Auto merge of #53830 - davidtwco:issue-53228, r=nikomatsakis

Add help message for missing IndexMut impl with NLL

Fixes #53228.

r? @nikomatsakis

src/librustc_mir/borrow_check/mod.rs

@@ -1591,7 +1591,10 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
  if let Some(&init_index) = first_init_index {
  // And, if so, report an error.
  let init = &self.move_data.inits[init_index];
- self.report_illegal_reassignment(context, place_span, init.span, place_span.0);
+ let span = init.span(&self.mir);
+ self.report_illegal_reassignment(
+ context, place_span, span, place_span.0
+ );
  }
  }
 

src/librustc_mir/borrow_check/mutability_errors.rs

@@ -10,18 +10,20 @@
 
 use rustc::hir;
 use rustc::hir::Node;
-use rustc::mir::{self, BindingForm, ClearCrossCrate, Local, Location, Mir};
-use rustc::mir::{Mutability, Place, Projection, ProjectionElem, Static};
-use rustc::ty::{self, TyCtxt};
+use rustc::mir::{self, BindingForm, Constant, ClearCrossCrate, Local, Location, Mir};
+use rustc::mir::{Mutability, Operand, Place, Projection, ProjectionElem, Static, Terminator};
+use rustc::mir::TerminatorKind;
+use rustc::ty::{self, Const, DefIdTree, TyS, TyKind, TyCtxt};
 use rustc_data_structures::indexed_vec::Idx;
 use syntax_pos::Span;
 
+use dataflow::move_paths::InitLocation;
 use borrow_check::MirBorrowckCtxt;
 use util::borrowck_errors::{BorrowckErrors, Origin};
 use util::collect_writes::FindAssignments;
 use util::suggest_ref_mut;
 
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub(super) enum AccessKind {
  MutableBorrow,
  Mutate,
@@ -393,6 +395,63 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
  );
  }
 
+ Place::Projection(box Projection {
+ base: Place::Local(local),
+ elem: ProjectionElem::Deref,
+ }) if error_access == AccessKind::MutableBorrow => {
+ err.span_label(span, format!("cannot {ACT}", ACT = act));
+
+ let mpi = self.move_data.rev_lookup.find_local(*local);
+ for i in self.move_data.init_path_map[mpi].iter() {
+ if let InitLocation::Statement(location) = self.move_data.inits[*i].location {
+ if let Some(
+ Terminator {
+ kind: TerminatorKind::Call {
+ func: Operand::Constant(box Constant {
+ literal: Const {
+ ty: &TyS {
+ sty: TyKind::FnDef(id, substs),
+ ..
+ },
+ ..
+ },
+ ..
+ }),
+ ..
+ },
+ ..
+ }
+ ) = &self.mir.basic_blocks()[location.block].terminator {
+ if self.tcx.parent(id) == self.tcx.lang_items().index_trait() {
+
+ let mut found = false;
+ self.tcx.for_each_relevant_impl(
+ self.tcx.lang_items().index_mut_trait().unwrap(),
+ substs.type_at(0),
+ |_relevant_impl| {
+ found = true;
+ }
+ );
+
+ let extra = if found {
+ String::from("")
+ } else {
+ format!(", but it is not implemented for `{}`",
+ substs.type_at(0))
+ };
+
+ err.help(
+ &format!(
+ "trait `IndexMut` is required to modify indexed content{}",
+ extra,
+ ),
+ );
+ }
+ }
+ }
+ }
+ }
+
  _ => {
  err.span_label(span, format!("cannot {ACT}", ACT = act));
  }

src/librustc_mir/dataflow/move_paths/builder.rs

@@ -20,7 +20,7 @@ use std::mem;
 use super::abs_domain::Lift;
 
 use super::{LocationMap, MoveData, MovePath, MovePathLookup, MovePathIndex, MoveOut, MoveOutIndex};
-use super::{MoveError, InitIndex, Init, LookupResult, InitKind};
+use super::{MoveError, InitIndex, Init, InitLocation, LookupResult, InitKind};
 use super::IllegalMoveOriginKind::*;
 
 struct MoveDataBuilder<'a, 'gcx: 'tcx, 'tcx: 'a> {
@@ -237,10 +237,9 @@ impl<'a, 'gcx, 'tcx> MoveDataBuilder<'a, 'gcx, 'tcx> {
  fn gather_args(&mut self) {
  for arg in self.mir.args_iter() {
  let path = self.data.rev_lookup.locals[arg];
- let span = self.mir.local_decls[arg].source_info.span;
 
