Auto merge of #130157 - eduardosm:stabilize-const_float_classify, r=RalfJung

Stabilize `const_float_classify`

Tracking issue: https://github.com/rust-lang/rust/issues/72505

Also reverts https://github.com/rust-lang/rust/pull/114486

Closes https://github.com/rust-lang/rust/issues/72505

Stabilized const API:

```rust
impl f32 {
    pub const fn is_nan(self) -> bool;
    pub const fn is_infinite(self) -> bool;
    pub const fn is_finite(self) -> bool;
    pub const fn is_subnormal(self) -> bool;
    pub const fn is_normal(self) -> bool;
    pub const fn classify(self) -> FpCategory;
    pub const fn is_sign_positive(self) -> bool;
    pub const fn is_sign_negative(self) -> bool;
}

impl f64 {
    pub const fn is_nan(self) -> bool;
    pub const fn is_infinite(self) -> bool;
    pub const fn is_finite(self) -> bool;
    pub const fn is_subnormal(self) -> bool;
    pub const fn is_normal(self) -> bool;
    pub const fn classify(self) -> FpCategory;
    pub const fn is_sign_positive(self) -> bool;
    pub const fn is_sign_negative(self) -> bool;
}
```

cc `@rust-lang/wg-const-eval` `@rust-lang/libs-api`

10 files changed, 43 insertions, 47 deletions

diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index 0045cfcaa56..8467c416f4a 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -1703,7 +1703,7 @@ pub(crate) enum InvalidNanComparisons {
     #[diag(lint_invalid_nan_comparisons_eq_ne)]
     EqNe {
         #[subdiagnostic]
-        suggestion: Option<InvalidNanComparisonsSuggestion>,
+        suggestion: InvalidNanComparisonsSuggestion,
     },
     #[diag(lint_invalid_nan_comparisons_lt_le_gt_ge)]
     LtLeGtGe,
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index 15fe18adbfb..75611d71025 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -209,36 +209,32 @@ fn lint_nan<'tcx>(
     }
 
     fn eq_ne(
-        cx: &LateContext<'_>,
         e: &hir::Expr<'_>,
         l: &hir::Expr<'_>,
         r: &hir::Expr<'_>,
         f: impl FnOnce(Span, Span) -> InvalidNanComparisonsSuggestion,
     ) -> InvalidNanComparisons {
-        // FIXME(#72505): This suggestion can be restored if `f{32,64}::is_nan` is made const.
-        let suggestion = (!cx.tcx.hir().is_inside_const_context(e.hir_id)).then(|| {
-            if let Some(l_span) = l.span.find_ancestor_inside(e.span)
-                && let Some(r_span) = r.span.find_ancestor_inside(e.span)
-            {
-                f(l_span, r_span)
-            } else {
-                InvalidNanComparisonsSuggestion::Spanless
-            }
-        });
+        let suggestion = if let Some(l_span) = l.span.find_ancestor_inside(e.span)
+            && let Some(r_span) = r.span.find_ancestor_inside(e.span)
+        {
+            f(l_span, r_span)
+        } else {
+            InvalidNanComparisonsSuggestion::Spanless
+        };
 
