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Note when a a move/borrow error is caused by a deref coercion #75304

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merged 1 commit into from
Sep 16, 2020

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Fixes #73268

When a deref coercion occurs, we may end up with a move error if the
base value has been partially moved out of. However, we do not indicate
anywhere that a deref coercion is occuring, resulting in an error
message with a confusing span.

This PR adds an explicit note to move errors when a deref coercion is
involved. We mention the name of the type that the deref-coercion
resolved to, as well as the Deref::Target associated type being used.

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r? @lcnr

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 8, 2020
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lcnr commented Aug 8, 2020

hmm, I don't see any obvious problems here, but am not really familiar enough with what's touched here,

maybe r? @estebank

@rust-highfive rust-highfive assigned estebank and unassigned lcnr Aug 8, 2020
|
LL | type Target = NotCopy;
| ^^^^^^^^^^^^^^^^^^^^^^
= note: move occurs because `val.first` has type `NotCopy`, which does not implement the `Copy` trait
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This note seems like it could go as the label of the main span in the previous note.

There's something missing in the new output, but I can't quite put my finger on it. Having said that, we can land this PR and improve it later.

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I don't think we should attach it to the span of val.inner;, since that's referring to the borrow. However, I think it would make sense to reorder it to go before the 'deref defined here' note.

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@estebank I've addressed your comments

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@estebank Are there any changes that you'd like me to make?

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@estebank: I've resolved the merge conflicts.

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@Aaron1011 Aaron1011 force-pushed the feature/diag-deref-move-out branch 2 times, most recently from 57f8be6 to 67d9ee6 Compare September 5, 2020 17:25
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Fixes rust-lang#73268

When a deref coercion occurs, we may end up with a move error if the
base value has been partially moved out of. However, we do not indicate
anywhere that a deref coercion is occuring, resulting in an error
message with a confusing span.

This PR adds an explicit note to move errors when a deref coercion is
involved. We mention the name of the type that the deref-coercion
resolved to, as well as the `Deref::Target` associated type being used.
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@estebank: This is now ready for review

@jyn514 jyn514 added A-diagnostics Area: Messages for errors, warnings, and lints T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Sep 15, 2020
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@bors r+

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bors commented Sep 15, 2020

📌 Commit d18b4bb has been approved by estebank

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 15, 2020
bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 16, 2020
Rollup of 10 pull requests

Successful merges:

 - rust-lang#73955 (deny(unsafe_op_in_unsafe_fn) in libstd/process.rs)
 - rust-lang#75146 (Detect overflow in proc_macro_server subspan)
 - rust-lang#75304 (Note when a a move/borrow error is caused by a deref coercion)
 - rust-lang#75749 (Consolidate some duplicate code in the sys modules.)
 - rust-lang#75882 (Use translated variable for test string)
 - rust-lang#75886 (Test that bounds checks are elided for [..index] after .position())
 - rust-lang#76048 (Initial support for riscv32gc_unknown_linux_gnu)
 - rust-lang#76198 (Make some Ordering methods const)
 - rust-lang#76689 (Upgrade to pulldown-cmark 0.8.0)
 - rust-lang#76763 (Update cargo)

Failed merges:

r? `@ghost`
@bors bors merged commit fa4cfeb into rust-lang:master Sep 16, 2020
@rustbot rustbot added this to the 1.48.0 milestone Sep 16, 2020
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Confusing error message on deref-coercion after partial move out
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