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Add by-value captured variable note on second use.
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This commit adds a note that was present in the AST borrow checker when
closures are invoked more than once and have captured variables
by-value.
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davidtwco committed Oct 18, 2018
1 parent aa70115 commit 375645a
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Showing 5 changed files with 140 additions and 47 deletions.
136 changes: 122 additions & 14 deletions src/librustc_mir/borrow_check/error_reporting.rs
Original file line number Diff line number Diff line change
Expand Up @@ -15,11 +15,11 @@ use rustc::hir;
use rustc::hir::def_id::DefId;
use rustc::middle::region::ScopeTree;
use rustc::mir::{
self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, Field, Local,
self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, Constant, Field, Local,
LocalDecl, LocalKind, Location, Operand, Place, PlaceProjection, ProjectionElem,
Rvalue, Statement, StatementKind, TerminatorKind, VarBindingForm,
};
use rustc::ty;
use rustc::ty::{self, DefIdTree};
use rustc::util::ppaux::with_highlight_region_for_bound_region;
use rustc_data_structures::fx::FxHashSet;
use rustc_data_structures::sync::Lrc;
Expand Down Expand Up @@ -131,6 +131,12 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
Origin::Mir,
);

self.add_closure_invoked_twice_with_moved_variable_suggestion(
context.loc,
used_place,
&mut err,
);

let mut is_loop_move = false;
for move_site in &move_site_vec {
let move_out = self.move_data.moves[(*move_site).moi];
Expand Down Expand Up @@ -1056,16 +1062,118 @@ enum StorageDeadOrDrop<'tcx> {
}

impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
// End-user visible description of `place` if one can be found. If the
// place is a temporary for instance, None will be returned.

/// Adds a suggestion when a closure is invoked twice with a moved variable.
///
/// ```text
/// note: closure cannot be invoked more than once because it moves the variable `dict` out of
/// its environment
/// --> $DIR/issue-42065.rs:16:29
/// |
/// LL | for (key, value) in dict {
/// | ^^^^
/// ```
pub(super) fn add_closure_invoked_twice_with_moved_variable_suggestion(
&self,
location: Location,
place: &Place<'tcx>,
diag: &mut DiagnosticBuilder<'_>,
) {
let mut target = place.local();
debug!(
"add_closure_invoked_twice_with_moved_variable_suggestion: location={:?} place={:?} \
target={:?}",
location, place, target,
);
for stmt in &self.mir[location.block].statements[location.statement_index..] {
debug!(
"add_closure_invoked_twice_with_moved_variable_suggestion: stmt={:?} \
target={:?}",
stmt, target,
);
if let StatementKind::Assign(into, box Rvalue::Use(from)) = &stmt.kind {
debug!(
"add_closure_invoked_twice_with_moved_variable_suggestion: into={:?} \
from={:?}",
into, from,
);
match from {
Operand::Copy(ref place) |
Operand::Move(ref place) if target == place.local() =>
target = into.local(),
_ => {},
}
}
}


let terminator = self.mir[location.block].terminator();
debug!(
"add_closure_invoked_twice_with_moved_variable_suggestion: terminator={:?}",
terminator,
);
if let TerminatorKind::Call {
func: Operand::Constant(box Constant {
literal: ty::Const { ty: &ty::TyS { sty: ty::TyKind::FnDef(id, _), .. }, .. },
..
}),
args,
..
} = &terminator.kind {
debug!("add_closure_invoked_twice_with_moved_variable_suggestion: id={:?}", id);
if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
let closure = match args.first() {
Some(Operand::Copy(ref place)) |
Some(Operand::Move(ref place)) if target == place.local() =>
place.local().unwrap(),
_ => return,
};
debug!(
"add_closure_invoked_twice_with_moved_variable_suggestion: closure={:?}",
closure,
);

