Auto merge of #124661 - RalfJung:only-structural-consts-in-patterns, r=pnkfelix

Turn remaining non-structural-const-in-pattern lints into hard errors

This completes the implementation of #120362 by turning our remaining future-compat lints into hard errors: indirect_structural_match and pointer_structural_match.

They have been future-compat lints for a while (indirect_structural_match for many years, pointer_structural_match since Rust 1.75 (released Dec 28, 2023)), and have shown up in dependency breakage reports since Rust 1.78 (just released on May 2, 2024). I don't expect a lot of code will still depend on them, but we will of course do a crater run.

A lot of cleanup is now possible in const_to_pat, but that is deferred to a later PR.

Fixes #70861

Author: bors

compiler/rustc_lint/src/lib.rs

@@ -539,6 +539,16 @@ fn register_builtins(store: &mut LintStore) {
         "converted into hard error, see RFC #3535 \
          <https://rust-lang.github.io/rfcs/3535-constants-in-patterns.html> for more information",
     );
+    store.register_removed(
+        "indirect_structural_match",
+        "converted into hard error, see RFC #3535 \
+         <https://rust-lang.github.io/rfcs/3535-constants-in-patterns.html> for more information",
+    );
+    store.register_removed(
+        "pointer_structural_match",
+        "converted into hard error, see RFC #3535 \
+         <https://rust-lang.github.io/rfcs/3535-constants-in-patterns.html> for more information",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {

compiler/rustc_lint_defs/src/builtin.rs

@@ -49,7 +49,6 @@ declare_lint_pass! {
         HIDDEN_GLOB_REEXPORTS,
         ILL_FORMED_ATTRIBUTE_INPUT,
         INCOMPLETE_INCLUDE,
-        INDIRECT_STRUCTURAL_MATCH,
         INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
         INLINE_NO_SANITIZE,
         INVALID_DOC_ATTRIBUTES,
@@ -74,7 +73,6 @@ declare_lint_pass! {
         ORDER_DEPENDENT_TRAIT_OBJECTS,
         OVERLAPPING_RANGE_ENDPOINTS,
         PATTERNS_IN_FNS_WITHOUT_BODY,
-        POINTER_STRUCTURAL_MATCH,
         PRIVATE_BOUNDS,
         PRIVATE_INTERFACES,
         PROC_MACRO_BACK_COMPAT,
@@ -2351,52 +2349,6 @@ declare_lint! {
     "outlives requirements can be inferred"
 }
 
-declare_lint! {
-    /// The `indirect_structural_match` lint detects a `const` in a pattern
-    /// that manually implements [`PartialEq`] and [`Eq`].
-    ///
-    /// [`PartialEq`]: https://doc.rust-lang.org/std/cmp/trait.PartialEq.html
-    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
-    ///
-    /// ### Example
-    ///
-    /// ```rust,compile_fail
-    /// #![deny(indirect_structural_match)]
-    ///
-    /// struct NoDerive(i32);
-    /// impl PartialEq for NoDerive { fn eq(&self, _: &Self) -> bool { false } }
-    /// impl Eq for NoDerive { }
-    /// #[derive(PartialEq, Eq)]
-    /// struct WrapParam<T>(T);
-    /// const WRAP_INDIRECT_PARAM: & &WrapParam<NoDerive> = & &WrapParam(NoDerive(0));
-    /// fn main() {
-    ///     match WRAP_INDIRECT_PARAM {
-    ///         WRAP_INDIRECT_PARAM => { }
-    ///         _ => { }
-    ///     }
-    /// }
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// The compiler unintentionally accepted this form in the past. This is a
-    /// [future-incompatible] lint to transition this to a hard error in the
-    /// future. See [issue #62411] for a complete description of the problem,
-    /// and some possible solutions.
-    ///
-    /// [issue #62411]: https://github.com/rust-lang/rust/issues/62411
-    /// [future-incompatible]: ../index.md#future-incompatible-lints
-    pub INDIRECT_STRUCTURAL_MATCH,
-    Warn,
-    "constant used in pattern contains value of non-structural-match type in a field or a variant",
-    @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
-        reference: "issue #120362 <https://github.com/rust-lang/rust/issues/120362>",
-    };
-}
-
 declare_lint! {
     /// The `deprecated_in_future` lint is internal to rustc and should not be
     /// used by user code.
@@ -2414,45 +2366,6 @@ declare_lint! {
     report_in_external_macro
 }
 
