513 lines
17 KiB
Rust
513 lines
17 KiB
Rust
use crate::utils::paths;
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use crate::utils::{get_trait_def_id, in_macro, span_lint, trait_ref_of_method};
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use rustc_data_structures::fx::{FxHashMap, FxHashSet};
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use rustc_hir::intravisit::{
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walk_fn_decl, walk_generic_param, walk_generics, walk_item, walk_param_bound, walk_poly_trait_ref, walk_ty,
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NestedVisitorMap, Visitor,
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};
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use rustc_hir::FnRetTy::Return;
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use rustc_hir::{
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BareFnTy, BodyId, FnDecl, GenericArg, GenericBound, GenericParam, GenericParamKind, Generics, ImplItem,
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ImplItemKind, Item, ItemKind, Lifetime, LifetimeName, ParamName, PolyTraitRef, TraitBoundModifier, TraitFn,
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TraitItem, TraitItemKind, Ty, TyKind, WhereClause, WherePredicate,
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};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::hir::map::Map;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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use rustc_span::symbol::{kw, Symbol};
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use std::iter::FromIterator;
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declare_clippy_lint! {
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/// **What it does:** Checks for lifetime annotations which can be removed by
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/// relying on lifetime elision.
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///
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/// **Why is this bad?** The additional lifetimes make the code look more
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/// complicated, while there is nothing out of the ordinary going on. Removing
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/// them leads to more readable code.
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///
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/// **Known problems:**
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/// - We bail out if the function has a `where` clause where lifetimes
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/// are mentioned due to potenial false positives.
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/// - Lifetime bounds such as `impl Foo + 'a` and `T: 'a` must be elided with the
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/// placeholder notation `'_` because the fully elided notation leaves the type bound to `'static`.
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///
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/// **Example:**
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/// ```rust
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/// // Bad: unnecessary lifetime annotations
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/// fn in_and_out<'a>(x: &'a u8, y: u8) -> &'a u8 {
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/// x
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/// }
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///
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/// // Good
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/// fn elided(x: &u8, y: u8) -> &u8 {
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/// x
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/// }
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/// ```
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pub NEEDLESS_LIFETIMES,
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complexity,
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"using explicit lifetimes for references in function arguments when elision rules \
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would allow omitting them"
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for lifetimes in generics that are never used
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/// anywhere else.
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///
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/// **Why is this bad?** The additional lifetimes make the code look more
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/// complicated, while there is nothing out of the ordinary going on. Removing
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/// them leads to more readable code.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// // Bad: unnecessary lifetimes
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/// fn unused_lifetime<'a>(x: u8) {
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/// // ..
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/// }
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///
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/// // Good
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/// fn no_lifetime(x: u8) {
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/// // ...
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/// }
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/// ```
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pub EXTRA_UNUSED_LIFETIMES,
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complexity,
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"unused lifetimes in function definitions"
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}
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declare_lint_pass!(Lifetimes => [NEEDLESS_LIFETIMES, EXTRA_UNUSED_LIFETIMES]);
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impl<'tcx> LateLintPass<'tcx> for Lifetimes {
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fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
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if let ItemKind::Fn(ref sig, ref generics, id) = item.kind {
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check_fn_inner(cx, &sig.decl, Some(id), generics, item.span, true);
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}
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}
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fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
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if let ImplItemKind::Fn(ref sig, id) = item.kind {
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let report_extra_lifetimes = trait_ref_of_method(cx, item.hir_id).is_none();
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check_fn_inner(
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cx,
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&sig.decl,
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Some(id),
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&item.generics,
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item.span,
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report_extra_lifetimes,
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);
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}
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}
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fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
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if let TraitItemKind::Fn(ref sig, ref body) = item.kind {
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let body = match *body {
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TraitFn::Required(_) => None,
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TraitFn::Provided(id) => Some(id),
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};
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check_fn_inner(cx, &sig.decl, body, &item.generics, item.span, true);
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}
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}
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}
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/// The lifetime of a &-reference.
