rust-clippy/src/lifetimes.rs

266 lines
9 KiB
Rust

use rustc_front::hir::*;
use reexport::*;
use rustc::lint::*;
use syntax::codemap::Span;
use rustc_front::intravisit::{Visitor, walk_ty, walk_ty_param_bound};
use rustc::middle::def::Def::{DefTy, DefTrait, DefStruct};
use std::collections::HashSet;
use utils::{in_external_macro, span_lint};
declare_lint!(pub NEEDLESS_LIFETIMES, Warn,
"using explicit lifetimes for references in function arguments when elision rules \
would allow omitting them");
#[derive(Copy,Clone)]
pub struct LifetimePass;
impl LintPass for LifetimePass {
fn get_lints(&self) -> LintArray {
lint_array!(NEEDLESS_LIFETIMES)
}
}
impl LateLintPass for LifetimePass {
fn check_item(&mut self, cx: &LateContext, item: &Item) {
if let ItemFn(ref decl, _, _, _, ref generics, _) = item.node {
check_fn_inner(cx, decl, None, &generics, item.span);
}
}
fn check_impl_item(&mut self, cx: &LateContext, item: &ImplItem) {
if let ImplItemKind::Method(ref sig, _) = item.node {
check_fn_inner(cx, &sig.decl, Some(&sig.explicit_self),
&sig.generics, item.span);
}
}
fn check_trait_item(&mut self, cx: &LateContext, item: &TraitItem) {
if let MethodTraitItem(ref sig, _) = item.node {
check_fn_inner(cx, &sig.decl, Some(&sig.explicit_self),
&sig.generics, item.span);
}
}
}
/// The lifetime of a &-reference.
#[derive(PartialEq, Eq, Hash, Debug)]
enum RefLt {
Unnamed,
Static,
Named(Name),
}
use self::RefLt::*;
fn check_fn_inner(cx: &LateContext, decl: &FnDecl, slf: Option<&ExplicitSelf>,
generics: &Generics, span: Span) {
if in_external_macro(cx, span) || has_where_lifetimes(cx, &generics.where_clause) {
return;
}
if could_use_elision(cx, decl, slf, &generics.lifetimes) {
span_lint(cx, NEEDLESS_LIFETIMES, span,
"explicit lifetimes given in parameter types where they could be elided");
}
}
fn could_use_elision(cx: &LateContext, func: &FnDecl, slf: Option<&ExplicitSelf>,
named_lts: &[LifetimeDef]) -> bool {
// There are two scenarios where elision works:
// * no output references, all input references have different LT
// * output references, exactly one input reference with same LT
// All lifetimes must be unnamed, 'static or defined without bounds on the
// level of the current item.
// check named LTs
let allowed_lts = allowed_lts_from(named_lts);
// these will collect all the lifetimes for references in arg/return types
let mut input_visitor = RefVisitor::new(cx);
let mut output_visitor = RefVisitor::new(cx);
// extract lifetime in "self" argument for methods (there is a "self" argument
// in func.inputs, but its type is TyInfer)
if let Some(slf) = slf {
match slf.node {
SelfRegion(ref opt_lt, _, _) => input_visitor.record(opt_lt),
SelfExplicit(ref ty, _) => walk_ty(&mut input_visitor, ty),
_ => { }
}
}
// extract lifetimes in input argument types
for arg in &func.inputs {
input_visitor.visit_ty(&arg.ty);
}
// extract lifetimes in output type
if let Return(ref ty) = func.output {
output_visitor.visit_ty(ty);
}
let input_lts = input_visitor.into_vec();
let output_lts = output_visitor.into_vec();
// check for lifetimes from higher scopes
for lt in input_lts.iter().chain(output_lts.iter()) {
if !allowed_lts.contains(lt) {
return false;
}
}
// no input lifetimes? easy case!
