of generics
443 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
444 self.map.remove(&lifetime.name.ident().name);
447 fn visit_generic_param(&mut self, param: &'tcx GenericParam) {
448 // don't actually visit `<'a>` or `<'a: 'b>`
449 // we've already visited the `'a` declarations and
450 // don't want to spuriously remove them
451 // `'b` in `'a: 'b` is useless unless used elsewhere in
452 // a non-lifetime bound
453 if let GenericParamKind::Type { .. } = param.kind {
454 walk_generic_param(self, param)
457 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
458 NestedVisitorMap::None
462 fn report_extra_lifetimes<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, func: &'tcx FnDecl, generics: &'tcx Generics) {
466 .filter_map(|par| match par.kind {
467 GenericParamKind::Lifetime { .. } => Some((par.name.ident().name, par.span)),
471 let mut checker = LifetimeChecker { map: hs };
473 walk_generics(&mut checker, generics);
474 walk_fn_decl(&mut checker, func);
476 for &v in checker.map.values() {
479 EXTRA_UNUSED_LIFETIMES,
481 "this lifetime isn't used in the function definition",
486 struct BodyLifetimeChecker {
487 lifetimes_used_in_body: bool,
490 impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
491 // for lifetimes as parameters of generics
492 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
493 if lifetime.name.ident().name != kw::Invalid && lifetime.name.ident().name != kw::StaticLifetime {
494 self.lifetimes_used_in_body = true;
498 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
499 NestedVisitorMap::None