From 968ea1ce32ac894a7d58702c409233638aa5592d Mon Sep 17 00:00:00 2001 From: Matthew Jasper Date: Thu, 4 Apr 2019 21:25:08 +0100 Subject: [PATCH] Mark variables captured by reference as mutable correctly --- src/librustc_mir/borrow_check/mod.rs | 96 ++++++++++++++++++++++------ src/test/ui/nll/extra-unused-mut.rs | 19 +++--- 2 files changed, 87 insertions(+), 28 deletions(-) diff --git a/src/librustc_mir/borrow_check/mod.rs b/src/librustc_mir/borrow_check/mod.rs index a8c151a22eebc..ab3239820e3a2 100644 --- a/src/librustc_mir/borrow_check/mod.rs +++ b/src/librustc_mir/borrow_check/mod.rs @@ -28,7 +28,7 @@ use std::collections::BTreeMap; use syntax_pos::Span; use crate::dataflow::indexes::{BorrowIndex, InitIndex, MoveOutIndex, MovePathIndex}; -use crate::dataflow::move_paths::{HasMoveData, LookupResult, MoveData, MoveError}; +use crate::dataflow::move_paths::{HasMoveData, InitLocation, LookupResult, MoveData, MoveError}; use crate::dataflow::Borrows; use crate::dataflow::DataflowResultsConsumer; use crate::dataflow::FlowAtLocation; @@ -1206,25 +1206,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> { } = self.infcx.tcx.mir_borrowck(def_id); debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars); for field in used_mut_upvars { - // This relies on the current way that by-value - // captures of a closure are copied/moved directly - // when generating MIR. - match operands[field.index()] { - Operand::Move(Place::Base(PlaceBase::Local(local))) - | Operand::Copy(Place::Base(PlaceBase::Local(local))) => { - self.used_mut.insert(local); - } - Operand::Move(ref place @ Place::Projection(_)) - | Operand::Copy(ref place @ Place::Projection(_)) => { - if let Some(field) = place.is_upvar_field_projection( - self.mir, &self.infcx.tcx) { - self.used_mut_upvars.push(field); - } - } - Operand::Move(Place::Base(PlaceBase::Static(..))) - | Operand::Copy(Place::Base(PlaceBase::Static(..))) - | Operand::Constant(..) => {} - } + self.propagate_closure_used_mut_upvar(&operands[field.index()]); } } AggregateKind::Adt(..) @@ -1239,6 +1221,80 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> { } } + fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) { + let propagate_closure_used_mut_place = |this: &mut Self, place: &Place<'tcx>| { + match *place { + Place::Projection { .. } => { + if let Some(field) = place.is_upvar_field_projection( + this.mir, &this.infcx.tcx) { + this.used_mut_upvars.push(field); + } + } + Place::Base(PlaceBase::Local(local)) => { + this.used_mut.insert(local); + } + Place::Base(PlaceBase::Static(_)) => {} + } + }; + + // This relies on the current way that by-value + // captures of a closure are copied/moved directly + // when generating MIR. + match *operand { + Operand::Move(Place::Base(PlaceBase::Local(local))) + | Operand::Copy(Place::Base(PlaceBase::Local(local))) + if self.mir.local_decls[local].is_user_variable.is_none() => + { + if self.mir.local_decls[local].ty.is_mutable_pointer() { + // The variable will be marked as mutable by the borrow. + return; + } + // This is an edge case where we have a `move` closure + // inside a non-move closure, and the inner closure + // contains a mutation: + // + // let mut i = 0; + // || { move || { i += 1; }; }; + // + // In this case our usual strategy of assuming that the + // variable will be captured by mutable reference is + // wrong, since `i` can be copied into the inner + // closure from a shared reference. + // + // As such we have to search for the local that this + // capture comes from and mark it as being used as mut. + + let temp_mpi = self.move_data.rev_lookup.find_local(local); + let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] { + &self.move_data.inits[init_index] + } else { + bug!("temporary should be initialized exactly once") + }; + + let loc = match init.location { + InitLocation::Statement(stmt) => stmt, + _ => bug!("temporary initialized in arguments"), + }; + + let bbd = &self.mir[loc.block]; + let stmt = &bbd.statements[loc.statement_index]; + debug!("temporary assigned in: stmt={:?}", stmt); + + if let StatementKind::Assign(_, box Rvalue::Ref(_, _, ref source)) = stmt.kind { + propagate_closure_used_mut_place(self, source); + } else { + bug!("closures should only capture user variables \ + or references to user variables"); + } + } + Operand::Move(ref place) + | Operand::Copy(ref place) => { + propagate_closure_used_mut_place(self, place); + } + Operand::Constant(..) => {} + } + } + fn consume_operand( &mut self, context: Context, diff --git a/src/test/ui/nll/extra-unused-mut.rs b/src/test/ui/nll/extra-unused-mut.rs index d5f0b0ddf18bf..6d0d6e16a6775 100644 --- a/src/test/ui/nll/extra-unused-mut.rs +++ b/src/test/ui/nll/extra-unused-mut.rs @@ -1,6 +1,6 @@ // extra unused mut lint tests for #51918 -// run-pass +// compile-pass #![feature(generators, nll)] #![deny(unused_mut)] @@ -53,11 +53,14 @@ fn if_guard(x: Result) { } } -fn main() { - ref_argument(0); - mutable_upvar(); - generator_mutable_upvar(); - ref_closure_argument(); - parse_dot_or_call_expr_with(Vec::new()); - if_guard(Ok(0)); +// #59620 +fn nested_closures() { + let mut i = 0; + [].iter().for_each(|_: &i32| { + [].iter().for_each(move |_: &i32| { + i += 1; + }); + }); } + +fn main() {}