  let init = self.data.inits.push(Init {
- path, span, kind: InitKind::Deep
+ path, kind: InitKind::Deep, location: InitLocation::Argument(arg),
  });
 
  debug!("gather_args: adding init {:?} of {:?} for argument {:?}",
@@ -428,7 +427,7 @@ impl<'b, 'a, 'gcx, 'tcx> Gatherer<'b, 'a, 'gcx, 'tcx> {
 
  if let LookupResult::Exact(path) = self.builder.data.rev_lookup.find(place) {
  let init = self.builder.data.inits.push(Init {
- span: self.builder.mir.source_info(self.loc).span,
+ location: InitLocation::Statement(self.loc),
  path,
  kind,
  });

src/librustc_mir/dataflow/move_paths/mod.rs

@@ -196,12 +196,21 @@ impl fmt::Debug for MoveOut {
 pub struct Init {
  /// path being initialized
  pub path: MovePathIndex,
- /// span of initialization
- pub span: Span,
+ /// location of initialization
+ pub location: InitLocation,
  /// Extra information about this initialization
  pub kind: InitKind,
 }
 
+
+/// Initializations can be from an argument or from a statement. Arguments
+/// do not have locations, in those cases the `Local` is kept..
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum InitLocation {
+ Argument(Local),
+ Statement(Location),
+}
+
 /// Additional information about the initialization.
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum InitKind {
@@ -215,7 +224,16 @@ pub enum InitKind {
 
 impl fmt::Debug for Init {
  fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
- write!(fmt, "{:?}@{:?} ({:?})", self.path, self.span, self.kind)
+ write!(fmt, "{:?}@{:?} ({:?})", self.path, self.location, self.kind)
+ }
+}
+
+impl Init {
+ crate fn span<'gcx>(&self, mir: &Mir<'gcx>) -> Span {
+ match self.location {
+ InitLocation::Argument(local) => mir.local_decls[local].source_info.span,
+ InitLocation::Statement(location) => mir.source_info(location).span,
+ }
  }
 }
 

src/test/ui/borrowck/index-mut-help-with-impl.nll.stderr

@@ -0,0 +1,11 @@
+error[E0596]: cannot borrow data in a `&` reference as mutable
+ --> $DIR/index-mut-help-with-impl.rs:19:5
+ |
+LL | Index::index(&v, 1..2).make_ascii_uppercase(); //~ ERROR
+ | ^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
+ |
+ = help: trait `IndexMut` is required to modify indexed content
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.

src/test/ui/borrowck/index-mut-help-with-impl.rs

@@ -0,0 +1,20 @@
+// 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.
+
+// When mutably indexing a type that implements `Index` and `IndexMut` but
+// `Index::index` is being used specifically, the normal special help message
+// should not mention a missing `IndexMut` impl.
+
+fn main() {
+ use std::ops::Index;
+
+ let v = String::from("dinosaur");
+ Index::index(&v, 1..2).make_ascii_uppercase(); //~ ERROR
+}

src/test/ui/borrowck/index-mut-help-with-impl.stderr

@@ -0,0 +1,9 @@
+error[E0596]: cannot borrow immutable borrowed content as mutable
+ --> $DIR/index-mut-help-with-impl.rs:19:5
+ |
+LL | Index::index(&v, 1..2).make_ascii_uppercase(); //~ ERROR
+ | ^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.

src/test/ui/borrowck/index-mut-help.nll.stderr

@@ -3,6 +3,8 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
  |
 LL | map["peter"].clear(); //~ ERROR
  | ^^^^^^^^^^^^ cannot borrow as mutable
+ |
+ = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<&str, std::string::String>`
 
 error[E0594]: cannot assign to data in a `&` reference
  --> $DIR/index-mut-help.rs:22:5
@@ -15,6 +17,8 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
  |
 LL | let _ = &mut map["peter"]; //~ ERROR
  | ^^^^^^^^^^^^^^^^^ cannot borrow as mutable
+ |
+ = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<&str, std::string::String>`
 
 error: aborting due to 3 previous errors
 

src/test/ui/issues/issue-41726.nll.stderr

@@ -3,6 +3,8 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
  |
 LL | things[src.as_str()].sort(); //~ ERROR cannot borrow immutable
  | ^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
+ |
+ = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<std::string::String, std::vec::Vec<std::string::String>>`
 
 error: aborting due to previous error