2018-10-06 16:18:06 +00:00
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// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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2018-09-15 07:21:58 +00:00
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use crate::rustc::hir::*;
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use crate::rustc::hir::intravisit as visit;
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use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use crate::rustc::{declare_tool_lint, lint_array};
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use crate::rustc::middle::expr_use_visitor::*;
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use crate::rustc::middle::mem_categorization::{cmt_, Categorization};
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use crate::rustc::ty::{self, Ty};
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use crate::rustc::ty::layout::LayoutOf;
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use crate::rustc::util::nodemap::NodeSet;
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use crate::syntax::ast::NodeId;
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use crate::syntax::source_map::Span;
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2018-05-30 08:15:50 +00:00
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use crate::utils::span_lint;
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2015-12-04 10:12:53 +00:00
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2016-07-10 13:23:50 +00:00
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pub struct Pass {
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pub too_large_for_stack: u64,
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}
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2015-12-04 10:12:53 +00:00
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2016-08-06 07:55:04 +00:00
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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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2015-12-13 03:38:58 +00:00
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///
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2016-08-06 07:55:04 +00:00
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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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2015-12-13 03:38:58 +00:00
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///
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2016-08-06 07:55:04 +00:00
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/// **Known problems:** None.
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2015-12-13 03:38:58 +00:00
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///
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/// **Example:**
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/// ```rust
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/// fn main() {
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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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2015-12-14 20:17:11 +00:00
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/// ```
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2018-03-28 13:24:26 +00:00
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declare_clippy_lint! {
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2016-08-06 08:18:36 +00:00
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pub BOXED_LOCAL,
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2018-03-28 13:24:26 +00:00
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perf,
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2016-08-06 08:18:36 +00:00
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"using `Box<T>` where unnecessary"
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2016-02-05 23:13:29 +00:00
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}
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2015-12-04 10:12:53 +00:00
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2018-07-23 11:01:12 +00:00
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fn is_non_trait_box(ty: Ty<'_>) -> bool {
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2017-02-03 10:52:13 +00:00
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ty.is_box() && !ty.boxed_ty().is_trait()
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2015-12-28 14:12:57 +00:00
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}
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2016-12-22 13:16:07 +00:00
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struct EscapeDelegate<'a, 'tcx: 'a> {
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2017-06-11 02:34:47 +00:00
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cx: &'a LateContext<'a, 'tcx>,
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2015-12-04 10:12:53 +00:00
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set: NodeSet,
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2016-07-10 13:23:50 +00:00
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too_large_for_stack: u64,
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2015-12-04 10:12:53 +00:00
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}
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2016-06-10 14:17:20 +00:00
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impl LintPass for Pass {
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2015-12-04 10:12:53 +00:00
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fn get_lints(&self) -> LintArray {
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lint_array!(BOXED_LOCAL)
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}
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}
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2016-12-07 12:13:40 +00:00
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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2018-10-15 18:20:50 +00:00
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2016-12-21 09:25:14 +00:00
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fn check_fn(
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2016-12-21 11:14:54 +00:00
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&mut self,
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cx: &LateContext<'a, 'tcx>,
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_: visit::FnKind<'tcx>,
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2017-01-04 04:40:42 +00:00
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_: &'tcx FnDecl,
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body: &'tcx Body,
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2016-12-21 11:14:54 +00:00
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_: Span,
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2017-08-09 07:30:56 +00:00
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node_id: NodeId,
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2016-12-21 09:25:14 +00:00
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) {
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2018-10-15 18:20:50 +00:00
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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(node_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(_, _, _, _, Some(..), _, _) = item.node {
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return;
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}
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}
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2015-12-04 10:12:53 +00:00
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let mut v = EscapeDelegate {
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2018-03-15 15:07:15 +00:00
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cx,
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2015-12-04 10:12:53 +00:00
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set: NodeSet(),
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2016-07-10 13:23:50 +00:00
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too_large_for_stack: self.too_large_for_stack,
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2015-12-04 10:12:53 +00:00
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};
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2016-05-12 17:11:13 +00:00
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2018-10-15 18:20:50 +00:00
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let fn_def_id = cx.tcx.hir.local_def_id(node_id);
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2017-09-04 14:10:36 +00:00
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let region_scope_tree = &cx.tcx.region_scope_tree(fn_def_id);
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2017-10-19 16:27:58 +00:00
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ExprUseVisitor::new(&mut v, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).consume_body(body);
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2016-05-12 17:11:13 +00:00
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2015-12-04 10:12:53 +00:00
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for node in v.set {
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2017-08-09 07:30:56 +00:00
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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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2015-12-04 10:12:53 +00:00
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}
