Tracking issue for RFC 2302, Tuple struct construction with Self(v1, v2, ..)

This is a tracking issue for the RFC "Tuple struct construction with Self(v1, v2, ..)" (rust-lang/rfcs#2302).

Steps:

Implement the RFC (Implement RFC 2302: tuple_struct_self_ctor #53751)
Adjust documentation (see instructions on forge)
Stabilization PR (see instructions on forge)

Unresolved questions:

None

Auto merge of #53751 - F001:tuple-struct-self-ctor, r=petrochenkov,va…

Code that implements this has been merged.

#![feature(self_struct_ctor)]

struct Example(i32, bool);

impl Example {
    fn new() -> Self {
        Self(42, true)
    }
}

playground

@rfcbot

@rfcbot merge

Stabilization report & proposal

Feature name: #![feature(self_struct_ctor)]
Version target: 1.32 (2019-01-18)

Originally accepted in rust-lang/rfcs#2302, I propose that we stabilize self_struct_ctor.
This has been in nightly since 2018-09-15 which is ~8 weeks ago.

The proposed change is not a blocker for anyone but it is a nice quality of life feature in some cases and more importantly, it makes the language less surprising and easier to learn. Furthermore, we do already permit Self { foo: ... }.

What is being stabilized

Relevant artefacts:

The changes are:

Self becomes a legal pattern and expression for unit structs in impls (both inherent and trait impls...).

match Self {
    Self => ...
}

Self(x1, x2, ...) becomes a legal pattern and expression for tuple structs in impls (both inherent and trait impls...).

match Self(0, 1) {
    Self(x, y) => ...
}

Self becomes a legal function pointer in impls (...).

opt.map(Self)

Points 1-3 work through type aliases just like Self { field: <thing> } does.

What is not being stabilized

Mentions of enum variants through Self is not being stabilized. For example:

enum Foo { Variant(u8), }

impl Foo {
    fn bar() {
        let x = Self::Variant(1);
    }
}

Divergences from RFC

None

@Centril

Team member @Centril has proposed to merge this. The next step is review by the rest of the tagged teams:

No concerns currently listed.

Once a majority of reviewers approve (and none object), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

🔔 This is now entering its final comment period, as per the review above. 🔔

A variant of what is not being stabilized gave me an internal compiler error.

Code:

#![feature(self_struct_ctor)]
#![allow(dead_code)]

enum Foo {}

impl Foo {
    fn bar() {
        Self(1u8);
    }
}

fn main() {}

Compiler output:

C:/Users/Caio/.cargo/bin/cargo.exe run --package nespera --bin nespera
   Compiling nespera v0.1.0 (C:\Users\Caio\projects\nespera)
error: internal compiler error: cat_expr Errd
 --> src\main.rs:7:14
  |
7 |       fn bar() {
  |  ______________^
8 | |         Self(1u8);
9 | |     }
  | |_____^

error: internal compiler error: cat_expr Errd
 --> src\main.rs:8:9
  |
8 |         Self(1u8);
  |         ^^^^^^^^^

error: internal compiler error: cat_expr Errd
 --> src\main.rs:8:9
  |
8 |         Self(1u8);
  |         ^^^^

error: internal compiler error: QualifyAndPromoteConstants: Mir had errors
 --> src\main.rs:7:5
  |
7 | /     fn bar() {
8 | |         Self(1u8);
9 | |     }
  | |_____^

error: internal compiler error: broken MIR in DefId(0/0:5 ~ nespera[1ed1]::{{impl}}[0]::bar[0]) ("return type"): bad type [type error]
 --> src\main.rs:7:5
  |
7 | /     fn bar() {
8 | |         Self(1u8);
9 | |     }
  | |_____^

error: internal compiler error: broken MIR in DefId(0/0:5 ~ nespera[1ed1]::{{impl}}[0]::bar[0]) (LocalDecl { mutability: Mut, is_user_variable: None, internal: false, is_block_tail: None, ty: [type error], user_ty: UserTypeProjections { contents: [] }, name: None, source_info: SourceInfo { span: src\main.rs:7:5: 9:6, scope: scope[0] }, visibility_scope: scope[0] }): bad type [type error]
 --> src\main.rs:7:5
  |
7 | /     fn bar() {
8 | |         Self(1u8);
9 | |     }
  | |_____^

thread 'main' panicked at 'no errors encountered even though `delay_span_bug` issued', src\librustc_errors\lib.rs:334:17
stack backtrace:
   0: std::sys_common::alloc::realloc_fallback
   1: std::panicking::take_hook
   2: std::panicking::take_hook
   3: rustc::ty::structural_impls::<impl rustc::ty::context::Lift<'tcx> for rustc::ty::instance::InstanceDef<'a>>::lift_to_tcx
   4: std::panicking::rust_panic_with_hook
   5: <rustc_errors::diagnostic::SubDiagnostic as core::fmt::Debug>::fmt
   6: <rustc_errors::Handler as core::ops::drop::Drop>::drop
   7: <humantime::duration::Error as std::error::Error>::cause
   8: <humantime::duration::Error as std::error::Error>::cause
   9: <humantime::duration::Error as std::error::Error>::cause
  10: <rustc_driver::derive_registrar::Finder as rustc::hir::itemlikevisit::ItemLikeVisitor<'v>>::visit_item
  11: _rust_maybe_catch_panic
  12: rustc_driver::profile::dump
  13: rustc_driver::main
  14: <unknown>
  15: std::panicking::update_panic_count
  16: _rust_maybe_catch_panic
  17: std::rt::lang_start_internal
  18: <unknown>
  19: <unknown>
  20: BaseThreadInitThunk
  21: RtlUserThreadStart
query stack during panic:
end of query stack

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.32.0-nightly (1f57e4841 2018-11-23) running on x86_64-pc-windows-msvc

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

note: some of the compiler flags provided by cargo are hidden

error: Could not compile `nespera`.

To learn more, run the command again with --verbose.

Process finished with exit code 101

@caiopsouza

@caiopsouza Thanks for reporting this! Could you file this as a separate issue so that we can track and fix it?

Stabilization PR

The final comment period, with a disposition to merge, as per the review above, is now complete.

may I ask, in which release of rust was this merged? ~~I hit it with rustc-1.31.1?~~

fixed in rustc-1.32.0, sry for the noise :-)

Bump MSRV for deps

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Tracking issue for RFC 2302, Tuple struct construction with `Self(v1, v2, ..)` #51994

Stabilization report & proposal

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Tracking issue for RFC 2302, Tuple struct construction with Self(v1, v2, ..) #51994

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shepmaster commented on Sep 15, 2018

Centril commented on Nov 11, 2018

Stabilization report & proposal

What is being stabilized

What is not being stabilized

Divergences from RFC

rfcbot commented on Nov 11, 2018

rfcbot commented on Nov 23, 2018

caiopsouza commented on Nov 24, 2018

Centril commented on Nov 24, 2018

alexreg commented on Nov 30, 2018

rfcbot commented on Dec 3, 2018

stefson commented on Apr 22, 2019

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Tracking issue for RFC 2302, Tuple struct construction with `Self(v1, v2, ..)` #51994