remove 'illegal_floating_point_literal_pattern' future-compat lint

Author: RalfJung

compiler/rustc_lint/src/lib.rs

@@ -505,6 +505,10 @@ fn register_builtins(store: &mut LintStore) {
         "replaced with another group of lints, see RFC \
          <https://rust-lang.github.io/rfcs/2145-type-privacy.html> for more information",
     );
+    store.register_removed(
+        "illegal_floating_point_literal_pattern",
+        "no longer a warning, float patterns behave the same as `==`",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {

compiler/rustc_lint/src/types.rs

@@ -21,6 +21,7 @@ use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::{
     self, AdtKind, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt,
 };
+use rustc_session::lint::builtin;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::source_map;
 use rustc_span::symbol::sym;
@@ -114,35 +115,14 @@ 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, INVALID_NAN_COMPARISONS]);
+// This pass also emits `INVALID_NAN_COMPARISONS` but adding that to the list here leads to ICEs.
+impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
 
 impl TypeLimits {
     pub fn new() -> TypeLimits {
@@ -615,7 +595,7 @@ fn lint_nan<'tcx>(
         _ => return,
     };
 
-    cx.emit_spanned_lint(INVALID_NAN_COMPARISONS, e.span, lint);
+    cx.emit_spanned_lint(builtin::INVALID_NAN_COMPARISONS, e.span, lint);
 }
 
 impl<'tcx> LateLintPass<'tcx> for TypeLimits {

compiler/rustc_lint_defs/src/builtin.rs

@@ -1754,55 +1754,6 @@ declare_lint! {
      };
 }
 
-declare_lint! {
-    /// The `illegal_floating_point_literal_pattern` lint detects
-    /// floating-point literals used in patterns.
-    ///
-    /// ### Example
-    ///
-    /// ```rust
-    /// let x = 42.0;
-    ///
-    /// match x {
-    ///     5.0 => {}
-    ///     _ => {}
-    /// }
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// Previous versions of the compiler accepted floating-point literals in
-    /// patterns, but it was later determined this was a mistake. The
-    /// semantics of comparing floating-point values may not be clear in a
-    /// pattern when contrasted with "structural equality". Typically you can
-    /// work around this by using a [match guard], such as:
-    ///
-    /// ```rust
-    /// # let x = 42.0;
-    ///
-    /// match x {
-    ///     y if y == 5.0 => {}
-    ///     _ => {}
-    /// }
-    /// ```
-    ///
-    /// This is a [future-incompatible] lint to transition this to a hard
-    /// error in the future. See [issue #41620] for more details.
-    ///
-    /// [issue #41620]: https://github.com/rust-lang/rust/issues/41620
-    /// [match guard]: https://doc.rust-lang.org/reference/expressions/match-expr.html#match-guards
-    /// [future-incompatible]: ../index.md#future-incompatible-lints
-    pub ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
-    Warn,
-    "floating-point literals cannot be used in patterns",
-    @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
-        reference: "issue #41620 <https://github.com/rust-lang/rust/issues/41620>",
-    };
-}
-
 declare_lint! {
     /// The `unstable_name_collisions` lint detects that you have used a name
     /// that the standard library plans to add in the future.
@@ -3334,6 +3285,31 @@ declare_lint! {
     "name introduced by a private item shadows a name introduced by a public glob re-export",
 }
 
