Implement RFC 2338, "Type alias enum variants" #56225

alexreg · 2018-11-26T04:16:38Z

This PR implements RFC 2338, allowing one to write code like the following.

#![feature(type_alias_enum_variants)]

enum Foo {
    Bar(i32),
    Baz { i: i32 },
}

type Alias = Foo;

fn main() {
    let t = Alias::Bar(0);
    let t = Alias::Baz { i: 0 };
    match t {
        Alias::Bar(_i) => {}
        Alias::Baz { i: _i } => {}
    }
}

Since Self can be considered a type alias in this context, it also enables using Self::Variant as both a constructor and pattern.

Fixes issues #56199 and #56611.

N.B., after discussing the syntax for type arguments on enum variants with @petrochenkov and @eddyb (there are also a few comments on the tracking issue), the consensus seems to be treat the syntax as follows, which ought to be backwards-compatible.

Option::<u8>::None; // OK
Option::None::<u8>; // OK, but lint in near future (hard error next edition?)
Alias::<u8>::None; // OK
Alias::None::<u8>; // Error

I do not know if this will need an FCP, but let's start one if so.

alexreg · 2018-11-26T04:18:15Z

The tricky part of handling type parameters is still to be done, but basic cases are working already. Any advice on this expanding on your previous comment would be appreciated, @petrochenkov. (Hope you don't mind I r?ed you, as well.)

src/librustc/hir/def.rs

src/librustc_typeck/astconv.rs

src/librustc_typeck/check/method/mod.rs

petrochenkov · 2018-11-26T23:58:51Z

Everything about generic arguments should be in instantiate_value_path (at least for values).
Can't say more, last time I looked at that code a couple of years ago and it was rewritten since then at least twice, IIRC (by eddyb and varkor).

src/librustc/hir/mod.rs

src/librustc/ich/impls_hir.rs

alexreg · 2018-12-02T05:19:10Z

Big push coming up... I should be able to finish this tomorrow.

@petrochenkov

Implement RFC 2338, "Type alias enum variants" This PR implements [RFC 2338](rust-lang/rfcs#2338), allowing one to write code like the following. ```rust #![feature(type_alias_enum_variants)] enum Foo { Bar(i32), Baz { i: i32 }, } type Alias = Foo; fn main() { let t = Alias::Bar(0); let t = Alias::Baz { i: 0 }; match t { Alias::Bar(_i) => {} Alias::Baz { i: _i } => {} } } ``` Since `Self` can be considered a type alias in this context, it also enables using `Self::Variant` as both a constructor and pattern. Fixes issues #56199 and #56611. N.B., after discussing the syntax for type arguments on enum variants with @petrochenkov and @eddyb (there are also a few comments on the [tracking issue](#49683)), the consensus seems to be treat the syntax as follows, which ought to be backwards-compatible. ```rust Option::<u8>::None; // OK Option::None::<u8>; // OK, but lint in near future (hard error next edition?) Alias::<u8>::None; // OK Alias::None::<u8>; // Error ``` I do not know if this will need an FCP, but let's start one if so.

bors · 2018-12-29T23:45:39Z

☀️ Test successful - status-appveyor, status-travis
Approved by: petrochenkov
Pushing 5918318 to master...

rust-highfive · 2018-12-29T23:47:26Z

📣 Toolstate changed by #56225!

Tested on commit 5918318.
Direct link to PR: #56225

💔 clippy-driver on windows: test-pass → build-fail (cc @Manishearth @llogiq @mcarton @oli-obk, @rust-lang/infra).
💔 clippy-driver on linux: test-pass → build-fail (cc @Manishearth @llogiq @mcarton @oli-obk, @rust-lang/infra).
💔 rls on windows: test-pass → build-fail (cc @nrc @Xanewok, @rust-lang/infra).
💔 rls on linux: test-pass → build-fail (cc @nrc @Xanewok, @rust-lang/infra).

