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Better suggestions when user tries to collect into an unsized [_] #91443

Merged
merged 2 commits into from
Feb 10, 2022
Merged

Better suggestions when user tries to collect into an unsized [_] #91443

merged 2 commits into from
Feb 10, 2022

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compiler-errors
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  1. Extend the predicate on rustc_on_unimplemented to support substitutions like note, label, etc (i.e. treat it as a OnUnimplementedFormatString) so we can have slightly more general rustc_on_unimplemented special-cases.
  2. Add a rustc_on_unimplemented if we fail on FromIterator<A> for [A] which happens when we don't explicitly collect into a vec<A>, but then pass the return from a .collect call into something that takes a slice.

Fixes #91423

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r? @matthewjasper

(rust-highfive has picked a reviewer for you, use r? to override)

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 2, 2021
@apiraino apiraino added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Dec 9, 2021
@Aaron1011
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Could you add a test case demonstrating the new behavior?

@compiler-errors
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@Aaron1011 added a test. Still unclear what the best wording for this specific suggestion is, but demonstrating that it works.

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bors commented Jan 27, 2022

☔ The latest upstream changes (presumably #93352) made this pull request unmergeable. Please resolve the merge conflicts.

@compiler-errors
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howdy @matthewjasper, should I reassign this PR to someone else on the high-five queue?

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Yes please

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reassigning per reviewer request

r? rust-lang/compiler

@wesleywiser
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@compiler-errors This looks great! My only suggestion was going to be to mention the Sized trait but I see the other errors and notes generated do that already. Could you rebase and fix the merge conflict? Thanks!

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Alright @wesleywiser, rebased and confirmed tests still pass!

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@bors r+

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bors commented Feb 9, 2022

📌 Commit fea0015 has been approved by wesleywiser

@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 Feb 9, 2022
@matthiaskrgr matthiaskrgr mentioned this pull request Feb 9, 2022
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matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Feb 9, 2022
@matthiaskrgr
Rollup merge of rust-lang#91443 - compiler-errors:bad_collect_into_sl…
ba6b5df 
…ice, r=wesleywiser

Better suggestions when user tries to collect into an unsized `[_]`

1. Extend the predicate on `rustc_on_unimplemented` to support substitutions like note, label, etc (i.e. treat it as a `OnUnimplementedFormatString`) so we can have slightly more general `rustc_on_unimplemented` special-cases.
2. Add a `rustc_on_unimplemented` if we fail on `FromIterator<A> for [A]` which happens when we don't explicitly collect into a `vec<A>`, but then pass the return from a `.collect` call into something that takes a slice.

Fixes rust-lang#91423
@matthiaskrgr matthiaskrgr mentioned this pull request Feb 9, 2022
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bors added a commit to rust-lang-ci/rust that referenced this pull request Feb 10, 2022
@bors
Auto merge of rust-lang#93836 - matthiaskrgr:rollup-d1ssiwl, r=matthi…
5d6ee0d 
…askrgr

Rollup of 6 pull requests

Successful merges:

 - rust-lang#91443 (Better suggestions when user tries to collect into an unsized `[_]`)
 - rust-lang#91504 (`#[used(linker)]` attribute)
 - rust-lang#93503 (debuginfo: Fix DW_AT_containing_type vtable debuginfo regression)
 - rust-lang#93753 (Complete removal of #[main] attribute from compiler)
 - rust-lang#93799 (Fix typo in `std::fmt` docs)
 - rust-lang#93813 (Make a few cleanup MIR passes public)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 9634559 into rust-lang:master Feb 10, 2022
@rustbot rustbot added this to the 1.60.0 milestone Feb 10, 2022
@meithecatte
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What would it take to add a structured suggestion to this diagnostic?

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@NieDzejkob, what do you mean by this? I don't think the rustc_on_unimplemented attribute supports suggestions. You'd probably need to rip this PR out and replace it with a full-fledged diagnostic that is emitted from the compiler itself.

If you're interested in that route, you probably have a good bet putting some logic to detect this case in report_selection_error in rustc_trait_selection::traits::error_reporting.

@compiler-errors compiler-errors deleted the bad_collect_into_slice branch November 2, 2022 02:49
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@wesleywiser wesleywiser wesleywiser approved these changes

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Type inference around Iterator::collect can result in confusing error messages
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@compiler-errors @rust-highfive @Aaron1011 @bors @matthewjasper @wesleywiser @meithecatte @apiraino @rustbot