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[NLL] Use smaller spans for errors involving closure captures #52959

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Aug 5, 2018
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[NLL] Use smaller spans for errors involving closure captures #52959

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903851f
Highlight closure spans for borrow and initialization errors
matthewjasper Aug 1, 2018
5639e21
Tests for closure spans
matthewjasper Aug 1, 2018
12af36a
Update tests for new spans for nll errors involving closures
matthewjasper Aug 1, 2018
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519 changes: 359 additions & 160 deletions src/librustc_mir/borrow_check/error_reporting.rs
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2 changes: 1 addition & 1 deletion src/librustc_mir/borrow_check/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1542,7 +1542,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
if borrow_of_local_data(&borrow.borrowed_place) {
let err = self.tcx
.cannot_borrow_across_generator_yield(
self.retrieve_borrow_span(borrow),
self.retrieve_borrow_spans(borrow).var_or_use(),
yield_span,
Origin::Mir,
);
Expand Down
43 changes: 17 additions & 26 deletions src/librustc_mir/borrow_check/mutability_errors.rs
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Expand Up @@ -160,7 +160,6 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
let act;
let acted_on;


let span = match error_access {
AccessKind::Move => {
err = self.tcx
Expand All @@ -180,31 +179,23 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
act = "borrow as mutable";
acted_on = "borrowed as mutable";

let closure_span = self.find_closure_span(span, location);
if let Some((args, var)) = closure_span {
err = self.tcx.cannot_borrow_path_as_mutable_because(
args,
&item_msg,
&reason,
Origin::Mir,
);
err.span_label(
var,
format!(
"mutable borrow occurs due to use of `{}` in closure",
self.describe_place(access_place).unwrap(),
),
);
args
} else {
err = self.tcx.cannot_borrow_path_as_mutable_because(
span,
&item_msg,
&reason,
Origin::Mir,
);
span
}
let borrow_spans = self.borrow_spans(span, location);
let borrow_span = borrow_spans.args_or_use();
err = self.tcx.cannot_borrow_path_as_mutable_because(
borrow_span,
&item_msg,
&reason,
Origin::Mir,
);
borrow_spans.var_span_label(
&mut err,
format!(
"mutable borrow occurs due to use of `{}` in closure",
// always Some() if the message is printed.
self.describe_place(access_place).unwrap_or(String::new()),
)
);
borrow_span
}
};

Expand Down
28 changes: 17 additions & 11 deletions src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -62,18 +62,24 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
);

match find_use::find(mir, regioncx, tcx, region_sub, context.loc) {
Some(Cause::LiveVar(_local, location)) => {
if self.is_borrow_location_in_loop(context.loc) {
err.span_label(
mir.source_info(location).span,
"borrow used here in later iteration of loop".to_string(),
);
Some(Cause::LiveVar(local, location)) => {
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) {
if spans.for_closure() {
"borrow captured here by closure in later iteration of loop"
} else {
"borrow used here in later iteration of loop"
}
} else {
err.span_label(
mir.source_info(location).span,
"borrow later used here".to_string(),
);
}
if spans.for_closure() {
"borrow later captured here by closure"
} else {
"borrow later used here"
}
};
err.span_label(spans.var_or_use(), message);
}