if input_lts.is_empty() {
return false;
} else if output_lts.is_empty() {
// no output lifetimes, check distinctness of input lifetimes
// only unnamed and static, ok
if input_lts.iter().all(|lt| *lt == Unnamed || *lt == Static) {
return false;
}
// we have no output reference, so we only need all distinct lifetimes
if input_lts.len() == unique_lifetimes(&input_lts) {
return true;
}
} else {
// we have output references, so we need one input reference,
// and all output lifetimes must be the same
if unique_lifetimes(&output_lts) > 1 {
return false;
}
if input_lts.len() == 1 {
match (&input_lts[0], &output_lts[0]) {
(&Named(n1), &Named(n2)) if n1 == n2 => { return true; }
(&Named(_), &Unnamed) => { return true; }
(&Unnamed, &Named(_)) => { return true; }
_ => { } // already elided, different named lifetimes
// or something static going on
}
}
}
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(Named(lt.lifetime.name));
}
}
allowed_lts.insert(Unnamed);
allowed_lts.insert(Static);
allowed_lts
}
/// Number of unique lifetimes in the given vector.
fn unique_lifetimes(lts: &[RefLt]) -> usize {
lts.iter().collect::<HashSet<_>>().len()
}
/// A visitor usable for rustc_front::visit::walk_ty().
struct RefVisitor<'v, 't: 'v> {
cx: &'v LateContext<'v, 't>, // context reference
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(Static);
} else {
self.lts.push(Named(lt.name));
}
} else {
self.lts.push(Unnamed);
}
}
fn into_vec(self) -> Vec<RefLt> {
self.lts
}
fn collect_anonymous_lifetimes(&mut self, path: &Path, ty: &Ty) {
let last_path_segment = path.segments.last().map(|s| &s.parameters);
if let Some(&AngleBracketedParameters(ref params)) = last_path_segment {
if params.lifetimes.is_empty() {
if let Some(def) = self.cx.tcx.def_map.borrow().get(&ty.id).map(|r| r.full_def()) {
match def {
DefTy(def_id, _) | DefStruct(def_id) => {
let type_scheme = self.cx.tcx.lookup_item_type(def_id);
for _ in type_scheme.generics.regions.as_slice() {
self.record(&None);
}
},
DefTrait(def_id) => {
let trait_def = self.cx.tcx.trait_defs.borrow()[&def_id];
for _ in &trait_def.generics.regions {
self.record(&None);
}
},
_ => {}
}
}
}
}
}
}
impl<'v, 't> Visitor<'v> for RefVisitor<'v, 't> {
// for lifetimes as parameters of generics
fn visit_lifetime(&mut self, lifetime: &'v Lifetime) {
self.record(&Some(*lifetime));
}
fn visit_ty(&mut self, ty: &'v Ty) {
match ty.node {
TyRptr(None, _) => {
self.record(&None);
}
TyPath(_, ref path) => {
self.collect_anonymous_lifetimes(path, ty);
}
_ => {}
}
walk_ty(self, ty);
}
}
/// Are any lifetimes mentioned in the `where` clause? If yes, we don't try to
/// reason about elision.
fn has_where_lifetimes(cx: &LateContext, where_clause: &WhereClause) -> bool {
for predicate in &where_clause.predicates {
match *predicate {
WherePredicate::RegionPredicate(..) => return true,
WherePredicate::BoundPredicate(ref pred) => {
// a predicate like F: Trait or F: for<'a> Trait<'a>
let mut visitor = RefVisitor::new(cx);
// walk the type F, it may not contain LT refs
walk_ty(&mut visitor, &pred.bounded_ty);
if !visitor.lts.is_empty() { return true; }
// if the bounds define new lifetimes, they are fine to occur
let allowed_lts = allowed_lts_from(&pred.bound_lifetimes);
// now walk the bounds
for bound in pred.bounds.iter() {
walk_ty_param_bound(&mut visitor, bound);
}
// and check that all lifetimes are allowed
for lt in visitor.into_vec() {
if !allowed_lts.contains(&lt) {
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
}