         InvalidNanComparisons::EqNe { suggestion }
     }
 
     let lint = match binop.node {
         hir::BinOpKind::Eq | hir::BinOpKind::Ne if is_nan(cx, l) => {
-            eq_ne(cx, e, l, r, |l_span, r_span| InvalidNanComparisonsSuggestion::Spanful {
+            eq_ne(e, l, r, |l_span, r_span| InvalidNanComparisonsSuggestion::Spanful {
                 nan_plus_binop: l_span.until(r_span),
                 float: r_span.shrink_to_hi(),
                 neg: (binop.node == hir::BinOpKind::Ne).then(|| r_span.shrink_to_lo()),
             })
         }
         hir::BinOpKind::Eq | hir::BinOpKind::Ne if is_nan(cx, r) => {
-            eq_ne(cx, e, l, r, |l_span, r_span| InvalidNanComparisonsSuggestion::Spanful {
+            eq_ne(e, l, r, |l_span, r_span| InvalidNanComparisonsSuggestion::Spanful {
                 nan_plus_binop: l_span.shrink_to_hi().to(r_span),
                 float: l_span.shrink_to_hi(),
                 neg: (binop.node == hir::BinOpKind::Ne).then(|| l_span.shrink_to_lo()),
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 817d9e3b962..e816da890da 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -122,7 +122,6 @@
 #![feature(const_char_encode_utf8)]
 #![feature(const_eval_select)]
 #![feature(const_exact_div)]
-#![feature(const_float_classify)]
 #![feature(const_fmt_arguments_new)]
 #![feature(const_hash)]
 #![feature(const_heap)]
diff --git a/library/core/src/num/f128.rs b/library/core/src/num/f128.rs
index 100271fa54c..133d6e3fc9a 100644
--- a/library/core/src/num/f128.rs
+++ b/library/core/src/num/f128.rs
@@ -288,7 +288,7 @@ impl f128 {
     // concerns about portability, so this implementation is for
     // private use internally.
     #[inline]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f128", issue = "116909")]
     pub(crate) const fn abs_private(self) -> f128 {
         // SAFETY: This transmutation is fine just like in `to_bits`/`from_bits`.
         unsafe {
@@ -319,7 +319,7 @@ impl f128 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f128", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f128", issue = "116909")]
     pub const fn is_infinite(self) -> bool {
         (self == f128::INFINITY) | (self == f128::NEG_INFINITY)
     }
@@ -346,7 +346,7 @@ impl f128 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f128", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f128", issue = "116909")]
     pub const fn is_finite(self) -> bool {
         // There's no need to handle NaN separately: if self is NaN,
         // the comparison is not true, exactly as desired.
@@ -380,7 +380,7 @@ impl f128 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f128", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f128", issue = "116909")]
     pub const fn is_subnormal(self) -> bool {
         matches!(self.classify(), FpCategory::Subnormal)
     }
@@ -412,7 +412,7 @@ impl f128 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f128", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f128", issue = "116909")]
     pub const fn is_normal(self) -> bool {
         matches!(self.classify(), FpCategory::Normal)
     }
@@ -437,7 +437,7 @@ impl f128 {
     /// ```
     #[inline]
     #[unstable(feature = "f128", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f128", issue = "116909")]
     pub const fn classify(self) -> FpCategory {
         let bits = self.to_bits();
         match (bits & Self::MAN_MASK, bits & Self::EXP_MASK) {
diff --git a/library/core/src/num/f16.rs b/library/core/src/num/f16.rs
index 6bdc569df28..e50f5e7e8fb 100644
--- a/library/core/src/num/f16.rs
+++ b/library/core/src/num/f16.rs
@@ -282,7 +282,7 @@ impl f16 {
     // concerns about portability, so this implementation is for
     // private use internally.
     #[inline]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f16", issue = "116909")]
     pub(crate) const fn abs_private(self) -> f16 {
         // SAFETY: This transmutation is fine just like in `to_bits`/`from_bits`.
         unsafe { mem::transmute::<u16, f16>(mem::transmute::<f16, u16>(self) & !Self::SIGN_MASK) }
@@ -310,7 +310,7 @@ impl f16 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f16", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f16", issue = "116909")]
     pub const fn is_infinite(self) -> bool {
         (self == f16::INFINITY) | (self == f16::NEG_INFINITY)
     }
@@ -336,7 +336,7 @@ impl f16 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f16", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f16", issue = "116909")]
     pub const fn is_finite(self) -> bool {
         // There's no need to handle NaN separately: if self is NaN,
         // the comparison is not true, exactly as desired.
@@ -368,7 +368,7 @@ impl f16 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f16", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f16", issue = "116909")]
     pub const fn is_subnormal(self) -> bool {
         matches!(self.classify(), FpCategory::Subnormal)
     }
@@ -398,7 +398,7 @@ impl f16 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f16", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f16", issue = "116909")]
     pub const fn is_normal(self) -> bool {
         matches!(self.classify(), FpCategory::Normal)
     }
@@ -422,7 +422,7 @@ impl f16 {
     /// ```
     #[inline]
     #[unstable(feature = "f16", issue = "116909")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_unstable(feature = "f16", issue = "116909")]
     pub const fn classify(self) -> FpCategory {
         let b = self.to_bits();
         match (b & Self::MAN_MASK, b & Self::EXP_MASK) {
diff --git a/library/core/src/num/f32.rs b/library/core/src/num/f32.rs
index d0eb6bb3f28..a9a2595c25c 100644
--- a/library/core/src/num/f32.rs
+++ b/library/core/src/num/f32.rs
@@ -517,7 +517,7 @@ impl f32 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     #[allow(clippy::eq_op)] // > if you intended to check if the operand is NaN, use `.is_nan()` instead :)
     pub const fn is_nan(self) -> bool {
@@ -528,7 +528,6 @@ impl f32 {
     // concerns about portability, so this implementation is for
     // private use internally.
     #[inline]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
     pub(crate) const fn abs_private(self) -> f32 {
         // SAFETY: This transmutation is fine just like in `to_bits`/`from_bits`.
         unsafe { mem::transmute::<u32, f32>(mem::transmute::<f32, u32>(self) & !Self::SIGN_MASK) }
@@ -551,7 +550,7 @@ impl f32 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_infinite(self) -> bool {
         // Getting clever with transmutation can result in incorrect answers on some FPUs
@@ -576,7 +575,7 @@ impl f32 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_finite(self) -> bool {
         // There's no need to handle NaN separately: if self is NaN,
@@ -604,7 +603,7 @@ impl f32 {
     /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
     #[must_use]
     #[stable(feature = "is_subnormal", since = "1.53.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_subnormal(self) -> bool {
         matches!(self.classify(), FpCategory::Subnormal)
@@ -631,7 +630,7 @@ impl f32 {
     /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_normal(self) -> bool {
         matches!(self.classify(), FpCategory::Normal)
@@ -651,7 +650,7 @@ impl f32 {
     /// assert_eq!(inf.classify(), FpCategory::Infinite);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     pub const fn classify(self) -> FpCategory {
         // We used to have complicated logic here that avoids the simple bit-based tests to work
         // around buggy codegen for x87 targets (see
@@ -687,7 +686,7 @@ impl f32 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_sign_positive(self) -> bool {
         !self.is_sign_negative()
@@ -712,7 +711,7 @@ impl f32 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_sign_negative(self) -> bool {
         // IEEE754 says: isSignMinus(x) is true if and only if x has negative sign. isSignMinus
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs
index 4bc275ad147..aa7a54ca650 100644
--- a/library/core/src/num/f64.rs
+++ b/library/core/src/num/f64.rs
@@ -516,7 +516,7 @@ impl f64 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     #[allow(clippy::eq_op)] // > if you intended to check if the operand is NaN, use `.is_nan()` instead :)
     pub const fn is_nan(self) -> bool {
@@ -527,7 +527,6 @@ impl f64 {
     // concerns about portability, so this implementation is for
     // private use internally.
     #[inline]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
     pub(crate) const fn abs_private(self) -> f64 {
         // SAFETY: This transmutation is fine just like in `to_bits`/`from_bits`.
         unsafe { mem::transmute::<u64, f64>(mem::transmute::<f64, u64>(self) & !Self::SIGN_MASK) }
@@ -550,7 +549,7 @@ impl f64 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_infinite(self) -> bool {
         // Getting clever with transmutation can result in incorrect answers on some FPUs
@@ -575,7 +574,7 @@ impl f64 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_finite(self) -> bool {
         // There's no need to handle NaN separately: if self is NaN,
@@ -603,7 +602,7 @@ impl f64 {
     /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
     #[must_use]
     #[stable(feature = "is_subnormal", since = "1.53.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_subnormal(self) -> bool {
         matches!(self.classify(), FpCategory::Subnormal)
@@ -630,7 +629,7 @@ impl f64 {
     /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_normal(self) -> bool {
         matches!(self.classify(), FpCategory::Normal)
@@ -650,7 +649,7 @@ impl f64 {
     /// assert_eq!(inf.classify(), FpCategory::Infinite);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     pub const fn classify(self) -> FpCategory {
         // We used to have complicated logic here that avoids the simple bit-based tests to work
         // around buggy codegen for x87 targets (see
@@ -686,7 +685,7 @@ impl f64 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_sign_positive(self) -> bool {
         !self.is_sign_negative()
@@ -720,7 +719,7 @@ impl f64 {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[rustc_const_stable(feature = "const_float_classify", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn is_sign_negative(self) -> bool {
         // IEEE754 says: isSignMinus(x) is true if and only if x has negative sign. isSignMinus
diff --git a/tests/ui/float/classify-runtime-const.rs b/tests/ui/float/classify-runtime-const.rs
index b19e67d5284..2a24e51cabb 100644
--- a/tests/ui/float/classify-runtime-const.rs
+++ b/tests/ui/float/classify-runtime-const.rs
@@ -8,7 +8,6 @@
 
