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Tweak move error
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Point at method definition that causes type to be consumed.

Fix rust-lang#94056.
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@estebank
estebank committed Mar 3, 2022
1 parent 32cbc76 commit 9875277
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Showing 21 changed files with 289 additions and 242 deletions.
155 changes: 15 additions & 140 deletions compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
View file
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
use either::Either;
use rustc_const_eval::util::{CallDesugaringKind, CallKind};
use rustc_const_eval::util::CallKind;
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
use rustc_hir as hir;
Expand All @@ -17,7 +17,7 @@ use rustc_middle::ty::{
};
use rustc_mir_dataflow::move_paths::{InitKind, MoveOutIndex, MovePathIndex};
use rustc_span::symbol::sym;
use rustc_span::{BytePos, MultiSpan, Span, DUMMY_SP};
use rustc_span::{BytePos, MultiSpan, Span};
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::TraitEngineExt as _;

Expand Down Expand Up @@ -195,144 +195,19 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
is_loop_move = true;
}

if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } = move_spans {
let place_name = self
.describe_place(moved_place.as_ref())
.map(|n| format!("`{}`", n))
.unwrap_or_else(|| "value".to_owned());
match kind {
CallKind::FnCall { fn_trait_id, .. }
if Some(fn_trait_id) == self.infcx.tcx.lang_items().fn_once_trait() =>
{
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this call{}",
place_name, partially_str, loop_message
),
);
err.span_note(
var_span,
"this value implements `FnOnce`, which causes it to be moved when called",
);
}
CallKind::Operator { self_arg, .. } => {
let self_arg = self_arg.unwrap();
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to usage in operator{}",
place_name, partially_str, loop_message
),
);
if self.fn_self_span_reported.insert(fn_span) {
err.span_note(
// Check whether the source is accessible
if self
.infcx
.tcx
.sess
.source_map()
.span_to_snippet(self_arg.span)
.is_ok()
{
self_arg.span
} else {
fn_call_span
},
"calling this operator moves the left-hand side",
);
}
}
CallKind::Normal { self_arg, desugaring, is_option_or_result } => {
let self_arg = self_arg.unwrap();
if let Some((CallDesugaringKind::ForLoopIntoIter, _)) = desugaring {
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this implicit call to `.into_iter()`{}",
place_name, partially_str, loop_message
),
);
let sess = self.infcx.tcx.sess;
let ty = used_place.ty(self.body, self.infcx.tcx).ty;
// If we have a `&mut` ref, we need to reborrow.
if let ty::Ref(_, _, hir::Mutability::Mut) = ty.kind() {
// If we are in a loop this will be suggested later.
if !is_loop_move {
err.span_suggestion_verbose(
move_span.shrink_to_lo(),
&format!(
"consider creating a fresh reborrow of {} here",
self.describe_place(moved_place.as_ref())
.map(|n| format!("`{}`", n))
.unwrap_or_else(
|| "the mutable reference".to_string()
),
),
"&mut *".to_string(),
Applicability::MachineApplicable,
);
}
} else if let Ok(snippet) =
sess.source_map().span_to_snippet(move_span)
{
err.span_suggestion(
move_span,
"consider borrowing to avoid moving into the for loop",
format!("&{}", snippet),
Applicability::MaybeIncorrect,
);
}
} else {
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this method call{}",
place_name, partially_str, loop_message
),
);
}
if is_option_or_result && maybe_reinitialized_locations.is_empty() {
err.span_suggestion_verbose(
fn_call_span.shrink_to_lo(),
"consider calling `.as_ref()` to borrow the type's contents",
"as_ref().".to_string(),
Applicability::MachineApplicable,
);
}
// Avoid pointing to the same function in multiple different
// error messages.
if span != DUMMY_SP && self.fn_self_span_reported.insert(self_arg.span)
{
err.span_note(
self_arg.span,
&format!("this function takes ownership of the receiver `self`, which moves {}", place_name)
);
}
}
// Other desugarings takes &self, which cannot cause a move
_ => unreachable!(),
}
} else {
err.span_label(
move_span,
format!("value {}moved{} here{}", partially_str, move_msg, loop_message),
);
// If the move error occurs due to a loop, don't show
// another message for the same span
if loop_message.is_empty() {
move_spans.var_span_label(
&mut err,
format!(
"variable {}moved due to use{}",
partially_str,
move_spans.describe()
),
"moved",
);
}
}
self.explain_captures(
&mut err,
span,
move_span,
move_spans,
*moved_place,
Some(used_place),
partially_str,
loop_message,
move_msg,
is_loop_move,
maybe_reinitialized_locations.is_empty(),
);

if let (UseSpans::PatUse(span), []) =
(move_spans, &maybe_reinitialized_locations[..])
Expand Down
179 changes: 174 additions & 5 deletions compiler/rustc_borrowck/src/diagnostics/mod.rs
View file
Original file line number Diff line number Diff line change
@@ -1,20 +1,22 @@
//! Borrow checker diagnostics.
use rustc_const_eval::util::call_kind;
use rustc_errors::Diagnostic;
use rustc_const_eval::util::{call_kind, CallDesugaringKind};
use rustc_errors::{Applicability, Diagnostic};
use rustc_hir as hir;
use rustc_hir::def::Namespace;
use rustc_hir::def_id::DefId;
use rustc_hir::GeneratorKind;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_middle::mir::{
AggregateKind, Constant, FakeReadCause, Field, Local, LocalInfo, LocalKind, Location, Operand,
Place, PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
};
use rustc_middle::ty::print::Print;
use rustc_middle::ty::{self, DefIdTree, Instance, Ty, TyCtxt};
use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult};
use rustc_span::{symbol::sym, Span};
use rustc_span::{symbol::sym, Span, DUMMY_SP};
use rustc_target::abi::VariantIdx;
use rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions;

