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Auto merge of #54088 - matthewjasper:use-reason-in-dlle-errors, r=pnkfelix

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[NLL] Suggest let binding

Closes #49821

Also adds an alternative to `explain_why_borrow_contains_point` that allows changing error messages based on the reason that will be given. This will also be useful for #51026, #51169 and maybe further changes to does not live long enough messages.
This commit is contained in:
bors 2018-09-14 15:45:02 +00:00
commit 052d24e6c8
15 changed files with 133 additions and 32 deletions
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32
src/librustc_mir/borrow_check/error_reporting.rs
View File

@ -24,6 +24,7 @@ use super::borrow_set::BorrowData;
use super::{Context, MirBorrowckCtxt};
use super::{InitializationRequiringAction, PrefixSet};
use borrow_check::nll::explain_borrow::BorrowContainsPointReason;
use dataflow::drop_flag_effects;
use dataflow::move_paths::indexes::MoveOutIndex;
use dataflow::move_paths::MovePathIndex;
@ -409,6 +410,8 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
self.access_place_error_reported
.insert((root_place.clone(), borrow_span));
let borrow_reason = self.find_why_borrow_contains_point(context, borrow);
let mut err = match &self.describe_place(&borrow.borrowed_place) {
Some(_) if self.is_place_thread_local(root_place) => {
self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span)
@ -418,17 +421,17 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
name,
&scope_tree,
&borrow,
borrow_reason,
drop_span,
borrow_span,
proper_span,
kind.map(|k| (k, place_span.0)),
),
None => self.report_temporary_value_does_not_live_long_enough(
context,
&scope_tree,
&borrow,
borrow_reason,
drop_span,
borrow_span,
proper_span,
),
};
@ -444,16 +447,16 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
name: &String,
scope_tree: &Lrc<ScopeTree>,
borrow: &BorrowData<'tcx>,
reason: BorrowContainsPointReason<'tcx>,
drop_span: Span,
borrow_span: Span,
_proper_span: Span,
kind_place: Option<(WriteKind, &Place<'tcx>)>,
) -> DiagnosticBuilder<'cx> {
debug!(
"report_local_value_does_not_live_long_enough(\
{:?}, {:?}, {:?}, {:?}, {:?}, {:?}\
{:?}, {:?}, {:?}, {:?}, {:?}, {:?}, {:?}\
)",
context, name, scope_tree, borrow, drop_span, borrow_span
context, name, scope_tree, borrow, reason, drop_span, borrow_span
);
let mut err = self.tcx.path_does_not_live_long_enough(
@ -468,7 +471,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
format!("`{}` dropped here while still borrowed", name),
);
self.explain_why_borrow_contains_point(context, borrow, kind_place, &mut err);
self.report_why_borrow_contains_point(&mut err, reason, kind_place);
err
}
@ -501,15 +504,15 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
context: Context,
scope_tree: &Lrc<ScopeTree>,
borrow: &BorrowData<'tcx>,
reason: BorrowContainsPointReason<'tcx>,
drop_span: Span,
_borrow_span: Span,
proper_span: Span,
) -> DiagnosticBuilder<'cx> {
debug!(
"report_temporary_value_does_not_live_long_enough(\
{:?}, {:?}, {:?}, {:?}, {:?}\
{:?}, {:?}, {:?}, {:?}, {:?}, {:?}\
)",
context, scope_tree, borrow, drop_span, proper_span
context, scope_tree, borrow, reason, drop_span, proper_span
);
let tcx = self.tcx;
@ -518,7 +521,16 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
err.span_label(proper_span, "temporary value does not live long enough");
err.span_label(drop_span, "temporary value only lives until here");
self.explain_why_borrow_contains_point(context, borrow, None, &mut err);
// Only give this note and suggestion if they could be relevant
match reason {
BorrowContainsPointReason::Liveness {..}
| BorrowContainsPointReason::DropLiveness {..} => {
err.note("consider using a `let` binding to create a longer lived value");
}
BorrowContainsPointReason::OutlivesFreeRegion {..} => (),
}
self.report_why_borrow_contains_point(&mut err, reason, None);
err
}

