loan paths leaking into borrowck errors #41962

Manishearth · 2017-05-12T22:19:04Z

pub fn main(){
    let maybe = Some(vec![true, true]);

    loop {
        if let Some(thing) = maybe {
        }
    }
}

(playpen)

gives the error

error[E0382]: use of partially moved value: `maybe`
 --> test.rs:7:30
  |
7 |         if let Some(thing) = maybe {
  |                     -----    ^^^^^ value used here after move
  |                     |
  |                     value moved here
  |
  = note: move occurs because `(maybe:std::prelude::v1::Some).0` has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

error[E0382]: use of moved value: `(maybe:std::prelude::v1::Some).0`
 --> test.rs:7:21
  |
7 |         if let Some(thing) = maybe {
  |                     ^^^^^ value moved here in previous iteration of loop
  |
  = note: move occurs because `(maybe:std::prelude::v1::Some).0` has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

error: aborting due to 2 previous errors

(maybe:std::prelude::v1::Some).0 seems to be MIR leaking into the UI

cc @jonathandturner @eddyb

The text was updated successfully, but these errors were encountered:

eddyb · 2017-05-13T05:17:03Z

I think those are just the loan paths that borrowck uses. It's not like MIR is hooked up to it.

eddyb · 2017-05-13T05:17:19Z

cc @rust-lang/compiler

nikomatsakis · 2017-05-16T01:56:55Z

Yes, this is not MIR, but just regular loan-paths. Nonetheless, a suboptimal experience. I'm not sure what's the best way to present this. Probably we would want to (at minimum) filter on paths that the user couldn't write and try a more ambiguous phrasing (e.g., 'move occurs because bound value has type Vec<u8>')

(cc @estebank)

nikomatsakis · 2017-05-16T01:57:14Z

Or maybe we can give the name of the binding (when there is one)? That might take a bit of plumbing.

estebank · 2017-05-17T23:27:06Z

There probably should be only one move error in this code, should't it?

Would the following output be enough (with very small changes to the existing code)?

error[E0382]: use of partially moved value: `maybe`
 --> test.rs:7:30
  |
7 |         if let Some(thing) = maybe {
  |                     -----    ^^^^^ value used here after move
  |                     |
  |                     value moved here, because it has type `std::vec::Vec<bool>`, which does't implement the `Copy` trait

error: aborting due to previous error

arielb1 · 2017-05-18T08:20:23Z

I think so.

nikomatsakis · 2017-05-25T17:34:31Z

@estebank that output looks good to me

estebank · 2017-09-05T17:42:24Z

I'll post a PR later today, but I'm not entirely convinced with the output, too long a label in my eyes:

error[E0382]: use of partially moved value: `maybe`
 --> file.rs:5:30
  |
5 |         if let Some(thing) = maybe {
  |                     -----    ^^^^^ value used here after move
  |                     |
  |                     value moved here because it has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

error[E0382]: use of moved value: `maybe.0`
 --> file.rs:5:21
  |
5 |         if let Some(thing) = maybe {
  |                     ^^^^^ value moved here in previous iteration of loop because it has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

error: aborting due to 2 previous errors

vs the current

error[E0382]: use of partially moved value: `maybe`
 --> file.rs:5:30
  |
5 |         if let Some(thing) = maybe {
  |                     -----    ^^^^^ value used here after move
  |                     |
  |                     value moved here
  |
  = note: move occurs because `(maybe:std::prelude::v1::Some).0` has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

error[E0382]: use of moved value: `(maybe:std::prelude::v1::Some).0`
 --> file.rs:5:21
  |
5 |         if let Some(thing) = maybe {
  |                     ^^^^^ value moved here in previous iteration of loop
  |
  = note: move occurs because `(maybe:std::prelude::v1::Some).0` has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

error: aborting due to previous error(s)

