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EpicatSupercell opened this issue Sep 6, 2018 · 2 comments · Fixed by #56584
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2018 edition - confusing error message when declaring unnamed parameters #53990

EpicatSupercell opened this issue Sep 6, 2018 · 2 comments · Fixed by #56584
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@davidtwco
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A-diagnostics Area: Messages for errors, warnings, and lints A-frontend Area: Compiler frontend (errors, parsing and HIR) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-diagnostics Working group: Diagnostics

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@EpicatSupercell
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EpicatSupercell commented Sep 6, 2018 •
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This code works correctly on nightly and stable

trait Trait {
    fn func(u8);
}

but not on 2018 edition, where it returns the error

error: expected one of `:` or `@`, found `)`
 --> src/main.rs:2:15
  |
2 |     fn func(u8);
  |               ^ expected one of `:` or `@` here

Changing it to func(_: u8) solves it.

Is this an intended change?
I couldn't find anything about it in the edition guide.
@EpicatSupercell EpicatSupercell changed the title 2018 edition regression - associated types access with Self 2018 edition regression - function parameters in traits inconsistency Sep 6, 2018
@EpicatSupercell EpicatSupercell changed the title 2018 edition regression - function parameters in traits inconsistency 2018 edition inconsistency - parameters of functions in traits Sep 6, 2018
@jonas-schievink
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Yes, this was done in #53612

@EpicatSupercell
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So apparently it was part of RFC 1685. In that case we should at least fix the error message, since it doesn't explain the source of the error at all.

@EpicatSupercell EpicatSupercell changed the title 2018 edition inconsistency - parameters of functions in traits 2018 edition - confusing error message when declaring unnamed parameters Sep 6, 2018
@Centril Centril 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. WG-diagnostics Working group: Diagnostics A-frontend Area: Compiler frontend (errors, parsing and HIR) labels Sep 7, 2018
@davidtwco davidtwco mentioned this issue Dec 7, 2018
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@davidtwco davidtwco self-assigned this Dec 7, 2018
bors added a commit that referenced this issue Dec 15, 2018
@bors
Auto merge of #56584 - davidtwco:issue-53990, r=nikomatsakis
747a5e5 
2018 edition - confusing error message when declaring unnamed parameters

Fixes #53990.

This PR adds a note providing context for the change to argument
names being required in the 2018 edition for trait methods and a
suggestion for the fix.
@ehuss ehuss mentioned this issue Mar 3, 2021
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A-diagnostics Area: Messages for errors, warnings, and lints A-frontend Area: Compiler frontend (errors, parsing and HIR) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-diagnostics Working group: Diagnostics
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2018 edition - confusing error message when declaring unnamed parameters davidtwco/rust
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@Centril @davidtwco @jonas-schievink @EpicatSupercell