1 use crate::reexport::*;
3 use rustc::hir::def::Def;
5 use rustc::hir::intravisit::*;
6 use std::collections::{HashMap, HashSet};
7 use syntax::codemap::Span;
8 use crate::utils::{in_external_macro, last_path_segment, span_lint};
9 use syntax::symbol::keywords;
11 /// **What it does:** Checks for lifetime annotations which can be removed by
12 /// relying on lifetime elision.
14 /// **Why is this bad?** The additional lifetimes make the code look more
15 /// complicated, while there is nothing out of the ordinary going on. Removing
16 /// them leads to more readable code.
18 /// **Known problems:** Potential false negatives: we bail out if the function
19 /// has a `where` clause where lifetimes are mentioned.
23 /// fn in_and_out<'a>(x: &'a u8, y: u8) -> &'a u8 { x }
25 declare_clippy_lint! {
26 pub NEEDLESS_LIFETIMES,
28 "using explicit lifetimes for references in function arguments when elision rules \
29 would allow omitting them"
32 /// **What it does:** Checks for lifetimes in generics that are never used
35 /// **Why is this bad?** The additional lifetimes make the code look more
36 /// complicated, while there is nothing out of the ordinary going on. Removing
37 /// them leads to more readable code.
39 /// **Known problems:** None.
43 /// fn unused_lifetime<'a>(x: u8) { .. }
45 declare_clippy_lint! {
46 pub EXTRA_UNUSED_LIFETIMES,
48 "unused lifetimes in function definitions"
51 #[derive(Copy, Clone)]
52 pub struct LifetimePass;
54 impl LintPass for LifetimePass {
55 fn get_lints(&self) -> LintArray {
56 lint_array!(NEEDLESS_LIFETIMES, EXTRA_UNUSED_LIFETIMES)
60 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LifetimePass {
61 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
62 if let ItemFn(ref decl, _, ref generics, id) = item.node {
63 check_fn_inner(cx, decl, Some(id), generics, item.span);
67 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
68 if let ImplItemKind::Method(ref sig, id) = item.node {
69 check_fn_inner(cx, &sig.decl, Some(id), &item.generics, item.span);
73 fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
74 if let TraitItemKind::Method(ref sig, ref body) = item.node {
75 let body = match *body {
76 TraitMethod::Required(_) => None,
77 TraitMethod::Provided(id) => Some(id),
79 check_fn_inner(cx, &sig.decl, body, &item.generics, item.span);
84 /// The lifetime of a &-reference.
85 #[derive(PartialEq, Eq, Hash, Debug)]
92 fn check_fn_inner<'a, 'tcx>(
93 cx: &LateContext<'a, 'tcx>,
96 generics: &'tcx Generics,
99 if in_external_macro(cx, span) || has_where_lifetimes(cx, &generics.where_clause) {
103 let mut bounds_lts = Vec::new();
104 generics.params.iter().for_each(|param| match param.kind {
105 GenericParamKind::Lifetime { .. } => {},
106 GenericParamKind::Type { .. } => {
107 for bound in ¶m.bounds {
108 let mut visitor = RefVisitor::new(cx);
109 walk_param_bound(&mut visitor, bound);
110 if visitor.lts.iter().any(|lt| matches!(lt, RefLt::Named(_))) {
113 if let GenericBound::Trait(ref trait_ref, _) = *bound {
114 let params = &trait_ref
119 .expect("a path must have at least one segment")
121 if let Some(ref params) = *params {
122 for bound in ¶ms.lifetimes {
123 if bound.name.name() != "'static" && !bound.is_elided() {
126 bounds_lts.push(bound);
133 if could_use_elision(cx, decl, body, &generics.params, bounds_lts) {
138 "explicit lifetimes given in parameter types where they could be elided",
141 report_extra_lifetimes(cx, decl, generics);
144 fn could_use_elision<'a, 'tcx: 'a>(
145 cx: &LateContext<'a, 'tcx>,
147 body: Option<BodyId>,
148 named_generics: &'tcx [GenericParam],
149 bounds_lts: Vec<&'tcx Lifetime>,
151 // There are two scenarios where elision works:
152 // * no output references, all input references have different LT
153 // * output references, exactly one input reference with same LT
154 // All lifetimes must be unnamed, 'static or defined without bounds on the
155 // level of the current item.
