Open
Description
With this code,
#![no_std]
#![no_main]
#[panic_handler]
fn panic(_panic: &core::panic::PanicInfo<'_>) -> ! {
loop {}
}This builds fine for thumbv6m-none-eabi target:
cargo build --target thumbv6m-none-eabi -Z build-std=core --release
However, adding optimize_for_size to build-std-features as follows causes the build to fail
cargo build --target thumbv6m-none-eabi -Z build-std=core -Z build-std-features=optimize_for_size --release
with this error
Compiling core v0.0.0 (/home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
error[E0428]: the name `_inner_slow_integer_to_str` is defined multiple times
--> /home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/num.rs:415:9
|
415 | fn _inner_slow_integer_to_str(mut n: $u, buf: &mut [MaybeUninit::<u8>]) -> usize {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| `_inner_slow_integer_to_str` redefined here
| previous definition of the value `_inner_slow_integer_to_str` here
...
643 | / impl_Display!(
644 | | i8, u8,
645 | | i16, u16,
646 | | i32, u32,
647 | | isize, usize,
648 | | ; as u32 via to_u32 named fmt_u32);
| |__________________________________________- in this macro invocation
|
= note: `_inner_slow_integer_to_str` must be defined only once in the value namespace of this module
= note: this error originates in the macro `impl_Display` (in Nightly builds, run with -Z macro-backtrace for more info)
I am not familiar with the Rust code base, but I think the cause is that #142098 resulted in _inner_slow_integer_to_str being defined multiple times.
In fact, this compiles without error in nightly-2025-07-08.
Meta
rustc --version --verbose:
rustc 1.90.0-nightly (2a023bf80 2025-07-10)
binary: rustc
commit-hash: 2a023bf80a6fbd6a06d5460a34eb247b986286ed
commit-date: 2025-07-10
host: x86_64-unknown-linux-gnu
release: 1.90.0-nightly
LLVM version: 20.1.7
Backtrace
Compiling core v0.0.0 (/home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
error[E0428]: the name `_inner_slow_integer_to_str` is defined multiple times
--> /home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/num.rs:415:9
|
415 | fn _inner_slow_integer_to_str(mut n: $u, buf: &mut [MaybeUninit::<u8>]) -> usize {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| `_inner_slow_integer_to_str` redefined here
| previous definition of the value `_inner_slow_integer_to_str` here
...
643 | / impl_Display!(
644 | | i8, u8,
645 | | i16, u16,
646 | | i32, u32,
647 | | isize, usize,
648 | | ; as u32 via to_u32 named fmt_u32);
| |__________________________________________- in this macro invocation
|
= note: `_inner_slow_integer_to_str` must be defined only once in the value namespace of this module
= note: this error originates in the macro `impl_Display` (in Nightly builds, run with -Z macro-backtrace for more info)
error[E0308]: mismatched types
--> /home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/num.rs:361:57
|
361 | offset = _inner_slow_integer_to_str(self.unsigned_abs().$conv_fn(), &mut buf.buf);
| -------------------------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `u32`, found `u64`
| |
| arguments to this function are incorrect
...
649 | / impl_Display!(
650 | | i64, u64,
651 | | ; as u64 via to_u64 named fmt_u64);
| |__________________________________________- in this macro invocation
|
note: function defined here
--> /home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/num.rs:415:12
|
415 | fn _inner_slow_integer_to_str(mut n: $u, buf: &mut [MaybeUninit::<u8>]) -> usize {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ ---------
...
643 | / impl_Display!(
644 | | i8, u8,
645 | | i16, u16,
646 | | i32, u32,
647 | | isize, usize,
648 | | ; as u32 via to_u32 named fmt_u32);
| |__________________________________________- in this macro invocation
= note: this error originates in the macro `impl_Display` (in Nightly builds, run with -Z macro-backtrace for more info)
help: you can convert a `u64` to a `u32` and panic if the converted value doesn't fit
|
361 | offset = _inner_slow_integer_to_str(self.unsigned_abs().$conv_fn().try_into().unwrap(), &mut buf.buf);
| ++++++++++++++++++++
error[E0308]: mismatched types
--> /home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/num.rs:404:57
|
404 | offset = _inner_slow_integer_to_str(self.$conv_fn(), &mut buf.buf);
| -------------------------- ^^^^^^^^^^^^^^^ expected `u32`, found `u64`
| |
| arguments to this function are incorrect
...
649 | / impl_Display!(
650 | | i64, u64,
651 | | ; as u64 via to_u64 named fmt_u64);
| |__________________________________________- in this macro invocation
|
note: function defined here
--> /home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/num.rs:415:12
|
415 | fn _inner_slow_integer_to_str(mut n: $u, buf: &mut [MaybeUninit::<u8>]) -> usize {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ ---------
...
643 | / impl_Display!(
644 | | i8, u8,
645 | | i16, u16,
646 | | i32, u32,
647 | | isize, usize,
648 | | ; as u32 via to_u32 named fmt_u32);
| |__________________________________________- in this macro invocation
= note: this error originates in the macro `impl_Display` (in Nightly builds, run with -Z macro-backtrace for more info)
help: you can convert a `u64` to a `u32` and panic if the converted value doesn't fit
|
404 | offset = _inner_slow_integer_to_str(self.$conv_fn().try_into().unwrap(), &mut buf.buf);
| ++++++++++++++++++++
error[E0308]: mismatched types
--> /home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/num.rs:440:53
|
440 | let offset = _inner_slow_integer_to_str(n, &mut buf);
| -------------------------- ^ expected `u32`, found `u64`
| |
| arguments to this function are incorrect
...
649 | / impl_Display!(
650 | | i64, u64,
651 | | ; as u64 via to_u64 named fmt_u64);
| |__________________________________________- in this macro invocation
|
note: function defined here
--> /home/nazo/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/num.rs:415:12
|
415 | fn _inner_slow_integer_to_str(mut n: $u, buf: &mut [MaybeUninit::<u8>]) -> usize {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ ---------
...
643 | / impl_Display!(
644 | | i8, u8,
645 | | i16, u16,
646 | | i32, u32,
647 | | isize, usize,
648 | | ; as u32 via to_u32 named fmt_u32);
| |__________________________________________- in this macro invocation
= note: this error originates in the macro `impl_Display` (in Nightly builds, run with -Z macro-backtrace for more info)
help: you can convert a `u64` to a `u32` and panic if the converted value doesn't fit
|
440 | let offset = _inner_slow_integer_to_str(n.try_into().unwrap(), &mut buf);
| ++++++++++++++++++++
Some errors have detailed explanations: E0308, E0428.
For more information about an error, try `rustc --explain E0308`.
error: could not compile `core` (lib) due to 4 previous errors