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Bad lint suggestion: '_ in type definition #61124

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mark-i-m opened this issue May 24, 2019 · 0 comments · Fixed by #61679
Closed

Bad lint suggestion: '_ in type definition #61124

mark-i-m opened this issue May 24, 2019 · 0 comments · Fixed by #61679
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A-diagnostics Area: Messages for errors, warnings, and lints A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix`. C-bug Category: This is a bug. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@mark-i-m
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https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=af7140af40052d9c78faf8897ce19525

#![deny(rust_2018_idioms)]

struct Bar<'a> { x: &'a u8 }

struct Foo(Bar);
error: hidden lifetime parameters in types are deprecated
 --> src/lib.rs:6:12
  |
6 | struct Foo(Bar);
  |            ^^^- help: indicate the anonymous lifetime: `<'_>`
  |

Except that using '_ is not allowed in the type definition...
@jonas-schievink jonas-schievink added A-diagnostics Area: Messages for errors, warnings, and lints A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix`. C-bug Category: This is a bug. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels May 24, 2019
@memoryruins memoryruins mentioned this issue May 30, 2019
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@zackmdavis zackmdavis mentioned this issue Jun 9, 2019
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zackmdavis added a commit to zackmdavis/rust that referenced this issue Jun 14, 2019
@zackmdavis
in which we decline to suggest the anonymous lifetime in declarations
7a3184a 
The elided-lifetimes-in-path lint (part of our suite of Rust 2018
idiom lints which we are hoping to promote to Warn status) was firing
with an illegal suggestion to write an anonymous lifetime in a
struct/item declaration (where we don't allow it). The linting code
was already deciding whether to act on the basis of a `ParamMode`
enum, indicating whether the present path-segment was part of an
expression, or anywhere else. The present case seemed to be part of
the "anywhere else", and yet meriting different rules as far as the
lint was concerned, so it seemed expedient to introduce a new enum
member. We yank out a `TyKind::Path` arm into its own method so that
we can call it with our new `ParamMode` specifically when lowering
struct fields. (The alternative strategy of changing the signature of
`lower_ty` to take a `ParamMode` would be inelegant given that most of
the `TyKind` match arm bodies therein don't concern themselves with
`ParamMode`.)

Resolves rust-lang#61124.
bors added a commit that referenced this issue Jun 14, 2019
@bors
Auto merge of #61679 - zackmdavis:maybe_dont_indicate_the_anonymous_l…
e699ea0 
…ifetime, r=oli-obk

in which we decline to suggest the anonymous lifetime in declarations

The elided-lifetimes-in-path lint (part of our suite of Rust 2018 idiom lints which we are hoping to promote to Warn status) was firing with an illegal suggestion to write an anonymous lifetime in a
struct/item declaration (where we don't allow it). The linting code was already deciding whether to act on the basis of a `ParamMode` enum, indicating whether the present path-segment was part of an
expression, or anywhere else. The present case seemed to be part of the "anywhere else", and yet meriting different rules as far as the lint was concerned, so it seemed expedient to introduce a new enum member. We yank out `TyKind::Path` arm into its own method so that we can call it with our new `ParamMode` specifically when lowering struct fields—one would have hoped to think of something more elegant than this, but it definitely beats changing the signature of `lower_ty` to take a `ParamMode`!

Resolves #61124.

cc @memoryruins
r? @oli-obk
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A-diagnostics Area: Messages for errors, warnings, and lints A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix`. C-bug Category: This is a bug. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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in which we decline to suggest the anonymous lifetime in declarations zackmdavis/rust
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