if let ty::TyKind::Closure(did, substs) = self.mir.local_decls[closure].ty.sty {
let upvar_tys = substs.upvar_tys(did, self.infcx.tcx);
let node_id = match self.infcx.tcx.hir.as_local_node_id(did) {
Some(node_id) => node_id,
_ => return,
};

self.infcx.tcx.with_freevars(node_id, |freevars| {
for (freevar, upvar_ty) in freevars.iter().zip(upvar_tys) {
debug!(
"add_closure_invoked_twice_with_moved_variable_suggestion: \
freevar={:?} upvar_ty={:?}",
freevar, upvar_ty,
);
if !upvar_ty.is_region_ptr() {
diag.span_note(
freevar.span,
&format!(
"closure cannot be invoked more than once because it \
moves the variable `{}` out of its environment",
self.infcx.tcx.hir.name(freevar.var_id()),
),
);
}
}
});
}
}
}
}

/// End-user visible description of `place` if one can be found. If the
/// place is a temporary for instance, None will be returned.
pub(super) fn describe_place(&self, place: &Place<'tcx>) -> Option<String> {
self.describe_place_with_options(place, IncludingDowncast(false))
}

// End-user visible description of `place` if one can be found. If the
// place is a temporary for instance, None will be returned.
// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
// `Downcast` and `IncludingDowncast` is true
/// End-user visible description of `place` if one can be found. If the
/// place is a temporary for instance, None will be returned.
/// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
/// `Downcast` and `IncludingDowncast` is true
pub(super) fn describe_place_with_options(
&self,
place: &Place<'tcx>,
Expand All @@ -1078,7 +1186,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
}
}

// Appends end-user visible description of `place` to `buf`.
/// Appends end-user visible description of `place` to `buf`.
fn append_place_to_string(
&self,
place: &Place<'tcx>,
Expand Down Expand Up @@ -1213,8 +1321,8 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
Ok(())
}

// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
// a name, then `Err` is returned
/// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
/// a name, then `Err` is returned
fn append_local_to_string(&self, local_index: Local, buf: &mut String) -> Result<(), ()> {
let local = &self.mir.local_decls[local_index];
match local.name {
Expand All @@ -1226,7 +1334,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
}
}

// End-user visible description of the `field`nth field of `base`
/// End-user visible description of the `field`nth field of `base`
fn describe_field(&self, base: &Place, field: Field) -> String {
match *base {
Place::Local(local) => {
Expand All @@ -1251,7 +1359,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
}
}

// End-user visible description of the `field_index`nth field of `ty`
/// End-user visible description of the `field_index`nth field of `ty`
fn describe_field_from_ty(&self, ty: &ty::Ty, field: Field) -> String {
if ty.is_box() {
// If the type is a box, the field is described from the boxed type
Expand Down Expand Up @@ -1294,7 +1402,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
}
}

// Retrieve type of a place for the current MIR representation
/// Retrieve type of a place for the current MIR representation
fn retrieve_type_for_place(&self, place: &Place<'tcx>) -> Option<ty::Ty> {
match place {
Place::Local(local) => {
Expand Down
11 changes: 0 additions & 11 deletions src/test/ui/closure_context/issue-42065.nll.stderr

This file was deleted.

18 changes: 18 additions & 0 deletions src/test/ui/issues/issue-12127.nll.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
error[E0382]: use of moved value: `f`
--> $DIR/issue-12127.rs:21:9
|
LL | f();
| - value moved here
LL | f();
| ^ value used here after move
|
note: closure cannot be invoked more than once because it moves the variable `x` out of its environment
--> $DIR/issue-12127.rs:18:39
|
LL | let f = to_fn_once(move|| do_it(&*x));
| ^
= note: move occurs because `f` has type `[closure@$DIR/issue-12127.rs:18:24: 18:41 x:std::boxed::Box<isize>]`, which does not implement the `Copy` trait

error: aborting due to previous error

For more information about this error, try `rustc --explain E0382`.

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