cast-lossless breaks macro #15348
Description
Using the following flags
--force-warn clippy::cast-lossless
this code:
//@ build-pass
#![crate_type = "lib"]
#![allow(arithmetic_overflow)]
pub trait BitSplit {
type Half;
fn merge(halves: [Self::Half; 2]) -> Self;
}
macro_rules! impl_ints {
($int:ty => $half:ty; $mask:expr) => {
impl BitSplit for $int {
type Half = $half;
#[inline]
fn merge(halves: [Self::Half; 2]) -> Self {
const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
(halves[0] << HALF_SIZE) as $int | halves[1] as $int
}
}
};
}
impl_ints!(u128 => u64; 0x0000_0000_0000_0000_FFFF_FFFF_FFFF_FFFF);
impl_ints!( u64 => u32; 0x0000_0000_FFFF_FFFF);
impl_ints!( u32 => u16; 0x0000_FFFF);
impl_ints!( u16 => u8; 0x00FF);caused the following diagnostics:
Checking _ice-issue-96944 v0.1.0 (/tmp/icemaker_global_tempdir.0gE5D6KlClUx/icemaker_clippyfix_tempdir.ArOqbDGioPwO/_ice-issue-96944)
warning: casts from `u64` to `u128` can be expressed infallibly using `From`
--> src/lib.rs:12:27
|
12 | impl BitSplit for $int {
| ___________________________^
13 | | type Half = $half;
14 | | #[inline]
15 | | fn merge(halves: [Self::Half; 2]) -> Self {
16 | | const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 | | (halves[0] << HALF_SIZE) as $int | halves[1] as $int
| |________________________________________^
...
23 | impl_ints!(u128 => u64; 0x0000_0000_0000_0000_FFFF_FFFF_FFFF_FFFF);
| ------------------------------------------------------------------ in this macro invocation
|
= help: an `as` cast can become silently lossy if the types change in the future
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
= note: requested on the command line with `--force-warn clippy::cast-lossless`
= note: this warning originates in the macro `impl_ints` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `<u128>::from` instead
|
12 - impl BitSplit for $int {
13 - type Half = $half;
14 - #[inline]
15 - fn merge(halves: [Self::Half; 2]) -> Self {
16 - const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 - (halves[0] << HALF_SIZE) as $int | halves[1] as $int
12 + impl BitSplit for <u128>::from(halves[0] << HALF_SIZE) as $int | halves[1] as $int
|
warning: casts from `u64` to `u128` can be expressed infallibly using `From`
--> src/lib.rs:12:27
|
12 | impl BitSplit for $int {
| ___________________________^
13 | | type Half = $half;
14 | | #[inline]
15 | | fn merge(halves: [Self::Half; 2]) -> Self {
16 | | const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 | | (halves[0] << HALF_SIZE) as $int | halves[1] as $int
| |____________________________________________________________^
...
23 | impl_ints!(u128 => u64; 0x0000_0000_0000_0000_FFFF_FFFF_FFFF_FFFF);
| ------------------------------------------------------------------ in this macro invocation
|
= help: an `as` cast can become silently lossy if the types change in the future
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
= note: this warning originates in the macro `impl_ints` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `<u128>::from` instead
|
12 - impl BitSplit for $int {
13 - type Half = $half;
14 - #[inline]
15 - fn merge(halves: [Self::Half; 2]) -> Self {
16 - const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 - (halves[0] << HALF_SIZE) as $int | halves[1] as $int
12 + impl BitSplit for <u128>::from(halves[1]) as $int
|
warning: casts from `u32` to `u64` can be expressed infallibly using `From`
--> src/lib.rs:12:27
|
12 | impl BitSplit for $int {
| ___________________________^
13 | | type Half = $half;
14 | | #[inline]
15 | | fn merge(halves: [Self::Half; 2]) -> Self {
16 | | const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 | | (halves[0] << HALF_SIZE) as $int | halves[1] as $int
| |________________________________________^
...
