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), &sig.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, &sig.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 bounds = &trait_ref
112 .expect("a path must have at least one segment")
115 for bound in bounds {
116 if bound.name.name() != "'static" && !bound.is_elided() {
119 bounds_lts.push(bound);
124 if could_use_elision(cx, decl, body, &generics.lifetimes, bounds_lts) {
129 "explicit lifetimes given in parameter types where they could be elided",
132 report_extra_lifetimes(cx, decl, generics);
135 fn could_use_elision<'a, 'tcx: 'a>(
136 cx: &LateContext<'a, 'tcx>,
138 body: Option<BodyId>,
139 named_lts: &'tcx [LifetimeDef],
140 bounds_lts: Vec<&'tcx Lifetime>,
142 // There are two scenarios where elision works:
143 // * no output references, all input references have different LT
144 // * output references, exactly one input reference with same LT
145 // All lifetimes must be unnamed, 'static or defined without bounds on the
146 // level of the current item.
149 let allowed_lts = allowed_lts_from(named_lts);
151 // these will collect all the lifetimes for references in arg/return types
152 let mut input_visitor = RefVisitor::new(cx);
153 let mut output_visitor = RefVisitor::new(cx);
155 // extract lifetimes in input argument types
156 for arg in &func.inputs {
157 input_visitor.visit_ty(arg);
159 // extract lifetimes in output type
160 if let Return(ref ty) = func.output {
161 output_visitor.visit_ty(ty);
164 let input_lts = match input_visitor.into_vec() {
165 Some(lts) => lts_from_bounds(lts, bounds_lts.into_iter()),
166 None => return false,
168 let output_lts = match output_visitor.into_vec() {
170 None => return false,
173 if let Some(body_id) = body {
174 let mut checker = BodyLifetimeChecker {
175 lifetimes_used_in_body: false,
177 checker.visit_expr(&cx.tcx.hir.body(body_id).value);
178 if checker.lifetimes_used_in_body {
183 // check for lifetimes from higher scopes
184 for lt in input_lts.iter().chain(output_lts.iter()) {
185 if !allowed_lts.contains(lt) {
190 // no input lifetimes? easy case!
191 if input_lts.is_empty() {
193 } else if output_lts.is_empty() {
194 // no output lifetimes, check distinctness of input lifetimes
196 // only unnamed and static, ok
197 let unnamed_and_static = input_lts
199 .all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static);
200 if unnamed_and_static {
203 // we have no output reference, so we only need all distinct lifetimes
204 input_lts.len() == unique_lifetimes(&input_lts)
206 // we have output references, so we need one input reference,
207 // and all output lifetimes must be the same
208 if unique_lifetimes(&output_lts) > 1 {
211 if input_lts.len() == 1 {
212 match (&input_lts[0], &output_lts[0]) {
213 (&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
214 (&RefLt::Named(_), &RefLt::Unnamed) => true,
215 _ => false, /* already elided, different named lifetimes
216 * or something static going on */
224 fn allowed_lts_from(named_lts: &[LifetimeDef]) -> HashSet<RefLt> {
225 let mut allowed_lts = HashSet::new();
226 for lt in named_lts {
227 if lt.bounds.is_empty() {
228 allowed_lts.insert(RefLt::Named(lt.lifetime.name.name()));
231 allowed_lts.insert(RefLt::Unnamed);
232 allowed_lts.insert(RefLt::Static);
236 fn lts_from_bounds<'a, T: Iterator<Item = &'a Lifetime>>(mut vec: Vec<RefLt>, bounds_lts: T) -> Vec<RefLt> {
237 for lt in bounds_lts {
238 if lt.name.name() != "'static" {
239 vec.push(RefLt::Named(lt.name.name()));
246 /// Number of unique lifetimes in the given vector.
247 fn unique_lifetimes(lts: &[RefLt]) -> usize {
248 lts.iter().collect::<HashSet<_>>().len()
251 /// A visitor usable for `rustc_front::visit::walk_ty()`.