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#[derive(PartialEq, Eq, Hash, Debug, Clone)]
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enum RefLt {
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Unnamed,
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Static,
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Named(Symbol),
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}
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fn check_fn_inner<'tcx>(
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cx: &LateContext<'tcx>,
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decl: &'tcx FnDecl<'_>,
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body: Option<BodyId>,
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generics: &'tcx Generics<'_>,
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span: Span,
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report_extra_lifetimes: bool,
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) {
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if in_macro(span) || has_where_lifetimes(cx, &generics.where_clause) {
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return;
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}
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let types = generics
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.params
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.iter()
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.filter(|param| matches!(param.kind, GenericParamKind::Type { .. }));
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for typ in types {
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for bound in typ.bounds {
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let mut visitor = RefVisitor::new(cx);
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walk_param_bound(&mut visitor, bound);
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if visitor.lts.iter().any(|lt| matches!(lt, RefLt::Named(_))) {
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return;
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}
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if let GenericBound::Trait(ref trait_ref, _) = *bound {
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let params = &trait_ref
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.trait_ref
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.path
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.segments
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.last()
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.expect("a path must have at least one segment")
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.args;
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if let Some(ref params) = *params {
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let lifetimes = params.args.iter().filter_map(|arg| match arg {
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GenericArg::Lifetime(lt) => Some(lt),
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_ => None,
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});
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for bound in lifetimes {
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if bound.name != LifetimeName::Static && !bound.is_elided() {
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return;
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}
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}
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}
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}
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}
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}
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if could_use_elision(cx, decl, body, &generics.params) {
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span_lint(
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cx,
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NEEDLESS_LIFETIMES,
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span.with_hi(decl.output.span().hi()),
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"explicit lifetimes given in parameter types where they could be elided \
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(or replaced with `'_` if needed by type declaration)",
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);
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}
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if report_extra_lifetimes {
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self::report_extra_lifetimes(cx, decl, generics);
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}
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}
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fn could_use_elision<'tcx>(
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cx: &LateContext<'tcx>,
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func: &'tcx FnDecl<'_>,
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body: Option<BodyId>,
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named_generics: &'tcx [GenericParam<'_>],
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) -> bool {
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// There are two scenarios where elision works:
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// * no output references, all input references have different LT
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// * output references, exactly one input reference with same LT
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// All lifetimes must be unnamed, 'static or defined without bounds on the
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// level of the current item.
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// check named LTs
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let allowed_lts = allowed_lts_from(named_generics);
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// these will collect all the lifetimes for references in arg/return types
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let mut input_visitor = RefVisitor::new(cx);
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let mut output_visitor = RefVisitor::new(cx);
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// extract lifetimes in input argument types
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for arg in func.inputs {
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input_visitor.visit_ty(arg);
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}
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// extract lifetimes in output type
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if let Return(ref ty) = func.output {
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output_visitor.visit_ty(ty);
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}
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for lt in named_generics {
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input_visitor.visit_generic_param(lt)
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}
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if input_visitor.abort() || output_visitor.abort() {
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return false;
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}
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if allowed_lts
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.intersection(&FxHashSet::from_iter(
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input_visitor
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.nested_elision_site_lts
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.iter()
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.chain(output_visitor.nested_elision_site_lts.iter())
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.cloned()
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.filter(|v| matches!(v, RefLt::Named(_))),
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))
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.next()
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.is_some()
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{
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return false;
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}
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let input_lts = input_visitor.lts;
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let output_lts = output_visitor.lts;
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if let Some(body_id) = body {
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let mut checker = BodyLifetimeChecker {
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lifetimes_used_in_body: false,
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};
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checker.visit_expr(&cx.tcx.hir().body(body_id).value);
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if checker.lifetimes_used_in_body {
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return false;
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}
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}
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// check for lifetimes from higher scopes
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for lt in input_lts.iter().chain(output_lts.iter()) {
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if !allowed_lts.contains(lt) {
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return false;
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}
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}
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// no input lifetimes? easy case!
