Uplift improved version of `clippy::cmp_nan` to rustc

compiler/rustc_lint/messages.ftl

@@ -314,6 +314,11 @@ lint_invalid_from_utf8_checked = calls to `{$method}` with a invalid literal alw
 lint_invalid_from_utf8_unchecked = calls to `{$method}` with a invalid literal are undefined behavior
     .label = the literal was valid UTF-8 up to the {$valid_up_to} bytes
 
+lint_invalid_nan_comparisons_eq_ne = incorrect NaN comparison, NaN cannot be directly compared to itself
+    .suggestion = use `f32::is_nan()` or `f64::is_nan()` instead
+
+lint_invalid_nan_comparisons_lt_le_gt_ge = incorrect NaN comparison, NaN is not orderable
+
 lint_lintpass_by_hand = implementing `LintPass` by hand
     .help = try using `declare_lint_pass!` or `impl_lint_pass!` instead
 

compiler/rustc_lint/src/lints.rs

@@ -1434,6 +1434,36 @@ pub struct OverflowingLiteral<'a> {
 #[diag(lint_unused_comparisons)]
 pub struct UnusedComparisons;
 
+#[derive(LintDiagnostic)]
+pub enum InvalidNanComparisons {
+    #[diag(lint_invalid_nan_comparisons_eq_ne)]
+    EqNe {
+        #[subdiagnostic]
+        suggestion: InvalidNanComparisonsSuggestion,
+    },
+    #[diag(lint_invalid_nan_comparisons_lt_le_gt_ge)]
+    LtLeGtGe,
+}
+
+#[derive(Subdiagnostic)]
+pub enum InvalidNanComparisonsSuggestion {
+    #[multipart_suggestion(
+        lint_suggestion,
+        style = "verbose",
+        applicability = "machine-applicable"
+    )]
+    Spanful {
+        #[suggestion_part(code = "!")]
+        neg: Option<Span>,
+        #[suggestion_part(code = ".is_nan()")]
+        float: Span,
+        #[suggestion_part(code = "")]
+        nan_plus_binop: Span,
+    },
+    #[help(lint_suggestion)]
+    Spanless,
+}
+
 pub struct ImproperCTypes<'a> {
     pub ty: Ty<'a>,
     pub desc: &'a str,

compiler/rustc_lint/src/types.rs

@@ -2,10 +2,10 @@ use crate::{
     fluent_generated as fluent,
     lints::{
         AtomicOrderingFence, AtomicOrderingLoad, AtomicOrderingStore, ImproperCTypes,
-        InvalidAtomicOrderingDiag, OnlyCastu8ToChar, OverflowingBinHex, OverflowingBinHexSign,
-        OverflowingBinHexSub, OverflowingInt, OverflowingIntHelp, OverflowingLiteral,
-        OverflowingUInt, RangeEndpointOutOfRange, UnusedComparisons, UseInclusiveRange,
-        VariantSizeDifferencesDiag,
+        InvalidAtomicOrderingDiag, InvalidNanComparisons, InvalidNanComparisonsSuggestion,
+        OnlyCastu8ToChar, OverflowingBinHex, OverflowingBinHexSign, OverflowingBinHexSub,
+        OverflowingInt, OverflowingIntHelp, OverflowingLiteral, OverflowingUInt,
+        RangeEndpointOutOfRange, UnusedComparisons, UseInclusiveRange, VariantSizeDifferencesDiag,
     },
 };
 use crate::{LateContext, LateLintPass, LintContext};
@@ -113,13 +113,35 @@ declare_lint! {
     "detects enums with widely varying variant sizes"
 }
 
+declare_lint! {
+    /// The `invalid_nan_comparisons` lint checks comparison with `f32::NAN` or `f64::NAN`
+    /// as one of the operand.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// let a = 2.3f32;
+    /// if a == f32::NAN {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// NaN does not compare meaningfully to anything – not
+    /// even itself – so those comparisons are always false.
+    INVALID_NAN_COMPARISONS,
+    Warn,
+    "detects invalid floating point NaN comparisons"
+}
+
 #[derive(Copy, Clone)]
 pub struct TypeLimits {
     /// Id of the last visited negated expression
     negated_expr_id: Option<hir::HirId>,
 }
 
-impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
+impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS, INVALID_NAN_COMPARISONS]);
 
 impl TypeLimits {
     pub fn new() -> TypeLimits {
@@ -486,6 +508,68 @@ fn lint_literal<'tcx>(
     }
 }
 
+fn lint_nan<'tcx>(
+    cx: &LateContext<'tcx>,
+    e: &'tcx hir::Expr<'tcx>,
+    binop: hir::BinOp,
+    l: &'tcx hir::Expr<'tcx>,
+    r: &'tcx hir::Expr<'tcx>,
+) {
+    fn is_nan(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
+        let expr = expr.peel_blocks().peel_borrows();
+        match expr.kind {
+            ExprKind::Path(qpath) => {
+                let Some(def_id) = cx.typeck_results().qpath_res(&qpath, expr.hir_id).opt_def_id() else { return false; };
+
+                matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::f32_nan | sym::f64_nan))
+            }
+            _ => false,
+        }
+    }
+
+    fn eq_ne(
+        e: &hir::Expr<'_>,
+        l: &hir::Expr<'_>,
+        r: &hir::Expr<'_>,
+        f: impl FnOnce(Span, Span) -> InvalidNanComparisonsSuggestion,
+    ) -> InvalidNanComparisons {
+        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(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(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()),
+            })
+        }
+        hir::BinOpKind::Lt | hir::BinOpKind::Le | hir::BinOpKind::Gt | hir::BinOpKind::Ge
+            if is_nan(cx, l) || is_nan(cx, r) =>
+        {
+            InvalidNanComparisons::LtLeGtGe
+        }
+        _ => return,
+    };
+
+    cx.emit_spanned_lint(INVALID_NAN_COMPARISONS, e.span, lint);
+}
+
 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
         match e.kind {
@@ -496,8 +580,12 @@ impl<'tcx> LateLintPass<'tcx> for TypeLimits {
                 }
             }
             hir::ExprKind::Binary(binop, ref l, ref r) => {
-                if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
-                    cx.emit_spanned_lint(UNUSED_COMPARISONS, e.span, UnusedComparisons);
+                if is_comparison(binop) {
+                    if !check_limits(cx, binop, &l, &r) {
+                        cx.emit_spanned_lint(UNUSED_COMPARISONS, e.span, UnusedComparisons);
+                    } else {
+                        lint_nan(cx, e, binop, l, r);
+                    }
                 }
             }
             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),

tests/ui/issues/issue-50811.rs

@@ -1,5 +1,6 @@
 // run-pass
 #![feature(test)]
+#![allow(invalid_nan_comparisons)]
 
 extern crate test;
 

tests/ui/lint/invalid-nan-comparison-suggestion.fixed

@@ -0,0 +1,36 @@
+// check-pass
+// run-rustfix
+
+fn main() {
+    let x = 5f32;
+    let _ = x.is_nan();
+    //~^ WARN incorrect NaN comparison
+    let _ = !x.is_nan();
+    //~^ WARN incorrect NaN comparison
+
+    let x = 5f64;
+    let _ = x.is_nan();
+    //~^ WARN incorrect NaN comparison
+    let _ = !x.is_nan();
+    //~^ WARN incorrect NaN comparison
+
+    let b = &2.3f32;
+    if !b.is_nan() {}
+    //~^ WARN incorrect NaN comparison
+
+    let b = &2.3f32;
+    if !b.is_nan() {}
+    //~^ WARN incorrect NaN comparison
+
+    let _ =
+        !b.is_nan();
+
+    #[allow(unused_macros)]
+    macro_rules! nan { () => { f32::NAN }; }
+    macro_rules! number { () => { 5f32 }; }
+
+    let _ = number!().is_nan();
+    //~^ WARN incorrect NaN comparison
+    let _ = !number!().is_nan();
+    //~^ WARN incorrect NaN comparison
+}