@Manishearth

Tested on commit rust-lang/rust@5918318. Direct link to PR: <rust-lang/rust#56225> 💔 clippy-driver on windows: test-pass → build-fail (cc @Manishearth @llogiq @mcarton @oli-obk, @rust-lang/infra). 💔 clippy-driver on linux: test-pass → build-fail (cc @Manishearth @llogiq @mcarton @oli-obk, @rust-lang/infra). 💔 rls on windows: test-pass → build-fail (cc @nrc @Xanewok, @rust-lang/infra). 💔 rls on linux: test-pass → build-fail (cc @nrc @Xanewok, @rust-lang/infra).

item.name -> item.ident.name

rustup rust-lang/rust#56225 item.name -> item.ident.name

Changes: ```` UI test cleanup: Extract iter_skip_next from methods.rs Update test output after rebase Remove false negatives from known problems Implement use_self for tuple structs Document known problems rustup rust-lang#56225 Remove unnecessary `use` statements after `cargo fix` Apply cargo fix --edition-idioms fixes Use match ergonomics for booleans lint Use match ergonomics for block_in_if_condition lint Use match ergonomics for bit_mask lint Use match ergonomics for attrs lint Use match ergonomics for assign_ops lint Use match ergonomics for artithmetic lint Use match ergonomics for approx_const lint Remove crate:: prefixes from crate paths Support array indexing expressions in unused write to a constant Mark writes to constants as side-effect-less Update README local run command to remove syspath Remove unsafe from consts clippy lints Fix formatting Merge new_without_default_derive into new_without_default Only print out question_mark lint when it actually triggered Add failing test Reinserted commata Recomend `.as_ref()?` in certain situations Deduplicate some code? ````

@oli-obk

submodules: update clippy from f7bdf50 to 39bd844 Fixes clippy toolstate Changes: ```` UI test cleanup: Extract iter_skip_next from methods.rs Update test output after rebase Remove false negatives from known problems Implement use_self for tuple structs Document known problems rustup #56225 Remove unnecessary `use` statements after `cargo fix` Apply cargo fix --edition-idioms fixes Use match ergonomics for booleans lint Use match ergonomics for block_in_if_condition lint Use match ergonomics for bit_mask lint Use match ergonomics for attrs lint Use match ergonomics for assign_ops lint Use match ergonomics for artithmetic lint Use match ergonomics for approx_const lint Remove crate:: prefixes from crate paths Support array indexing expressions in unused write to a constant Mark writes to constants as side-effect-less Update README local run command to remove syspath Remove unsafe from consts clippy lints Fix formatting Merge new_without_default_derive into new_without_default Only print out question_mark lint when it actually triggered Add failing test Reinserted commata Recomend `.as_ref()?` in certain situations Deduplicate some code? ```` r? @oli-obk or anyone else

Changes: ```` UI test cleanup: Extract iter_skip_next from methods.rs Update test output after rebase Remove false negatives from known problems Implement use_self for tuple structs Document known problems rustup rust-lang#56225 Remove unnecessary `use` statements after `cargo fix` Apply cargo fix --edition-idioms fixes Use match ergonomics for booleans lint Use match ergonomics for block_in_if_condition lint Use match ergonomics for bit_mask lint Use match ergonomics for attrs lint Use match ergonomics for assign_ops lint Use match ergonomics for artithmetic lint Use match ergonomics for approx_const lint Remove crate:: prefixes from crate paths Support array indexing expressions in unused write to a constant Mark writes to constants as side-effect-less Update README local run command to remove syspath Remove unsafe from consts clippy lints Fix formatting Merge new_without_default_derive into new_without_default Only print out question_mark lint when it actually triggered Add failing test Reinserted commata Recomend `.as_ref()?` in certain situations Deduplicate some code? ````

[WIP] High priority resolutions for associated variants cc #56225 (comment)