use super::borrow_set::BorrowData;
use super::MirBorrowckCtxt;
Expand Down Expand Up @@ -482,9 +484,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
BorrowedContentSource::DerefSharedRef
}
}
}

impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
/// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
/// name where required.
pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
Expand Down Expand Up @@ -995,4 +995,173 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
let span = self.body.source_info(borrow.reserve_location).span;
self.borrow_spans(span, borrow.reserve_location)
}

fn explain_captures(
&mut self,
err: &mut Diagnostic,
span: Span,
move_span: Span,
move_spans: UseSpans<'tcx>,
moved_place: Place<'tcx>,
used_place: Option<PlaceRef<'tcx>>,
partially_str: &str,
loop_message: &str,
move_msg: &str,
is_loop_move: bool,
maybe_reinitialized_locations_is_empty: bool,
) {
if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } = move_spans {
let place_name = self
.describe_place(moved_place.as_ref())
.map(|n| format!("`{}`", n))
.unwrap_or_else(|| "value".to_owned());
match kind {
CallKind::FnCall { fn_trait_id, .. }
if Some(fn_trait_id) == self.infcx.tcx.lang_items().fn_once_trait() =>
{
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this call{}",
place_name, partially_str, loop_message
),
);
err.span_note(
var_span,
"this value implements `FnOnce`, which causes it to be moved when called",
);
}
CallKind::Operator { self_arg, .. } => {
let self_arg = self_arg.unwrap();
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to usage in operator{}",
place_name, partially_str, loop_message
),
);
if self.fn_self_span_reported.insert(fn_span) {
err.span_note(
// Check whether the source is accessible
if self
.infcx
.tcx
.sess
.source_map()
.span_to_snippet(self_arg.span)
.is_ok()
{
self_arg.span
} else {
fn_call_span
},
"calling this operator moves the left-hand side",
);
}
}
CallKind::Normal { self_arg, desugaring, is_option_or_result } => {
let self_arg = self_arg.unwrap();
if let Some((CallDesugaringKind::ForLoopIntoIter, _)) = desugaring {
let ty = moved_place.ty(self.body, self.infcx.tcx).ty;
let suggest = match self.infcx.tcx.get_diagnostic_item(sym::IntoIterator) {
Some(def_id) => self.infcx.tcx.infer_ctxt().enter(|infcx| {
type_known_to_meet_bound_modulo_regions(
&infcx,
self.param_env,
infcx.tcx.mk_imm_ref(
infcx.tcx.lifetimes.re_erased,
infcx.tcx.erase_regions(ty),
),
def_id,
DUMMY_SP,
)
}),
_ => false,
};
if suggest {
err.span_suggestion_verbose(
move_span.shrink_to_lo(),
&format!(
"consider iterating over a slice of the `{}`'s content to \
avoid moving into the `for` loop",
ty,
),
"&".to_string(),
Applicability::MaybeIncorrect,
);
}

err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this implicit call to `.into_iter()`{}",
place_name, partially_str, loop_message
),
);
// If we have a `&mut` ref, we need to reborrow.
if let Some(ty::Ref(_, _, hir::Mutability::Mut)) = used_place
.map(|used_place| used_place.ty(self.body, self.infcx.tcx).ty.kind())
{
// If we are in a loop this will be suggested later.
if !is_loop_move {
err.span_suggestion_verbose(
move_span.shrink_to_lo(),
&format!(
"consider creating a fresh reborrow of {} here",
self.describe_place(moved_place.as_ref())
.map(|n| format!("`{}`", n))
.unwrap_or_else(|| "the mutable reference".to_string()),
),
"&mut *".to_string(),
Applicability::MachineApplicable,
);
}
}
} else {
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this method call{}",
place_name, partially_str, loop_message
),
);
}
if is_option_or_result && maybe_reinitialized_locations_is_empty {
err.span_suggestion_verbose(
fn_call_span.shrink_to_lo(),
"consider calling `.as_ref()` to borrow the type's contents",
"as_ref().".to_string(),
Applicability::MachineApplicable,
);
}
// Avoid pointing to the same function in multiple different
// error messages.
if span != DUMMY_SP && self.fn_self_span_reported.insert(self_arg.span) {
err.span_note(
self_arg.span,
&format!("this function takes ownership of the receiver `self`, which moves {}", place_name)
);
}
}
// Other desugarings takes &self, which cannot cause a move
_ => {}
}
} else {
if move_span != span || !loop_message.is_empty() {
err.span_label(
move_span,
format!("value {}moved{} here{}", partially_str, move_msg, loop_message),
);
}
// If the move error occurs due to a loop, don't show
// another message for the same span
if loop_message.is_empty() {
move_spans.var_span_label(
err,
format!("variable {}moved due to use{}", partially_str, move_spans.describe()),
"moved",
);
}
}
}
}
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