mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-22 02:53:20 +00:00
201 lines
6.6 KiB
Rust
201 lines
6.6 KiB
Rust
use clippy_utils::diagnostics::span_lint;
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use clippy_utils::ty::contains_ty;
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use rustc_hir::intravisit;
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use rustc_hir::{self, AssocItemKind, Body, FnDecl, HirId, HirIdSet, Impl, ItemKind, Node};
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use rustc_infer::infer::TyCtxtInferExt;
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::mir::FakeReadCause;
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use rustc_middle::ty::{self, TraitRef, Ty};
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::source_map::Span;
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use rustc_span::symbol::kw;
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use rustc_target::abi::LayoutOf;
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use rustc_target::spec::abi::Abi;
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use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
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#[derive(Copy, Clone)]
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pub struct BoxedLocal {
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pub too_large_for_stack: u64,
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for usage of `Box<T>` where an unboxed `T` would
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/// work fine.
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///
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/// **Why is this bad?** This is an unnecessary allocation, and bad for
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/// performance. It is only necessary to allocate if you wish to move the box
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/// into something.
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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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/// # fn foo(bar: usize) {}
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/// // Bad
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/// let x = Box::new(1);
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/// foo(*x);
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/// println!("{}", *x);
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///
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/// // Good
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/// let x = 1;
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/// foo(x);
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/// println!("{}", x);
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/// ```
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pub BOXED_LOCAL,
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perf,
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"using `Box<T>` where unnecessary"
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}
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fn is_non_trait_box(ty: Ty<'_>) -> bool {
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ty.is_box() && !ty.boxed_ty().is_trait()
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}
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struct EscapeDelegate<'a, 'tcx> {
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cx: &'a LateContext<'tcx>,
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set: HirIdSet,
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trait_self_ty: Option<Ty<'a>>,
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too_large_for_stack: u64,
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}
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impl_lint_pass!(BoxedLocal => [BOXED_LOCAL]);
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impl<'tcx> LateLintPass<'tcx> for BoxedLocal {
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fn check_fn(
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&mut self,
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cx: &LateContext<'tcx>,
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fn_kind: intravisit::FnKind<'tcx>,
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_: &'tcx FnDecl<'_>,
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body: &'tcx Body<'_>,
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_: Span,
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hir_id: HirId,
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) {
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if let Some(header) = fn_kind.header() {
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if header.abi != Abi::Rust {
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return;
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}
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}
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let parent_id = cx.tcx.hir().get_parent_item(hir_id);
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let parent_node = cx.tcx.hir().find(parent_id);
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let mut trait_self_ty = None;
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if let Some(Node::Item(item)) = parent_node {
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// If the method is an impl for a trait, don't warn.
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if let ItemKind::Impl(Impl { of_trait: Some(_), .. }) = item.kind {
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return;
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}
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// find `self` ty for this trait if relevant
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if let ItemKind::Trait(_, _, _, _, items) = item.kind {
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for trait_item in items {
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if trait_item.id.hir_id() == hir_id {
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// be sure we have `self` parameter in this function
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if let AssocItemKind::Fn { has_self: true } = trait_item.kind {
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trait_self_ty =
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Some(TraitRef::identity(cx.tcx, trait_item.id.def_id.to_def_id()).self_ty());
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}
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}
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}
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}
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}
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let mut v = EscapeDelegate {
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cx,
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set: HirIdSet::default(),
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trait_self_ty,
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too_large_for_stack: self.too_large_for_stack,
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};
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let fn_def_id = cx.tcx.hir().local_def_id(hir_id);
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cx.tcx.infer_ctxt().enter(|infcx| {
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ExprUseVisitor::new(&mut v, &infcx, fn_def_id, cx.param_env, cx.typeck_results()).consume_body(body);
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});
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for node in v.set {
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span_lint(
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cx,
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BOXED_LOCAL,
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cx.tcx.hir().span(node),
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"local variable doesn't need to be boxed here",
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);
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}
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}
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}
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// TODO: Replace with Map::is_argument(..) when it's fixed
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fn is_argument(map: rustc_middle::hir::map::Map<'_>, id: HirId) -> bool {
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match map.find(id) {
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Some(Node::Binding(_)) => (),
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_ => return false,
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}
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matches!(map.find(map.get_parent_node(id)), Some(Node::Param(_)))
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}
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impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
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fn consume(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId, mode: ConsumeMode) {
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if cmt.place.projections.is_empty() {
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if let PlaceBase::Local(lid) = cmt.place.base {
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if let ConsumeMode::Move = mode {
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// moved out or in. clearly can't be localized
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self.set.remove(&lid);
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}
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let map = &self.cx.tcx.hir();
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if let Some(Node::Binding(_)) = map.find(cmt.hir_id) {
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if self.set.contains(&lid) {
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// let y = x where x is known
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// remove x, insert y
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self.set.insert(cmt.hir_id);
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self.set.remove(&lid);
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}
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}
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}
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}
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}
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fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId, _: ty::BorrowKind) {
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if cmt.place.projections.is_empty() {
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if let PlaceBase::Local(lid) = cmt.place.base {
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self.set.remove(&lid);
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}
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}
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}
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fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId) {
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if cmt.place.projections.is_empty() {
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let map = &self.cx.tcx.hir();
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if is_argument(*map, cmt.hir_id) {
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// Skip closure arguments
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let parent_id = map.get_parent_node(cmt.hir_id);
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if let Some(Node::Expr(..)) = map.find(map.get_parent_node(parent_id)) {
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return;
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}
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// skip if there is a `self` parameter binding to a type
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// that contains `Self` (i.e.: `self: Box<Self>`), see #4804
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if let Some(trait_self_ty) = self.trait_self_ty {
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if map.name(cmt.hir_id) == kw::SelfLower && contains_ty(cmt.place.ty(), trait_self_ty) {
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return;
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}
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}
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if is_non_trait_box(cmt.place.ty()) && !self.is_large_box(cmt.place.ty()) {
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self.set.insert(cmt.hir_id);
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}
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}
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}
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}
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fn fake_read(&mut self, _: rustc_typeck::expr_use_visitor::Place<'tcx>, _: FakeReadCause, _: HirId) {}
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}
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impl<'a, 'tcx> EscapeDelegate<'a, 'tcx> {
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fn is_large_box(&self, ty: Ty<'tcx>) -> bool {
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// Large types need to be boxed to avoid stack overflows.
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if ty.is_box() {
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self.cx.layout_of(ty.boxed_ty()).map_or(0, |l| l.size.bytes()) > self.too_large_for_stack
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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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