Making a mistake in a match can lead to infinite recursion without any hint to what is going on
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- Dominant language
- Rust
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Description
Code
pub struct SubMenu;
impl SubMenu {
pub fn test(&self) {
}
}
pub enum Item {
Back,
SubMenu(SubMenu)
}
impl Item {
pub fn test(&self) {
match self {
Item::Back => (),
// This recurses because I messed up the match
// I really want Item::SubMenu(x) but there is
// no warning at all that this can cause an issue
sub => sub.test()
}
}
}
fn main() {
let itm = Item::SubMenu(SubMenu{});
itm.test();
}
Current output
(Running in rust playground)
Compiling playground v0.0.1 (/playground)
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.46s
(Clippy output in rust playground)
Checking playground v0.0.1 (/playground)
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.88s
Desired output
Anything that tells the user that there is an infinite loop waiting to happen
Something like:
sub => sub.test()
^^^^^^^^^^ this will recurse infinitely
Rationale and extra context
I made a mistake while writing the match seen above. I really wanted Item::SubMenu(sub) => sub.test() but mistakenly thought sub => sub.test() will be enough. While the error was of course made by me, after I found it I was surprised that neither rustc, clippy nor rust-analyzer will warn me that this will cause infinite recursion.
I ran the code on an embedded target which made the error search very hard, since any debug connection died when the stack overflowed without any error message, leading to a two day search for the cause
Other cases
No response
Rust Version
rustc 1.81.0 (eeb90cda1 2024-09-04)
binary: rustc
commit-hash: eeb90cda1969383f56a2637cbd3037bdf598841c
commit-date: 2024-09-04
host: x86_64-pc-windows-msvc
release: 1.81.0
LLVM version: 18.1.7
(The exact same issue/missing diagnostic is also true on the beta and nightly channels)
Anything else?
No response
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the supplied Rust match example and compare the behavior of rustc, Clippy, and rust-analyzer described in the issue. Determine a diagnostic approach for recognizing the unintended recursive match arm; done means the example produces a clear warning without incorrectly flagging valid matches.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100