-declare_lint! {
-    /// The `pointer_structural_match` lint detects pointers used in patterns whose behaviour
-    /// cannot be relied upon across compiler versions and optimization levels.
-    ///
-    /// ### Example
-    ///
-    /// ```rust,compile_fail
-    /// #![deny(pointer_structural_match)]
-    /// fn foo(a: usize, b: usize) -> usize { a + b }
-    /// const FOO: fn(usize, usize) -> usize = foo;
-    /// fn main() {
-    ///     match FOO {
-    ///         FOO => {},
-    ///         _ => {},
-    ///     }
-    /// }
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// Previous versions of Rust allowed function pointers and all raw pointers in patterns.
-    /// While these work in many cases as expected by users, it is possible that due to
-    /// optimizations pointers are "not equal to themselves" or pointers to different functions
-    /// compare as equal during runtime. This is because LLVM optimizations can deduplicate
-    /// functions if their bodies are the same, thus also making pointers to these functions point
-    /// to the same location. Additionally functions may get duplicated if they are instantiated
-    /// in different crates and not deduplicated again via LTO. Pointer identity for memory
-    /// created by `const` is similarly unreliable.
-    pub POINTER_STRUCTURAL_MATCH,
-    Warn,
-    "pointers are not structural-match",
-    @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
-        reference: "issue #120362 <https://github.com/rust-lang/rust/issues/120362>",
-    };
-}
-
 declare_lint! {
     /// The `ambiguous_associated_items` lint detects ambiguity between
     /// [associated items] and [enum variants].

compiler/rustc_mir_build/messages.ftl

@@ -109,9 +109,6 @@ 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_indirect_structural_match =
-    to use a constant of type `{$non_sm_ty}` in a pattern, `{$non_sm_ty}` must be annotated with `#[derive(PartialEq)]`
-
 mir_build_inform_irrefutable = `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
 
 mir_build_initializing_type_with_requires_unsafe =
@@ -257,9 +254,6 @@ mir_build_non_exhaustive_patterns_type_not_empty = non-exhaustive patterns: type
 mir_build_non_partial_eq_match =
     to use a constant of type `{$non_peq_ty}` in a pattern, the type must implement `PartialEq`
 
-mir_build_nontrivial_structural_match =
-    to use a constant of type `{$non_sm_ty}` in a pattern, the constant's initializer must be trivial or `{$non_sm_ty}` must be annotated with `#[derive(PartialEq)]`
-
 mir_build_pattern_not_covered = refutable pattern in {$origin}
     .pattern_ty = the matched value is of type `{$pattern_ty}`
 

compiler/rustc_mir_build/src/errors.rs

@@ -794,9 +794,12 @@ pub struct NaNPattern {
     pub span: Span,
 }
 
-#[derive(LintDiagnostic)]
+#[derive(Diagnostic)]
 #[diag(mir_build_pointer_pattern)]
-pub struct PointerPattern;
+pub struct PointerPattern {
+    #[primary_span]
+    pub span: Span,
+}
 
 #[derive(Diagnostic)]
 #[diag(mir_build_non_empty_never_pattern)]
@@ -808,22 +811,6 @@ pub struct NonEmptyNeverPattern<'tcx> {
     pub ty: Ty<'tcx>,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(mir_build_indirect_structural_match)]
-#[note(mir_build_type_not_structural_tip)]
-#[note(mir_build_type_not_structural_more_info)]
-pub struct IndirectStructuralMatch<'tcx> {
-    pub non_sm_ty: Ty<'tcx>,
-}
-
-#[derive(LintDiagnostic)]
-#[diag(mir_build_nontrivial_structural_match)]
-#[note(mir_build_type_not_structural_tip)]
-#[note(mir_build_type_not_structural_more_info)]
-pub struct NontrivialStructuralMatch<'tcx> {
-    pub non_sm_ty: Ty<'tcx>,
-}
-
 #[derive(Diagnostic)]
 #[diag(mir_build_exceeds_mcdc_condition_num_limit)]
 pub(crate) struct MCDCExceedsConditionNumLimit {