tests/ui/lint/invalid-nan-comparison-suggestion.rs

@@ -0,0 +1,39 @@
+// check-pass
+// run-rustfix
+
+fn main() {
+    let x = 5f32;
+    let _ = x == f32::NAN;
+    //~^ WARN incorrect NaN comparison
+    let _ = x != f32::NAN;
+    //~^ WARN incorrect NaN comparison
+
+    let x = 5f64;
+    let _ = x == f64::NAN;
+    //~^ WARN incorrect NaN comparison
+    let _ = x != f64::NAN;
+    //~^ WARN incorrect NaN comparison
+
+    let b = &2.3f32;
+    if b != &f32::NAN {}
+    //~^ WARN incorrect NaN comparison
+
+    let b = &2.3f32;
+    if b != { &f32::NAN } {}
+    //~^ WARN incorrect NaN comparison
+
+    let _ =
+        b != {
+    //~^ WARN incorrect NaN comparison
+            &f32::NAN
+        };
+
+    #[allow(unused_macros)]
+    macro_rules! nan { () => { f32::NAN }; }
+    macro_rules! number { () => { 5f32 }; }
+
+    let _ = nan!() == number!();
+    //~^ WARN incorrect NaN comparison
+    let _ = number!() != nan!();
+    //~^ WARN incorrect NaN comparison
+}

tests/ui/lint/invalid-nan-comparison-suggestion.stderr

@@ -0,0 +1,114 @@
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison-suggestion.rs:6:13
+   |
+LL |     let _ = x == f32::NAN;
+   |             ^^^^^^^^^^^^^
+   |
+   = note: `#[warn(invalid_nan_comparisons)]` on by default
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     let _ = x == f32::NAN;
+LL +     let _ = x.is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison-suggestion.rs:8:13
+   |
+LL |     let _ = x != f32::NAN;
+   |             ^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     let _ = x != f32::NAN;
+LL +     let _ = !x.is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison-suggestion.rs:12:13
+   |
+LL |     let _ = x == f64::NAN;
+   |             ^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     let _ = x == f64::NAN;
+LL +     let _ = x.is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison-suggestion.rs:14:13
+   |
+LL |     let _ = x != f64::NAN;
+   |             ^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     let _ = x != f64::NAN;
+LL +     let _ = !x.is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison-suggestion.rs:18:8
+   |
+LL |     if b != &f32::NAN {}
+   |        ^^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     if b != &f32::NAN {}
+LL +     if !b.is_nan() {}
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison-suggestion.rs:22:8
+   |
+LL |     if b != { &f32::NAN } {}
+   |        ^^^^^^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     if b != { &f32::NAN } {}
+LL +     if !b.is_nan() {}
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison-suggestion.rs:26:9
+   |
+LL | /         b != {
+LL | |
+LL | |             &f32::NAN
+LL | |         };
+   | |_________^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -         b != {
+LL +         !b.is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison-suggestion.rs:35:13
+   |
+LL |     let _ = nan!() == number!();
+   |             ^^^^^^^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     let _ = nan!() == number!();
+LL +     let _ = number!().is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison-suggestion.rs:37:13
+   |
+LL |     let _ = number!() != nan!();
+   |             ^^^^^^^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     let _ = number!() != nan!();
+LL +     let _ = !number!().is_nan();
+   |
+
+warning: 9 warnings emitted
+

tests/ui/lint/invalid-nan-comparison.rs

@@ -0,0 +1,51 @@
+// check-pass
+
+fn main() {
+    f32();
+    f64();
+}
+
+const TEST: bool = 5f32 == f32::NAN;
+//~^ WARN incorrect NaN comparison
+
+fn f32() {
+    macro_rules! number { () => { 5f32 }; }
+    let x = number!();
+    x == f32::NAN;
+    //~^ WARN incorrect NaN comparison
+    x != f32::NAN;
+    //~^ WARN incorrect NaN comparison
+    x < f32::NAN;
+    //~^ WARN incorrect NaN comparison
+    x > f32::NAN;
+    //~^ WARN incorrect NaN comparison
+    x <= f32::NAN;
+    //~^ WARN incorrect NaN comparison
+    x >= f32::NAN;
+    //~^ WARN incorrect NaN comparison
+    number!() == f32::NAN;
+    //~^ WARN incorrect NaN comparison
+    f32::NAN != number!();
+    //~^ WARN incorrect NaN comparison
+}
+
+fn f64() {
+    macro_rules! number { () => { 5f64 }; }
+    let x = number!();
+    x == f64::NAN;
+    //~^ WARN incorrect NaN comparison
+    x != f64::NAN;
+    //~^ WARN incorrect NaN comparison
+    x < f64::NAN;
+    //~^ WARN incorrect NaN comparison
+    x > f64::NAN;
+    //~^ WARN incorrect NaN comparison
+    x <= f64::NAN;
+    //~^ WARN incorrect NaN comparison
+    x >= f64::NAN;
+    //~^ WARN incorrect NaN comparison
+    number!() == f64::NAN;
+    //~^ WARN incorrect NaN comparison
+    f64::NAN != number!();
+    //~^ WARN incorrect NaN comparison
+}

