rust/clippy_lints/src/escape.rs
2018-07-16 11:46:37 +02:00

175 lines
5.5 KiB
Rust

use rustc::hir::*;
use rustc::hir::intravisit as visit;
use rustc::hir::map::Node::{NodeExpr, NodeStmt};
use rustc::lint::*;
use rustc::middle::expr_use_visitor::*;
use rustc::middle::mem_categorization::{cmt_, Categorization};
use rustc::ty::{self, Ty};
use rustc::ty::layout::LayoutOf;
use rustc::util::nodemap::NodeSet;
use syntax::ast::NodeId;
use syntax::codemap::Span;
use crate::utils::span_lint;
pub struct Pass {
pub too_large_for_stack: u64,
}
/// **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.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// fn main() {
/// let x = Box::new(1);
/// foo(*x);
/// println!("{}", *x);
/// }
/// ```
declare_clippy_lint! {
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: 'a> {
cx: &'a LateContext<'a, 'tcx>,
set: NodeSet,
too_large_for_stack: u64,
}
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(BOXED_LOCAL)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_fn(
&mut self,
cx: &LateContext<'a, 'tcx>,
_: visit::FnKind<'tcx>,
_: &'tcx FnDecl,
body: &'tcx Body,
_: Span,
node_id: NodeId,
) {
let fn_def_id = cx.tcx.hir.local_def_id(node_id);
let mut v = EscapeDelegate {
cx,
set: NodeSet(),
too_large_for_stack: self.too_large_for_stack,
};
let region_scope_tree = &cx.tcx.region_scope_tree(fn_def_id);
ExprUseVisitor::new(&mut v, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).consume_body(body);
for node in v.set {
span_lint(
cx,
BOXED_LOCAL,
cx.tcx.hir.span(node),
"local variable doesn't need to be boxed here",
);
}
}
}
impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
fn consume(&mut self, _: NodeId, _: Span, cmt: &cmt_<'tcx>, mode: ConsumeMode) {
if let Categorization::Local(lid) = cmt.cat {
if let Move(DirectRefMove) = mode {
// moved out or in. clearly can't be localized
self.set.remove(&lid);
}
}
}
fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
fn consume_pat(&mut self, consume_pat: &Pat, cmt: &cmt_<'tcx>, _: ConsumeMode) {
let map = &self.cx.tcx.hir;
if map.is_argument(consume_pat.id) {
// Skip closure arguments
if let Some(NodeExpr(..)) = map.find(map.get_parent_node(consume_pat.id)) {
return;
}
if is_non_trait_box(cmt.ty) && !self.is_large_box(cmt.ty) {
self.set.insert(consume_pat.id);
}
return;
}
if let Categorization::Rvalue(..) = cmt.cat {
let id = map.hir_to_node_id(cmt.hir_id);
if let Some(NodeStmt(st)) = map.find(map.get_parent_node(id)) {
if let StmtDecl(ref decl, _) = st.node {
if let DeclLocal(ref loc) = decl.node {
if let Some(ref ex) = loc.init {
if let ExprKind::Box(..) = ex.node {
if is_non_trait_box(cmt.ty) && !self.is_large_box(cmt.ty) {
// let x = box (...)
self.set.insert(consume_pat.id);
}
// TODO Box::new
// TODO vec![]
// TODO "foo".to_owned() and friends
}
}
}
}
}
}
if let Categorization::Local(lid) = cmt.cat {
if self.set.contains(&lid) {
// let y = x where x is known
// remove x, insert y
self.set.insert(consume_pat.id);
self.set.remove(&lid);
}
}
}
fn borrow(&mut self, _: NodeId, _: Span, cmt: &cmt_<'tcx>, _: ty::Region, _: ty::BorrowKind, loan_cause: LoanCause) {
if let Categorization::Local(lid) = cmt.cat {
match loan_cause {
// x.foo()
// Used without autodereffing (i.e. x.clone())
LoanCause::AutoRef |
// &x
// foo(&x) where no extra autoreffing is happening
LoanCause::AddrOf |
// `match x` can move
LoanCause::MatchDiscriminant => {
self.set.remove(&lid);
}
// do nothing for matches, etc. These can't escape
_ => {}
}
}
}
fn decl_without_init(&mut self, _: NodeId, _: Span) {}
fn mutate(&mut self, _: NodeId, _: Span, _: &cmt_<'tcx>, _: MutateMode) {}
}
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()).ok().map_or(0, |l| l.size.bytes()) > self.too_large_for_stack
} else {
false
}
}
}