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 let types = generics.params.iter().filter_map(|param| match param.kind {
105 GenericParamKind::Type { .. } => Some(param),
106 GenericParamKind::Lifetime { .. } => None,
109 for bound in &typ.bounds {
110 let mut visitor = RefVisitor::new(cx);
111 walk_param_bound(&mut visitor, bound);
112 if visitor.lts.iter().any(|lt| matches!(lt, RefLt::Named(_))) {
115 if let GenericBound::Trait(ref trait_ref, _) = *bound {
116 let params = &trait_ref
121 .expect("a path must have at least one segment")
123 if let Some(ref params) = *params {
124 let lifetimes = params.args.iter().filter_map(|arg| match arg {
125 GenericArg::Lifetime(lt) => Some(lt),
126 GenericArg::Type(_) => None,
128 for bound in lifetimes {
129 if bound.name != LifetimeName::Static && !bound.is_elided() {
132 bounds_lts.push(bound);
138 if could_use_elision(cx, decl, body, &generics.params, bounds_lts) {
143 "explicit lifetimes given in parameter types where they could be elided",
146 report_extra_lifetimes(cx, decl, generics);
149 fn could_use_elision<'a, 'tcx: 'a>(
150 cx: &LateContext<'a, 'tcx>,
152 body: Option<BodyId>,
153 named_generics: &'tcx [GenericParam],
154 bounds_lts: Vec<&'tcx Lifetime>,
156 // There are two scenarios where elision works:
157 // * no output references, all input references have different LT
158 // * output references, exactly one input reference with same LT
159 // All lifetimes must be unnamed, 'static or defined without bounds on the
160 // level of the current item.
163 let allowed_lts = allowed_lts_from(named_generics);
165 // these will collect all the lifetimes for references in arg/return types
166 let mut input_visitor = RefVisitor::new(cx);
167 let mut output_visitor = RefVisitor::new(cx);
169 // extract lifetimes in input argument types
170 for arg in &func.inputs {
171 input_visitor.visit_ty(arg);
173 // extract lifetimes in output type
174 if let Return(ref ty) = func.output {
175 output_visitor.visit_ty(ty);
178 let input_lts = match input_visitor.into_vec() {
179 Some(lts) => lts_from_bounds(lts, bounds_lts.into_iter()),
180 None => return false,
182 let output_lts = match output_visitor.into_vec() {
184 None => return false,
187 if let Some(body_id) = body {
188 let mut checker = BodyLifetimeChecker {
189 lifetimes_used_in_body: false,
191 checker.visit_expr(&cx.tcx.hir.body(body_id).value);
192 if checker.lifetimes_used_in_body {
197 // check for lifetimes from higher scopes
198 for lt in input_lts.iter().chain(output_lts.iter()) {
199 if !allowed_lts.contains(lt) {
204 // no input lifetimes? easy case!
205 if input_lts.is_empty() {
207 } else if output_lts.is_empty() {
208 // no output lifetimes, check distinctness of input lifetimes
210 // only unnamed and static, ok
211 let unnamed_and_static = input_lts
213 .all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static);
214 if unnamed_and_static {
217 // we have no output reference, so we only need all distinct lifetimes
218 input_lts.len() == unique_lifetimes(&input_lts)
220 // we have output references, so we need one input reference,
221 // and all output lifetimes must be the same
222 if unique_lifetimes(&output_lts) > 1 {
225 if input_lts.len() == 1 {
226 match (&input_lts[0], &output_lts[0]) {
227 (&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
228 (&RefLt::Named(_), &RefLt::Unnamed) => true,
229 _ => false, /* already elided, different named lifetimes
230 * or something static going on */
238 fn allowed_lts_from(named_generics: &[GenericParam]) -> HashSet<RefLt> {
239 let mut allowed_lts = HashSet::new();
240 for par in named_generics.iter() {
241 if let GenericParamKind::Lifetime { .. } = par.kind {
242 if par.bounds.is_empty() {
243 allowed_lts.insert(RefLt::Named(par.name.ident().name));
247 allowed_lts.insert(RefLt::Unnamed);
248 allowed_lts.insert(RefLt::Static);
252 fn lts_from_bounds<'a, T: Iterator<Item = &'a Lifetime>>(mut vec: Vec<RefLt>, bounds_lts: T) -> Vec<RefLt> {
253 for lt in bounds_lts {
254 if lt.name != LifetimeName::Static {
255 vec.push(RefLt::Named(lt.name.ident().name));
262 /// Number of unique lifetimes in the given vector.
263 fn unique_lifetimes(lts: &[RefLt]) -> usize {
264 lts.iter().collect::<HashSet<_>>().len()
267 /// A visitor usable for `rustc_front::visit::walk_ty()`.
