3 use rustc::hir::def::Def;
5 use rustc::hir::intravisit::{Visitor, walk_ty, walk_ty_param_bound, walk_fn_decl, walk_generics, NestedVisitorMap};
6 use std::collections::{HashSet, HashMap};
7 use syntax::codemap::Span;
8 use utils::{in_external_macro, span_lint, last_path_segment};
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"
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.trait_ref
111 .expect("a path must have at least one segment")
114 for bound in bounds {
115 if bound.name != "'static" && !bound.is_elided() {
118 bounds_lts.push(bound);
123 if could_use_elision(cx, decl, body, &generics.lifetimes, bounds_lts) {
127 "explicit lifetimes given in parameter types where they could be elided");
129 report_extra_lifetimes(cx, decl, generics);
132 fn could_use_elision<'a, 'tcx: 'a>(
133 cx: &LateContext<'a, 'tcx>,
135 body: Option<BodyId>,
136 named_lts: &'tcx [LifetimeDef],
137 bounds_lts: Vec<&'tcx Lifetime>
139 // There are two scenarios where elision works:
140 // * no output references, all input references have different LT
141 // * output references, exactly one input reference with same LT
142 // All lifetimes must be unnamed, 'static or defined without bounds on the
143 // level of the current item.
146 let allowed_lts = allowed_lts_from(named_lts);
148 // these will collect all the lifetimes for references in arg/return types
149 let mut input_visitor = RefVisitor::new(cx);
150 let mut output_visitor = RefVisitor::new(cx);
152 // extract lifetimes in input argument types
153 for arg in &func.inputs {
154 input_visitor.visit_ty(arg);
156 // extract lifetimes in output type
157 if let Return(ref ty) = func.output {
158 output_visitor.visit_ty(ty);
161 let input_lts = match input_visitor.into_vec() {
162 Some(lts) => lts_from_bounds(lts, bounds_lts.into_iter()),
163 None => return false,
165 let output_lts = match output_visitor.into_vec() {
167 None => return false,
170 if let Some(body_id) = body {
171 let mut checker = BodyLifetimeChecker { lifetimes_used_in_body: false };
172 checker.visit_expr(&cx.tcx.hir.body(body_id).value);
173 if checker.lifetimes_used_in_body {
178 // check for lifetimes from higher scopes
179 for lt in input_lts.iter().chain(output_lts.iter()) {
180 if !allowed_lts.contains(lt) {
185 // no input lifetimes? easy case!
186 if input_lts.is_empty() {
188 } else if output_lts.is_empty() {
189 // no output lifetimes, check distinctness of input lifetimes
191 // only unnamed and static, ok
192 if input_lts.iter().all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static) {
195 // we have no output reference, so we only need all distinct lifetimes
196 input_lts.len() == unique_lifetimes(&input_lts)
198 // we have output references, so we need one input reference,
199 // and all output lifetimes must be the same
200 if unique_lifetimes(&output_lts) > 1 {
203 if input_lts.len() == 1 {
204 match (&input_lts[0], &output_lts[0]) {
205 (&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
206 (&RefLt::Named(_), &RefLt::Unnamed) => true,
207 _ => false, // already elided, different named lifetimes
208 // or something static going on
216 fn allowed_lts_from(named_lts: &[LifetimeDef]) -> HashSet<RefLt> {
217 let mut allowed_lts = HashSet::new();
218 for lt in named_lts {
219 if lt.bounds.is_empty() {
220 allowed_lts.insert(RefLt::Named(lt.lifetime.name));
223 allowed_lts.insert(RefLt::Unnamed);
224 allowed_lts.insert(RefLt::Static);
228 fn lts_from_bounds<'a, T: Iterator<Item = &'a Lifetime>>(mut vec: Vec<RefLt>, bounds_lts: T) -> Vec<RefLt> {
229 for lt in bounds_lts {
230 if lt.name != "'static" {
231 vec.push(RefLt::Named(lt.name));
238 /// Number of unique lifetimes in the given vector.
239 fn unique_lifetimes(lts: &[RefLt]) -> usize {
240 lts.iter().collect::<HashSet<_>>().len()
243 /// A visitor usable for `rustc_front::visit::walk_ty()`.
