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use reexport::*;
use rustc::lint::*;
use rustc::hir::def::Def;
use rustc::hir::*;
use rustc::hir::intravisit::{Visitor, walk_ty, walk_ty_param_bound, walk_fn_decl, walk_generics, NestedVisitorMap};
use std::collections::{HashSet, HashMap};
use syntax::codemap::Span;
use utils::{in_external_macro, span_lint, last_path_segment};
declare_lint! {
pub NEEDLESS_LIFETIMES,
Warn,
"using explicit lifetimes for references in function arguments when elision rules \
would allow omitting them"
}
declare_lint! {
pub UNUSED_LIFETIMES,
Warn,
"unused lifetimes in function definitions"
}
#[derive(Copy,Clone)]
pub struct LifetimePass;
impl LintPass for LifetimePass {
fn get_lints(&self) -> LintArray {
lint_array!(NEEDLESS_LIFETIMES, UNUSED_LIFETIMES)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LifetimePass {
fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
if let ItemFn(ref decl, _, _, _, ref generics, _) = item.node {
check_fn_inner(cx, decl, generics, item.span);
}
}
fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
if let ImplItemKind::Method(ref sig, _) = item.node {
check_fn_inner(cx, &sig.decl, &sig.generics, item.span);
}
}
fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
if let TraitItemKind::Method(ref sig, _) = item.node {
check_fn_inner(cx, &sig.decl, &sig.generics, item.span);
}
}
}
#[derive(PartialEq, Eq, Hash, Debug)]
enum RefLt {
Unnamed,
Static,
Named(Name),
}
fn bound_lifetimes(bound: &TyParamBound) -> HirVec<&Lifetime> {
if let TraitTyParamBound(ref trait_ref, _) = *bound {
trait_ref.trait_ref
.path
.segments
.last()
.expect("a path must have at least one segment")
.parameters
.lifetimes()
} else {
HirVec::new()
}
}
fn check_fn_inner<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, decl: &'tcx FnDecl, generics: &'tcx Generics, span: Span) {
if in_external_macro(cx, span) || has_where_lifetimes(cx, &generics.where_clause) {
return;
}
let bounds_lts = generics.ty_params
.iter()
.flat_map(|typ| typ.bounds.iter().flat_map(bound_lifetimes));
if could_use_elision(cx, decl, &generics.lifetimes, bounds_lts) {
span_lint(cx,
NEEDLESS_LIFETIMES,
span,
"explicit lifetimes given in parameter types where they could be elided");
}
report_extra_lifetimes(cx, decl, generics);
}
fn could_use_elision<'a, 'tcx: 'a, T: Iterator<Item = &'tcx Lifetime>>(
cx: &LateContext<'a, 'tcx>,
func: &'tcx FnDecl,
named_lts: &'tcx [LifetimeDef],
bounds_lts: T
) -> bool {
let allowed_lts = allowed_lts_from(named_lts);
let mut input_visitor = RefVisitor::new(cx);
let mut output_visitor = RefVisitor::new(cx);
for arg in &func.inputs {
input_visitor.visit_ty(arg);
}
if let Return(ref ty) = func.output {
output_visitor.visit_ty(ty);
}
let input_lts = lts_from_bounds(input_visitor.into_vec(), bounds_lts);
let output_lts = output_visitor.into_vec();
for lt in input_lts.iter().chain(output_lts.iter()) {
if !allowed_lts.contains(lt) {
return false;
}
}
if input_lts.is_empty() {
false
} else if output_lts.is_empty() {
if input_lts.iter().all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static) {
return false;
}
input_lts.len() == unique_lifetimes(&input_lts)
} else {
if unique_lifetimes(&output_lts) > 1 {
return false;
}
if input_lts.len() == 1 {
match (&input_lts[0], &output_lts[0]) {
(&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
(&RefLt::Named(_), &RefLt::Unnamed) => true,
_ => false,
}
} else {
false
}
}
}
fn allowed_lts_from(named_lts: &[LifetimeDef]) -> HashSet<RefLt> {
let mut allowed_lts = HashSet::new();
for lt in named_lts {
if lt.bounds.is_empty() {
