-// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
use rustc::mir::visit::{PlaceContext, Visitor};
-use rustc::mir::{Local, Location, Place};
+use rustc::mir::{BasicBlock, Local, Location, Place, Statement, StatementKind, TerminatorKind};
use rustc_data_structures::fx::FxHashSet;
use borrow_check::MirBorrowckCtxt;
impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
- /// Walks the MIR looking for assignments to a set of locals, as part of the unused mutable
- /// local variables lint, to update the context's `used_mut` in a single walk.
- crate fn gather_used_muts(&mut self, locals: FxHashSet<Local>) {
- let mut visitor = GatherUsedMutsVisitor {
- needles: locals,
- mbcx: self,
- };
- visitor.visit_mir(visitor.mbcx.mir);
+ /// Walks the MIR adding to the set of `used_mut` locals that will be ignored for the purposes
+ /// of the `unused_mut` lint.
+ ///
+ /// `temporary_used_locals` should contain locals that were found to be temporary, mutable and
+ /// used from borrow checking. This function looks for assignments into these locals from
+ /// user-declared locals and adds those user-defined locals to the `used_mut` set. This can
+ /// occur due to a rare case involving upvars in closures.
+ ///
+ /// `never_initialized_mut_locals` should contain the set of user-declared mutable locals
+ /// (not arguments) that have not already been marked as being used.
+ /// This function then looks for assignments from statements or the terminator into the locals
+ /// from this set and removes them from the set. This leaves only those locals that have not
+ /// been assigned to - this set is used as a proxy for locals that were not initialized due to
+ /// unreachable code. These locals are then considered "used" to silence the lint for them.
+ /// See #55344 for context.
+ crate fn gather_used_muts(
+ &mut self,
+ temporary_used_locals: FxHashSet<Local>,
+ mut never_initialized_mut_locals: FxHashSet<Local>,
+ ) {
+ {
+ let mut visitor = GatherUsedMutsVisitor {
+ temporary_used_locals,
+ never_initialized_mut_locals: &mut never_initialized_mut_locals,
+ mbcx: self,
+ };
+ visitor.visit_mir(visitor.mbcx.mir);
+ }
+
+ // Take the union of the existed `used_mut` set with those variables we've found were
+ // never initialized.
+ debug!("gather_used_muts: never_initialized_mut_locals={:?}", never_initialized_mut_locals);
+ self.used_mut = self.used_mut.union(&never_initialized_mut_locals).cloned().collect();
}
}
-/// MIR visitor gathering the assignments to a set of locals, in a single walk.
-/// 'visit = the duration of the MIR walk
+/// MIR visitor for collecting used mutable variables.
+/// The 'visit lifetime represents the duration of the MIR walk.
struct GatherUsedMutsVisitor<'visit, 'cx: 'visit, 'gcx: 'tcx, 'tcx: 'cx> {
- needles: FxHashSet<Local>,
+ temporary_used_locals: FxHashSet<Local>,
+ never_initialized_mut_locals: &'visit mut FxHashSet<Local>,
mbcx: &'visit mut MirBorrowckCtxt<'cx, 'gcx, 'tcx>,
}
impl<'visit, 'cx, 'gcx, 'tcx> Visitor<'tcx> for GatherUsedMutsVisitor<'visit, 'cx, 'gcx, 'tcx> {
+ fn visit_terminator_kind(
+ &mut self,
+ _block: BasicBlock,
+ kind: &TerminatorKind<'tcx>,
+ _location: Location,
+ ) {
+ debug!("visit_terminator_kind: kind={:?}", kind);
+ match &kind {
+ TerminatorKind::Call { destination: Some((into, _)), .. } => {
+ if let Some(local) = into.base_local() {
+ debug!(
+ "visit_terminator_kind: kind={:?} local={:?} \
+ never_initialized_mut_locals={:?}",
+ kind, local, self.never_initialized_mut_locals
+ );
+ let _ = self.never_initialized_mut_locals.remove(&local);
+ }
+ },
+ _ => {},
+ }
+ }
+
+ fn visit_statement(
+ &mut self,
+ _block: BasicBlock,
+ statement: &Statement<'tcx>,
+ _location: Location,
+ ) {
+ match &statement.kind {
+ StatementKind::Assign(into, _) => {
+ // Remove any locals that we found were initialized from the
+ // `never_initialized_mut_locals` set. At the end, the only remaining locals will
+ // be those that were never initialized - we will consider those as being used as
+ // they will either have been removed by unreachable code optimizations; or linted
+ // as unused variables.
+ if let Some(local) = into.base_local() {
+ debug!(
+ "visit_statement: statement={:?} local={:?} \
+ never_initialized_mut_locals={:?}",
+ statement, local, self.never_initialized_mut_locals
+ );
+ let _ = self.never_initialized_mut_locals.remove(&local);
+ }
+ },
+ _ => {},
+ }
+ }
+
fn visit_local(
&mut self,
local: &Local,
place_context: PlaceContext<'tcx>,
location: Location,
) {
- if !self.needles.contains(local) {
- return;
- }
-
- if place_context.is_place_assignment() {
+ if place_context.is_place_assignment() && self.temporary_used_locals.contains(local) {
// Propagate the Local assigned at this Location as a used mutable local variable
for moi in &self.mbcx.move_data.loc_map[location] {
let mpi = &self.mbcx.move_data.moves[*moi].path;
projects / rust.git / blobdiff