src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs

   1 // Copyright 2017 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.
   4 //
   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.
  10
  11 use borrow_check::borrow_set::BorrowData;
  12 use borrow_check::nll::region_infer::Cause;
  13 use borrow_check::{Context, MirBorrowckCtxt, WriteKind};
  14 use rustc::mir::Place;
  15 use rustc_errors::DiagnosticBuilder;
  16
  17 mod find_use;
  18
  19 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
  20     /// Adds annotations to `err` explaining *why* the borrow contains the
  21     /// point from `context`. This is key for the "3-point errors"
  22     /// [described in the NLL RFC][d].
  23     ///
  24     /// # Parameters
  25     ///
  26     /// - `borrow`: the borrow in question
  27     /// - `context`: where the borrow occurs
  28     /// - `kind_place`: if Some, this describes the statement that triggered the error.
  29     ///   - first half is the kind of write, if any, being performed
  30     ///   - second half is the place being accessed
  31     /// - `err`: where the error annotations are going to be added
  32     ///
  33     /// [d]: https://rust-lang.github.io/rfcs/2094-nll.html#leveraging-intuition-framing-errors-in-terms-of-points
  34     pub(in borrow_check) fn explain_why_borrow_contains_point(
  35         &mut self,
  36         context: Context,
  37         borrow: &BorrowData<'tcx>,
  38         kind_place: Option<(WriteKind, &Place<'tcx>)>,
  39         err: &mut DiagnosticBuilder<'_>,
  40     ) {
  41         debug!(
  42             "explain_why_borrow_contains_point(context={:?}, borrow={:?}, kind_place={:?})",
  43             context, borrow, kind_place,
  44         );
  45
  46         let regioncx = &self.nonlexical_regioncx;
  47         let mir = self.mir;
  48         let tcx = self.tcx;
  49
  50         let borrow_region_vid = regioncx.to_region_vid(borrow.region);
  51
  52         debug!(
  53             "explain_why_borrow_contains_point: borrow_region_vid={:?}",
  54             borrow_region_vid
  55         );
  56
  57         let region_sub = regioncx.find_sub_region_live_at(borrow_region_vid, context.loc);
  58
  59         debug!(
  60             "explain_why_borrow_contains_point: region_sub={:?}",
  61             region_sub
  62         );
  63
  64         match find_use::find(mir, regioncx, tcx, region_sub, context.loc) {
  65             Some(Cause::LiveVar(_local, location)) => {
  66                 err.span_label(
  67                     mir.source_info(location).span,
  68                     "borrow later used here".to_string(),
  69                 );
  70             }
  71
  72             Some(Cause::DropVar(local, location)) => match &mir.local_decls[local].name {
  73                 Some(local_name) => {
  74                     err.span_label(
  75                         mir.source_info(location).span,
  76                         format!("borrow later used here, when `{}` is dropped", local_name),
  77                     );
  78
  79                     if let Some((WriteKind::StorageDeadOrDrop, place)) = kind_place {
  80                         if let Place::Local(borrowed_local) = place {
  81                             let dropped_local_scope = mir.local_decls[local].visibility_scope;
  82                             let borrowed_local_scope =
  83                                 mir.local_decls[*borrowed_local].visibility_scope;
  84
  85                             if mir.is_sub_scope(borrowed_local_scope, dropped_local_scope) {
  86                                 err.note(
  87                                     "values in a scope are dropped \
  88                                      in the opposite order they are defined",
  89                                 );
  90                             }
  91                         }
  92                     }
  93                 }
  94
  95                 None => {}
  96             },
  97
  98             None => {
  99                 if let Some(region) = regioncx.to_error_region(region_sub) {
 100                     self.tcx.note_and_explain_free_region(
 101                         err,
 102                         "borrowed value must be valid for ",
 103                         region,
 104                         "...",
 105                     );
 106                 }
 107             }
 108         }
 109     }
 110 }