Some(Cause::DropVar(local, location)) => match &mir.local_decls[local].name {
Expand Down
11 changes: 9 additions & 2 deletions src/librustc_mir/util/borrowck_errors.rs
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Expand Up @@ -203,8 +203,15 @@ pub trait BorrowckErrors<'cx>: Sized + Copy {
desc,
OGN = o
);
err.span_label(old_loan_span, "first closure is constructed here");
err.span_label(new_loan_span, "second closure is constructed here");
if old_loan_span == new_loan_span {
err.span_label(
old_loan_span,
"closures are constructed here in different iterations of loop"
);
} else {
err.span_label(old_loan_span, "first closure is constructed here");
err.span_label(new_loan_span, "second closure is constructed here");
}
if let Some(old_load_end_span) = old_load_end_span {
err.span_label(old_load_end_span, "borrow from first closure ends here");
}
Expand Down
20 changes: 10 additions & 10 deletions src/test/ui/borrowck/borrowck-closures-two-mut.stderr
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Expand Up @@ -77,11 +77,11 @@ error[E0499]: cannot borrow `x` as mutable more than once at a time (Mir)
--> $DIR/borrowck-closures-two-mut.rs:24:24
|
LL | let c1 = to_fn_mut(|| x = 4);
| -- - previous borrow occurs due to use of `x` in closure
| -- - first borrow occurs due to use of `x` in closure
| |
| first mutable borrow occurs here
LL | let c2 = to_fn_mut(|| x = 5); //~ ERROR cannot borrow `x` as mutable more than once
| ^^ - borrow occurs due to use of `x` in closure
| ^^ - second borrow occurs due to use of `x` in closure
| |
| second mutable borrow occurs here
LL | //~| ERROR cannot borrow `x` as mutable more than once
Expand All @@ -92,11 +92,11 @@ error[E0499]: cannot borrow `x` as mutable more than once at a time (Mir)
--> $DIR/borrowck-closures-two-mut.rs:36:24
|
LL | let c1 = to_fn_mut(|| set(&mut x));
| -- - previous borrow occurs due to use of `x` in closure
| -- - first borrow occurs due to use of `x` in closure
| |
| first mutable borrow occurs here
LL | let c2 = to_fn_mut(|| set(&mut x)); //~ ERROR cannot borrow `x` as mutable more than once
| ^^ - borrow occurs due to use of `x` in closure
| ^^ - second borrow occurs due to use of `x` in closure
| |
| second mutable borrow occurs here
LL | //~| ERROR cannot borrow `x` as mutable more than once
Expand All @@ -107,11 +107,11 @@ error[E0499]: cannot borrow `x` as mutable more than once at a time (Mir)
--> $DIR/borrowck-closures-two-mut.rs:44:24
|
LL | let c1 = to_fn_mut(|| x = 5);
| -- - previous borrow occurs due to use of `x` in closure
| -- - first borrow occurs due to use of `x` in closure
| |
| first mutable borrow occurs here
LL | let c2 = to_fn_mut(|| set(&mut x)); //~ ERROR cannot borrow `x` as mutable more than once
| ^^ - borrow occurs due to use of `x` in closure
| ^^ - second borrow occurs due to use of `x` in closure
| |
| second mutable borrow occurs here
LL | //~| ERROR cannot borrow `x` as mutable more than once
Expand All @@ -122,11 +122,11 @@ error[E0499]: cannot borrow `x` as mutable more than once at a time (Mir)
--> $DIR/borrowck-closures-two-mut.rs:52:24
|
LL | let c1 = to_fn_mut(|| x = 5);