 #![feature(f16_const)]
 #![feature(f128_const)]
-#![feature(const_float_classify)]
 
 use std::num::FpCategory::*;
 
diff --git a/tests/ui/float/conv-bits-runtime-const.rs b/tests/ui/float/conv-bits-runtime-const.rs
index e85a889d2c2..60c45cc4cc1 100644
--- a/tests/ui/float/conv-bits-runtime-const.rs
+++ b/tests/ui/float/conv-bits-runtime-const.rs
@@ -3,7 +3,6 @@
 
 // This tests the float classification functions, for regular runtime code and for const evaluation.
 
-#![feature(const_float_classify)]
 #![feature(f16)]
 #![feature(f128)]
 #![feature(f16_const)]
diff --git a/tests/ui/lint/invalid-nan-comparison.stderr b/tests/ui/lint/invalid-nan-comparison.stderr
index f2d55c107ba..054c06d38b3 100644
--- a/tests/ui/lint/invalid-nan-comparison.stderr
+++ b/tests/ui/lint/invalid-nan-comparison.stderr
@@ -5,6 +5,11 @@ LL | const TEST: bool = 5f32 == f32::NAN;
    |                    ^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(invalid_nan_comparisons)]` on by default
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL - const TEST: bool = 5f32 == f32::NAN;
+LL + const TEST: bool = 5f32.is_nan();
+   |
 
 warning: incorrect NaN comparison, NaN cannot be directly compared to itself
   --> $DIR/invalid-nan-comparison.rs:14:5