High priority resolutions for associated variants In rust-lang#56225 variants were assigned lowest priority during name resolution to avoid crater run and potential breakage. This PR changes the rules to give variants highest priority instead. Some motivation: - If variants (and their constructors) are treated as associated items, then they are obviously *inherent* associated items since they don't come from traits. - Inherent associated items have higher priority during resolution than associated items from traits. - The reason is that there is a way to disambiguate in favor of trait items (`<Type as Trait>::Ambiguous`), but there's no way to disambiguate in favor of inherent items, so they became unusable in case of ambiguities if they have low priority. - It's technically problematic to fallback from associated types to anything until lazy normalization (?) is implemented. Crater found some regressions from this change, but they are all in type positions, e.g. ```rust fn f() -> Self::Ambiguos { ... } // Variant `Ambiguous` or associated type `Ambiguous`? ``` , so variants are not usable there right now, but they may become usable in the future if rust-lang/rfcs#2593 is accepted. This PR keeps code like this successfully resolving, but introduces a future-compatibility lint `ambiguous_associated_items` that recommends rewriting it as `<Self as Trait>::Ambiguous`.

Changes: ```` UI test cleanup: Extract iter_skip_next from methods.rs Update test output after rebase Remove false negatives from known problems Implement use_self for tuple structs Document known problems rustup rust-lang/rust#56225 Remove unnecessary `use` statements after `cargo fix` Apply cargo fix --edition-idioms fixes Use match ergonomics for booleans lint Use match ergonomics for block_in_if_condition lint Use match ergonomics for bit_mask lint Use match ergonomics for attrs lint Use match ergonomics for assign_ops lint Use match ergonomics for artithmetic lint Use match ergonomics for approx_const lint Remove crate:: prefixes from crate paths Support array indexing expressions in unused write to a constant Mark writes to constants as side-effect-less Update README local run command to remove syspath Remove unsafe from consts clippy lints Fix formatting Merge new_without_default_derive into new_without_default Only print out question_mark lint when it actually triggered Add failing test Reinserted commata Recomend `.as_ref()?` in certain situations Deduplicate some code? ````

rust-highfive assigned petrochenkov Nov 26, 2018

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alexreg force-pushed the type_alias_enum_variants branch from c9d9926 to 45f338d Compare November 30, 2018 01:27

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Suggestion Span for non_upper_case_globals could be more precise #48103

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bors merged commit a4fa7ef into rust-lang:master Dec 29, 2018

bors mentioned this pull request Dec 29, 2018

Various cosmetic and minor changes #57016

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matthiaskrgr added a commit to matthiaskrgr/rust-clippy that referenced this pull request Dec 30, 2018

rustup rust-lang/rust#56225

e590025

item.name -> item.ident.name

bors added a commit to rust-lang/rust-clippy that referenced this pull request Dec 30, 2018

Auto merge of #3602 - matthiaskrgr:rustup, r=phansch

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rustup rust-lang/rust#56225 item.name -> item.ident.name

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High priority resolutions for associated variants #57501

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Auto merge of #57501 - petrochenkov:highvar, r=<try>

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[WIP] High priority resolutions for associated variants cc #56225 (comment)

petrochenkov mentioned this pull request Jan 14, 2019

type items do not work with enums #26264

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axic mentioned this pull request Mar 19, 2019

rust: add enum aliases ethereum/evmc#206

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Centril mentioned this pull request Jun 9, 2019

Stabilize type_alias_enum_variants in Rust 1.37.0 #61682

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alexreg added the A-typesystem Area: The type system label Nov 24, 2019

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Implement RFC 2338, "Type alias enum variants" #56225

Implement RFC 2338, "Type alias enum variants" #56225

alexreg commented Nov 26, 2018 •

edited by petrochenkov

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rust-highfive commented Dec 29, 2018

Implement RFC 2338, "Type alias enum variants" #56225

Implement RFC 2338, "Type alias enum variants" #56225

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alexreg commented Nov 26, 2018 •

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