Rollup merge of #102271 - lopopolo:lopopolo/stabilize-duration-try-from-secs-float, r=dtolnay

Stabilize `duration_checked_float`

## Stabilization Report

This stabilization report is for a stabilization of `duration_checked_float`, tracking issue: #83400.

### Implementation History

- #82179
- #90247
- #96051
- Changed error type to `FromFloatSecsError` in #90247
- #96051 changes the rounding mode to round-to-nearest instead of truncate.

## API Summary

This stabilization report proposes the following API to be stabilized in `core`, along with their re-exports in `std`:

```rust
// core::time

impl Duration {
    pub const fn try_from_secs_f32(secs: f32) -> Result<Duration, TryFromFloatSecsError>;
    pub const fn try_from_secs_f64(secs: f64) -> Result<Duration, TryFromFloatSecsError>;
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct TryFromFloatSecsError { ... }

impl core::fmt::Display for TryFromFloatSecsError { ... }
impl core::error::Error for TryFromFloatSecsError { ... }
```

These functions are made const unstable under `duration_consts_float`, tracking issue #72440.

There is an open question in the tracking issue around what the error type should be called which I was hoping to resolve in the context of an FCP.

In this stabilization PR, I have altered the name of the error type to `TryFromFloatSecsError`. In my opinion, the error type shares the name of the method (adjusted to accommodate both types of floats), which is consistent with other error types in `core`, `alloc` and `std` like `TryReserveError` and `TryFromIntError`.

## Experience Report

Code such as this is ready to be converted to a checked API to ensure it is panic free:

```rust
impl Time {
    pub fn checked_add_f64(&self, seconds: f64) -> Result<Self, TimeError> {
        // Fail safely during `f64` conversion to duration
        if seconds.is_nan() || seconds.is_infinite() {
            return Err(TzOutOfRangeError::new().into());
        }

        if seconds.is_sign_positive() {
            self.checked_add(Duration::from_secs_f64(seconds))
        } else {
            self.checked_sub(Duration::from_secs_f64(-seconds))
        }
    }
}
```

See: artichoke/artichoke#2194.

`@rustbot` label +T-libs-api -T-libs

cc `@mbartlett21`

Author: Yuki Okushi

library/core/src/error.rs

@@ -493,8 +493,8 @@ impl Error for crate::char::ParseCharError {
     }
 }
 
-#[unstable(feature = "duration_checked_float", issue = "83400")]
-impl Error for crate::time::FromFloatSecsError {}
+#[stable(feature = "duration_checked_float", since = "CURRENT_RUSTC_VERSION")]
+impl Error for crate::time::TryFromFloatSecsError {}
 
 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
 impl Error for crate::ffi::FromBytesWithNulError {

library/core/src/time.rs

@@ -1225,41 +1225,40 @@ impl fmt::Debug for Duration {
 /// # Example
 ///
 /// ```
-/// #![feature(duration_checked_float)]
 /// use std::time::Duration;
 ///
 /// if let Err(e) = Duration::try_from_secs_f32(-1.0) {
 ///     println!("Failed conversion to Duration: {e}");
 /// }
 /// ```
 #[derive(Debug, Clone, PartialEq, Eq)]
-#[unstable(feature = "duration_checked_float", issue = "83400")]
-pub struct FromFloatSecsError {
-    kind: FromFloatSecsErrorKind,
+#[stable(feature = "duration_checked_float", since = "CURRENT_RUSTC_VERSION")]
+pub struct TryFromFloatSecsError {
+    kind: TryFromFloatSecsErrorKind,
 }
 
-impl FromFloatSecsError {
+impl TryFromFloatSecsError {
     const fn description(&self) -> &'static str {
         match self.kind {
-            FromFloatSecsErrorKind::Negative => {
+            TryFromFloatSecsErrorKind::Negative => {
                 "can not convert float seconds to Duration: value is negative"
             }
-            FromFloatSecsErrorKind::OverflowOrNan => {
+            TryFromFloatSecsErrorKind::OverflowOrNan => {
                 "can not convert float seconds to Duration: value is either too big or NaN"
             }
         }
     }
 }
 