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

@@ -7,7 +7,6 @@ use rustc_middle::mir;
 use rustc_middle::span_bug;
 use rustc_middle::thir::{FieldPat, Pat, PatKind};
 use rustc_middle::ty::{self, Ty, TyCtxt, ValTree};
-use rustc_session::lint;
 use rustc_span::{ErrorGuaranteed, Span};
 use rustc_target::abi::{FieldIdx, VariantIdx};
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
@@ -18,8 +17,8 @@ use std::cell::Cell;
 
 use super::PatCtxt;
 use crate::errors::{
-    IndirectStructuralMatch, InvalidPattern, NaNPattern, PointerPattern, TypeNotPartialEq,
-    TypeNotStructural, UnionPattern, UnsizedPattern,
+    InvalidPattern, NaNPattern, PointerPattern, TypeNotPartialEq, TypeNotStructural, UnionPattern,
+    UnsizedPattern,
 };
 
 impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
@@ -51,15 +50,6 @@ struct ConstToPat<'tcx> {
     // value.
     saw_const_match_error: Cell<Option<ErrorGuaranteed>>,
 
-    // This tracks if we emitted some diagnostic for a given const value, so that
-    // we will not subsequently issue an irrelevant lint for the same const
-    // value.
-    saw_const_match_lint: Cell<bool>,
-
-    // For backcompat we need to keep allowing non-structurally-eq types behind references.
-    // See also all the `cant-hide-behind` tests.
-    behind_reference: Cell<bool>,
-
     // inference context used for checking `T: Structural` bounds.
     infcx: InferCtxt<'tcx>,
 
@@ -86,8 +76,6 @@ impl<'tcx> ConstToPat<'tcx> {
             infcx,
             param_env: pat_ctxt.param_env,
             saw_const_match_error: Cell::new(None),
-            saw_const_match_lint: Cell::new(false),
-            behind_reference: Cell::new(false),
             treat_byte_string_as_slice: pat_ctxt
                 .typeck_results
                 .treat_byte_string_as_slice
@@ -199,15 +187,12 @@ impl<'tcx> ConstToPat<'tcx> {
                     // complained about structural match violations there, so we don't
                     // have to check anything any more.
                 }
-            } else if !have_valtree && !self.saw_const_match_lint.get() {
+            } else if !have_valtree {
                 // The only way valtree construction can fail without the structural match
                 // checker finding a violation is if there is a pointer somewhere.
-                self.tcx().emit_node_span_lint(
-                    lint::builtin::POINTER_STRUCTURAL_MATCH,
-                    self.id,
-                    self.span,
-                    PointerPattern,
-                );
+                let e = self.tcx().dcx().emit_err(PointerPattern { span: self.span });
+                let kind = PatKind::Error(e);
+                return Box::new(Pat { span: self.span, ty: cv.ty(), kind });
             }
 
             // Always check for `PartialEq` if we had no other errors yet.
@@ -276,36 +261,11 @@ impl<'tcx> ConstToPat<'tcx> {
         cv: ValTree<'tcx>,
         ty: Ty<'tcx>,
     ) -> Result<Box<Pat<'tcx>>, FallbackToOpaqueConst> {
-        let id = self.id;
         let span = self.span;
         let tcx = self.tcx();
         let param_env = self.param_env;
 