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if input_lts.is_empty() {
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false
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} else if output_lts.is_empty() {
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// no output lifetimes, check distinctness of input lifetimes
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// only unnamed and static, ok
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let unnamed_and_static = input_lts.iter().all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static);
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if unnamed_and_static {
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return false;
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}
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// we have no output reference, so we only need all distinct lifetimes
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input_lts.len() == unique_lifetimes(&input_lts)
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} else {
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// we have output references, so we need one input reference,
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// and all output lifetimes must be the same
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if unique_lifetimes(&output_lts) > 1 {
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return false;
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}
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if input_lts.len() == 1 {
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match (&input_lts[0], &output_lts[0]) {
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(&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
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(&RefLt::Named(_), &RefLt::Unnamed) => true,
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_ => false, /* already elided, different named lifetimes
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* or something static going on */
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}
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} else {
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false
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}
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}
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}
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fn allowed_lts_from(named_generics: &[GenericParam<'_>]) -> FxHashSet<RefLt> {
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let mut allowed_lts = FxHashSet::default();
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for par in named_generics.iter() {
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if let GenericParamKind::Lifetime { .. } = par.kind {
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if par.bounds.is_empty() {
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allowed_lts.insert(RefLt::Named(par.name.ident().name));
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}
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}
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}
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allowed_lts.insert(RefLt::Unnamed);
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allowed_lts.insert(RefLt::Static);
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allowed_lts
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}
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/// Number of unique lifetimes in the given vector.
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#[must_use]
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fn unique_lifetimes(lts: &[RefLt]) -> usize {
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lts.iter().collect::<FxHashSet<_>>().len()
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}
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const CLOSURE_TRAIT_BOUNDS: [&[&str]; 3] = [&paths::FN, &paths::FN_MUT, &paths::FN_ONCE];
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/// A visitor usable for `rustc_front::visit::walk_ty()`.
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struct RefVisitor<'a, 'tcx> {
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cx: &'a LateContext<'tcx>,
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lts: Vec<RefLt>,
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nested_elision_site_lts: Vec<RefLt>,
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unelided_trait_object_lifetime: bool,
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}
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impl<'a, 'tcx> RefVisitor<'a, 'tcx> {
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fn new(cx: &'a LateContext<'tcx>) -> Self {
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Self {
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cx,
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lts: Vec::new(),
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nested_elision_site_lts: Vec::new(),
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unelided_trait_object_lifetime: false,
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}
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}
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fn record(&mut self, lifetime: &Option<Lifetime>) {
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if let Some(ref lt) = *lifetime {
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if lt.name == LifetimeName::Static {
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self.lts.push(RefLt::Static);
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} else if let LifetimeName::Param(ParamName::Fresh(_)) = lt.name {
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// Fresh lifetimes generated should be ignored.
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} else if lt.is_elided() {
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self.lts.push(RefLt::Unnamed);
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} else {
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self.lts.push(RefLt::Named(lt.name.ident().name));
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}
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} else {
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self.lts.push(RefLt::Unnamed);
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}
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}
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fn all_lts(&self) -> Vec<RefLt> {
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self.lts
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.iter()
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.chain(self.nested_elision_site_lts.iter())
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.cloned()
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.collect::<Vec<_>>()
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}
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fn abort(&self) -> bool {
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self.unelided_trait_object_lifetime
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}
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}
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impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
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type Map = Map<'tcx>;
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// for lifetimes as parameters of generics
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fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
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self.record(&Some(*lifetime));
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}
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fn visit_poly_trait_ref(&mut self, poly_tref: &'tcx PolyTraitRef<'tcx>, tbm: TraitBoundModifier) {
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let trait_ref = &poly_tref.trait_ref;
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if CLOSURE_TRAIT_BOUNDS
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.iter()
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.any(|trait_path| trait_ref.trait_def_id() == get_trait_def_id(self.cx, trait_path))
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{
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let mut sub_visitor = RefVisitor::new(self.cx);
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sub_visitor.visit_trait_ref(trait_ref);
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self.nested_elision_site_lts.append(&mut sub_visitor.all_lts());
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} else {
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walk_poly_trait_ref(self, poly_tref, tbm);
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}
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}
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fn visit_ty(&mut self, ty: &'tcx Ty<'_>) {
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match ty.kind {
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TyKind::OpaqueDef(item, _) => {
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let map = self.cx.tcx.hir();
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let item = map.expect_item(item.id);
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walk_item(self, item);
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walk_ty(self, ty);
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},
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TyKind::BareFn(&BareFnTy { decl, .. }) => {
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let mut sub_visitor = RefVisitor::new(self.cx);
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sub_visitor.visit_fn_decl(decl);
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self.nested_elision_site_lts.append(&mut sub_visitor.all_lts());
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return;
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},
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TyKind::TraitObject(bounds, ref lt) => {
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if !lt.is_elided() {
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self.unelided_trait_object_lifetime = true;
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}
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for bound in bounds {
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self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
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}
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return;
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},
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_ => (),
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}
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walk_ty(self, ty);
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}
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fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
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NestedVisitorMap::None
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}
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}
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/// Are any lifetimes mentioned in the `where` clause? If so, we don't try to
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/// reason about elision.
