1 // Copyright 2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use rustc::mir::visit::{PlaceContext, Visitor};
12 use rustc::mir::{Local, Location, Place};
14 use rustc_data_structures::fx::FxHashSet;
16 use borrow_check::MirBorrowckCtxt;
18 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
19 /// Walks the MIR looking for assignments to a set of locals, as part of the unused mutable
20 /// local variables lint, to update the context's `used_mut` in a single walk.
21 crate fn gather_used_muts(&mut self, locals: FxHashSet<Local>) {
22 let mut visitor = GatherUsedMutsVisitor {
26 visitor.visit_mir(visitor.mbcx.mir);
30 /// MIR visitor gathering the assignments to a set of locals, in a single walk.
31 /// 'visit = the duration of the MIR walk
32 struct GatherUsedMutsVisitor<'visit, 'cx: 'visit, 'gcx: 'tcx, 'tcx: 'cx> {
33 needles: FxHashSet<Local>,
34 mbcx: &'visit mut MirBorrowckCtxt<'cx, 'gcx, 'tcx>,
37 impl<'visit, 'cx, 'gcx, 'tcx> Visitor<'tcx> for GatherUsedMutsVisitor<'visit, 'cx, 'gcx, 'tcx> {
41 place_context: PlaceContext<'tcx>,
44 if !self.needles.contains(local) {
48 if place_context.is_place_assignment() {
49 // Propagate the Local assigned at this Location as a used mutable local variable
50 for moi in &self.mbcx.move_data.loc_map[location] {
51 let mpi = &self.mbcx.move_data.moves[*moi].path;
52 let path = &self.mbcx.move_data.move_paths[*mpi];
54 "assignment of {:?} to {:?}, adding {:?} to used mutable set",
55 path.place, local, path.place
57 if let Place::Local(user_local) = path.place {
58 self.mbcx.used_mut.insert(user_local);