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Rollup merge of #123830 - tgross35:f16-f128-from-inference-fix, r=Nilstrieb

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Remove `From` impls for unstable types that break inference

Adding additional `From` implementations that fit `f32::from(<unaffixed float>)` broke inference. Remove these for now.

I added a test to make sure this doesn't quietly change in the future, even though the behavior is not technically guaranteed https://github.com/rust-lang/rust/issues/123824#issuecomment-2050628184

Fixes: <https://github.com/rust-lang/rust/issues/123824>
This commit is contained in:
Matthias Krüger 2024-04-12 13:35:30 +02:00 • committed by GitHub
commit bcf24d6467
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2 changed files with 11 additions and 2 deletions
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4
library/core/src/convert/num.rs
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@ -165,8 +165,8 @@ impl_from!(u16 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0"
impl_from!(u32 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
// float -> float
impl_from!(f16 => f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
impl_from!(f16 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
// FIXME(f16_f128): adding additional `From` impls for existing types breaks inference. See
// <https://github.com/rust-lang/rust/issues/123824>
impl_from!(f16 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
impl_from!(f32 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
impl_from!(f32 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);

9
tests/ui/inference/untyped-primitives.rs Normal file
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@ -0,0 +1,9 @@
//@ check-pass
// issue: rust-lang/rust#123824
// This test is a sanity check and does not enforce any stable API, so may be
// removed at a future point.
fn main() {
let x = f32::from(3.14);
let y = f64::from(3.14);
}