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Auto merge of #5978 - montrivo:needless-lifetime, r=ebroto

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needless-lifetime - nested elision sites

Closes #2944

changelog: fix needless-lifetime nested elision site FPs
This commit is contained in:
bors 2020-10-01 13:43:24 +00:00
commit d4313737d8
6 changed files with 251 additions and 93 deletions
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169
clippy_lints/src/lifetimes.rs
View File

@ -1,21 +1,22 @@
use crate::utils::paths;
use crate::utils::{get_trait_def_id, in_macro, span_lint, trait_ref_of_method};
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir::def::{DefKind, Res};
use rustc_hir::intravisit::{
walk_fn_decl, walk_generic_param, walk_generics, walk_param_bound, walk_ty, NestedVisitorMap, Visitor,
walk_fn_decl, walk_generic_param, walk_generics, walk_item, walk_param_bound, walk_poly_trait_ref, walk_ty,
NestedVisitorMap, Visitor,
};
use rustc_hir::FnRetTy::Return;
use rustc_hir::{
BodyId, FnDecl, GenericArg, GenericBound, GenericParam, GenericParamKind, Generics, ImplItem, ImplItemKind, Item,
ItemKind, Lifetime, LifetimeName, ParamName, QPath, TraitBoundModifier, TraitFn, TraitItem, TraitItemKind, Ty,
TyKind, WhereClause, WherePredicate,
BareFnTy, BodyId, FnDecl, GenericArg, GenericBound, GenericParam, GenericParamKind, Generics, ImplItem,
ImplItemKind, Item, ItemKind, Lifetime, LifetimeName, ParamName, PolyTraitRef, TraitBoundModifier, TraitFn,
TraitItem, TraitItemKind, Ty, TyKind, WhereClause, WherePredicate,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::hir::map::Map;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use rustc_span::symbol::{kw, Symbol};
use crate::utils::{in_macro, last_path_segment, span_lint, trait_ref_of_method};
use std::iter::FromIterator;
declare_clippy_lint! {
/// **What it does:** Checks for lifetime annotations which can be removed by
@ -25,8 +26,11 @@ declare_clippy_lint! {
/// complicated, while there is nothing out of the ordinary going on. Removing
/// them leads to more readable code.
///
/// **Known problems:** Potential false negatives: we bail out if the function
/// has a `where` clause where lifetimes are mentioned.
/// **Known problems:**
/// - We bail out if the function has a `where` clause where lifetimes
/// are mentioned due to potenial false positives.
/// - Lifetime bounds such as `impl Foo + 'a` and `T: 'a` must be elided with the
/// placeholder notation `'_` because the fully elided notation leaves the type bound to `'static`.
///
/// **Example:**
/// ```rust
@ -108,7 +112,7 @@ impl<'tcx> LateLintPass<'tcx> for Lifetimes {
}
/// The lifetime of a &-reference.
#[derive(PartialEq, Eq, Hash, Debug)]
#[derive(PartialEq, Eq, Hash, Debug, Clone)]
enum RefLt {
Unnamed,
Static,
@ -127,7 +131,6 @@ fn check_fn_inner<'tcx>(
return;
}
let mut bounds_lts = Vec::new();
let types = generics
.params
.iter()
@ -156,13 +159,12 @@ fn check_fn_inner<'tcx>(
if bound.name != LifetimeName::Static && !bound.is_elided() {
return;
}
bounds_lts.push(bound);
}
}
}
}
}
if could_use_elision(cx, decl, body, &generics.params, bounds_lts) {
if could_use_elision(cx, decl, body, &generics.params) {
span_lint(
cx,
NEEDLESS_LIFETIMES,
@ -181,7 +183,6 @@ fn could_use_elision<'tcx>(
func: &'tcx FnDecl<'_>,
body: Option<BodyId>,
named_generics: &'tcx [GenericParam<'_>],
bounds_lts: Vec<&'tcx Lifetime>,
) -> bool {
// There are two scenarios where elision works:
// * no output references, all input references have different LT
@ -204,15 +205,31 @@ fn could_use_elision<'tcx>(
if let Return(ref ty) = func.output {
output_visitor.visit_ty(ty);
}
for lt in named_generics {
input_visitor.visit_generic_param(lt)
}
let input_lts = match input_visitor.into_vec() {
Some(lts) => lts_from_bounds(lts, bounds_lts.into_iter()),
None => return false,
};
let output_lts = match output_visitor.into_vec() {
Some(val) => val,
None => return false,
};
if input_visitor.abort() || output_visitor.abort() {
return false;
}
if allowed_lts
.intersection(&FxHashSet::from_iter(
input_visitor
.nested_elision_site_lts
.iter()
.chain(output_visitor.nested_elision_site_lts.iter())
.cloned()