tests/ui/lint/invalid-nan-comparison.stderr

@@ -0,0 +1,159 @@
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison.rs:8:20
+   |
+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
+   |
+LL |     x == f32::NAN;
+   |     ^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     x == f32::NAN;
+LL +     x.is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison.rs:16:5
+   |
+LL |     x != f32::NAN;
+   |     ^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     x != f32::NAN;
+LL +     !x.is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN is not orderable
+  --> $DIR/invalid-nan-comparison.rs:18:5
+   |
+LL |     x < f32::NAN;
+   |     ^^^^^^^^^^^^
+
+warning: incorrect NaN comparison, NaN is not orderable
+  --> $DIR/invalid-nan-comparison.rs:20:5
+   |
+LL |     x > f32::NAN;
+   |     ^^^^^^^^^^^^
+
+warning: incorrect NaN comparison, NaN is not orderable
+  --> $DIR/invalid-nan-comparison.rs:22:5
+   |
+LL |     x <= f32::NAN;
+   |     ^^^^^^^^^^^^^
+
+warning: incorrect NaN comparison, NaN is not orderable
+  --> $DIR/invalid-nan-comparison.rs:24:5
+   |
+LL |     x >= f32::NAN;
+   |     ^^^^^^^^^^^^^
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison.rs:26:5
+   |
+LL |     number!() == f32::NAN;
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     number!() == f32::NAN;
+LL +     number!().is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison.rs:28:5
+   |
+LL |     f32::NAN != number!();
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     f32::NAN != number!();
+LL +     !number!().is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison.rs:35:5
+   |
+LL |     x == f64::NAN;
+   |     ^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     x == f64::NAN;
+LL +     x.is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison.rs:37:5
+   |
+LL |     x != f64::NAN;
+   |     ^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     x != f64::NAN;
+LL +     !x.is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN is not orderable
+  --> $DIR/invalid-nan-comparison.rs:39:5
+   |
+LL |     x < f64::NAN;
+   |     ^^^^^^^^^^^^
+
+warning: incorrect NaN comparison, NaN is not orderable
+  --> $DIR/invalid-nan-comparison.rs:41:5
+   |
+LL |     x > f64::NAN;
+   |     ^^^^^^^^^^^^
+
+warning: incorrect NaN comparison, NaN is not orderable
+  --> $DIR/invalid-nan-comparison.rs:43:5
+   |
+LL |     x <= f64::NAN;
+   |     ^^^^^^^^^^^^^
+
+warning: incorrect NaN comparison, NaN is not orderable
+  --> $DIR/invalid-nan-comparison.rs:45:5
+   |
+LL |     x >= f64::NAN;
+   |     ^^^^^^^^^^^^^
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison.rs:47:5
+   |
+LL |     number!() == f64::NAN;
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     number!() == f64::NAN;
+LL +     number!().is_nan();
+   |
+
+warning: incorrect NaN comparison, NaN cannot be directly compared to itself
+  --> $DIR/invalid-nan-comparison.rs:49:5
+   |
+LL |     f64::NAN != number!();
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+help: use `f32::is_nan()` or `f64::is_nan()` instead
+   |
+LL -     f64::NAN != number!();
+LL +     !number!().is_nan();
+   |
+
+warning: 17 warnings emitted
+