`$lit:literal` chokes on `-(1)`
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- Dominant language
- Rust
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Description
I tried this code:
macro_rules! is_literal {
($l:literal) => { true };
($e:expr) => { false };
}
fn main() {
println!("{}", is_literal!(-(1)));
}
I expected to see this happen: one of true or false being printed
Given that -(1) is a valid expression, it should be picked up by $e:expr rather than failing at $lit:literal. Or it should be considered a valid literal expression.
Note that it also chokes on similar expressions, such as -(x) and -(x.method()).
Instead, this happened:
error: unexpected token: `(`
--> src/main.rs:8:33
|
2 | ($l:literal) => { true };
| ---------- while parsing argument for this `literal` macro fragment
...
8 | println!("{}", is_literal!(-(1)));
| ^
Meta
rustc --version --verbose:
rustc 1.73.0 (cc66ad468 2023-10-03)
binary: rustc
commit-hash: cc66ad468955717ab92600c770da8c1601a4ff33
commit-date: 2023-10-03
host: aarch64-apple-darwin
release: 1.73.0
LLVM version: 17.0.2
Happens on beta and nightly too.
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
Reproduce the macro-fragment parsing failure in src/main.rs using the is_literal! example and the reported rustc version. Investigate how literal and expression fragments handle parenthesized unary expressions; done means -(1), -(x), and -(x.method()) no longer fail during macro matching and produce a defined result.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100