| -- - previous borrow occurs due to use of `x` in closure
| -- - first borrow occurs due to use of `x` in closure
| |
| first mutable borrow occurs here
LL | let c2 = to_fn_mut(|| { let _y = to_fn_mut(|| set(&mut x)); }); // (nested closure)
| ^^ - borrow occurs due to use of `x` in closure
| ^^ - second borrow occurs due to use of `x` in closure
| |
| second mutable borrow occurs here
...
Expand All @@ -137,11 +137,11 @@ error[E0499]: cannot borrow `x` as mutable more than once at a time (Mir)
--> $DIR/borrowck-closures-two-mut.rs:65:24
|
LL | let c1 = to_fn_mut(|| set(&mut *x.f));
| -- - previous borrow occurs due to use of `x` in closure
| -- - first borrow occurs due to use of `x` in closure
| |
| first mutable borrow occurs here
LL | let c2 = to_fn_mut(|| set(&mut *x.f));
| ^^ - borrow occurs due to use of `x` in closure
| ^^ - second borrow occurs due to use of `x` in closure
| |
| second mutable borrow occurs here
...
Expand Down
6 changes: 4 additions & 2 deletions src/test/ui/borrowck/borrowck-escaping-closure-error-1.nll.stderr
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Original file line number Diff line number Diff line change
@@ -1,8 +1,10 @@
error[E0597]: `books` does not live long enough
--> $DIR/borrowck-escaping-closure-error-1.rs:23:11
--> $DIR/borrowck-escaping-closure-error-1.rs:23:14
|
LL | spawn(|| books.push(4));
| ^^^^^^^^^^^^^^^^ borrowed value does not live long enough
| -- ^^^^^ borrowed value does not live long enough
| |
| value captured here
LL | //~^ ERROR E0373
LL | }
| - `books` dropped here while still borrowed
Expand Down
6 changes: 4 additions & 2 deletions src/test/ui/borrowck/borrowck-escaping-closure-error-2.nll.stderr
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@@ -1,8 +1,10 @@
error[E0597]: `books` does not live long enough
--> $DIR/borrowck-escaping-closure-error-2.rs:21:14
--> $DIR/borrowck-escaping-closure-error-2.rs:21:17
|
LL | Box::new(|| books.push(4))
| ^^^^^^^^^^^^^^^^ borrowed value does not live long enough
| -- ^^^^^ borrowed value does not live long enough
| |
| value captured here
LL | //~^ ERROR E0373
LL | }
| - `books` dropped here while still borrowed
Expand Down
17 changes: 8 additions & 9 deletions src/test/ui/error-codes/E0504.nll.stderr
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@@ -1,17 +1,16 @@
error[E0505]: cannot move out of `fancy_num` because it is borrowed
--> $DIR/E0504.rs:19:13
|
LL | let fancy_ref = &fancy_num;
| ---------- borrow of `fancy_num` occurs here
LL | let fancy_ref = &fancy_num;
| ---------- borrow of `fancy_num` occurs here
LL |
LL | let x = move || {
| _____________^
LL | | println!("child function: {}", fancy_num.num); //~ ERROR E0504
LL | | };
| |_____^ move out of `fancy_num` occurs here
LL | let x = move || {
| ^^^^^^^ move out of `fancy_num` occurs here
LL | println!("child function: {}", fancy_num.num); //~ ERROR E0504
| --------- move occurs due to use in closure
...
LL | println!("main function: {}", fancy_ref.num);
| ------------- borrow later used here
LL | println!("main function: {}", fancy_ref.num);
| ------------- borrow later used here