158 let allowed_lts = allowed_lts_from(named_generics);
160 // these will collect all the lifetimes for references in arg/return types
161 let mut input_visitor = RefVisitor::new(cx);
162 let mut output_visitor = RefVisitor::new(cx);
164 // extract lifetimes in input argument types
165 for arg in &func.inputs {
166 input_visitor.visit_ty(arg);
168 // extract lifetimes in output type
169 if let Return(ref ty) = func.output {
170 output_visitor.visit_ty(ty);
173 let input_lts = match input_visitor.into_vec() {
174 Some(lts) => lts_from_bounds(lts, bounds_lts.into_iter()),
175 None => return false,
177 let output_lts = match output_visitor.into_vec() {
179 None => return false,
182 if let Some(body_id) = body {
183 let mut checker = BodyLifetimeChecker {
184 lifetimes_used_in_body: false,
186 checker.visit_expr(&cx.tcx.hir.body(body_id).value);
187 if checker.lifetimes_used_in_body {
192 // check for lifetimes from higher scopes
193 for lt in input_lts.iter().chain(output_lts.iter()) {
194 if !allowed_lts.contains(lt) {
199 // no input lifetimes? easy case!
200 if input_lts.is_empty() {
202 } else if output_lts.is_empty() {
203 // no output lifetimes, check distinctness of input lifetimes
205 // only unnamed and static, ok
206 let unnamed_and_static = input_lts
208 .all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static);
209 if unnamed_and_static {
212 // we have no output reference, so we only need all distinct lifetimes
213 input_lts.len() == unique_lifetimes(&input_lts)
215 // we have output references, so we need one input reference,
216 // and all output lifetimes must be the same
217 if unique_lifetimes(&output_lts) > 1 {
220 if input_lts.len() == 1 {
221 match (&input_lts[0], &output_lts[0]) {
222 (&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
223 (&RefLt::Named(_), &RefLt::Unnamed) => true,
224 _ => false, /* already elided, different named lifetimes
225 * or something static going on */
233 fn allowed_lts_from(named_generics: &[GenericParam]) -> HashSet<RefLt> {
234 let mut allowed_lts = HashSet::new();
235 for par in named_generics.iter() {
236 if let GenericParam::Lifetime(ref lt) = *par {
237 if lt.bounds.is_empty() {
238 allowed_lts.insert(RefLt::Named(lt.lifetime.name.name()));
242 allowed_lts.insert(RefLt::Unnamed);
243 allowed_lts.insert(RefLt::Static);
247 fn lts_from_bounds<'a, T: Iterator<Item = &'a Lifetime>>(mut vec: Vec<RefLt>, bounds_lts: T) -> Vec<RefLt> {
248 for lt in bounds_lts {
249 if lt.name.name() != "'static" {
250 vec.push(RefLt::Named(lt.name.name()));
257 /// Number of unique lifetimes in the given vector.
258 fn unique_lifetimes(lts: &[RefLt]) -> usize {
259 lts.iter().collect::<HashSet<_>>().len()
262 /// A visitor usable for `rustc_front::visit::walk_ty()`.