244 struct RefVisitor<'a, 'tcx: 'a> {
245 cx: &'a LateContext<'a, 'tcx>,
250 impl<'v, 't> RefVisitor<'v, 't> {
251 fn new(cx: &'v LateContext<'v, 't>) -> RefVisitor<'v, 't> {
259 fn record(&mut self, lifetime: &Option<Lifetime>) {
260 if let Some(ref lt) = *lifetime {
261 if lt.name == "'static" {
262 self.lts.push(RefLt::Static);
263 } else if lt.is_elided() {
264 self.lts.push(RefLt::Unnamed);
266 self.lts.push(RefLt::Named(lt.name));
269 self.lts.push(RefLt::Unnamed);
273 fn into_vec(self) -> Option<Vec<RefLt>> {
274 if self.abort { None } else { Some(self.lts) }
277 fn collect_anonymous_lifetimes(&mut self, qpath: &QPath, ty: &Ty) {
278 let last_path_segment = &last_path_segment(qpath).parameters;
279 if let AngleBracketedParameters(ref params) = *last_path_segment {
280 if params.lifetimes.is_empty() {
281 match self.cx.tables.qpath_def(qpath, ty.id) {
282 Def::TyAlias(def_id) |
283 Def::Struct(def_id) => {
284 let generics = self.cx.tcx.generics_of(def_id);
285 for _ in generics.regions.as_slice() {
289 Def::Trait(def_id) => {
290 let trait_def = self.cx.tcx.trait_def(def_id);
291 for _ in &self.cx.tcx.generics_of(trait_def.def_id).regions {
302 impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
303 // for lifetimes as parameters of generics
304 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
305 self.record(&Some(*lifetime));
308 fn visit_ty(&mut self, ty: &'tcx Ty) {
310 TyRptr(ref lt, _) if lt.is_elided() => {
313 TyPath(ref path) => {
314 self.collect_anonymous_lifetimes(path, ty);
316 TyImplTrait(ref param_bounds) => {
317 for bound in param_bounds {
318 if let RegionTyParamBound(_) = *bound {
323 TyTraitObject(ref bounds, ref lt) => {
327 for bound in bounds {
328 self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
336 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
337 NestedVisitorMap::None
341 /// Are any lifetimes mentioned in the `where` clause? If yes, we don't try to
342 /// reason about elision.
343 fn has_where_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, where_clause: &'tcx WhereClause) -> bool {
344 for predicate in &where_clause.predicates {
346 WherePredicate::RegionPredicate(..) => return true,
347 WherePredicate::BoundPredicate(ref pred) => {
348 // a predicate like F: Trait or F: for<'a> Trait<'a>
349 let mut visitor = RefVisitor::new(cx);
350 // walk the type F, it may not contain LT refs
351 walk_ty(&mut visitor, &pred.bounded_ty);
352 if !visitor.lts.is_empty() {
355 // if the bounds define new lifetimes, they are fine to occur
356 let allowed_lts = allowed_lts_from(&pred.bound_lifetimes);
357 // now walk the bounds
358 for bound in pred.bounds.iter() {
359 walk_ty_param_bound(&mut visitor, bound);
361 // and check that all lifetimes are allowed
362 match visitor.into_vec() {
363 None => return false,
366 if !allowed_lts.contains(<) {
373 WherePredicate::EqPredicate(ref pred) => {
374 let mut visitor = RefVisitor::new(cx);
375 walk_ty(&mut visitor, &pred.lhs_ty);
376 walk_ty(&mut visitor, &pred.rhs_ty);
377 if !visitor.lts.is_empty() {
386 struct LifetimeChecker {
387 map: HashMap<Name, Span>,
390 impl<'tcx> Visitor<'tcx> for LifetimeChecker {
391 // for lifetimes as parameters of generics
392 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
393 self.map.remove(&lifetime.name);
396 fn visit_lifetime_def(&mut self, _: &'tcx LifetimeDef) {
397 // don't actually visit `<'a>` or `<'a: 'b>`
398 // we've already visited the `'a` declarations and
399 // don't want to spuriously remove them
400 // `'b` in `'a: 'b` is useless unless used elsewhere in
401 // a non-lifetime bound
403 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
404 NestedVisitorMap::None
408 fn report_extra_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, func: &'tcx FnDecl, generics: &'tcx Generics) {
409 let hs = generics.lifetimes
411 .map(|lt| (lt.lifetime.name, lt.lifetime.span))
413 let mut checker = LifetimeChecker { map: hs };
415 walk_generics(&mut checker, generics);
416 walk_fn_decl(&mut checker, func);
418 for &v in checker.map.values() {
419 span_lint(cx, UNUSED_LIFETIMES, v, "this lifetime isn't used in the function definition");
423 struct BodyLifetimeChecker {
424 lifetimes_used_in_body: bool,
427 impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
428 // for lifetimes as parameters of generics
429 fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
430 if lifetime.name != keywords::Invalid.name() && lifetime.name != "'static" {
431 self.lifetimes_used_in_body = true;
435 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
436 NestedVisitorMap::None