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}
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}
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2017-06-11 02:34:47 +00:00
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impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
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2018-05-06 12:05:41 +00:00
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fn consume(&mut self, _: NodeId, _: Span, cmt: &cmt_<'tcx>, mode: ConsumeMode) {
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2015-12-04 10:12:53 +00:00
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if let Categorization::Local(lid) = cmt.cat {
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2017-06-04 21:28:01 +00:00
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if let Move(DirectRefMove) = 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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2015-12-04 10:12:53 +00:00
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}
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}
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}
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2018-05-06 12:05:41 +00:00
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fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
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fn consume_pat(&mut self, consume_pat: &Pat, cmt: &cmt_<'tcx>, _: ConsumeMode) {
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2017-06-11 02:34:47 +00:00
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let map = &self.cx.tcx.hir;
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2016-02-01 11:35:01 +00:00
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if map.is_argument(consume_pat.id) {
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// Skip closure arguments
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2018-08-28 11:13:42 +00:00
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if let Some(Node::Expr(..)) = map.find(map.get_parent_node(consume_pat.id)) {
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2016-02-01 11:35:01 +00:00
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return;
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}
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2016-07-10 13:23:50 +00:00
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if is_non_trait_box(cmt.ty) && !self.is_large_box(cmt.ty) {
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2015-12-28 14:12:57 +00:00
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self.set.insert(consume_pat.id);
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}
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return;
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}
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2015-12-04 10:12:53 +00:00
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if let Categorization::Rvalue(..) = cmt.cat {
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2018-07-03 08:52:59 +00:00
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let id = map.hir_to_node_id(cmt.hir_id);
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2018-08-28 11:13:42 +00:00
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if let Some(Node::Stmt(st)) = map.find(map.get_parent_node(id)) {
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2018-07-12 08:53:53 +00:00
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if let StmtKind::Decl(ref decl, _) = st.node {
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2018-07-16 13:07:39 +00:00
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if let DeclKind::Local(ref loc) = decl.node {
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2015-12-04 10:12:53 +00:00
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if let Some(ref ex) = loc.init {
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2018-07-12 07:30:57 +00:00
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if let ExprKind::Box(..) = ex.node {
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2016-07-10 13:23:50 +00:00
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if is_non_trait_box(cmt.ty) && !self.is_large_box(cmt.ty) {
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2015-12-04 10:12:53 +00:00
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// let x = box (...)
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self.set.insert(consume_pat.id);
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}
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// TODO Box::new
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// TODO vec![]
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// TODO "foo".to_owned() and friends
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}
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}
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}
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}
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}
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}
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if let Categorization::Local(lid) = cmt.cat {
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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(consume_pat.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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2018-07-23 11:01:12 +00:00
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fn borrow(&mut self, _: NodeId, _: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, _: ty::BorrowKind, loan_cause: LoanCause) {
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2015-12-04 10:12:53 +00:00
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if let Categorization::Local(lid) = cmt.cat {
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2017-06-04 21:28:01 +00:00
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match loan_cause {
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// x.foo()
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// Used without autodereffing (i.e. x.clone())
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LoanCause::AutoRef |
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2015-12-04 10:12:53 +00:00
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2017-06-04 21:28:01 +00:00
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// &x
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// foo(&x) where no extra autoreffing is happening
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LoanCause::AddrOf |
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// `match x` can move
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LoanCause::MatchDiscriminant => {
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self.set.remove(&lid);
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2015-12-04 10:12:53 +00:00
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}
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2017-06-04 21:28:01 +00:00
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2015-12-04 10:12:53 +00:00
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// do nothing for matches, etc. These can't escape
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2017-06-04 21:28:01 +00:00
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_ => {}
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2015-12-04 10:12:53 +00:00
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}
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}
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}
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fn decl_without_init(&mut self, _: NodeId, _: Span) {}
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2018-05-06 12:05:41 +00:00
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fn mutate(&mut self, _: NodeId, _: Span, _: &cmt_<'tcx>, _: MutateMode) {}
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2015-12-04 10:12:53 +00:00
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}
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2016-07-10 13:23:50 +00:00
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2017-06-11 02:34:47 +00:00
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impl<'a, 'tcx> EscapeDelegate<'a, 'tcx> {
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2017-06-11 02:57:25 +00:00
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fn is_large_box(&self, ty: Ty<'tcx>) -> bool {
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2016-07-10 13:23:50 +00:00
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// Large types need to be boxed to avoid stack
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// overflows.
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2017-02-03 10:52:13 +00:00
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if ty.is_box() {
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2018-02-09 13:22:41 +00:00
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self.cx.layout_of(ty.boxed_ty()).ok().map_or(0, |l| l.size.bytes()) > self.too_large_for_stack
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2017-06-11 02:34:47 +00:00
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} else {
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false
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2016-07-10 13:23:50 +00:00
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}
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}
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}
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