rust-clippy/src/escape.rs

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use rustc::front::map::Node::{NodeExpr, NodeStmt};
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use rustc::lint::*;
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use rustc::middle::expr_use_visitor::*;
use rustc::middle::infer;
use rustc::middle::mem_categorization::{cmt, Categorization};
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use rustc::middle::ty::adjustment::AutoAdjustment;
use rustc::middle::ty;
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use rustc::util::nodemap::NodeSet;
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use rustc_front::hir::*;
use rustc_front::intravisit as visit;
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use syntax::ast::NodeId;
use syntax::codemap::Span;
use utils::span_lint;
pub struct EscapePass;
/// **What it does:** This lint checks for usage of `Box<T>` where an unboxed `T` would work fine.
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///
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/// **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.
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///
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/// **Known problems:** None
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///
/// **Example:**
///
/// ```rust
/// fn main() {
/// let x = Box::new(1);
/// foo(*x);
/// println!("{}", *x);
/// }
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/// ```
declare_lint! {
pub BOXED_LOCAL, Warn, "using Box<T> where unnecessary"
}
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fn is_non_trait_box(ty: ty::Ty) -> bool {
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match ty.sty {
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ty::TyBox(ref inner) => !inner.is_trait(),
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_ => false,
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}
}
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struct EscapeDelegate<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
set: NodeSet,
}
impl LintPass for EscapePass {
fn get_lints(&self) -> LintArray {
lint_array!(BOXED_LOCAL)
}
}
impl LateLintPass for EscapePass {
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fn check_fn(&mut self, cx: &LateContext, _: visit::FnKind, decl: &FnDecl, body: &Block, _: Span, id: NodeId) {
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let param_env = ty::ParameterEnvironment::for_item(cx.tcx, id);
let infcx = infer::new_infer_ctxt(cx.tcx, &cx.tcx.tables, Some(param_env));
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let mut v = EscapeDelegate {
cx: cx,
set: NodeSet(),
};
{
let mut vis = ExprUseVisitor::new(&mut v, &infcx);
vis.walk_fn(decl, body);
}
for node in v.set {
span_lint(cx,
BOXED_LOCAL,
cx.tcx.map.span(node),
"local variable doesn't need to be boxed here");
}
}
}
impl<'a, 'tcx: 'a> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
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fn consume(&mut self, _: NodeId, _: Span, cmt: cmt<'tcx>, mode: ConsumeMode) {
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if let Categorization::Local(lid) = cmt.cat {
if self.set.contains(&lid) {
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.map;
if map.is_argument(consume_pat.id) {
// Skip closure arguments
if let Some(NodeExpr(..)) = map.find(map.get_parent_node(consume_pat.id)) {
return;
}
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if is_non_trait_box(cmt.ty) {
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self.set.insert(consume_pat.id);
}
return;
}
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if let Categorization::Rvalue(..) = cmt.cat {
if let Some(NodeStmt(st)) = map.find(map.get_parent_node(cmt.id)) {
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if let StmtDecl(ref decl, _) = st.node {
if let DeclLocal(ref loc) = decl.node {
if let Some(ref ex) = loc.init {
if let ExprBox(..) = ex.node {
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if is_non_trait_box(cmt.ty) {
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// 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);
}
}
}
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fn borrow(&mut self, borrow_id: NodeId, _: Span, cmt: cmt<'tcx>, _: ty::Region, _: ty::BorrowKind,
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loan_cause: LoanCause) {
if let Categorization::Local(lid) = cmt.cat {
if self.set.contains(&lid) {
if let Some(&AutoAdjustment::AdjustDerefRef(adj)) = self.cx
.tcx
.tables
.borrow()
.adjustments
.get(&borrow_id) {
if LoanCause::AutoRef == loan_cause {
// x.foo()
if adj.autoderefs == 0 {
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self.set.remove(&lid); // Used without autodereffing (i.e. x.clone())
}
} else {
self.cx.sess().span_bug(cmt.span, "Unknown adjusted AutoRef");
}
} else if LoanCause::AddrOf == loan_cause {
// &x
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if let Some(&AutoAdjustment::AdjustDerefRef(adj)) = self.cx
.tcx
.tables
.borrow()
.adjustments
.get(&self.cx
.tcx
.map
.get_parent_node(borrow_id)) {
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if adj.autoderefs <= 1 {
// foo(&x) where no extra autoreffing is happening
self.set.remove(&lid);
}
}
} else if LoanCause::MatchDiscriminant == loan_cause {
self.set.remove(&lid); // `match x` can move
}
// do nothing for matches, etc. These can't escape
}
}
}
fn decl_without_init(&mut self, _: NodeId, _: Span) {}
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fn mutate(&mut self, _: NodeId, _: Span, _: cmt<'tcx>, _: MutateMode) {}
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}