Auto merge of rust-lang#87141 - spastorino:remove_impl_trait_in_bindings, r=oli-obk

Remove impl trait in bindings

Closes rust-lang#86729

r? `@oli-obk`

Author: bors

compiler/rustc_ast_lowering/src/item.rs

@@ -343,9 +343,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 // opaque type Foo1: Trait
                 let ty = self.lower_ty(
                     ty,
-                    ImplTraitContext::OtherOpaqueTy {
+                    ImplTraitContext::TypeAliasesOpaqueTy {
                         capturable_lifetimes: &mut FxHashSet::default(),
-                        origin: hir::OpaqueTyOrigin::TyAlias,
                     },
                 );
                 let generics = self.lower_generics(gen, ImplTraitContext::disallowed());
@@ -484,17 +483,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         span: Span,
         body: Option<&Expr>,
     ) -> (&'hir hir::Ty<'hir>, hir::BodyId) {
-        let mut capturable_lifetimes;
-        let itctx = if self.sess.features_untracked().impl_trait_in_bindings {
-            capturable_lifetimes = FxHashSet::default();
-            ImplTraitContext::OtherOpaqueTy {
-                capturable_lifetimes: &mut capturable_lifetimes,
-                origin: hir::OpaqueTyOrigin::Misc,
-            }
-        } else {
-            ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
-        };
-        let ty = self.lower_ty(ty, itctx);
+        let ty = self.lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::Binding));
         (ty, self.lower_const_body(span, body))
     }
 
@@ -926,9 +915,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     Some(ty) => {
                         let ty = self.lower_ty(
                             ty,
-                            ImplTraitContext::OtherOpaqueTy {
+                            ImplTraitContext::TypeAliasesOpaqueTy {
                                 capturable_lifetimes: &mut FxHashSet::default(),
-                                origin: hir::OpaqueTyOrigin::TyAlias,
                             },
                         );
                         hir::ImplItemKind::TyAlias(ty)

compiler/rustc_ast_lowering/src/lib.rs

@@ -264,8 +264,8 @@ enum ImplTraitContext<'b, 'a> {
         /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
         origin: hir::OpaqueTyOrigin,
     },
-    /// Impl trait in type aliases, consts and statics.
-    OtherOpaqueTy {
+    /// Impl trait in type aliases.
+    TypeAliasesOpaqueTy {
         /// Set of lifetimes that this opaque type can capture, if it uses
         /// them. This includes lifetimes bound since we entered this context.
         /// For example:
@@ -280,8 +280,6 @@ enum ImplTraitContext<'b, 'a> {
         // FIXME(impl_trait): but `required_region_bounds` will ICE later
         // anyway.
         capturable_lifetimes: &'b mut FxHashSet<hir::LifetimeName>,
-        /// Origin: Either OpaqueTyOrigin::Misc or OpaqueTyOrigin::Binding,
-        origin: hir::OpaqueTyOrigin,
     },
     /// `impl Trait` is not accepted in this position.
     Disallowed(ImplTraitPosition),
@@ -310,8 +308,8 @@ impl<'a> ImplTraitContext<'_, 'a> {
             ReturnPositionOpaqueTy { fn_def_id, origin } => {
                 ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin }
             }
-            OtherOpaqueTy { capturable_lifetimes, origin } => {
-                OtherOpaqueTy { capturable_lifetimes, origin: *origin }
+            TypeAliasesOpaqueTy { capturable_lifetimes } => {
+                TypeAliasesOpaqueTy { capturable_lifetimes }
             }
             Disallowed(pos) => Disallowed(*pos),
         }
@@ -1126,7 +1124,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     //
                     //     fn foo() -> impl Iterator<Item = impl Debug>
                     ImplTraitContext::ReturnPositionOpaqueTy { .. }
-                    | ImplTraitContext::OtherOpaqueTy { .. } => (true, itctx),
+                    | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
 
                     // We are in the argument position, but within a dyn type:
                     //
@@ -1150,9 +1148,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         capturable_lifetimes = FxHashSet::default();
                         (
                             true,
-                            ImplTraitContext::OtherOpaqueTy {
+                            ImplTraitContext::TypeAliasesOpaqueTy {
                                 capturable_lifetimes: &mut capturable_lifetimes,
-                                origin: hir::OpaqueTyOrigin::Misc,
                             },
                         )
                     }
@@ -1416,18 +1413,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             None,
                             |this| this.lower_param_bounds(bounds, itctx),
                         ),
-                    ImplTraitContext::OtherOpaqueTy { ref capturable_lifetimes, origin } => {
+                    ImplTraitContext::TypeAliasesOpaqueTy { ref capturable_lifetimes } => {
                         // Reset capturable lifetimes, any nested impl trait
                         // types will inherit lifetimes from this opaque type,
                         // so don't need to capture them again.
-                        let nested_itctx = ImplTraitContext::OtherOpaqueTy {
+                        let nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy {
                             capturable_lifetimes: &mut FxHashSet::default(),
-                            origin,
                         };
                         self.lower_opaque_impl_trait(
                             span,
                             None,
-                            origin,
+                            hir::OpaqueTyOrigin::TyAlias,
                             def_node_id,
                             Some(capturable_lifetimes),
                             |this| this.lower_param_bounds(bounds, nested_itctx),
@@ -1464,25 +1460,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             }),
                         ))
                     }
-                    ImplTraitContext::Disallowed(pos) => {
-                        let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
-                            "bindings or function and inherent method return types"
-                        } else {
-                            "function and inherent method return types"
-                        };
+                    ImplTraitContext::Disallowed(_) => {
                         let mut err = struct_span_err!(
                             self.sess,
                             t.span,
                             E0562,
                             "`impl Trait` not allowed outside of {}",
-                            allowed_in,
+                            "function and method return types",
                         );
-                        if pos == ImplTraitPosition::Binding && self.sess.is_nightly_build() {
-                            err.help(
-                                "add `#![feature(impl_trait_in_bindings)]` to the crate \
-                                   attributes to enable",
-                            );
-                        }
                         err.emit();
                         hir::TyKind::Err
                     }
@@ -1767,21 +1752,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     }
 