263 struct RefVisitor<'a, 'tcx: 'a> {
264 cx: &'a LateContext<'a, 'tcx>,
269 impl<'v, 't> RefVisitor<'v, 't> {
270 fn new(cx: &'v LateContext<'v, 't>) -> Self {
278 fn record(&mut self, lifetime: &Option<Lifetime>) {
279 if let Some(ref lt) = *lifetime {
280 if lt.name.name() == "'static" {
281 self.lts.push(RefLt::Static);
282 } else if lt.is_elided() {
283 self.lts.push(RefLt::Unnamed);
285 self.lts.push(RefLt::Named(lt.name.name()));
288 self.lts.push(RefLt::Unnamed);
292 fn into_vec(self) -> Option<Vec<RefLt>> {
300 fn collect_anonymous_lifetimes(&mut self, qpath: &QPath, ty: &Ty) {
301 if let Some(ref last_path_segment) = last_path_segment(qpath).args {
302 if !last_path_segment.parenthesized && last_path_segment.lifetimes.is_empty() {
303 let hir_id = self.cx.tcx.hir.node_to_hir_id(ty.id);
304 match self.cx.tables.qpath_def(qpath, hir_id) {
305 Def::TyAlias(def_id) | Def::Struct(def_id) => {
306 let generics = self.cx.tcx.generics_of(def_id);
307 for _ in generics.params.as_slice() {
311 Def::Trait(def_id) => {
312 let trait_def = self.cx.tcx.trait_def(def_id);
313 for _ in &self.cx.tcx.generics_of(trait_def.def_id).params {
324 impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
325 // for lifetimes as parameters of generics
326 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
327 self.record(&Some(*lifetime));
330 fn visit_ty(&mut self, ty: &'tcx Ty) {
332 TyRptr(ref lt, _) if lt.is_elided() => {
335 TyPath(ref path) => {
336 self.collect_anonymous_lifetimes(path, ty);
338 TyImplTraitExistential(exist_ty_id, _, _) => {
339 if let ItemExistential(ref exist_ty) = self.cx.tcx.hir.expect_item(exist_ty_id.id).node {
340 for bound in &exist_ty.bounds {
341 if let GenericBound::Outlives(_) = *bound {
347 TyTraitObject(ref bounds, ref lt) => {
351 for bound in bounds {
352 self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
360 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
361 NestedVisitorMap::None
365 /// Are any lifetimes mentioned in the `where` clause? If yes, we don't try to
366 /// reason about elision.
367 fn has_where_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, where_clause: &'tcx WhereClause) -> bool {
368 for predicate in &where_clause.predicates {
370 WherePredicate::RegionPredicate(..) => return true,
371 WherePredicate::BoundPredicate(ref pred) => {
372 // a predicate like F: Trait or F: for<'a> Trait<'a>
373 let mut visitor = RefVisitor::new(cx);
374 // walk the type F, it may not contain LT refs
375 walk_ty(&mut visitor, &pred.bounded_ty);
376 if !visitor.lts.is_empty() {
379 // if the bounds define new lifetimes, they are fine to occur
380 let allowed_lts = allowed_lts_from(&pred.bound_generic_params);
381 // now walk the bounds
382 for bound in pred.bounds.iter() {
383 walk_param_bound(&mut visitor, bound);
385 // and check that all lifetimes are allowed
386 match visitor.into_vec() {
387 None => return false,
388 Some(lts) => for lt in lts {
389 if !allowed_lts.contains(<) {
395 WherePredicate::EqPredicate(ref pred) => {
396 let mut visitor = RefVisitor::new(cx);
397 walk_ty(&mut visitor, &pred.lhs_ty);
398 walk_ty(&mut visitor, &pred.rhs_ty);
399 if !visitor.lts.is_empty() {
408 struct LifetimeChecker {
409 map: HashMap<Name, Span>,
412 impl<'tcx> Visitor<'tcx> for LifetimeChecker {
413 // for lifetimes as parameters of generics
414 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
415 self.map.remove(&lifetime.name.name());
418 fn visit_generic_param(&mut self, param: &'tcx GenericParam) {
419 // don't actually visit `<'a>` or `<'a: 'b>`
420 // we've already visited the `'a` declarations and
421 // don't want to spuriously remove them
422 // `'b` in `'a: 'b` is useless unless used elsewhere in
423 // a non-lifetime bound
424 if let GenericParamKind::Type { .. } = param.kind {
425 walk_generic_param(self, param)
428 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
429 NestedVisitorMap::None
433 fn report_extra_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, func: &'tcx FnDecl, generics: &'tcx Generics) {
436 .map(|lt| (lt.lifetime.name.name(), lt.lifetime.span))
438 let mut checker = LifetimeChecker { map: hs };
440 walk_generics(&mut checker, generics);
441 walk_fn_decl(&mut checker, func);
443 for &v in checker.map.values() {
444 span_lint(cx, EXTRA_UNUSED_LIFETIMES, v, "this lifetime isn't used in the function definition");
448 struct BodyLifetimeChecker {
449 lifetimes_used_in_body: bool,
452 impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
453 // for lifetimes as parameters of generics
454 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
455 if lifetime.name.name() != keywords::Invalid.name() && lifetime.name.name() != "'static" {
456 self.lifetimes_used_in_body = true;
460 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
461 NestedVisitorMap::None