.filter(|v| matches!(v, RefLt::Named(_))),
))
.next()
.is_some()
{
return false;
}
let input_lts = input_visitor.lts;
let output_lts = output_visitor.lts;
if let Some(body_id) = body {
let mut checker = BodyLifetimeChecker {
@ -277,27 +294,20 @@ fn allowed_lts_from(named_generics: &[GenericParam<'_>]) -> FxHashSet<RefLt> {
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 != LifetimeName::Static {
vec.push(RefLt::Named(lt.name.ident().name));
}
}
vec
}
/// Number of unique lifetimes in the given vector.
#[must_use]
fn unique_lifetimes(lts: &[RefLt]) -> usize {
lts.iter().collect::<FxHashSet<_>>().len()
}
const CLOSURE_TRAIT_BOUNDS: [&[&str]; 3] = [&paths::FN, &paths::FN_MUT, &paths::FN_ONCE];
/// A visitor usable for `rustc_front::visit::walk_ty()`.
struct RefVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
lts: Vec<RefLt>,
abort: bool,
nested_elision_site_lts: Vec<RefLt>,
unelided_trait_object_lifetime: bool,
}
impl<'a, 'tcx> RefVisitor<'a, 'tcx> {
@ -305,7 +315,8 @@ impl<'a, 'tcx> RefVisitor<'a, 'tcx> {
Self {
cx,
lts: Vec::new(),
abort: false,
nested_elision_site_lts: Vec::new(),
unelided_trait_object_lifetime: false,
}
}
@ -325,40 +336,16 @@ impl<'a, 'tcx> RefVisitor<'a, 'tcx> {
}
}
fn into_vec(self) -> Option<Vec<RefLt>> {
if self.abort {
None
} else {
Some(self.lts)
}
fn all_lts(&self) -> Vec<RefLt> {
self.lts
.iter()
.chain(self.nested_elision_site_lts.iter())
.cloned()
.collect::<Vec<_>>()
}
fn collect_anonymous_lifetimes(&mut self, qpath: &QPath<'_>, ty: &Ty<'_>) {
if let Some(ref last_path_segment) = last_path_segment(qpath).args {
if !last_path_segment.parenthesized
&& !last_path_segment
.args
.iter()
.any(|arg| matches!(arg, GenericArg::Lifetime(_)))
{
let hir_id = ty.hir_id;
match self.cx.qpath_res(qpath, hir_id) {
Res::Def(DefKind::TyAlias | DefKind::Struct, def_id) => {
let generics = self.cx.tcx.generics_of(def_id);
for _ in generics.params.as_slice() {
self.record(&None);
}
},
Res::Def(DefKind::Trait, def_id) => {
let trait_def = self.cx.tcx.trait_def(def_id);
for _ in &self.cx.tcx.generics_of(trait_def.def_id).params {
self.record(&None);
}
},
_ => (),
}
}
}
fn abort(&self) -> bool {
self.unelided_trait_object_lifetime
}
}
@ -370,30 +357,37 @@ impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
self.record(&Some(*lifetime));
}
fn visit_poly_trait_ref(&mut self, poly_tref: &'tcx PolyTraitRef<'tcx>, tbm: TraitBoundModifier) {
let trait_ref = &poly_tref.trait_ref;
if CLOSURE_TRAIT_BOUNDS
.iter()
.any(|trait_path| trait_ref.trait_def_id() == get_trait_def_id(self.cx, trait_path))
{
let mut sub_visitor = RefVisitor::new(self.cx);
sub_visitor.visit_trait_ref(trait_ref);
self.nested_elision_site_lts.append(&mut sub_visitor.all_lts());
} else {
walk_poly_trait_ref(self, poly_tref, tbm);
}
}
fn visit_ty(&mut self, ty: &'tcx Ty<'_>) {
match ty.kind {
TyKind::Rptr(ref lt, _) if lt.is_elided() => {
self.record(&None);
},
TyKind::Path(ref path) => {
self.collect_anonymous_lifetimes(path, ty);
},
TyKind::OpaqueDef(item, _) => {
let map = self.cx.tcx.hir();
if let ItemKind::OpaqueTy(ref exist_ty) = map.expect_item(item.id).kind {
for bound in exist_ty.bounds {
if let GenericBound::Outlives(_) = *bound {
self.record(&None);
}
}
} else {
unreachable!()
}
let item = map.expect_item(item.id);
walk_item(self, item);
walk_ty(self, ty);
},
TyKind::BareFn(&BareFnTy { decl, .. }) => {
let mut sub_visitor = RefVisitor::new(self.cx);
sub_visitor.visit_fn_decl(decl);
self.nested_elision_site_lts.append(&mut sub_visitor.all_lts());
return;
},
TyKind::TraitObject(bounds, ref lt) => {
if !lt.is_elided() {
self.abort = true;
self.unelided_trait_object_lifetime = true;
}
for bound in bounds {
self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
@ -430,16 +424,7 @@ fn has_where_lifetimes<'tcx>(cx: &LateContext<'tcx>, where_clause: &'tcx WhereCl
walk_param_bound(&mut visitor, bound);
}
// and check that all lifetimes are allowed
match visitor.into_vec() {
None => return false,
Some(lts) => {
for lt in lts {
if !allowed_lts.contains(&lt) {
return true;
}
}
},
}
return visitor.all_lts().iter().any(|it| !allowed_lts.contains(it));
},
WherePredicate::EqPredicate(ref pred) => {
let mut visitor = RefVisitor::new(cx);