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fn has_where_lifetimes<'tcx>(cx: &LateContext<'tcx>, where_clause: &'tcx WhereClause<'_>) -> bool {
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for predicate in where_clause.predicates {
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match *predicate {
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WherePredicate::RegionPredicate(..) => return true,
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WherePredicate::BoundPredicate(ref pred) => {
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// a predicate like F: Trait or F: for<'a> Trait<'a>
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let mut visitor = RefVisitor::new(cx);
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// walk the type F, it may not contain LT refs
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walk_ty(&mut visitor, &pred.bounded_ty);
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if !visitor.all_lts().is_empty() {
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return true;
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}
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// if the bounds define new lifetimes, they are fine to occur
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let allowed_lts = allowed_lts_from(&pred.bound_generic_params);
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// now walk the bounds
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for bound in pred.bounds.iter() {
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walk_param_bound(&mut visitor, bound);
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}
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// and check that all lifetimes are allowed
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if visitor.all_lts().iter().any(|it| !allowed_lts.contains(it)) {
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return true;
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}
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},
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WherePredicate::EqPredicate(ref pred) => {
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let mut visitor = RefVisitor::new(cx);
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walk_ty(&mut visitor, &pred.lhs_ty);
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walk_ty(&mut visitor, &pred.rhs_ty);
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if !visitor.lts.is_empty() {
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return true;
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}
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},
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}
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}
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false
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}
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|
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struct LifetimeChecker {
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map: FxHashMap<Symbol, Span>,
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}
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impl<'tcx> Visitor<'tcx> for LifetimeChecker {
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type Map = Map<'tcx>;
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|
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// for lifetimes as parameters of generics
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fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
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self.map.remove(&lifetime.name.ident().name);
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}
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fn visit_generic_param(&mut self, param: &'tcx GenericParam<'_>) {
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// don't actually visit `<'a>` or `<'a: 'b>`
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// we've already visited the `'a` declarations and
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// don't want to spuriously remove them
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// `'b` in `'a: 'b` is useless unless used elsewhere in
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// a non-lifetime bound
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if let GenericParamKind::Type { .. } = param.kind {
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walk_generic_param(self, param)
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}
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}
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fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
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NestedVisitorMap::None
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}
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}
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fn report_extra_lifetimes<'tcx>(cx: &LateContext<'tcx>, func: &'tcx FnDecl<'_>, generics: &'tcx Generics<'_>) {
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let hs = generics
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.params
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.iter()
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.filter_map(|par| match par.kind {
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GenericParamKind::Lifetime { .. } => Some((par.name.ident().name, par.span)),
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_ => None,
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})
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.collect();
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let mut checker = LifetimeChecker { map: hs };
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walk_generics(&mut checker, generics);
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walk_fn_decl(&mut checker, func);
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|
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for &v in checker.map.values() {
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span_lint(
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cx,
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EXTRA_UNUSED_LIFETIMES,
|
|
v,
|
|
"this lifetime isn't used in the function definition",
|
|
);
|
|
}
|
|
}
|
|
|
|
struct BodyLifetimeChecker {
|
|
lifetimes_used_in_body: bool,
|
|
}
|
|
|
|
impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
|
|
type Map = Map<'tcx>;
|
|
|
|
// for lifetimes as parameters of generics
|
|
fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
|
|
if lifetime.name.ident().name != kw::Invalid && lifetime.name.ident().name != kw::StaticLifetime {
|
|
self.lifetimes_used_in_body = true;
|
|
}
|
|
}
|
|
|
|
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
|
|
NestedVisitorMap::None
|
|
}
|
|
}
|