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Stabilize extern "custom" #158504

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4 changes: 1 addition & 3 deletions compiler/rustc_ast_lowering/src/stability.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,7 @@ pub fn extern_abi_stability(abi: ExternAbi) -> Result<(), UnstableAbi> {
ExternAbi::Rust
| ExternAbi::C { .. }
| ExternAbi::Cdecl { .. }
| ExternAbi::Custom
| ExternAbi::Stdcall { .. }
| ExternAbi::Fastcall { .. }
| ExternAbi::Thiscall { .. }
Expand Down Expand Up @@ -144,9 +145,6 @@ pub fn extern_abi_stability(abi: ExternAbi) -> Result<(), UnstableAbi> {
feature: sym::cmse_nonsecure_entry,
explain: GateReason::Experimental,
}),
ExternAbi::Custom => {
Err(UnstableAbi { abi, feature: sym::abi_custom, explain: GateReason::Experimental })
}
ExternAbi::Swift => {
Err(UnstableAbi { abi, feature: sym::abi_swift, explain: GateReason::Experimental })
}
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2 changes: 2 additions & 0 deletions compiler/rustc_feature/src/accepted.rs
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Expand Up @@ -46,6 +46,8 @@ declare_features! (

/// Allows `#[target_feature(...)]` on aarch64 platforms
(accepted, aarch64_target_feature, "1.61.0", Some(44839)),
/// Allows `extern "custom" fn()`.
(accepted, abi_custom, "CURRENT_RUSTC_VERSION", Some(140829)),
/// Allows using the `efiapi` ABI.
(accepted, abi_efiapi, "1.68.0", Some(65815)),
/// Allows the sysV64 ABI to be specified on all platforms
Expand Down
2 changes: 0 additions & 2 deletions compiler/rustc_feature/src/unstable.rs
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Expand Up @@ -372,8 +372,6 @@ declare_features! (
(unstable, abi_avr_interrupt, "1.45.0", Some(69664)),
/// Allows `extern "cmse-nonsecure-call" fn()`.
(unstable, abi_cmse_nonsecure_call, "1.90.0", Some(81391)),
/// Allows `extern "custom" fn()`.
(unstable, abi_custom, "1.89.0", Some(140829)),
/// Allows `extern "gpu-kernel" fn()`.
(unstable, abi_gpu_kernel, "1.86.0", Some(135467)),
/// Allows `extern "msp430-interrupt" fn()`.
Expand Down
1 change: 0 additions & 1 deletion library/compiler-builtins/compiler-builtins/src/lib.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
#![cfg_attr(feature = "compiler-builtins", compiler_builtins)]
#![cfg_attr(all(target_family = "wasm"), feature(wasm_numeric_instr))]
#![feature(abi_custom)]
#![feature(abi_unadjusted)]
#![feature(asm_experimental_arch)]
#![feature(cfg_target_has_atomic)]
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1 change: 0 additions & 1 deletion src/doc/unstable-book/src/compiler-flags/instrument-mcount.md
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Expand Up @@ -40,7 +40,6 @@ The following example can be compiled with `-Zinstrument-mcount=yes` or `-Zinstr

```rust
#![feature(instrument_fn)]
#![feature(abi_custom)]

fn main() {
// Ensure all the early startup occurs before attempting to call this trivial, single-threaded
Expand Down
1 change: 0 additions & 1 deletion tests/ui/abi/bad-custom.rs
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@tgross35 tgross35 Aug 9, 2026

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Since the docs say returning the unit type is okay, it would be good to add a -> () and -> SomeAlias to make sure that actually works and it's not an AST gate (seems like it is fine)

@folkertdev folkertdev Aug 9, 2026 •
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No it is an AST gate, the alias fails https://godbolt.org/z/G35o3EGW6.

Doing it truly based on the type is all kinds of nasty in the case of generics

trait MyTrait {
    type T;

    #[unsafe(naked)]
    unsafe extern "custom" foo() -> Self::T { // error?
        core::arch::asm!("");
    }
}

We also lose span information about the function header I believe, so it would be harder go generate a good error message if we delay.

Original file line number Diff line number Diff line change
@@ -1,7 +1,6 @@
//@ edition: 2021
//@ check-fail
//@ needs-asm-support
#![feature(abi_custom)]

#[unsafe(naked)]
extern "custom" fn must_be_unsafe(a: i64) -> i64 {
Expand Down
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