remove IndirectStructuralMatch lint, emit the usual hard error instead

Author: RalfJung

compiler/rustc_lint/src/lib.rs

@@ -539,6 +539,11 @@ 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",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {

compiler/rustc_lint_defs/src/builtin.rs

@@ -50,7 +50,6 @@ 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,
@@ -2355,52 +2354,6 @@ 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.

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

@@ -802,22 +802,6 @@ 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

@@ -16,8 +16,8 @@ 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> {
@@ -49,15 +49,6 @@ 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>,
 
@@ -84,8 +75,6 @@ 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
@@ -197,7 +186,7 @@ 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(
@@ -274,36 +263,11 @@ 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));
@@ -377,38 +341,6 @@ 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.
@@ -419,7 +351,6 @@ 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
@@ -434,7 +365,6 @@ 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/consts/const_in_pattern/accept_structural.rs

@@ -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

tests/ui/consts/const_in_pattern/cross-crate-fail.rs

@@ -1,7 +1,5 @@
 //@ aux-build:consts.rs
 
-#![warn(indirect_structural_match)]
-
 extern crate consts;
 
 struct Defaulted;

tests/ui/consts/const_in_pattern/cross-crate-fail.stderr

@@ -1,5 +1,5 @@
 error: to use a constant of type `CustomEq` in a pattern, `CustomEq` must be annotated with `#[derive(PartialEq)]`
-  --> $DIR/cross-crate-fail.rs:13:9
+  --> $DIR/cross-crate-fail.rs:11:9
    |
 LL |         consts::SOME => panic!(),
    |         ^^^^^^^^^^^^
@@ -8,7 +8,7 @@ LL |         consts::SOME => panic!(),
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details
 
 error: to use a constant of type `CustomEq` in a pattern, `CustomEq` must be annotated with `#[derive(PartialEq)]`
-  --> $DIR/cross-crate-fail.rs:20:9
+  --> $DIR/cross-crate-fail.rs:18:9
    |
 LL |         <Defaulted as consts::AssocConst>::SOME  => panic!(),
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

tests/ui/consts/const_in_pattern/cross-crate-pass.rs

@@ -1,8 +1,6 @@
 //@ run-pass
 //@ aux-build:consts.rs
 
-#![warn(indirect_structural_match)]
-
 extern crate consts;
 use consts::CustomEq;
 

tests/ui/consts/const_in_pattern/custom-eq-branch-pass.rs

@@ -1,7 +1,5 @@
 //@ run-pass
 
-#![warn(indirect_structural_match)]
-
 struct CustomEq;
 
 impl Eq for CustomEq {}