         let kind = match ty.kind() {
-            // 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.
-            // So instead of specific errors, you just get blanket errors about the whole
-            // const type. See
-            // https://github.com/rust-lang/rust/pull/70743#discussion_r404701963 for
-            // details.
-            // Backwards compatibility hack because we can't cause hard errors on these
-            // types, so we compare them via `PartialEq::eq` at runtime.
-            ty::Adt(..) if !self.type_marked_structural(ty) && self.behind_reference.get() => {
-                if self.saw_const_match_error.get().is_none() && !self.saw_const_match_lint.get() {
-                    self.saw_const_match_lint.set(true);
-                    tcx.emit_node_span_lint(
-                        lint::builtin::INDIRECT_STRUCTURAL_MATCH,
-                        id,
-                        span,
-                        IndirectStructuralMatch { non_sm_ty: ty },
-                    );
-                }
-                // Since we are behind a reference, we can just bubble the error up so we get a
-                // constant at reference type, making it easy to let the fallback call
-                // `PartialEq::eq` on it.
-                return Err(FallbackToOpaqueConst);
-            }
             ty::FnDef(..) => {
                 let e = tcx.dcx().emit_err(InvalidPattern { span, non_sm_ty: ty });
                 self.saw_const_match_error.set(Some(e));
@@ -379,38 +339,6 @@ impl<'tcx> ConstToPat<'tcx> {
                 ty::Str => {
                     PatKind::Constant { value: mir::Const::Ty(ty::Const::new_value(tcx, cv, ty)) }
                 }
-                // Backwards compatibility hack: support references to non-structural types,
-                // but hard error if we aren't behind a double reference. We could just use
-                // the fallback code path below, but that would allow *more* of this fishy
-                // code to compile, as then it only goes through the future incompat lint
-                // instead of a hard error.
-                ty::Adt(_, _) if !self.type_marked_structural(*pointee_ty) => {
-                    if self.behind_reference.get() {
-                        if self.saw_const_match_error.get().is_none()
-                            && !self.saw_const_match_lint.get()
-                        {
-                            self.saw_const_match_lint.set(true);
-                            tcx.emit_node_span_lint(
-                                lint::builtin::INDIRECT_STRUCTURAL_MATCH,
-                                self.id,
-                                span,
-                                IndirectStructuralMatch { non_sm_ty: *pointee_ty },
-                            );
-                        }
-                        return Err(FallbackToOpaqueConst);
-                    } else {
-                        if let Some(e) = self.saw_const_match_error.get() {
-                            // We already errored. Signal that in the pattern, so that follow up errors can be silenced.
-                            PatKind::Error(e)
-                        } else {
-                            let err = TypeNotStructural { span, non_sm_ty: *pointee_ty };
-                            let e = tcx.dcx().emit_err(err);
-                            self.saw_const_match_error.set(Some(e));
-                            // We errored. Signal that in the pattern, so that follow up errors can be silenced.
-                            PatKind::Error(e)
-                        }
-                    }
-                }
                 // All other references are converted into deref patterns and then recursively
                 // convert the dereferenced constant to a pattern that is the sub-pattern of the
                 // deref pattern.
@@ -421,7 +349,6 @@ impl<'tcx> ConstToPat<'tcx> {
                         // We errored. Signal that in the pattern, so that follow up errors can be silenced.
                         PatKind::Error(e)
                     } else {
-                        let old = self.behind_reference.replace(true);
                         // `b"foo"` produces a `&[u8; 3]`, but you can't use constants of array type when
                         // matching against references, you can only use byte string literals.
                         // The typechecker has a special case for byte string literals, by treating them
@@ -436,7 +363,6 @@ impl<'tcx> ConstToPat<'tcx> {
                         };
                         // References have the same valtree representation as their pointee.
                         let subpattern = self.recur(cv, pointee_ty)?;
-                        self.behind_reference.set(old);
                         PatKind::Deref { subpattern }
                     }
                 }

tests/ui/closures/2229_closure_analysis/match/match-edge-cases_1.rs

@@ -2,8 +2,7 @@
 //@ edition:2021
 
 const PATTERN_REF: &str = "Hello World";
-const NUMBER: i32 = 30;
-const NUMBER_POINTER: *const i32 = &NUMBER;
+const NUMBER_POINTER: *const i32 = 30 as *const i32;
 
 pub fn edge_case_ref(event: &str) {
     let _ = || {
@@ -26,8 +25,7 @@ pub fn edge_case_str(event: String) {
 pub fn edge_case_raw_ptr(event: *const i32) {
     let _ = || {
         match event {
-            NUMBER_POINTER => (), //~WARN behave unpredictably
-            //~| previously accepted
+            NUMBER_POINTER => (),
             _ => (),
         };
     };

tests/ui/closures/2229_closure_analysis/match/match-edge-cases_1.stderr

@@ -1,7 +1,6 @@
 //@ run-pass
 
 #![allow(non_local_definitions)]
-#![warn(indirect_structural_match)]
 
 // This test is checking our logic for structural match checking by enumerating
 // the different kinds of const expressions. This test is collecting cases where