-#[unstable(feature = "duration_checked_float", issue = "83400")]
-impl fmt::Display for FromFloatSecsError {
+#[stable(feature = "duration_checked_float", since = "CURRENT_RUSTC_VERSION")]
+impl fmt::Display for TryFromFloatSecsError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.description().fmt(f)
     }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
-enum FromFloatSecsErrorKind {
+enum TryFromFloatSecsErrorKind {
     // Value is negative.
     Negative,
     // Value is either too big to be represented as `Duration` or `NaN`.
@@ -1280,7 +1279,7 @@ macro_rules! try_from_secs {
         const EXP_MASK: $bits_ty = (1 << $exp_bits) - 1;
 
         if $secs < 0.0 {
-            return Err(FromFloatSecsError { kind: FromFloatSecsErrorKind::Negative });
+            return Err(TryFromFloatSecsError { kind: TryFromFloatSecsErrorKind::Negative });
         }
 
         let bits = $secs.to_bits();
@@ -1339,7 +1338,7 @@ macro_rules! try_from_secs {
             let secs = u64::from(mant) << (exp - $mant_bits);
             (secs, 0)
         } else {
-            return Err(FromFloatSecsError { kind: FromFloatSecsErrorKind::OverflowOrNan });
+            return Err(TryFromFloatSecsError { kind: TryFromFloatSecsErrorKind::OverflowOrNan });
         };
 
         Ok(Duration::new(secs, nanos))
@@ -1355,8 +1354,6 @@ impl Duration {
     ///
     /// # Examples
     /// ```
-    /// #![feature(duration_checked_float)]
-    ///
     /// use std::time::Duration;
     ///
     /// let res = Duration::try_from_secs_f32(0.0);
@@ -1404,9 +1401,10 @@ impl Duration {
     /// let res = Duration::try_from_secs_f32(val);
     /// assert_eq!(res, Ok(Duration::new(1, 2_929_688)));
     /// ```
-    #[unstable(feature = "duration_checked_float", issue = "83400")]
+    #[stable(feature = "duration_checked_float", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_unstable(feature = "duration_consts_float", issue = "72440")]
     #[inline]
-    pub const fn try_from_secs_f32(secs: f32) -> Result<Duration, FromFloatSecsError> {
+    pub const fn try_from_secs_f32(secs: f32) -> Result<Duration, TryFromFloatSecsError> {
         try_from_secs!(
             secs = secs,
             mantissa_bits = 23,
@@ -1425,8 +1423,6 @@ impl Duration {
     ///
     /// # Examples
     /// ```
-    /// #![feature(duration_checked_float)]
-    ///
     /// use std::time::Duration;
     ///
     /// let res = Duration::try_from_secs_f64(0.0);
@@ -1482,9 +1478,10 @@ impl Duration {
     /// let res = Duration::try_from_secs_f64(val);
     /// assert_eq!(res, Ok(Duration::new(1, 2_929_688)));
     /// ```
-    #[unstable(feature = "duration_checked_float", issue = "83400")]
+    #[stable(feature = "duration_checked_float", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_unstable(feature = "duration_consts_float", issue = "72440")]
     #[inline]
-    pub const fn try_from_secs_f64(secs: f64) -> Result<Duration, FromFloatSecsError> {
+    pub const fn try_from_secs_f64(secs: f64) -> Result<Duration, TryFromFloatSecsError> {
         try_from_secs!(
             secs = secs,
             mantissa_bits = 52,

library/core/tests/lib.rs

@@ -103,7 +103,6 @@
 #![feature(provide_any)]
 #![feature(utf8_chunks)]
 #![feature(is_ascii_octdigit)]
-#![feature(duration_checked_float)]
 #![deny(unsafe_op_in_unsafe_fn)]
 
 extern crate test;

library/std/src/lib.rs

@@ -280,7 +280,6 @@
 #![feature(core_intrinsics)]
 #![feature(cstr_from_bytes_until_nul)]
 #![feature(cstr_internals)]
-#![feature(duration_checked_float)]
 #![feature(duration_constants)]
 #![feature(error_generic_member_access)]
 #![feature(error_in_core)]

library/std/src/time.rs

@@ -43,8 +43,8 @@ use crate::sys_common::{FromInner, IntoInner};
 #[stable(feature = "time", since = "1.3.0")]
 pub use core::time::Duration;
 
-#[unstable(feature = "duration_checked_float", issue = "83400")]
-pub use core::time::FromFloatSecsError;
+#[stable(feature = "duration_checked_float", since = "CURRENT_RUSTC_VERSION")]
+pub use core::time::TryFromFloatSecsError;
 
 /// A measurement of a monotonically nondecreasing clock.
 /// Opaque and useful only with [`Duration`].