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|
use clippy_utils::diagnostics::span_lint_hir;
use rustc_hir::intravisit;
use rustc_hir::{self, AssocItemKind, Body, FnDecl, HirId, HirIdSet, Impl, ItemKind, Node, Pat, PatKind};
use rustc_hir_typeck::expr_use_visitor::{Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::mir::FakeReadCause;
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::{self, TraitRef, Ty};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::def_id::LocalDefId;
use rustc_span::source_map::Span;
use rustc_span::symbol::kw;
use rustc_target::spec::abi::Abi;
#[derive(Copy, Clone)]
pub struct BoxedLocal {
pub too_large_for_stack: u64,
}
declare_clippy_lint! {
/// ### What it does
/// Checks for usage of `Box<T>` where an unboxed `T` would
/// work fine.
///
/// ### Why is this bad?
/// This is an unnecessary allocation, and bad for
/// performance. It is only necessary to allocate if you wish to move the box
/// into something.
///
/// ### Example
/// ```rust
/// fn foo(x: Box<u32>) {}
/// ```
///
/// Use instead:
/// ```rust
/// fn foo(x: u32) {}
/// ```
#[clippy::version = "pre 1.29.0"]
pub BOXED_LOCAL,
perf,
"using `Box<T>` where unnecessary"
}
fn is_non_trait_box(ty: Ty<'_>) -> bool {
ty.is_box() && !ty.boxed_ty().is_trait()
}
struct EscapeDelegate<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
set: HirIdSet,
trait_self_ty: Option<Ty<'tcx>>,
too_large_for_stack: u64,
}
impl_lint_pass!(BoxedLocal => [BOXED_LOCAL]);
impl<'tcx> LateLintPass<'tcx> for BoxedLocal {
fn check_fn(
&mut self,
cx: &LateContext<'tcx>,
fn_kind: intravisit::FnKind<'tcx>,
_: &'tcx FnDecl<'_>,
body: &'tcx Body<'_>,
_: Span,
fn_def_id: LocalDefId,
) {
if let Some(header) = fn_kind.header() {
if header.abi != Abi::Rust {
return;
}
}
let parent_id = cx
.tcx
.hir()
.get_parent_item(cx.tcx.hir().local_def_id_to_hir_id(fn_def_id))
.def_id;
let parent_node = cx.tcx.hir().find_by_def_id(parent_id);
let mut trait_self_ty = None;
if let Some(Node::Item(item)) = parent_node {
// If the method is an impl for a trait, don't warn.
if let ItemKind::Impl(Impl { of_trait: Some(_), .. }) = item.kind {
return;
}
// find `self` ty for this trait if relevant
if let ItemKind::Trait(_, _, _, _, items) = item.kind {
for trait_item in items {
if trait_item.id.owner_id.def_id == fn_def_id {
// be sure we have `self` parameter in this function
if trait_item.kind == (AssocItemKind::Fn { has_self: true }) {
trait_self_ty = Some(
TraitRef::identity(cx.tcx, trait_item.id.owner_id.to_def_id())
.self_ty()
.skip_binder(),
);
}
}
}
}
}
let mut v = EscapeDelegate {
cx,
set: HirIdSet::default(),
trait_self_ty,
too_large_for_stack: self.too_large_for_stack,
};
let infcx = cx.tcx.infer_ctxt().build();
ExprUseVisitor::new(&mut v, &infcx, fn_def_id, cx.param_env, cx.typeck_results()).consume_body(body);
for node in v.set {
span_lint_hir(
cx,
BOXED_LOCAL,
node,
cx.tcx.hir().span(node),
"local variable doesn't need to be boxed here",
);
}
}
}
// TODO: Replace with Map::is_argument(..) when it's fixed
fn is_argument(map: rustc_middle::hir::map::Map<'_>, id: HirId) -> bool {
match map.find(id) {
Some(Node::Pat(Pat {
kind: PatKind::Binding(..),
..
})) => (),
_ => return false,
}
matches!(map.find_parent(id), Some(Node::Param(_)))
}
impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
fn consume(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId) {
if cmt.place.projections.is_empty() {
if let PlaceBase::Local(lid) = cmt.place.base {
self.set.remove(&lid);
}
}
}
fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId, _: ty::BorrowKind) {
if cmt.place.projections.is_empty() {
if let PlaceBase::Local(lid) = cmt.place.base {
self.set.remove(&lid);
}
}
}
fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId) {
if cmt.place.projections.is_empty() {
let map = &self.cx.tcx.hir();
if is_argument(*map, cmt.hir_id) {
// Skip closure arguments
let parent_id = map.parent_id(cmt.hir_id);
if let Some(Node::Expr(..)) = map.find_parent(parent_id) {
return;
}
// skip if there is a `self` parameter binding to a type
// that contains `Self` (i.e.: `self: Box<Self>`), see #4804
if let Some(trait_self_ty) = self.trait_self_ty {
if map.name(cmt.hir_id) == kw::SelfLower && cmt.place.ty().contains(trait_self_ty) {
return;
}
}
if is_non_trait_box(cmt.place.ty()) && !self.is_large_box(cmt.place.ty()) {
self.set.insert(cmt.hir_id);
}
}
}
}
fn fake_read(&mut self, _: &rustc_hir_typeck::expr_use_visitor::PlaceWithHirId<'tcx>, _: FakeReadCause, _: HirId) {}
}
impl<'a, 'tcx> EscapeDelegate<'a, 'tcx> {
fn is_large_box(&self, ty: Ty<'tcx>) -> bool {
// Large types need to be boxed to avoid stack overflows.
if ty.is_box() {
self.cx.layout_of(ty.boxed_ty()).map_or(0, |l| l.size.bytes()) > self.too_large_for_stack
} else {
false
}
}
}
|
