Enum variants completely shadow inherent associated functions.

[leoyvens]

Consider the code below:

enum Foo { Bar(i32) }

impl Foo {
    fn Bar(x: i32) -> Foo { 
        println!("I'm uncallable"); 
        Foo::Bar(x) 
    }
}

fn main() {
    Foo::Bar(0); // Variant constructor.
   <Foo>::Bar(0); // Inherent function.
}

It compiles successfully and terminates with no output. There is an ambiguity between the variant and the associated function, though it seems we always prefer the variant, making the associated function uncallable. Having an inherent associated function with the same name as a variant should be an error.

Edit: @petrochenkov points out that it's not actually uncallable, you can call it with <Foo>::Bar(0). A deny-by-default lint then perhaps?

[leonardo-m]

I agree this a breaking change worth having.

It compiles successfully

It compiles, but it gives a clear warning and it's often a bad idea to ignore rustc warnings:

warning: method `Bar` should have a snake case name such as `bar`
 --> ...\test.rs:4:5
  |
4 | /     fn Bar(x: i32) -> Foo {
5 | |         println!("I'm uncallable");
6 | |         Foo::Bar(x)
7 | |     }
  | |_____^
  |
  = note: #[warn(non_snake_case)] on by default

[petrochenkov]

This is a duplicate of some old issue, the decision was to always prioritize variants over other associated items, thus breaking the currently working way to call the "uncallable" Bar - <Foo>::Bar.

[petrochenkov]

There was also a suggestion to make this an overlap error instead of leaving the associated fn Bar legal but uncallable.

[petrochenkov]

This issue is a part of #26264 / rust-lang/rfcs#2338 really.

[leoyvens]

#28320 is the closest I could find.

[estebank]

@petrochenkov should we lint on the shadowing at least? Should we add some way of referring to the method at all?

[petrochenkov]

Variants are inherent associated items now, so this should be reported as an overlap error, similarly to

struct S;
impl S { fn foo() {} }
impl S { fn foo() {} }

[Centril]

@petrochenkov It doesn't seem to generate an overlap error currently?

[petrochenkov]

No, the overlap error is not reported currently, someone needs to implement it.

[steveklabnik]

Triage: still compiles with no output. Which seems strange to me, given that <Foo>::Bar(0) is supposed to be able to call it?

[Nemo157]

From 1.0 to 1.33 (inclusive) <Foo>::Bar(0) worked to call the inherent method, 1.34 to 1.36 failed to compile with error: enum variants on type aliases are experimental, 1.37+ compile and resolve to the enum variant in both cases.

full test

> for v in 1.{0..7}.0 1.{8..53}; do rustc +$v --version && rustc +$v main.rs --allow=warnings && ./main; done
rustc 1.0.0 (a59de37e9 2015-05-13) (built 2015-05-14)
I'm uncallable
rustc 1.1.0 (35ceea399 2015-06-19)
I'm uncallable
rustc 1.2.0 (082e47636 2015-08-03)
I'm uncallable
rustc 1.3.0 (9a92aaf19 2015-09-15)
I'm uncallable
rustc 1.4.0 (8ab8581f6 2015-10-27)
I'm uncallable
rustc 1.5.0 (3d7cd77e4 2015-12-04)
I'm uncallable
rustc 1.6.0 (c30b771ad 2016-01-19)
I'm uncallable
rustc 1.7.0 (a5d1e7a59 2016-02-29)
I'm uncallable
rustc 1.8.0 (db2939409 2016-04-11)
I'm uncallable
rustc 1.9.0 (e4e8b6668 2016-05-18)
I'm uncallable
rustc 1.10.0 (cfcb716cf 2016-07-03)
I'm uncallable
rustc 1.11.0 (9b21dcd6a 2016-08-15)
I'm uncallable
rustc 1.12.1 (d4f39402a 2016-10-19)
I'm uncallable
rustc 1.13.0 (2c6933acc 2016-11-07)
I'm uncallable
rustc 1.14.0 (e8a012324 2016-12-16)
I'm uncallable
rustc 1.15.1 (021bd294c 2017-02-08)
I'm uncallable
rustc 1.16.0 (30cf806ef 2017-03-10)
I'm uncallable
rustc 1.17.0 (56124baa9 2017-04-24)
I'm uncallable
rustc 1.18.0 (03fc9d622 2017-06-06)
I'm uncallable
rustc 1.19.0 (0ade33941 2017-07-17)
I'm uncallable
rustc 1.20.0 (f3d6973f4 2017-08-27)
I'm uncallable
rustc 1.21.0 (3b72af97e 2017-10-09)
I'm uncallable
rustc 1.22.1 (05e2e1c41 2017-11-22)
I'm uncallable
rustc 1.23.0 (766bd11c8 2018-01-01)
I'm uncallable
rustc 1.24.1 (d3ae9a9e0 2018-02-27)
I'm uncallable
rustc 1.25.0 (84203cac6 2018-03-25)
I'm uncallable
rustc 1.26.2 (594fb253c 2018-06-01)
I'm uncallable
rustc 1.27.2 (58cc626de 2018-07-18)
I'm uncallable
rustc 1.28.0 (9634041f0 2018-07-30)
I'm uncallable
rustc 1.29.2 (17a9dc751 2018-10-05)
I'm uncallable
rustc 1.30.1 (1433507eb 2018-11-07)
I'm uncallable
rustc 1.31.1 (b6c32da9b 2018-12-18)
I'm uncallable
rustc 1.32.0 (9fda7c223 2019-01-16)
I'm uncallable
rustc 1.33.0 (2aa4c46cf 2019-02-28)
I'm uncallable
rustc 1.34.2 (6c2484dc3 2019-05-13)
error: enum variants on type aliases are experimental
  --> main.rs:12:5
   |
12 |     <Foo>::Bar(0); // Inherent function.
   |     ^^^^^^^^^^

error: aborting due to previous error

rustc 1.35.0 (3c235d560 2019-05-20)
error: enum variants on type aliases are experimental
  --> main.rs:12:5
   |
12 |     <Foo>::Bar(0); // Inherent function.
   |     ^^^^^^^^^^

error: aborting due to previous error

rustc 1.36.0 (a53f9df32 2019-07-03)
error: enum variants on type aliases are experimental
  --> main.rs:12:5
   |
12 |     <Foo>::Bar(0); // Inherent function.
   |     ^^^^^^^^^^

error: aborting due to previous error

rustc 1.37.0 (eae3437df 2019-08-13)
rustc 1.38.0 (625451e37 2019-09-23)
rustc 1.39.0 (4560ea788 2019-11-04)
rustc 1.40.0 (73528e339 2019-12-16)
rustc 1.41.1 (f3e1a954d 2020-02-24)
rustc 1.42.0 (b8cedc004 2020-03-09)
rustc 1.43.1 (8d69840ab 2020-05-04)
rustc 1.44.1 (c7087fe00 2020-06-17)
rustc 1.45.2 (d3fb005a3 2020-07-31)
rustc 1.46.0 (04488afe3 2020-08-24)
rustc 1.47.0 (18bf6b4f0 2020-10-07)
rustc 1.48.0 (7eac88abb 2020-11-16)
rustc 1.49.0 (e1884a8e3 2020-12-29)
rustc 1.50.0 (cb75ad5db 2021-02-10)
rustc 1.51.0 (2fd73fabe 2021-03-23)
rustc 1.52.1 (9bc8c42bb 2021-05-09)
rustc 1.53.0 (53cb7b09b 2021-06-17)

[petrochenkov]

#48758 (comment) describes the current status, the overlap error is still not implemented.