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Update NLL 3-point error message for fake reads in optimized let patterns
1 parent f5e3105 commit ab236df

8 files changed

+56
-29
lines changed

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

+26-2
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
1111
use borrow_check::borrow_set::BorrowData;
1212
use borrow_check::nll::region_infer::Cause;
1313
use borrow_check::{Context, MirBorrowckCtxt, WriteKind};
14-
use rustc::mir::{Local, Location, Place, TerminatorKind};
14+
use rustc::mir::{FakeReadCause, Local, Location, Place, StatementKind, TerminatorKind};
1515
use rustc_errors::DiagnosticBuilder;
1616
use rustc::ty::Region;
1717

@@ -142,7 +142,31 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
142142
if spans.for_closure() {
143143
"borrow later captured here by closure"
144144
} else {
145-
"borrow later used here"
145+
// Check if the location represents a `FakeRead`, and adapt the error
146+
// message to the `FakeReadCause` it is from: in particular,
147+
// the ones inserted in optimized `let var = <expr>` patterns.
148+
let is_fake_read_for_let = match self.mir.basic_blocks()[location.block]
149+
.statements
150+
.get(location.statement_index)
151+
{
152+
None => false,
153+
Some(stmt) => {
154+
if let StatementKind::FakeRead(ref cause, _) = stmt.kind {
155+
match cause {
156+
FakeReadCause::ForLet => true,
157+
_ => false,
158+
}
159+
} else {
160+
false
161+
}
162+
}
163+
};
164+
165+
if is_fake_read_for_let {
166+
"borrow later stored here"
167+
} else {
168+
"borrow later used here"
169+
}
146170
}
147171
};
148172
err.span_label(spans.var_or_use(), message);

‎src/test/ui/generator/borrowing.nll.stderr

+3-2
Original file line numberDiff line numberDiff line change
@@ -10,15 +10,16 @@ LL | };
1010
error[E0597]: `a` does not live long enough
1111
--> $DIR/borrowing.rs:24:9
1212
|
13+
LL | let _b = {
14+
| -- borrow later stored here
15+
LL | let a = 3;
1316
LL | / || {
1417
LL | | yield &a
1518
LL | | //~^ ERROR: `a` does not live long enough
1619
LL | | }
1720
| |_________^ borrowed value does not live long enough
1821
LL | };
1922
| - `a` dropped here while still borrowed
20-
LL | }
21-
| - borrow later used here, when `_b` is dropped
2223

2324
error: aborting due to 2 previous errors
2425

‎src/test/ui/regions/regions-steal-closure.nll.stderr

+3-2
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,15 @@
11
error[E0597]: `i` does not live long enough
22
--> $DIR/regions-steal-closure.rs:24:28
33
|
4+
LL | let mut cl_box = {
5+
| ---------- borrow later stored here
6+
LL | let mut i = 3;
47
LL | box_it(Box::new(|| i += 1)) //~ ERROR `i` does not live long enough
58
| -- ^ borrowed value does not live long enough
69
| |
710
| value captured here
811
LL | };
912
| - `i` dropped here while still borrowed
10-
LL | cl_box.cl.call_mut(());
11-
| --------- borrow later used here
1213

1314
error: aborting due to previous error
1415

‎src/test/ui/span/range-2.nll.stderr

+6-6
Original file line numberDiff line numberDiff line change
@@ -1,24 +1,24 @@
11
error[E0597]: `a` does not live long enough
22
--> $DIR/range-2.rs:17:9
33
|
4+
LL | let r = {
5+
| - borrow later stored here
6+
...
47
LL | &a..&b
58
| ^^ borrowed value does not live long enough
69
LL | };
710
| - `a` dropped here while still borrowed
8-
...
9-
LL | r.use_ref();
10-
| - borrow later used here
1111

1212
error[E0597]: `b` does not live long enough
1313
--> $DIR/range-2.rs:17:13
1414
|
15+
LL | let r = {
16+
| - borrow later stored here
17+
...
1518
LL | &a..&b
1619
| ^^ borrowed value does not live long enough
1720
LL | };
1821
| - `b` dropped here while still borrowed
19-
...
20-
LL | r.use_ref();
21-
| - borrow later used here
2222

