Closed
Description
openedon Feb 15, 2024
Code
If we try this code:
fn main() {
let m = 42u32;
let value = 'out: {
match value {
1 => break 'out Some(1u16),
2 => Some(2u16),
3 => break 'out Some(3u16),
4 => break 'out Some(4u16),
5 => break 'out Some(5u16),
_ => {}
}
None
};
}Current output
We get this output:
error[E0308]: `match` arms have incompatible types
--> src/main.rs:11:18
|
5 | / match value {
6 | | 1 => break 'out Some(1u16),
7 | | 2 => Some(2u16),
8 | | 3 => break 'out Some(3u16),
9 | | 4 => break 'out Some(4u16),
10 | | 5 => break 'out Some(5u16),
| | --------------------- this and all prior arms are found to be of type `Option<u16>`
11 | | _ => {}
| | ^^ expected `Option<u16>`, found `()`
12 | | }
| |_________- `match` arms have incompatible types
|
= note: expected enum `Option<u16>`
found unit type `()`
help: consider using a semicolon here, but this will discard any values in the match arms
|
12 | };
| +
Desired output
The diagnostic could point out which branch (or branches) caused the type to be Option<u16>, preferably skipping branches which are not reachable.
Other cases
Note that if we reduce the number of branches to 4, we get a complete enumeration of branches. While more helpful, could still be improved by skipping and possibly noting the number of branches that have been skipped due to not being reachable:
error[E0308]: `match` arms have incompatible types
--> src/main.rs:10:18
|
5 | / match value {
6 | | 1 => break 'out Some(1u16),
| | --------------------- this is found to be of type `Option<u16>`
7 | | 2 => Some(2u16),
| | ---------- this is found to be of type `Option<u16>`
8 | | 3 => break 'out Some(3u16),
| | --------------------- this is found to be of type `Option<u16>`
9 | | 4 => break 'out Some(4u16),
| | --------------------- this is found to be of type `Option<u16>`
10 | | _ => {}
| | ^^ expected `Option<u16>`, found `()`
11 | | }
| |_________- `match` arms have incompatible types
|
= note: expected enum `Option<u16>`
found unit type `()`
help: consider using a semicolon here, but this will discard any values in the match arms
|
11 | };
| +
Rust Version
rustc 1.76.0 (07dca489a 2024-02-04)
binary: rustc
commit-hash: 07dca489ac2d933c78d3c5158e3f43beefeb02ce
commit-date: 2024-02-04
host: x86_64-pc-windows-msvc
release: 1.76.0
LLVM version: 17.0.6Anything else?
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
