mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-13 23:02:43 +00:00
168 lines
5 KiB
Rust
168 lines
5 KiB
Rust
use rustc_hir::intravisit;
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use rustc_hir::{self, Body, FnDecl, HirId, HirIdSet, 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::ty::{self, 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_target::abi::LayoutOf;
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use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
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use crate::utils::span_lint;
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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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///
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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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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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_: 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 the method is an impl for a trait, don't warn.
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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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if let Some(Node::Item(item)) = parent_node {
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if let ItemKind::Impl { of_trait: Some(_), .. } = item.kind {
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return;
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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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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.tables()).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>, 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>, _: 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>) {
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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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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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return;
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}
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}
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}
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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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