3 use rustc::hir::def::Def;
5 use rustc::hir::intravisit::{walk_fn_decl, walk_generics, walk_ty, walk_ty_param_bound, NestedVisitorMap, Visitor};
6 use std::collections::{HashMap, HashSet};
7 use syntax::codemap::Span;
8 use 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 }
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) { .. }
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, 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 for typ in &generics.ty_params {
105 for bound in &typ.bounds {
106 if let TraitTyParamBound(ref trait_ref, _) = *bound {
107 let params = &trait_ref
112 .expect("a path must have at least one segment")
114 if let Some(ref params) = *params {
115 for bound in ¶ms.lifetimes {
116 if bound.name.name() != "'static" && !bound.is_elided() {
119 bounds_lts.push(bound);
125 if could_use_elision(cx, decl, body, &generics.lifetimes, bounds_lts) {
130 "explicit lifetimes given in parameter types where they could be elided",
133 report_extra_lifetimes(cx, decl, generics);
136 fn could_use_elision<'a, 'tcx: 'a>(
137 cx: &LateContext<'a, 'tcx>,
139 body: Option<BodyId>,
140 named_lts: &'tcx [LifetimeDef],
141 bounds_lts: Vec<&'tcx Lifetime>,
143 // There are two scenarios where elision works:
144 // * no output references, all input references have different LT
145 // * output references, exactly one input reference with same LT
146 // All lifetimes must be unnamed, 'static or defined without bounds on the
147 // level of the current item.
150 let allowed_lts = allowed_lts_from(named_lts);
152 // these will collect all the lifetimes for references in arg/return types
153 let mut input_visitor = RefVisitor::new(cx);
154 let mut output_visitor = RefVisitor::new(cx);
156 // extract lifetimes in input argument types
157 for arg in &func.inputs {
158 input_visitor.visit_ty(arg);
160 // extract lifetimes in output type
161 if let Return(ref ty) = func.output {
162 output_visitor.visit_ty(ty);
165 let input_lts = match input_visitor.into_vec() {
166 Some(lts) => lts_from_bounds(lts, bounds_lts.into_iter()),
167 None => return false,
169 let output_lts = match output_visitor.into_vec() {
171 None => return false,
174 if let Some(body_id) = body {
175 let mut checker = BodyLifetimeChecker {
176 lifetimes_used_in_body: false,
178 checker.visit_expr(&cx.tcx.hir.body(body_id).value);
179 if checker.lifetimes_used_in_body {
184 // check for lifetimes from higher scopes
185 for lt in input_lts.iter().chain(output_lts.iter()) {
186 if !allowed_lts.contains(lt) {
191 // no input lifetimes? easy case!
192 if input_lts.is_empty() {
194 } else if output_lts.is_empty() {
195 // no output lifetimes, check distinctness of input lifetimes
197 // only unnamed and static, ok
198 let unnamed_and_static = input_lts
200 .all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static);
201 if unnamed_and_static {
204 // we have no output reference, so we only need all distinct lifetimes
205 input_lts.len() == unique_lifetimes(&input_lts)
207 // we have output references, so we need one input reference,
208 // and all output lifetimes must be the same
209 if unique_lifetimes(&output_lts) > 1 {
212 if input_lts.len() == 1 {
213 match (&input_lts[0], &output_lts[0]) {
214 (&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
215 (&RefLt::Named(_), &RefLt::Unnamed) => true,
216 _ => false, /* already elided, different named lifetimes
217 * or something static going on */
225 fn allowed_lts_from(named_lts: &[LifetimeDef]) -> HashSet<RefLt> {
226 let mut allowed_lts = HashSet::new();
227 for lt in named_lts {
228 if lt.bounds.is_empty() {
229 allowed_lts.insert(RefLt::Named(lt.lifetime.name.name()));
232 allowed_lts.insert(RefLt::Unnamed);
233 allowed_lts.insert(RefLt::Static);
237 fn lts_from_bounds<'a, T: Iterator<Item = &'a Lifetime>>(mut vec: Vec<RefLt>, bounds_lts: T) -> Vec<RefLt> {
238 for lt in bounds_lts {
239 if lt.name.name() != "'static" {
240 vec.push(RefLt::Named(lt.name.name()));
247 /// Number of unique lifetimes in the given vector.
248 fn unique_lifetimes(lts: &[RefLt]) -> usize {
249 lts.iter().collect::<HashSet<_>>().len()
252 /// A visitor usable for `rustc_front::visit::walk_ty()`.