Three other alternatives I can think of are:

error[E0382]: use of partially moved value: `maybe`
 --> file.rs:5:30
  |
5 |         if let Some(thing) = maybe {
  |                     -----    ^^^^^ value used here after move
  |                     |
  |                     value moved here
  |                     because it has type `std::vec::Vec<bool>`
  |                     which does not implement the `Copy` trait

error[E0382]: use of moved value: `maybe.0`
 --> file.rs:5:21
  |
5 |         if let Some(thing) = maybe {
  |                     ^^^^^
  |                     |
  |                     value moved here in previous iteration of loop
  |                     because it has type `std::vec::Vec<bool>`
  |                     which does not implement the `Copy` trait

error: aborting due to 2 previous errors

error[E0382]: use of partially moved value: `maybe`
 --> file.rs:5:30
  |
5 |         if let Some(thing) = maybe {
  |                     -----    ^^^^^ value used here after move
  |                     |
  |                     value moved here because it has type `std::vec::Vec<bool>`
  = note: `std::vec::Vec<bool>` does not implement the `Copy` trait

error[E0382]: use of moved value: `maybe.0`
 --> file.rs:5:21
  |
5 |         if let Some(thing) = maybe {
  |                     ^^^^^ value moved here in previous iteration of loop because it has type `std::vec::Vec<bool>`
  = note: `std::vec::Vec<bool>` does not implement the `Copy` trait

error: aborting due to 2 previous errors

and

error[E0382]: use of partially moved value: `maybe`
 --> file.rs:5:30
  |
5 |         if let Some(thing) = maybe {
  |                     -----    ^^^^^ value used here after move
  |                     |
  |                     value moved here
  |
  = note: move occurs because `maybe.0` has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

error[E0382]: use of moved value: `maybe.0`
 --> file.rs:5:21
  |
5 |         if let Some(thing) = maybe {
  |                     ^^^^^ value moved here in previous iteration of loop
  |
  = note: move occurs because `maybe.0` has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

error: aborting due to previous error(s)

Does it make sense to refer to (maybe:std::prelude::v1::Some).0 as maybe.0? It is technically correct, if not very illuminating. Put in another way, when does (maybe:std::prelude::v1::Some).0 make sense, other than for rustc debugging output?

arielb1 · 2017-09-06T12:39:51Z

@estebank

(maybe as Some).0 is the name of the path. It is what counts for move conflicts.

eddyb · 2017-09-06T12:45:48Z

maybe.Some::0 could be an alternative - I think it works better with named fields.

estebank · 2017-09-07T06:58:01Z

@arielb1 is there any reason why LpDowncast types would be presented (x as full::path::to::Enum).0 in append_loan_path_to_string and (x:full::path::to::Enum).0 in append_autoderefd_loan_path_to_string?

I'll leave changing the presentation of a shorter path using the local scope's identifier to the purview of #21934.

arielb1 · 2017-09-07T16:40:27Z

@estebank

No. Maybe we should just change both (and the relevant MIR case) to x.$variantname::0? We don't ever need to list the full path - variant names are guaranteed to be distinct.

estebank · 2017-09-07T21:05:07Z

@arielb1 Shouldn't it be x::$variantname.0, x:$variantname.0 or x::$variantname::0 instead of x.$variantname::0?

eddyb · 2017-09-07T21:51:42Z

@estebank x::$variantname doesn't make sense because it implies x is some sort of module or type, but it's not. : is basically as by another name.
The reason I suggested x.$variantname::$field is because Variant::field looks like a path to the field definition, and so accessing that as a field in x makes some sense.