     fn lower_local(&mut self, l: &Local) -> hir::Local<'hir> {
-        let ty = l.ty.as_ref().map(|t| {
-            let mut capturable_lifetimes;
-            self.lower_ty(
-                t,
-                if self.sess.features_untracked().impl_trait_in_bindings {
-                    capturable_lifetimes = FxHashSet::default();
-                    ImplTraitContext::OtherOpaqueTy {
-                        capturable_lifetimes: &mut capturable_lifetimes,
-                        origin: hir::OpaqueTyOrigin::Binding,
-                    }
-                } else {
-                    ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
-                },
-            )
-        });
+        let ty = l
+            .ty
+            .as_ref()
+            .map(|t| self.lower_ty(t, ImplTraitContext::Disallowed(ImplTraitPosition::Binding)));
         let init = l.init.as_ref().map(|e| self.lower_expr(e));
         let hir_id = self.lower_node_id(l.id);
         self.lower_attrs(hir_id, &l.attrs);
@@ -2332,13 +2306,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 )),
                 _ => None,
             });
-            if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
+            if let ImplTraitContext::TypeAliasesOpaqueTy { ref mut capturable_lifetimes, .. } =
+                itctx
+            {
                 capturable_lifetimes.extend(lt_def_names.clone());
             }
 
             let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow());
 
-            if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
+            if let ImplTraitContext::TypeAliasesOpaqueTy { ref mut capturable_lifetimes, .. } =
+                itctx
+            {
                 for param in lt_def_names {
                     capturable_lifetimes.remove(&param);
                 }

compiler/rustc_feature/src/active.rs

@@ -455,9 +455,6 @@ declare_features! (
     /// Allows non-builtin attributes in inner attribute position.
     (active, custom_inner_attributes, "1.30.0", Some(54726), None),
 
-    /// Allows `impl Trait` in bindings (`let`, `const`, `static`).
-    (incomplete, impl_trait_in_bindings, "1.30.0", Some(63065), None),
-
     /// Allows using `reason` in lint attributes and the `#[expect(lint)]` lint check.
     (active, lint_reasons, "1.31.0", Some(54503), None),
 

compiler/rustc_feature/src/removed.rs

@@ -148,6 +148,10 @@ declare_features! (
     (removed, const_raw_ptr_to_usize_cast, "1.55.0", Some(51910), None,
      Some("at compile-time, pointers do not have an integer value, so these casts cannot be properly supported")),
 
+    /// Allows `impl Trait` in bindings (`let`, `const`, `static`).
+    (removed, impl_trait_in_bindings, "1.55.0", Some(63065), None,
+     Some("the implementation was not maintainable, the feature may get reintroduced once the current refactorings are done")),
+
     // -------------------------------------------------------------------------
     // feature-group-end: removed features
     // -------------------------------------------------------------------------

compiler/rustc_hir/src/hir.rs

@@ -2264,18 +2264,14 @@ pub struct OpaqueTy<'hir> {
 }
 
 /// From whence the opaque type came.
-#[derive(Copy, Clone, Encodable, Decodable, Debug, HashStable_Generic)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
 pub enum OpaqueTyOrigin {
     /// `-> impl Trait`
     FnReturn,
     /// `async fn`
     AsyncFn,
-    /// `let _: impl Trait = ...`
-    Binding,
     /// type aliases: `type Foo = impl Trait;`
     TyAlias,
-    /// Impl trait consts, statics, bounds.
-    Misc,
 }
 
 /// The various kinds of types recognized by the compiler.