3
clippy_lints/src/utils/paths.rs
View File

@ -42,6 +42,9 @@ pub const FILE_TYPE: [&str; 3] = ["std", "fs", "FileType"];
pub const FMT_ARGUMENTS_NEW_V1: [&str; 4] = ["core", "fmt", "Arguments", "new_v1"];
pub const FMT_ARGUMENTS_NEW_V1_FORMATTED: [&str; 4] = ["core", "fmt", "Arguments", "new_v1_formatted"];
pub const FMT_ARGUMENTV1_NEW: [&str; 4] = ["core", "fmt", "ArgumentV1", "new"];
pub const FN: [&str; 3] = ["core", "ops", "Fn"];
pub const FN_MUT: [&str; 3] = ["core", "ops", "FnMut"];
pub const FN_ONCE: [&str; 3] = ["core", "ops", "FnOnce"];
pub const FROM_FROM: [&str; 4] = ["core", "convert", "From", "from"];
pub const FROM_TRAIT: [&str; 3] = ["core", "convert", "From"];
pub const FUTURE_FROM_GENERATOR: [&str; 3] = ["core", "future", "from_generator"];

10
tests/ui/crashes/ice-2774.stderr Normal file
View File

@ -0,0 +1,10 @@
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/ice-2774.rs:15:1
|
LL | pub fn add_barfoos_to_foos<'a>(bars: &HashSet<&'a Bar>) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `-D clippy::needless-lifetimes` implied by `-D warnings`
error: aborting due to previous error

14
tests/ui/crashes/needless_lifetimes_impl_trait.stderr Normal file
View File

@ -0,0 +1,14 @@
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes_impl_trait.rs:15:5
|
LL | fn baz<'a>(&'a self) -> impl Foo + 'a {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: the lint level is defined here
--> $DIR/needless_lifetimes_impl_trait.rs:1:9
|
LL | #![deny(clippy::needless_lifetimes)]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to previous error

