Match expressions should sometimes have type !

[powerboat9]

Summary

Match expressions with no arms should give a value of type !

Reproducer

I tried this code:

pub enum X {}

pub fn foo(x: X) {
    let _a: i32 = match x {};
}

pub fn main() {}

Does the code make use of any (1.49) nightly feature ?

• Nightly

Godbolt link

link

Actual behavior

<source>:4:5: error: mismatched types, expected 'i32' but got '()' [E0308]
    4 |     let _a: i32 = match x {};
      |     ^~~     ~~~   ~~~~~

Expected behavior

No error

GCC Version

GCCRS master on godbolt

[philberty]

Whats the logic for never type here ? @flip1995

[CohenArthur]

@philberty https://github.com/rust-lang/rust/blob/3d1dba830a564d1118361345d7ada47a05241f45/compiler/rustc_hir_typeck/src/_match.rs#L32-L36 I believe

so it should be pretty simple - if there are no arms, then it returns !. if there are no arms when there should be arms, then it's up to the exhaustiveness checker to report an error