253 struct RefVisitor<'a, 'tcx: 'a> {
254 cx: &'a LateContext<'a, 'tcx>,
259 impl<'v, 't> RefVisitor<'v, 't> {
260 fn new(cx: &'v LateContext<'v, 't>) -> Self {
268 fn record(&mut self, lifetime: &Option<Lifetime>) {
269 if let Some(ref lt) = *lifetime {
270 if lt.name.name() == "'static" {
271 self.lts.push(RefLt::Static);
272 } else if lt.is_elided() {
273 self.lts.push(RefLt::Unnamed);
275 self.lts.push(RefLt::Named(lt.name.name()));
278 self.lts.push(RefLt::Unnamed);
282 fn into_vec(self) -> Option<Vec<RefLt>> {
290 fn collect_anonymous_lifetimes(&mut self, qpath: &QPath, ty: &Ty) {
291 if let Some(ref last_path_segment) = last_path_segment(qpath).parameters {
292 if !last_path_segment.parenthesized && last_path_segment.lifetimes.is_empty() {
293 let hir_id = self.cx.tcx.hir.node_to_hir_id(ty.id);
294 match self.cx.tables.qpath_def(qpath, hir_id) {
295 Def::TyAlias(def_id) | Def::Struct(def_id) => {
296 let generics = self.cx.tcx.generics_of(def_id);
297 for _ in generics.regions.as_slice() {
301 Def::Trait(def_id) => {
302 let trait_def = self.cx.tcx.trait_def(def_id);
303 for _ in &self.cx.tcx.generics_of(trait_def.def_id).regions {
314 impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
315 // for lifetimes as parameters of generics
316 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
317 self.record(&Some(*lifetime));
320 fn visit_ty(&mut self, ty: &'tcx Ty) {
322 TyRptr(ref lt, _) if lt.is_elided() => {
325 TyPath(ref path) => {
326 self.collect_anonymous_lifetimes(path, ty);
328 TyImplTrait(ref param_bounds) => for bound in param_bounds {
329 if let RegionTyParamBound(_) = *bound {
333 TyTraitObject(ref bounds, ref lt) => {
337 for bound in bounds {
338 self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
346 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
347 NestedVisitorMap::None
351 /// Are any lifetimes mentioned in the `where` clause? If yes, we don't try to
352 /// reason about elision.
353 fn has_where_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, where_clause: &'tcx WhereClause) -> bool {
354 for predicate in &where_clause.predicates {
356 WherePredicate::RegionPredicate(..) => return true,
357 WherePredicate::BoundPredicate(ref pred) => {
358 // a predicate like F: Trait or F: for<'a> Trait<'a>
359 let mut visitor = RefVisitor::new(cx);
360 // walk the type F, it may not contain LT refs
361 walk_ty(&mut visitor, &pred.bounded_ty);
362 if !visitor.lts.is_empty() {
365 // if the bounds define new lifetimes, they are fine to occur
366 let allowed_lts = allowed_lts_from(&pred.bound_lifetimes);
367 // now walk the bounds
368 for bound in pred.bounds.iter() {
369 walk_ty_param_bound(&mut visitor, bound);
371 // and check that all lifetimes are allowed
372 match visitor.into_vec() {
373 None => return false,
374 Some(lts) => for lt in lts {
375 if !allowed_lts.contains(<) {
381 WherePredicate::EqPredicate(ref pred) => {
382 let mut visitor = RefVisitor::new(cx);
383 walk_ty(&mut visitor, &pred.lhs_ty);
384 walk_ty(&mut visitor, &pred.rhs_ty);
385 if !visitor.lts.is_empty() {
394 struct LifetimeChecker {
395 map: HashMap<Name, Span>,
398 impl<'tcx> Visitor<'tcx> for LifetimeChecker {
399 // for lifetimes as parameters of generics
400 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
401 self.map.remove(&lifetime.name.name());
404 fn visit_lifetime_def(&mut self, _: &'tcx LifetimeDef) {
405 // don't actually visit `<'a>` or `<'a: 'b>`
406 // we've already visited the `'a` declarations and
407 // don't want to spuriously remove them
408 // `'b` in `'a: 'b` is useless unless used elsewhere in
409 // a non-lifetime bound
411 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
412 NestedVisitorMap::None
416 fn report_extra_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, func: &'tcx FnDecl, generics: &'tcx Generics) {
420 .map(|lt| (lt.lifetime.name.name(), lt.lifetime.span))
422 let mut checker = LifetimeChecker { map: hs };
424 walk_generics(&mut checker, generics);
425 walk_fn_decl(&mut checker, func);
427 for &v in checker.map.values() {
428 span_lint(cx, UNUSED_LIFETIMES, v, "this lifetime isn't used in the function definition");
432 struct BodyLifetimeChecker {
433 lifetimes_used_in_body: bool,
436 impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
437 // for lifetimes as parameters of generics
438 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
439 if lifetime.name.name() != keywords::Invalid.name() && lifetime.name.name() != "'static" {
440 self.lifetimes_used_in_body = true;
444 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
445 NestedVisitorMap::None