98
tests/ui/needless_lifetimes.rs
View File

@ -259,4 +259,102 @@ mod issue4291 {
}
}
mod issue2944 {
trait Foo {}
struct Bar {}
struct Baz<'a> {
bar: &'a Bar,
}
impl<'a> Foo for Baz<'a> {}
impl Bar {
fn baz<'a>(&'a self) -> impl Foo + 'a {
Baz { bar: self }
}
}
}
mod nested_elision_sites {
// issue #issue2944
// closure trait bounds subject to nested elision
// don't lint because they refer to outer lifetimes
fn trait_fn<'a>(i: &'a i32) -> impl Fn() -> &'a i32 {
move || i
}
fn trait_fn_mut<'a>(i: &'a i32) -> impl FnMut() -> &'a i32 {
move || i
}
fn trait_fn_once<'a>(i: &'a i32) -> impl FnOnce() -> &'a i32 {
move || i
}
// don't lint
fn impl_trait_in_input_position<'a>(f: impl Fn() -> &'a i32) -> &'a i32 {
f()
}
fn impl_trait_in_output_position<'a>(i: &'a i32) -> impl Fn() -> &'a i32 {
move || i
}
// lint
fn impl_trait_elidable_nested_named_lifetimes<'a>(i: &'a i32, f: impl for<'b> Fn(&'b i32) -> &'b i32) -> &'a i32 {
f(i)
}
fn impl_trait_elidable_nested_anonymous_lifetimes<'a>(i: &'a i32, f: impl Fn(&i32) -> &i32) -> &'a i32 {
f(i)
}
// don't lint
fn generics_not_elidable<'a, T: Fn() -> &'a i32>(f: T) -> &'a i32 {
f()
}
// lint
fn generics_elidable<'a, T: Fn(&i32) -> &i32>(i: &'a i32, f: T) -> &'a i32 {
f(i)
}
// don't lint
fn where_clause_not_elidable<'a, T>(f: T) -> &'a i32
where
T: Fn() -> &'a i32,
{
f()
}
// lint
fn where_clause_elidadable<'a, T>(i: &'a i32, f: T) -> &'a i32
where
T: Fn(&i32) -> &i32,
{
f(i)
}
// don't lint
fn pointer_fn_in_input_position<'a>(f: fn(&'a i32) -> &'a i32, i: &'a i32) -> &'a i32 {
f(i)
}
fn pointer_fn_in_output_position<'a>(_: &'a i32) -> fn(&'a i32) -> &'a i32 {
|i| i
}
// lint
fn pointer_fn_elidable<'a>(i: &'a i32, f: fn(&i32) -> &i32) -> &'a i32 {
f(i)
}
// don't lint
fn nested_fn_pointer_1<'a>(_: &'a i32) -> fn(fn(&'a i32) -> &'a i32) -> i32 {
|f| 42
}
fn nested_fn_pointer_2<'a>(_: &'a i32) -> impl Fn(fn(&'a i32)) {
|f| ()
}
// lint
fn nested_fn_pointer_3<'a>(_: &'a i32) -> fn(fn(&i32) -> &i32) -> i32 {
|f| 42
}
fn nested_fn_pointer_4<'a>(_: &'a i32) -> impl Fn(fn(&i32)) {
|f| ()
}
}
fn main() {}

50
tests/ui/needless_lifetimes.stderr
View File

@ -102,5 +102,53 @@ error: explicit lifetimes given in parameter types where they could be elided (o
LL | fn needless_lt<'a>(_x: &'a u8) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 17 previous errors
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:271:9
|
LL | fn baz<'a>(&'a self) -> impl Foo + 'a {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:300:5
|
LL | fn impl_trait_elidable_nested_named_lifetimes<'a>(i: &'a i32, f: impl for<'b> Fn(&'b i32) -> &'b i32) -> &'a i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:303:5
|
LL | fn impl_trait_elidable_nested_anonymous_lifetimes<'a>(i: &'a i32, f: impl Fn(&i32) -> &i32) -> &'a i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:312:5
|
LL | fn generics_elidable<'a, T: Fn(&i32) -> &i32>(i: &'a i32, f: T) -> &'a i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:324:5
|
LL | fn where_clause_elidadable<'a, T>(i: &'a i32, f: T) -> &'a i32
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:339:5
|
LL | fn pointer_fn_elidable<'a>(i: &'a i32, f: fn(&i32) -> &i32) -> &'a i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:352:5
|
LL | fn nested_fn_pointer_3<'a>(_: &'a i32) -> fn(fn(&i32) -> &i32) -> i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:355:5
|
LL | fn nested_fn_pointer_4<'a>(_: &'a i32) -> impl Fn(fn(&i32)) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 25 previous errors