2323
error: aborting due to 2 previous errors
2424

‎src/test/ui/span/send-is-not-static-ensures-scoping.nll.stderr

+6-6
Original file line numberDiff line numberDiff line change
@@ -1,28 +1,28 @@
11
error[E0597]: `x` does not live long enough
22
--> $DIR/send-is-not-static-ensures-scoping.rs:26:17
33
|
4+
LL | let bad = {
5+
| --- borrow later stored here
6+
LL | let x = 1;
47
LL | let y = &x;
58
| ^^ borrowed value does not live long enough
69
...
710
LL | };
811
| - `x` dropped here while still borrowed
9-
LL |
10-
LL | bad.join();
11-
| --- borrow later used here
1212

1313
error[E0597]: `y` does not live long enough
1414
--> $DIR/send-is-not-static-ensures-scoping.rs:30:22
1515
|
16+
LL | let bad = {
17+
| --- borrow later stored here
18+
...
1619
LL | scoped(|| {
1720
| -- value captured here
1821
LL | let _z = y;
1922
| ^ borrowed value does not live long enough
2023
...
2124
LL | };
2225
| - `y` dropped here while still borrowed
23-
LL |
24-
LL | bad.join();
25-
| --- borrow later used here
2626

2727
error: aborting due to 2 previous errors
2828

‎src/test/ui/span/send-is-not-static-std-sync-2.nll.stderr

+6-6
Original file line numberDiff line numberDiff line change
@@ -1,24 +1,24 @@
11
error[E0597]: `x` does not live long enough
22
--> $DIR/send-is-not-static-std-sync-2.rs:21:20
33
|
4+
LL | let lock = {
5+
| ---- borrow later stored here
6+
LL | let x = 1;
47
LL | Mutex::new(&x)
58
| ^^ borrowed value does not live long enough
69
LL | };
710
| - `x` dropped here while still borrowed
8-
...
9-
LL | let _dangling = *lock.lock().unwrap();
10-
| ---- borrow later used here
1111

1212
error[E0597]: `x` does not live long enough
1313
--> $DIR/send-is-not-static-std-sync-2.rs:31:21
1414
|
15+
LL | let lock = {
16+
| ---- borrow later stored here
17+
LL | let x = 1;
1518
LL | RwLock::new(&x)
1619
| ^^ borrowed value does not live long enough
1720
LL | };
1821
| - `x` dropped here while still borrowed
19-
LL | //~^^ ERROR `x` does not live long enough
20-
LL | let _dangling = *lock.read().unwrap();
21-
| ---- borrow later used here
2222

2323
error[E0597]: `x` does not live long enough
2424
--> $DIR/send-is-not-static-std-sync-2.rs:41:25

‎src/test/ui/span/wf-method-late-bound-regions.nll.stderr

+3-3
Original file line numberDiff line numberDiff line change
@@ -1,13 +1,13 @@
11
error[E0597]: `pointer` does not live long enough
22
--> $DIR/wf-method-late-bound-regions.rs:30:18
33
|
4+
LL | let dangling = {
5+
| -------- borrow later stored here
6+
LL | let pointer = Box::new(42);
47
LL | f2.xmute(&pointer)
58
| ^^^^^^^^ borrowed value does not live long enough
69
LL | };
710
| - `pointer` dropped here while still borrowed
8-
LL | //~^^ ERROR `pointer` does not live long enough
9-
LL | println!("{}", dangling);
10-
| -------- borrow later used here
1111

1212
error: aborting due to previous error
1313

‎src/test/ui/unboxed-closures/unboxed-closure-region.nll.stderr

+3-2
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,15 @@
11
error[E0597]: `x` does not live long enough
22
--> $DIR/unboxed-closure-region.rs:18:12
33
|
4+
LL | let _f = {
5+
| -- borrow later stored here
6+
LL | let x = 0;
47
LL | || x //~ ERROR `x` does not live long enough
58
| -- ^ borrowed value does not live long enough
69
| |
710
| value captured here
811
LL | };
912
| - `x` dropped here while still borrowed
10-
LL | _f;
11-
| -- borrow later used here
1213

1314
error: aborting due to previous error
1415

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