An unexpected expanded result from procedural macro
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A-pretty
A-proc-macros
C-bug
T-compiler
- Dominant language
- Rust
- Stars
- 119k
- Forks
- 16.1k
- PR merge metrics
- PR metrics pending
Description
I tried this code to check the expanded HIR by flag -Z unpretty=hir:
// file proc_macro
extern crate proc_macro;
use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, Expr};
#[proc_macro]
pub fn mdriver(input: TokenStream) -> TokenStream {
let expr = parse_macro_input!(input as Expr);
let expanded = quote! {
fn foo() {
#expr?;
}
};
TokenStream::from(expanded)
}
//file call the macro
mdriver!(0..10);
I expected to see this happen:
fn foo() {
match #[lang = "branch"](#[lang = "Range"]{ start: 0, end: 10,}) {
#[lang = "Break"] { 0: residual } =>
#[allow(unreachable_code)]
return #[lang = "from_residual"](residual),
#[lang = "Continue"] { 0: val } =>
#[allow(unreachable_code)]
val,
};
}
Instead, this happened:
fn foo() {
#[lang = "Range"]{
start: 0,
end:
match #[lang = "branch"](10) {
#[lang = "Break"] { 0: residual } =>
#[allow(unreachable_code)]
return #[lang = "from_residual"](residual),
#[lang = "Continue"] { 0: val } =>
#[allow(unreachable_code)]
val,
},};
}
Meta
rustc --version --verbose:
rustc 1.80.0-nightly (ef0027897 2024-05-12)
binary: rustc
commit-hash: ef0027897d2e9014766fb47dce9ddbb925d2f540
commit-date: 2024-05-12
host: x86_64-unknown-linux-gnu
release: 1.80.0-nightly
LLVM version: 18.1.4
Backtrace
<backtrace>
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 procedural-macro example with the nightly compiler and inspect its output using -Z unpretty=hir. Compare the expansion of mdriver!(0..10) with the expected and actual HIR shown in the issue; done means determining why the ? expression is expanded inside the range literal and correcting that behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100