24 | impl_ints!( u64 => u32; 0x0000_0000_FFFF_FFFF);
| ------------------------------------------------------------------ in this macro invocation
|
= help: an `as` cast can become silently lossy if the types change in the future
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
= note: this warning originates in the macro `impl_ints` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `<u64>::from` instead
|
12 - impl BitSplit for $int {
13 - type Half = $half;
14 - #[inline]
15 - fn merge(halves: [Self::Half; 2]) -> Self {
16 - const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 - (halves[0] << HALF_SIZE) as $int | halves[1] as $int
12 + impl BitSplit for <u64>::from(halves[0] << HALF_SIZE) as $int | halves[1] as $int
|
warning: casts from `u32` to `u64` can be expressed infallibly using `From`
--> src/lib.rs:12:27
|
12 | impl BitSplit for $int {
| ___________________________^
13 | | type Half = $half;
14 | | #[inline]
15 | | fn merge(halves: [Self::Half; 2]) -> Self {
16 | | const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 | | (halves[0] << HALF_SIZE) as $int | halves[1] as $int
| |____________________________________________________________^
...
24 | impl_ints!( u64 => u32; 0x0000_0000_FFFF_FFFF);
| ------------------------------------------------------------------ in this macro invocation
|
= help: an `as` cast can become silently lossy if the types change in the future
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
= note: this warning originates in the macro `impl_ints` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `<u64>::from` instead
|
12 - impl BitSplit for $int {
13 - type Half = $half;
14 - #[inline]
15 - fn merge(halves: [Self::Half; 2]) -> Self {
16 - const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 - (halves[0] << HALF_SIZE) as $int | halves[1] as $int
12 + impl BitSplit for <u64>::from(halves[1]) as $int
|
warning: casts from `u16` to `u32` can be expressed infallibly using `From`
--> src/lib.rs:12:27
|
12 | impl BitSplit for $int {
| ___________________________^
13 | | type Half = $half;
14 | | #[inline]
15 | | fn merge(halves: [Self::Half; 2]) -> Self {
16 | | const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 | | (halves[0] << HALF_SIZE) as $int | halves[1] as $int
| |________________________________________^
...
25 | impl_ints!( u32 => u16; 0x0000_FFFF);
| ------------------------------------------------------------------ in this macro invocation
|
= help: an `as` cast can become silently lossy if the types change in the future
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
= note: this warning originates in the macro `impl_ints` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `<u32>::from` instead
|
12 - impl BitSplit for $int {
13 - type Half = $half;
14 - #[inline]
15 - fn merge(halves: [Self::Half; 2]) -> Self {
16 - const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 - (halves[0] << HALF_SIZE) as $int | halves[1] as $int
12 + impl BitSplit for <u32>::from(halves[0] << HALF_SIZE) as $int | halves[1] as $int
|
warning: casts from `u16` to `u32` can be expressed infallibly using `From`
--> src/lib.rs:12:27
|
12 | impl BitSplit for $int {
| ___________________________^
13 | | type Half = $half;
14 | | #[inline]
15 | | fn merge(halves: [Self::Half; 2]) -> Self {
16 | | const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 | | (halves[0] << HALF_SIZE) as $int | halves[1] as $int
| |____________________________________________________________^
...
25 | impl_ints!( u32 => u16; 0x0000_FFFF);
| ------------------------------------------------------------------ in this macro invocation
|
= help: an `as` cast can become silently lossy if the types change in the future
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
= note: this warning originates in the macro `impl_ints` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `<u32>::from` instead
|
12 - impl BitSplit for $int {
13 - type Half = $half;
14 - #[inline]
15 - fn merge(halves: [Self::Half; 2]) -> Self {
16 - const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 - (halves[0] << HALF_SIZE) as $int | halves[1] as $int
12 + impl BitSplit for <u32>::from(halves[1]) as $int
|
warning: casts from `u8` to `u16` can be expressed infallibly using `From`
--> src/lib.rs:12:27
|
12 | impl BitSplit for $int {
| ___________________________^
13 | | type Half = $half;
14 | | #[inline]
15 | | fn merge(halves: [Self::Half; 2]) -> Self {
16 | | const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 | | (halves[0] << HALF_SIZE) as $int | halves[1] as $int
| |________________________________________^
...