108
src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs
View File

@ -11,11 +11,28 @@
use borrow_check::borrow_set::BorrowData;
use borrow_check::nll::region_infer::Cause;
use borrow_check::{Context, MirBorrowckCtxt, WriteKind};
use rustc::mir::{Location, Place, TerminatorKind};
use rustc::mir::{Local, Location, Place, TerminatorKind};
use rustc_errors::DiagnosticBuilder;
use rustc::ty::Region;
mod find_use;
#[derive(Copy, Clone, Debug)]
pub enum BorrowContainsPointReason<'tcx> {
Liveness {
local: Local,
location: Location,
in_loop: bool,
},
DropLiveness {
local: Local,
location: Location,
},
OutlivesFreeRegion {
outlived_region: Option<Region<'tcx>>,
},
}
impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
/// Adds annotations to `err` explaining *why* the borrow contains the
/// point from `context`. This is key for the "3-point errors"
@ -32,15 +49,30 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
///
/// [d]: https://rust-lang.github.io/rfcs/2094-nll.html#leveraging-intuition-framing-errors-in-terms-of-points
pub(in borrow_check) fn explain_why_borrow_contains_point(
&mut self,
&self,
context: Context,
borrow: &BorrowData<'tcx>,
kind_place: Option<(WriteKind, &Place<'tcx>)>,
err: &mut DiagnosticBuilder<'_>,
) {
let reason = self.find_why_borrow_contains_point(context, borrow);
self.report_why_borrow_contains_point(err, reason, kind_place);
}
/// Finds the reason that [explain_why_borrow_contains_point] will report
/// but doesn't add it to any message. This is a separate function in case
/// the caller wants to change the error they report based on the reason
/// that will be reported.
pub(in borrow_check) fn find_why_borrow_contains_point(
&self,
context: Context,
borrow: &BorrowData<'tcx>
) -> BorrowContainsPointReason<'tcx> {
use self::BorrowContainsPointReason::*;
debug!(
"explain_why_borrow_contains_point(context={:?}, borrow={:?}, kind_place={:?})",
context, borrow, kind_place,
"find_why_borrow_contains_point(context={:?}, borrow={:?})",
context, borrow,
);
let regioncx = &self.nonlexical_regioncx;
@ -62,11 +94,45 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
);
match find_use::find(mir, regioncx, tcx, region_sub, context.loc) {
Some(Cause::LiveVar(local, location)) => {
Some(Cause::LiveVar(local, location)) => Liveness {
local,
location,
in_loop: self.is_borrow_location_in_loop(context.loc),
},
Some(Cause::DropVar(local, location)) => DropLiveness {
local,
location,
},
None => OutlivesFreeRegion {
outlived_region: regioncx.to_error_region(region_sub),
},
}
}
/// Adds annotations to `err` for the explanation `reason`. This is a
/// separate method so that the caller can change their error message based
/// on the reason that is going to be reported.
pub (in borrow_check) fn report_why_borrow_contains_point(
&self,
err: &mut DiagnosticBuilder,
reason: BorrowContainsPointReason<'tcx>,
kind_place: Option<(WriteKind, &Place<'tcx>)>,
) {
use self::BorrowContainsPointReason::*;
debug!(
"find_why_borrow_contains_point(reason={:?}, kind_place={:?})",
reason, kind_place,
);
let mir = self.mir;
match reason {
Liveness { local, location, in_loop } => {
let span = mir.source_info(location).span;
let spans = self.move_spans(&Place::Local(local), location)
.or_else(|| self.borrow_spans(span, location));
let message = if self.is_borrow_location_in_loop(context.loc) {
let message = if in_loop {
if spans.for_closure() {
"borrow captured here by closure in later iteration of loop"
} else {
@ -81,8 +147,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
};
err.span_label(spans.var_or_use(), message);
}
Some(Cause::DropVar(local, location)) => match &mir.local_decls[local].name {
DropLiveness { local, location } => match &mir.local_decls[local].name {
Some(local_name) => {
err.span_label(
mir.source_info(location).span,
@ -93,12 +158,12 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
if let Place::Local(borrowed_local) = place {
let dropped_local_scope = mir.local_decls[local].visibility_scope;
let borrowed_local_scope =
mir.local_decls[*borrowed_local].visibility_scope;
mir.local_decls[*borrowed_local].visibility_scope;
if mir.is_sub_scope(borrowed_local_scope, dropped_local_scope) {
err.note(
"values in a scope are dropped \
in the opposite order they are defined",
"values in a scope are dropped \
in the opposite order they are defined",
);
}
}
@ -106,18 +171,16 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
}
None => {}
},
None => {
if let Some(region) = regioncx.to_error_region(region_sub) {
self.tcx.note_and_explain_free_region(
err,
"borrowed value must be valid for ",
region,
"...",
);
}
}
OutlivesFreeRegion { outlived_region: Some(region) } => {
self.tcx.note_and_explain_free_region(
err,
"borrowed value must be valid for ",
region,
"...",
);
}
OutlivesFreeRegion { outlived_region: None } => (),
}
}
@ -193,3 +256,4 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
false
}
}