@arielb1

Reword reason for move note On move errors, when encountering an enum variant, be more ambiguous and do not refer to the type on the cause note, to avoid referring to `(maybe as std::prelude::v1::Some).0`, and instead refer to `the value`. Sidesteps part of the problem with #41962: ``` error[E0382]: use of partially moved value: `maybe` --> file.rs:5:30 | 5 | if let Some(thing) = maybe { | ----- ^^^^^ value used here after move | | | value moved here = note: move occurs because the value has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait error[E0382]: use of moved value: `(maybe as std::prelude::v1::Some).0` --> file.rs:5:21 | 5 | if let Some(thing) = maybe { | ^^^^^ value moved here in previous iteration of loop = note: move occurs because the value has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait error: aborting due to 2 previous errors ``` Previous discussion: #44360 r? @arielb1

…to my code. In particular, I am adding an implicit injected borrow on the pattern matches, and when we go around the loop, the compiler is reporting that this injected borrow is conflicting with the move of the original value when the match succeeds.

estebank · 2019-01-25T22:57:58Z

Fixed in beta:

error[E0382]: use of partially moved value: `maybe`
 --> src/main.rs:6:30
  |
6 |         if let Some(thing) = maybe {
  |                     -----    ^^^^^ value used here after move
  |                     |
  |                     value moved here
  |
  = note: move occurs because the value has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

error[E0382]: use of moved value: `(maybe as std::prelude::v1::Some).0`
 --> src/main.rs:6:21
  |
6 |         if let Some(thing) = maybe {
  |                     ^^^^^ value moved here in previous iteration of loop
  |
  = note: move occurs because the value has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

estebank · 2019-01-25T22:58:25Z

Scratch that, didn't notice the second main message

estebank · 2019-05-17T01:14:09Z

Current output:

error[E0382]: use of moved value
 --> src/main.rs:6:21
  |
6 |         if let Some(thing) = maybe {
  |                     ^^^^^ value moved here, in previous iteration of loop
  |
  = note: move occurs because value has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait

Manishearth added A-diagnostics Area: Messages for errors, warnings, and lints I-papercut labels May 12, 2017

nikomatsakis changed the title ~~MIR leaking into borrowck errors~~ loan paths leaking into borrowck errors May 16, 2017

Mark-Simulacrum added C-bug Category: This is a bug. and removed I-wrong labels Jul 26, 2017

estebank mentioned this issue Sep 6, 2017

Move reason for move to label #44360

Closed

estebank mentioned this issue Jan 2, 2018

Reword reason for move note #47124

Merged

estebank closed this as completed Jan 25, 2019

estebank reopened this Jan 25, 2019

estebank closed this as completed May 17, 2019

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

loan paths leaking into borrowck errors #41962

loan paths leaking into borrowck errors #41962

Manishearth commented May 12, 2017

eddyb commented May 13, 2017

eddyb commented May 13, 2017

nikomatsakis commented May 16, 2017

nikomatsakis commented May 16, 2017

estebank commented May 17, 2017

arielb1 commented May 18, 2017

nikomatsakis commented May 25, 2017

estebank commented Sep 5, 2017 •

edited

Loading

arielb1 commented Sep 6, 2017

eddyb commented Sep 6, 2017

estebank commented Sep 7, 2017

arielb1 commented Sep 7, 2017

estebank commented Sep 7, 2017

eddyb commented Sep 7, 2017

estebank commented Jan 25, 2019

estebank commented Jan 25, 2019

estebank commented May 17, 2019

loan paths leaking into borrowck errors #41962

loan paths leaking into borrowck errors #41962

Comments

Manishearth commented May 12, 2017

eddyb commented May 13, 2017

eddyb commented May 13, 2017

nikomatsakis commented May 16, 2017

nikomatsakis commented May 16, 2017

estebank commented May 17, 2017

arielb1 commented May 18, 2017

nikomatsakis commented May 25, 2017

estebank commented Sep 5, 2017 • edited Loading

arielb1 commented Sep 6, 2017

eddyb commented Sep 6, 2017

estebank commented Sep 7, 2017

arielb1 commented Sep 7, 2017

estebank commented Sep 7, 2017

eddyb commented Sep 7, 2017

estebank commented Jan 25, 2019

estebank commented Jan 25, 2019

estebank commented May 17, 2019

estebank commented Sep 5, 2017 •

edited

Loading