26 | impl_ints!( u16 => u8; 0x00FF);
| ------------------------------------------------------------------ in this macro invocation
|
= help: an `as` cast can become silently lossy if the types change in the future
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
= note: this warning originates in the macro `impl_ints` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `<u16>::from` instead
|
12 - impl BitSplit for $int {
13 - type Half = $half;
14 - #[inline]
15 - fn merge(halves: [Self::Half; 2]) -> Self {
16 - const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 - (halves[0] << HALF_SIZE) as $int | halves[1] as $int
12 + impl BitSplit for <u16>::from(halves[0] << HALF_SIZE) as $int | halves[1] as $int
|
warning: casts from `u8` to `u16` can be expressed infallibly using `From`
--> src/lib.rs:12:27
|
12 | impl BitSplit for $int {
| ___________________________^
13 | | type Half = $half;
14 | | #[inline]
15 | | fn merge(halves: [Self::Half; 2]) -> Self {
16 | | const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 | | (halves[0] << HALF_SIZE) as $int | halves[1] as $int
| |____________________________________________________________^
...
26 | impl_ints!( u16 => u8; 0x00FF);
| ------------------------------------------------------------------ in this macro invocation
|
= help: an `as` cast can become silently lossy if the types change in the future
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
= note: this warning originates in the macro `impl_ints` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `<u16>::from` instead
|
12 - impl BitSplit for $int {
13 - type Half = $half;
14 - #[inline]
15 - fn merge(halves: [Self::Half; 2]) -> Self {
16 - const HALF_SIZE: usize = std::mem::size_of::<$half>() * 8;
17 - (halves[0] << HALF_SIZE) as $int | halves[1] as $int
12 + impl BitSplit for <u16>::from(halves[1]) as $int
|
warning: `_ice-issue-96944` (lib) generated 8 warnings
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.44s
However after applying these diagnostics, the resulting code:
//@ build-pass
#![crate_type = "lib"]
#![allow(arithmetic_overflow)]
pub trait BitSplit {
type Half;
fn merge(halves: [Self::Half; 2]) -> Self;
}
macro_rules! impl_ints {
($int:ty => $half:ty; $mask:expr) => {
impl BitSplit for <u16>::from(halves[1]) as $int
}
}
};
}
impl_ints!(u128 => u64; 0x0000_0000_0000_0000_FFFF_FFFF_FFFF_FFFF);
impl_ints!( u64 => u32; 0x0000_0000_FFFF_FFFF);
impl_ints!( u32 => u16; 0x0000_FFFF);
impl_ints!( u16 => u8; 0x00FF);no longer compiled:
Checking _ice-issue-96944 v0.1.0 (/tmp/icemaker_global_tempdir.0gE5D6KlClUx/icemaker_clippyfix_tempdir.ArOqbDGioPwO/_ice-issue-96944)
error: unexpected closing delimiter: `}`
--> src/lib.rs:15:5
|
11 | ($int:ty => $half:ty; $mask:expr) => {
| - this delimiter might not be properly closed...
12 | impl BitSplit for <u16>::from(halves[1]) as $int
13 | }
| - ...as it matches this but it has different indentation
14 | }
15 | };
| ^ unexpected closing delimiter
error: could not compile `_ice-issue-96944` (lib test) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `_ice-issue-96944` (lib) due to 1 previous error
Version:
rustc 1.90.0-nightly (f32b23204 2025-07-26)
binary: rustc
commit-hash: f32b23204a0efe2fe8383ed4be1a30b56c1bbf94
commit-date: 2025-07-26
host: x86_64-unknown-linux-gnu
release: 1.90.0-nightly
LLVM version: 20.1.8