error: aborting due to previous error

Expand Down
2 changes: 1 addition & 1 deletion src/test/ui/issue-11192.nll.stderr
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Expand Up @@ -5,7 +5,7 @@ LL | let mut test = |foo: &Foo| {
| ----------- mutable borrow occurs here
LL | println!("access {}", foo.x);
LL | ptr = box Foo { x: ptr.x + 1 };
| --- previous borrow occurs due to use of `ptr` in closure
| --- first borrow occurs due to use of `ptr` in closure
...
LL | test(&*ptr);
| -----^^^^^-
Expand Down
4 changes: 3 additions & 1 deletion src/test/ui/issue-11873.nll.stderr
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Expand Up @@ -2,7 +2,9 @@ error[E0505]: cannot move out of `v` because it is borrowed
--> $DIR/issue-11873.rs:14:14
|
LL | let mut f = || v.push(2);
| ------------ borrow of `v` occurs here
| -- - borrow occurs due to use in closure
| |
| borrow of `v` occurs here
LL | let _w = v; //~ ERROR: cannot move out of `v`
| ^ move out of `v` occurs here
LL |
Expand Down
8 changes: 4 additions & 4 deletions src/test/ui/issue-18783.nll.stderr
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Expand Up @@ -2,11 +2,11 @@ error[E0499]: cannot borrow `y` as mutable more than once at a time
--> $DIR/issue-18783.rs:17:21
|
LL | c.push(Box::new(|| y = 0));
| -- - previous borrow occurs due to use of `y` in closure
| -- - first borrow occurs due to use of `y` in closure
| |
| first mutable borrow occurs here
LL | c.push(Box::new(|| y = 0));
| ^^ - borrow occurs due to use of `y` in closure
| ^^ - second borrow occurs due to use of `y` in closure
| |
| second mutable borrow occurs here
LL | //~^ ERROR cannot borrow `y` as mutable more than once at a time
Expand All @@ -17,11 +17,11 @@ error[E0499]: cannot borrow `y` as mutable more than once at a time
--> $DIR/issue-18783.rs:26:29
|
LL | Push::push(&c, Box::new(|| y = 0));
| -- - previous borrow occurs due to use of `y` in closure
| -- - first borrow occurs due to use of `y` in closure
| |
| first mutable borrow occurs here
LL | Push::push(&c, Box::new(|| y = 0));
| ^^ - borrow occurs due to use of `y` in closure
| ^^ - second borrow occurs due to use of `y` in closure
| |
| second mutable borrow occurs here
LL | //~^ ERROR cannot borrow `y` as mutable more than once at a time
Expand Down
4 changes: 3 additions & 1 deletion src/test/ui/issue-24357.nll.stderr
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Expand Up @@ -2,7 +2,9 @@ error[E0382]: use of moved value: `x`
--> $DIR/issue-24357.rs:16:12
|
LL | let f = move || { let y = x; };
| ---------------------- value moved here
| ------- - variable moved due to use in closure
| |
| value moved into closure here
LL | //~^ NOTE value moved (into closure) here
LL | let z = x;
| ^ value used here after move
Expand Down
10 changes: 7 additions & 3 deletions src/test/ui/issue-27282-move-match-input-into-guard.stderr
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@@ -1,11 +1,13 @@
error[E0505]: cannot move out of `b` because it is borrowed
--> $DIR/issue-27282-move-match-input-into-guard.rs:26:16
--> $DIR/issue-27282-move-match-input-into-guard.rs:26:17
|
LL | match b {
| - borrow of `b` occurs here
LL | &mut false => {},
LL | _ if { (|| { let bar = b; *bar = false; })();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ move out of `b` occurs here
| ^^ - move occurs due to use in closure
| |
| move out of `b` occurs here
...
LL | &mut true => { println!("You might think we should get here"); },
| --------- borrow later used here
Expand All @@ -14,7 +16,9 @@ error[E0382]: use of moved value: `*b`
--> $DIR/issue-27282-move-match-input-into-guard.rs:29:14
|
LL | _ if { (|| { let bar = b; *bar = false; })();
| ----------------------------------- value moved here
| -- - variable moved due to use in closure
| |
| value moved into closure here
...
LL | &mut true => { println!("You might think we should get here"); },
| ^^^^ value used here after move
Expand Down
2 changes: 1 addition & 1 deletion src/test/ui/issue-27282-mutate-before-diverging-arm-1.stderr
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Expand Up @@ -5,7 +5,7 @@ LL | match x {
| - borrow occurs here
...
LL | (|| { *x = None; drop(force_fn_once); })();
| ^^ - borrow occurs due to use of `x` in closure
| ^^ - second borrow occurs due to use of `x` in closure
| |
| closure construction occurs here
...
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2 changes: 1 addition & 1 deletion src/test/ui/issue-27282-mutate-before-diverging-arm-2.stderr
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Expand Up @@ -5,7 +5,7 @@ LL | match x {
| - borrow occurs here
...
LL | (|| { *x = None; drop(force_fn_once); })();
| ^^ - borrow occurs due to use of `x` in closure
| ^^ - second borrow occurs due to use of `x` in closure
| |
| closure construction occurs here
...
Expand Down
6 changes: 4 additions & 2 deletions src/test/ui/issue-4335.nll.stderr
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Expand Up @@ -5,10 +5,12 @@ LL | id(Box::new(|| *v))
| ^^ cannot move out of captured variable in an `FnMut` closure

error[E0597]: `v` does not live long enough
--> $DIR/issue-4335.rs:16:17
--> $DIR/issue-4335.rs:16:21
|
LL | id(Box::new(|| *v))
| ^^^^^ borrowed value does not live long enough
| -- ^ borrowed value does not live long enough
| |
| value captured here
...
LL | }
| - `v` dropped here while still borrowed
Expand Down
4 changes: 3 additions & 1 deletion src/test/ui/issue-6801.nll.stderr
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Expand Up @@ -2,7 +2,9 @@ error[E0505]: cannot move out of `x` because it is borrowed
--> $DIR/issue-6801.rs:29:13
|
LL | let sq = || { *x * *x };
| -------------- borrow of `x` occurs here
| -- - borrow occurs due to use in closure
| |
| borrow of `x` occurs here
LL |
LL | twice(x); //~ ERROR: cannot move out of
| ^ move out of `x` occurs here
Expand Down
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