268 struct RefVisitor<'a, 'tcx: 'a> {
269 cx: &'a LateContext<'a, 'tcx>,
274 impl<'v, 't> RefVisitor<'v, 't> {
275 fn new(cx: &'v LateContext<'v, 't>) -> Self {
283 fn record(&mut self, lifetime: &Option<Lifetime>) {
284 if let Some(ref lt) = *lifetime {
285 if lt.name == LifetimeName::Static {
286 self.lts.push(RefLt::Static);
287 } else if lt.is_elided() {
288 self.lts.push(RefLt::Unnamed);
290 self.lts.push(RefLt::Named(lt.name.ident().name));
293 self.lts.push(RefLt::Unnamed);
297 fn into_vec(self) -> Option<Vec<RefLt>> {
305 fn collect_anonymous_lifetimes(&mut self, qpath: &QPath, ty: &Ty) {
306 if let Some(ref last_path_segment) = last_path_segment(qpath).args {
307 if !last_path_segment.parenthesized
308 && !last_path_segment.args.iter().any(|arg| match arg {
309 GenericArg::Lifetime(_) => true,
310 GenericArg::Type(_) => false,
312 let hir_id = self.cx.tcx.hir.node_to_hir_id(ty.id);
313 match self.cx.tables.qpath_def(qpath, hir_id) {
314 Def::TyAlias(def_id) | Def::Struct(def_id) => {
315 let generics = self.cx.tcx.generics_of(def_id);
316 for _ in generics.params.as_slice() {
320 Def::Trait(def_id) => {
321 let trait_def = self.cx.tcx.trait_def(def_id);
322 for _ in &self.cx.tcx.generics_of(trait_def.def_id).params {
333 impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
334 // for lifetimes as parameters of generics
335 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
336 self.record(&Some(*lifetime));
339 fn visit_ty(&mut self, ty: &'tcx Ty) {
341 TyRptr(ref lt, _) if lt.is_elided() => {
344 TyPath(ref path) => {
345 if let QPath::Resolved(_, ref path) = *path {
346 if let Def::Existential(def_id) = path.def {
347 let node_id = self.cx.tcx.hir.as_local_node_id(def_id).unwrap();
348 if let ItemExistential(ref exist_ty) = self.cx.tcx.hir.expect_item(node_id).node {
349 for bound in &exist_ty.bounds {
350 if let GenericBound::Outlives(_) = *bound {
361 self.collect_anonymous_lifetimes(path, ty);
363 TyTraitObject(ref bounds, ref lt) => {
367 for bound in bounds {
368 self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
376 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
377 NestedVisitorMap::None
381 /// Are any lifetimes mentioned in the `where` clause? If yes, we don't try to
382 /// reason about elision.
383 fn has_where_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, where_clause: &'tcx WhereClause) -> bool {
384 for predicate in &where_clause.predicates {
386 WherePredicate::RegionPredicate(..) => return true,
387 WherePredicate::BoundPredicate(ref pred) => {
388 // a predicate like F: Trait or F: for<'a> Trait<'a>
389 let mut visitor = RefVisitor::new(cx);
390 // walk the type F, it may not contain LT refs
391 walk_ty(&mut visitor, &pred.bounded_ty);
392 if !visitor.lts.is_empty() {
395 // if the bounds define new lifetimes, they are fine to occur
396 let allowed_lts = allowed_lts_from(&pred.bound_generic_params);
397 // now walk the bounds
398 for bound in pred.bounds.iter() {
399 walk_param_bound(&mut visitor, bound);
401 // and check that all lifetimes are allowed
402 match visitor.into_vec() {
403 None => return false,
404 Some(lts) => for lt in lts {
405 if !allowed_lts.contains(<) {
411 WherePredicate::EqPredicate(ref pred) => {
412 let mut visitor = RefVisitor::new(cx);
413 walk_ty(&mut visitor, &pred.lhs_ty);
414 walk_ty(&mut visitor, &pred.rhs_ty);
415 if !visitor.lts.is_empty() {
424 struct LifetimeChecker {
425 map: HashMap<Name, Span>,
428 impl<'tcx> Visitor<'tcx> for LifetimeChecker {
429 // for lifetimes as parameters of generics
430 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
431 self.map.remove(&lifetime.name.ident().name);
434 fn visit_generic_param(&mut self, param: &'tcx GenericParam) {
435 // don't actually visit `<'a>` or `<'a: 'b>`
436 // we've already visited the `'a` declarations and
437 // don't want to spuriously remove them
438 // `'b` in `'a: 'b` is useless unless used elsewhere in
439 // a non-lifetime bound
440 if let GenericParamKind::Type { .. } = param.kind {
441 walk_generic_param(self, param)
444 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
445 NestedVisitorMap::None
449 fn report_extra_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, func: &'tcx FnDecl, generics: &'tcx Generics) {
450 let hs = generics.params.iter()
451 .filter_map(|par| match par.kind {
452 GenericParamKind::Lifetime { .. } => Some((par.name.ident().name, par.span)),
456 let mut checker = LifetimeChecker { map: hs };
458 walk_generics(&mut checker, generics);
459 walk_fn_decl(&mut checker, func);
461 for &v in checker.map.values() {
462 span_lint(cx, EXTRA_UNUSED_LIFETIMES, v, "this lifetime isn't used in the function definition");
466 struct BodyLifetimeChecker {
467 lifetimes_used_in_body: bool,
470 impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
471 // for lifetimes as parameters of generics
472 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
473 if lifetime.name.ident().name != keywords::Invalid.name() && lifetime.name.ident().name != "'static" {
474 self.lifetimes_used_in_body = true;
478 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
479 NestedVisitorMap::None