allowed_lts.insert(RefLt::Named(lt.lifetime.name));
}
}
allowed_lts.insert(RefLt::Unnamed);
allowed_lts.insert(RefLt::Static);
allowed_lts
}
fn lts_from_bounds<'a, T: Iterator<Item = &'a Lifetime>>(mut vec: Vec<RefLt>, bounds_lts: T) -> Vec<RefLt> {
for lt in bounds_lts {
if &*lt.name.as_str() != "'static" {
vec.push(RefLt::Named(lt.name));
}
}
vec
}
fn unique_lifetimes(lts: &[RefLt]) -> usize {
lts.iter().collect::<HashSet<_>>().len()
}
struct RefVisitor<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
lts: Vec<RefLt>,
}
impl<'v, 't> RefVisitor<'v, 't> {
fn new(cx: &'v LateContext<'v, 't>) -> RefVisitor<'v, 't> {
RefVisitor {
cx: cx,
lts: Vec::new(),
}
}
fn record(&mut self, lifetime: &Option<Lifetime>) {
if let Some(ref lt) = *lifetime {
if &*lt.name.as_str() == "'static" {
self.lts.push(RefLt::Static);
} else {
self.lts.push(RefLt::Named(lt.name));
}
} else {
self.lts.push(RefLt::Unnamed);
}
}
fn into_vec(self) -> Vec<RefLt> {
self.lts
}
fn collect_anonymous_lifetimes(&mut self, qpath: &QPath, ty: &Ty) {
let last_path_segment = &last_path_segment(qpath).parameters;
if let AngleBracketedParameters(ref params) = *last_path_segment {
if params.lifetimes.is_empty() {
match self.cx.tcx.tables().qpath_def(qpath, ty.id) {
Def::TyAlias(def_id) |
Def::Struct(def_id) => {
let generics = self.cx.tcx.item_generics(def_id);
for _ in generics.regions.as_slice() {
self.record(&None);
}
},
Def::Trait(def_id) => {
let trait_def = self.cx.tcx.trait_defs.borrow()[&def_id];
for _ in &self.cx.tcx.item_generics(trait_def.def_id).regions {
self.record(&None);
}
},
_ => (),
}
}
}
}
}
impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
self.record(&Some(*lifetime));
}
fn visit_ty(&mut self, ty: &'tcx Ty) {
match ty.node {
TyRptr(None, _) => {
self.record(&None);
},
TyPath(ref path) => {
self.collect_anonymous_lifetimes(path, ty);
},
TyImplTrait(ref param_bounds) => {
for bound in param_bounds {
if let RegionTyParamBound(_) = *bound {
self.record(&None);
}
}
},
_ => (),
}
walk_ty(self, ty);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
fn has_where_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, where_clause: &'tcx WhereClause) -> bool {
for predicate in &where_clause.predicates {
match *predicate {
WherePredicate::RegionPredicate(..) => return true,
WherePredicate::BoundPredicate(ref pred) => {
let mut visitor = RefVisitor::new(cx);
walk_ty(&mut visitor, &pred.bounded_ty);
if !visitor.lts.is_empty() {
return true;
}
let allowed_lts = allowed_lts_from(&pred.bound_lifetimes);
for bound in pred.bounds.iter() {
walk_ty_param_bound(&mut visitor, bound);
}
for lt in visitor.into_vec() {
if !allowed_lts.contains(<) {
return true;
}
}
},
WherePredicate::EqPredicate(ref pred) => {
let mut visitor = RefVisitor::new(cx);
walk_ty(&mut visitor, &pred.ty);
if !visitor.lts.is_empty() {
return true;
}
},
}
}
false
}
struct LifetimeChecker {
map: HashMap<Name, Span>,
}
impl<'tcx> Visitor<'tcx> for LifetimeChecker {
fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
self.map.remove(&lifetime.name);
}
fn visit_lifetime_def(&mut self, _: &'tcx LifetimeDef) {
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
fn report_extra_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, func: &'tcx FnDecl, generics: &'tcx Generics) {
let hs = generics.lifetimes
.iter()
.map(|lt| (lt.lifetime.name, lt.lifetime.span))
.collect();
let mut checker = LifetimeChecker { map: hs };
walk_generics(&mut checker, generics);
walk_fn_decl(&mut checker, func);
for &v in checker.map.values() {
span_lint(cx, UNUSED_LIFETIMES, v, "this lifetime isn't used in the function definition");
}
}