+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 {}
+    /// if matches!(a, f32::NAN) {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// NaN does not compare meaningfully to anything – not
+    /// even itself – so those comparisons are always false.
+    pub INVALID_NAN_COMPARISONS,
+    Warn,
+    "detects invalid floating point NaN comparisons"
+}
+
+// When removing any lint here, remember to add a call to `register_removed` in `fn
+// register_builtins` in the `rustc_lints` crate.
 declare_lint_pass! {
     /// Does nothing as a lint pass, but registers some `Lint`s
     /// that are used by other parts of the compiler.
@@ -3371,7 +3347,6 @@ declare_lint_pass! {
         FUZZY_PROVENANCE_CASTS,
         HIDDEN_GLOB_REEXPORTS,
         ILL_FORMED_ATTRIBUTE_INPUT,
-        ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
         IMPLIED_BOUNDS_ENTAILMENT,
         INCOMPLETE_INCLUDE,
         INDIRECT_STRUCTURAL_MATCH,
@@ -3380,6 +3355,7 @@ declare_lint_pass! {
         INVALID_ALIGNMENT,
         INVALID_DOC_ATTRIBUTES,
         INVALID_MACRO_EXPORT_ARGUMENTS,
+        INVALID_NAN_COMPARISONS,
         INVALID_TYPE_PARAM_DEFAULT,
         IRREFUTABLE_LET_PATTERNS,
         LARGE_ASSIGNMENTS,

compiler/rustc_mir_build/messages.ftl

@@ -87,8 +87,6 @@ mir_build_extern_static_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
     .note = extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
     .label = use of extern static
 
-mir_build_float_pattern = floating-point types cannot be used in patterns
-
 mir_build_indirect_structural_match =
     to use a constant of type `{$non_sm_ty}` in a pattern, `{$non_sm_ty}` must be annotated with `#[derive(PartialEq, Eq)]`
 
@@ -212,6 +210,8 @@ mir_build_mutation_of_layout_constrained_field_requires_unsafe_unsafe_op_in_unsa
     .note = mutating layout constrained fields cannot statically be checked for valid values
     .label = mutation of layout constrained field
 
+mir_build_nan_pattern = incorrect NaN comparison, NaN cannot be directly compared to itself
+
 mir_build_non_const_path = runtime values cannot be referenced in patterns
 
 mir_build_non_exhaustive_match_all_arms_guarded =

compiler/rustc_mir_build/src/errors.rs

@@ -725,8 +725,8 @@ pub struct UnsizedPattern<'tcx> {
 }
 
 #[derive(LintDiagnostic)]
-#[diag(mir_build_float_pattern)]
-pub struct FloatPattern;
+#[diag(mir_build_nan_pattern)]
+pub struct NaNPattern;
 
 #[derive(LintDiagnostic)]
 #[diag(mir_build_pointer_pattern)]

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

@@ -16,8 +16,8 @@ use std::cell::Cell;
 
 use super::PatCtxt;
 use crate::errors::{
-    FloatPattern, IndirectStructuralMatch, InvalidPattern, NontrivialStructuralMatch,
-    PointerPattern, TypeNotStructural, UnionPattern, UnsizedPattern,
+    IndirectStructuralMatch, InvalidPattern, NaNPattern, NontrivialStructuralMatch, PointerPattern,
+    TypeNotStructural, UnionPattern, UnsizedPattern,
 };
 
 impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
@@ -291,16 +291,6 @@ impl<'tcx> ConstToPat<'tcx> {
         let param_env = self.param_env;
 
         let kind = match ty.kind() {
-            ty::Float(_) => {
-                self.saw_const_match_lint.set(true);
-                tcx.emit_spanned_lint(
-                    lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
-                    id,
-                    span,
-                    FloatPattern,
-                );
-                return Err(FallbackToConstRef);
-            }
             // If the type is not structurally comparable, just emit the constant directly,
             // causing the pattern match code to treat it opaquely.
             // FIXME: This code doesn't emit errors itself, the caller emits the errors.
@@ -445,6 +435,25 @@ impl<'tcx> ConstToPat<'tcx> {
                     }
                 }
             },
+            ty::Float(fty) => {
+                // FIXME: Can this be done in a separate lint pass, rather than in the middle of
+                // const-to-pat conversion?
+                let val = cv.unwrap_leaf();
+                let is_nan = match fty {
+                    // FIXME: Do this without host floats.
+                    ty::FloatTy::F32 => f32::from_bits(val.try_to_u32().unwrap()).is_nan(),
+                    ty::FloatTy::F64 => f64::from_bits(val.try_to_u64().unwrap()).is_nan(),
+                };
+                if is_nan {
+                    tcx.emit_spanned_lint(
+                        lint::builtin::INVALID_NAN_COMPARISONS,
+                        id,
+                        span,
+                        NaNPattern,
+                    );
+                }
+                PatKind::Constant { value: mir::Const::Ty(ty::Const::new_value(tcx, cv, ty)) }
+            }
             ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) => {
                 PatKind::Constant { value: mir::Const::Ty(ty::Const::new_value(tcx, cv, ty)) }
             }

