rust-lang / rust-lang/rust

When a `proc_macro` has a stack overflow, rustc crashes and errors confusingly

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A-error-handling A-proc-macros C-bug I-crash T-compiler
Dominant language
Rust
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Description

Code
// --- macro_crate/src/lib.rs ---
use proc_macro::TokenStream;

#[proc_macro_derive(Trait)]
pub fn derive_trait(tokens: TokenStream) -> TokenStream {
    if true {
        derive_trait(tokens)
    } else {
        TokenStream::new()
    }
}


// --- my-crate/src/main.rs ---
#[derive(Trait)]
struct S;

fn main() {}
Current output
error: rustc interrupted by SIGSEGV, printing backtrace

~/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/librustc_driver-fd05879751a9d790.so(+0x3104966)[0x7f5e85f04966]
/lib64/libc.so.6(+0x3e9a0)[0x7f5e82ac49a0]
.../test-issue/target/debug/deps/libmacro_crate-a1b04264bf77fcce.so(+0x21420)[0x7f5e79482420]

### cycle encountered after 3 frames with period 4
.../test-issue/target/debug/deps/libmacro_crate-a1b04264bf77fcce.so(+0x21425)[0x7f5e79482425]
.../test-issue/target/debug/deps/libmacro_crate-a1b04264bf77fcce.so(+0x21425)[0x7f5e79482425]
.../test-issue/target/debug/deps/libmacro_crate-a1b04264bf77fcce.so(+0x21425)[0x7f5e79482425]
.../test-issue/target/debug/deps/libmacro_crate-a1b04264bf77fcce.so(+0x21425)[0x7f5e79482425]
### recursed 63 times

.../test-issue/target/debug/deps/libmacro_crate-a1b04264bf77fcce.so(+0x21425)[0x7f5e79482425]

note: rustc unexpectedly overflowed its stack! this is a bug
note: maximum backtrace depth reached, frames may have been lost
note: we would appreciate a report at https://github.com/rust-lang/rust
error: could not compile `test-issue` (bin "test-issue")

Caused by:
  process didn't exit successfully: `~/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustc --crate-name test_issue --edition=2021 src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=212 --crate-type bin --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 -C metadata=10df6c618bb41553 -C extra-filename=-10df6c618bb41553 --out-dir .../test-issue/target/debug/deps -C incremental=.../test-issue/target/debug/incremental -L dependency=.../test-issue/target/debug/deps --extern askama=.../test-issue/target/debug/deps/libaskama-a71517d66164d0f1.rlib --extern macro_crate=.../test-issue/target/debug/deps/libmacro_crate-a1b04264bf77fcce.so --extern serde=.../test-issue/target/debug/deps/libserde-916cd61b435466f2.rlib -C link-arg=-fuse-ld=lld` (signal: 11, SIGSEGV: invalid memory reference)
Desired output
Macro at `#[derive(Trait)]` has overflowed.

Or something that specifies the place where the macro overflowed, its crate, and that doesn't imply the issue is with rustc.
Rationale and extra context

No response

Other cases

No response

Anything else?

No response

Contributor guide

Open the contributing guide

First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the crash using macro_crate/src/lib.rs and my-crate/src/main.rs, where the derive proc macro recursively calls itself. Compare the current SIGSEGV and stack-overflow output with the requested diagnostic identifying #[derive(Trait)] and its location; the report does not name a rustc implementation file or test.

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
Mostly clear
Newbie friendliness
35/100

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