/
mod.rs
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/
mod.rs
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// Copyright 2017 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 borrow_check::{Context, MirBorrowckCtxt};
use borrow_check::nll::region_infer::{Cause, RegionInferenceContext};
use dataflow::BorrowData;
use rustc::mir::{Local, Location, Mir};
use rustc::mir::visit::{MirVisitable, PlaceContext, Visitor};
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::DiagnosticBuilder;
use util::liveness::{self, DefUse, LivenessMode};
impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
pub(in borrow_check) fn explain_why_borrow_contains_point(
&self,
context: Context,
borrow: &BorrowData<'_>,
err: &mut DiagnosticBuilder<'_>,
) {
if let Some(regioncx) = &self.nonlexical_regioncx {
if let Some(cause) = regioncx.why_region_contains_point(borrow.region, context.loc) {
let mir = self.mir;
match *cause.root_cause() {
Cause::LiveVar(local, location) => {
match find_regular_use(&mir, regioncx, borrow, location, local) {
Some(p) => {
err.span_label(
mir.source_info(p).span,
format!("borrow later used here"),
);
}
None => {
span_bug!(
mir.source_info(context.loc).span,
"Cause should end in a LiveVar"
);
}
}
}
Cause::DropVar(local, location) => {
match find_drop_use(&mir, regioncx, borrow, location, local) {
Some(p) => {
let local_name = &mir.local_decls[local].name.unwrap();
err.span_label(
mir.source_info(p).span,
format!(
"borrow later used here, when `{}` is dropped",
local_name
),
);
}
None => {
span_bug!(
mir.source_info(context.loc).span,
"Cause should end in a DropVar"
);
}
}
}
_ => {
cause.label_diagnostic(mir, err);
}
}
}
}
}
}
fn find_regular_use<'gcx, 'tcx>(
mir: &'gcx Mir,
regioncx: &'tcx RegionInferenceContext,
borrow: &'tcx BorrowData,
start_point: Location,
local: Local,
) -> Option<Location> {
let mut uf = UseFinder {
mir,
regioncx,
borrow,
start_point,
local,
liveness_mode: LivenessMode {
include_regular_use: true,
include_drops: false,
},
};
uf.find()
}
fn find_drop_use<'gcx, 'tcx>(
mir: &'gcx Mir,
regioncx: &'tcx RegionInferenceContext,
borrow: &'tcx BorrowData,
start_point: Location,
local: Local,
) -> Option<Location> {
let mut uf = UseFinder {
mir,
regioncx,
borrow,
start_point,
local,
liveness_mode: LivenessMode {
include_regular_use: false,
include_drops: true,
},
};
uf.find()
}
struct UseFinder<'gcx, 'tcx> {
mir: &'gcx Mir<'gcx>,
regioncx: &'tcx RegionInferenceContext<'tcx>,
borrow: &'tcx BorrowData<'tcx>,
start_point: Location,
local: Local,
liveness_mode: LivenessMode,
}
impl<'gcx, 'tcx> UseFinder<'gcx, 'tcx> {
fn find(&mut self) -> Option<Location> {
let mut stack = vec![];
let mut visited = FxHashSet();
stack.push(self.start_point);
while let Some(p) = stack.pop() {
if !self.regioncx.region_contains_point(self.borrow.region, p) {
continue;
}
if !visited.insert(p) {
continue;
}
let block_data = &self.mir[p.block];
let (defined, used) = self.def_use(p, block_data.visitable(p.statement_index));
if used {
return Some(p);
} else if !defined {
if p.statement_index < block_data.statements.len() {
stack.push(Location {
statement_index: p.statement_index + 1,
..p
});
} else {
stack.extend(
block_data
.terminator()
.successors()
.iter()
.map(|&basic_block| Location {
statement_index: 0,
block: basic_block,
}),
);
}
}
}
None
}
fn def_use(&self, location: Location, thing: &dyn MirVisitable<'tcx>) -> (bool, bool) {
let mut visitor = DefUseVisitor {
defined: false,
used: false,
local: self.local,
liveness_mode: self.liveness_mode,
};
thing.apply(location, &mut visitor);
(visitor.defined, visitor.used)
}
}
struct DefUseVisitor {
defined: bool,
used: bool,
local: Local,
liveness_mode: LivenessMode,
}
impl<'tcx> Visitor<'tcx> for DefUseVisitor {
fn visit_local(&mut self, &local: &Local, context: PlaceContext<'tcx>, _: Location) {
if local == self.local {
match liveness::categorize(context, self.liveness_mode) {
Some(DefUse::Def) => self.defined = true,
Some(DefUse::Use) => self.used = true,
None => (),
}
}
}
}