src/tools/clippy/tests/ui/expect_tool_lint_rfc_2383.rs

@@ -20,12 +20,8 @@ mod rustc_ok {
     pub fn rustc_lints() {
         let x = 42.0;
 
-        #[expect(illegal_floating_point_literal_pattern)]
-        match x {
-            5.0 => {}
-            6.0 => {}
-            _ => {}
-        }
+        #[expect(invalid_nan_comparisons)]
+        let _b = x == f32::NAN;
     }
 }
 
@@ -38,13 +34,9 @@ mod rustc_warn {
     pub fn rustc_lints() {
         let x = 42;
 
-        #[expect(illegal_floating_point_literal_pattern)]
+        #[expect(invalid_nan_comparisons)]
         //~^ ERROR: this lint expectation is unfulfilled
-        match x {
-            5 => {}
-            6 => {}
-            _ => {}
-        }
+        let _b = x == 5;
     }
 }
 

src/tools/clippy/tests/ui/expect_tool_lint_rfc_2383.stderr

@@ -1,5 +1,5 @@
 error: this lint expectation is unfulfilled
-  --> $DIR/expect_tool_lint_rfc_2383.rs:35:14
+  --> $DIR/expect_tool_lint_rfc_2383.rs:31:14
    |
 LL |     #[expect(dead_code)]
    |              ^^^^^^^^^
@@ -8,31 +8,31 @@ LL |     #[expect(dead_code)]
    = help: to override `-D warnings` add `#[allow(unfulfilled_lint_expectations)]`
 
 error: this lint expectation is unfulfilled
-  --> $DIR/expect_tool_lint_rfc_2383.rs:41:18
+  --> $DIR/expect_tool_lint_rfc_2383.rs:37:18
    |
-LL |         #[expect(illegal_floating_point_literal_pattern)]
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         #[expect(invalid_nan_comparisons)]
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^
 
 error: this lint expectation is unfulfilled
-  --> $DIR/expect_tool_lint_rfc_2383.rs:116:14
+  --> $DIR/expect_tool_lint_rfc_2383.rs:108:14
    |
 LL |     #[expect(clippy::almost_swapped)]
    |              ^^^^^^^^^^^^^^^^^^^^^^
 
 error: this lint expectation is unfulfilled
-  --> $DIR/expect_tool_lint_rfc_2383.rs:124:14
+  --> $DIR/expect_tool_lint_rfc_2383.rs:116:14
    |
 LL |     #[expect(clippy::bytes_nth)]
    |              ^^^^^^^^^^^^^^^^^
 
 error: this lint expectation is unfulfilled
-  --> $DIR/expect_tool_lint_rfc_2383.rs:130:14
+  --> $DIR/expect_tool_lint_rfc_2383.rs:122:14
    |
 LL |     #[expect(clippy::if_same_then_else)]
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: this lint expectation is unfulfilled
-  --> $DIR/expect_tool_lint_rfc_2383.rs:136:14
+  --> $DIR/expect_tool_lint_rfc_2383.rs:128:14
    |
 LL |     #[expect(clippy::overly_complex_bool_expr)]
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

tests/ui/array-slice-vec/vec-matching-autoslice.rs

@@ -1,5 +1,4 @@
 // run-pass
-#![allow(illegal_floating_point_literal_pattern)] // FIXME #41620
 
 pub fn main() {
     let x = [1, 2, 3];

tests/ui/binding/match-range.rs

@@ -1,5 +1,4 @@
 // run-pass
-#![allow(illegal_floating_point_literal_pattern)] // FIXME #41620
 #![feature(exclusive_range_pattern)]
 
 pub fn main() {