1
src/test/ui/borrowck/borrowck-borrowed-uniq-rvalue-2.nll.stderr
View File

@ -8,6 +8,7 @@ LL | let x = defer(&vec!["Goodbye", "world!"]);
LL | x.x[0];
| ------ borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: aborting due to previous error

2
src/test/ui/borrowck/borrowck-borrowed-uniq-rvalue.nll.stderr
View File

@ -8,6 +8,8 @@ LL | buggy_map.insert(42, &*Box::new(1)); //~ ERROR borrowed value does not
...
LL | buggy_map.insert(43, &*tmp);
| --------- borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
error: aborting due to previous error

2
src/test/ui/issues/issue-36082.ast.nll.stderr
View File

@ -8,6 +8,8 @@ LL | let val: &_ = x.borrow().0;
...
LL | println!("{}", val);
| --- borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
error: aborting due to previous error

2
src/test/ui/issues/issue-36082.mir.stderr
View File

@ -8,6 +8,8 @@ LL | let val: &_ = x.borrow().0;
...
LL | println!("{}", val);
| --- borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
error: aborting due to previous error

1
src/test/ui/issues/issue-36082.rs
View File

@ -28,6 +28,7 @@ fn main() {
//[mir]~^^^^^ ERROR borrowed value does not live long enough [E0597]
//[mir]~| NOTE temporary value does not live long enough
//[mir]~| NOTE temporary value only lives until here
//[mir]~| NOTE consider using a `let` binding to create a longer lived value
println!("{}", val);
//[mir]~^ borrow later used here
}

1
src/test/ui/lifetimes/borrowck-let-suggestion.nll.stderr
View File

@ -9,6 +9,7 @@ LL | //~^ ERROR borrowed value does not live long enough
LL | x.use_mut();
| - borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: aborting due to previous error

2
src/test/ui/nll/borrowed-temporary-error.stderr
View File

@ -8,6 +8,8 @@ LL | });
| - temporary value only lives until here
LL | println!("{:?}", x);
| - borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
error: aborting due to previous error

1
src/test/ui/regions/regions-var-type-out-of-scope.nll.stderr
View File

@ -8,6 +8,7 @@ LL | x = &id(3); //~ ERROR borrowed value does not live long enough
LL | assert_eq!(*x, 3);
| ------------------ borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: aborting due to previous error

6
src/test/ui/span/borrowck-let-suggestion-suffixes.nll.stderr
View File

@ -8,6 +8,8 @@ LL | v3.push(&id('x')); // statement 6
...
LL | (v1, v2, v3, /* v4 is above. */ v5).use_ref();
| -- borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
error[E0597]: borrowed value does not live long enough
--> $DIR/borrowck-let-suggestion-suffixes.rs:38:18
@ -19,6 +21,8 @@ LL | v4.push(&id('y'));
...
LL | v4.use_ref();
| -- borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
error[E0597]: borrowed value does not live long enough
--> $DIR/borrowck-let-suggestion-suffixes.rs:49:14
@ -30,6 +34,8 @@ LL | v5.push(&id('z'));
...
LL | (v1, v2, v3, /* v4 is above. */ v5).use_ref();
| -- borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
error: aborting due to 3 previous errors

2
src/test/ui/span/borrowck-ref-into-rvalue.nll.stderr
View File

@ -8,6 +8,8 @@ LL | }
| - temporary value only lives until here
LL | println!("{}", *msg);
| ---- borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
error: aborting due to previous error

2
src/test/ui/span/issue-15480.nll.stderr
View File

@ -8,6 +8,8 @@ LL | ];
...
LL | for &&x in &v {
| -- borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
error: aborting due to previous error

2
src/test/ui/span/regions-close-over-borrowed-ref-in-obj.nll.stderr
View File

@ -8,6 +8,8 @@ LL | }
| - temporary value only lives until here
LL | }
| - borrow later used here, when `blah` is dropped
|
= note: consider using a `let` binding to create a longer lived value
error: aborting due to previous error

1
src/test/ui/span/slice-borrow.nll.stderr
View File

@ -9,6 +9,7 @@ LL | }
LL | y.use_ref();
| - borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: aborting due to previous error