252 struct RefVisitor<'a, 'tcx: 'a> {
253 cx: &'a LateContext<'a, 'tcx>,
258 impl<'v, 't> RefVisitor<'v, 't> {
259 fn new(cx: &'v LateContext<'v, 't>) -> Self {
267 fn record(&mut self, lifetime: &Option<Lifetime>) {
268 if let Some(ref lt) = *lifetime {
269 if lt.name.name() == "'static" {
270 self.lts.push(RefLt::Static);
271 } else if lt.is_elided() {
272 self.lts.push(RefLt::Unnamed);
274 self.lts.push(RefLt::Named(lt.name.name()));
277 self.lts.push(RefLt::Unnamed);
281 fn into_vec(self) -> Option<Vec<RefLt>> {
289 fn collect_anonymous_lifetimes(&mut self, qpath: &QPath, ty: &Ty) {
290 let last_path_segment = &last_path_segment(qpath).parameters;
291 if !last_path_segment.parenthesized && last_path_segment.lifetimes.is_empty() {
292 let hir_id = self.cx.tcx.hir.node_to_hir_id(ty.id);
293 match self.cx.tables.qpath_def(qpath, hir_id) {
294 Def::TyAlias(def_id) | Def::Struct(def_id) => {
295 let generics = self.cx.tcx.generics_of(def_id);
296 for _ in generics.regions.as_slice() {
300 Def::Trait(def_id) => {
301 let trait_def = self.cx.tcx.trait_def(def_id);
302 for _ in &self.cx.tcx.generics_of(trait_def.def_id).regions {
312 impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
313 // for lifetimes as parameters of generics
314 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
315 self.record(&Some(*lifetime));
318 fn visit_ty(&mut self, ty: &'tcx Ty) {
320 TyRptr(ref lt, _) if lt.is_elided() => {
323 TyPath(ref path) => {
324 self.collect_anonymous_lifetimes(path, ty);
326 TyImplTrait(ref param_bounds) => for bound in param_bounds {
327 if let RegionTyParamBound(_) = *bound {
331 TyTraitObject(ref bounds, ref lt) => {
335 for bound in bounds {
336 self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
344 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
345 NestedVisitorMap::None
349 /// Are any lifetimes mentioned in the `where` clause? If yes, we don't try to
350 /// reason about elision.
351 fn has_where_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, where_clause: &'tcx WhereClause) -> bool {
352 for predicate in &where_clause.predicates {
354 WherePredicate::RegionPredicate(..) => return true,
355 WherePredicate::BoundPredicate(ref pred) => {
356 // a predicate like F: Trait or F: for<'a> Trait<'a>
357 let mut visitor = RefVisitor::new(cx);
358 // walk the type F, it may not contain LT refs
359 walk_ty(&mut visitor, &pred.bounded_ty);
360 if !visitor.lts.is_empty() {
363 // if the bounds define new lifetimes, they are fine to occur
364 let allowed_lts = allowed_lts_from(&pred.bound_lifetimes);
365 // now walk the bounds
366 for bound in pred.bounds.iter() {
367 walk_ty_param_bound(&mut visitor, bound);
369 // and check that all lifetimes are allowed
370 match visitor.into_vec() {
371 None => return false,
372 Some(lts) => for lt in lts {
373 if !allowed_lts.contains(<) {
379 WherePredicate::EqPredicate(ref pred) => {
380 let mut visitor = RefVisitor::new(cx);
381 walk_ty(&mut visitor, &pred.lhs_ty);
382 walk_ty(&mut visitor, &pred.rhs_ty);
383 if !visitor.lts.is_empty() {
392 struct LifetimeChecker {
393 map: HashMap<Name, Span>,
396 impl<'tcx> Visitor<'tcx> for LifetimeChecker {
397 // for lifetimes as parameters of generics
398 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
399 self.map.remove(&lifetime.name.name());
402 fn visit_lifetime_def(&mut self, _: &'tcx LifetimeDef) {
403 // don't actually visit `<'a>` or `<'a: 'b>`
404 // we've already visited the `'a` declarations and
405 // don't want to spuriously remove them
406 // `'b` in `'a: 'b` is useless unless used elsewhere in
407 // a non-lifetime bound
409 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
410 NestedVisitorMap::None
414 fn report_extra_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, func: &'tcx FnDecl, generics: &'tcx Generics) {
418 .map(|lt| (lt.lifetime.name.name(), lt.lifetime.span))
420 let mut checker = LifetimeChecker { map: hs };
422 walk_generics(&mut checker, generics);
423 walk_fn_decl(&mut checker, func);
425 for &v in checker.map.values() {
426 span_lint(cx, UNUSED_LIFETIMES, v, "this lifetime isn't used in the function definition");
430 struct BodyLifetimeChecker {
431 lifetimes_used_in_body: bool,
434 impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
435 // for lifetimes as parameters of generics
436 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
437 if lifetime.name.name() != keywords::Invalid.name() && lifetime.name.name() != "'static" {
438 self.lifetimes_used_in_body = true;
442 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
443 NestedVisitorMap::None