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -491,11 +491,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             span
         };
 
-        let is_named_and_not_impl_trait = |ty: Ty<'_>| {
-            &ty.to_string() != "_" &&
-                // FIXME: Remove this check after `impl_trait_in_bindings` is stabilized. #63527
-                (!ty.is_impl_trait() || self.tcx.features().impl_trait_in_bindings)
-        };
+        let is_named_and_not_impl_trait =
+            |ty: Ty<'_>| &ty.to_string() != "_" && !ty.is_impl_trait();
 
         let ty_msg = match (local_visitor.found_node_ty, local_visitor.found_exact_method_call) {
             (_, Some(_)) => String::new(),

compiler/rustc_mir/src/borrow_check/member_constraints.rs

@@ -1,5 +1,4 @@
 use rustc_data_structures::fx::FxHashMap;
-use rustc_hir::def_id::DefId;
 use rustc_index::vec::IndexVec;
 use rustc_middle::infer::MemberConstraint;
 use rustc_middle::ty::{self, Ty};
@@ -32,9 +31,6 @@ where
 crate struct NllMemberConstraint<'tcx> {
     next_constraint: Option<NllMemberConstraintIndex>,
 
-    /// The opaque type whose hidden type is being inferred. (Used in error reporting.)
-    crate opaque_type_def_id: DefId,
-
     /// The span where the hidden type was instantiated.
     crate definition_span: Span,
 
@@ -91,7 +87,6 @@ impl<'tcx> MemberConstraintSet<'tcx, ty::RegionVid> {
         let constraint_index = self.constraints.push(NllMemberConstraint {
             next_constraint,
             member_region_vid,
-            opaque_type_def_id: m_c.opaque_type_def_id,
             definition_span: m_c.definition_span,
             hidden_ty: m_c.hidden_ty,
             start_index,

compiler/rustc_mir/src/borrow_check/region_infer/mod.rs

@@ -551,7 +551,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         polonius_output: Option<Rc<PoloniusOutput>>,
     ) -> (Option<ClosureRegionRequirements<'tcx>>, RegionErrors<'tcx>) {
         let mir_def_id = body.source.def_id();
-        self.propagate_constraints(body, infcx.tcx);
+        self.propagate_constraints(body);
 
         let mut errors_buffer = RegionErrors::new();
 
@@ -599,7 +599,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// for each region variable until all the constraints are
     /// satisfied. Note that some values may grow **too** large to be
     /// feasible, but we check this later.
-    fn propagate_constraints(&mut self, _body: &Body<'tcx>, tcx: TyCtxt<'tcx>) {
+    fn propagate_constraints(&mut self, _body: &Body<'tcx>) {
         debug!("propagate_constraints()");
 
         debug!("propagate_constraints: constraints={:#?}", {
@@ -617,7 +617,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         // own.
         let constraint_sccs = self.constraint_sccs.clone();
         for scc in constraint_sccs.all_sccs() {
-            self.compute_value_for_scc(scc, tcx);
+            self.compute_value_for_scc(scc);
         }
 
         // Sort the applied member constraints so we can binary search
@@ -629,7 +629,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// computed, by unioning the values of its successors.
     /// Assumes that all successors have been computed already
     /// (which is assured by iterating over SCCs in dependency order).
-    fn compute_value_for_scc(&mut self, scc_a: ConstraintSccIndex, tcx: TyCtxt<'tcx>) {
+    fn compute_value_for_scc(&mut self, scc_a: ConstraintSccIndex) {
         let constraint_sccs = self.constraint_sccs.clone();
 
         // Walk each SCC `B` such that `A: B`...
@@ -652,12 +652,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         // Now take member constraints into account.
         let member_constraints = self.member_constraints.clone();
         for m_c_i in member_constraints.indices(scc_a) {
-            self.apply_member_constraint(
-                tcx,
-                scc_a,
-                m_c_i,
-                member_constraints.choice_regions(m_c_i),
-            );
+            self.apply_member_constraint(scc_a, m_c_i, member_constraints.choice_regions(m_c_i));
         }
 
         debug!(
@@ -680,31 +675,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// If we make any changes, returns true, else false.
     fn apply_member_constraint(
         &mut self,
-        tcx: TyCtxt<'tcx>,
         scc: ConstraintSccIndex,
         member_constraint_index: NllMemberConstraintIndex,
         choice_regions: &[ty::RegionVid],
     ) -> bool {
         debug!("apply_member_constraint(scc={:?}, choice_regions={:#?})", scc, choice_regions,);
 
-        if let Some(uh_oh) =
-            choice_regions.iter().find(|&&r| !self.universal_regions.is_universal_region(r))
-        {
-            // FIXME(#61773): This case can only occur with
-            // `impl_trait_in_bindings`, I believe, and we are just
-            // opting not to handle it for now. See #61773 for
-            // details.
-            tcx.sess.delay_span_bug(
-                self.member_constraints[member_constraint_index].definition_span,
-                &format!(
-                    "member constraint for `{:?}` has an option region `{:?}` \
-                     that is not a universal region",
-                    self.member_constraints[member_constraint_index].opaque_type_def_id, uh_oh,
-                ),
-            );
-            return false;
-        }
-
         // Create a mutable vector of the options. We'll try to winnow
         // them down.
         let mut choice_regions: Vec<ty::RegionVid> = choice_regions.to_vec();

compiler/rustc_mir/src/borrow_check/type_check/input_output.rs

@@ -122,7 +122,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         if let Err(terr) = self.eq_opaque_type_and_type(
             mir_output_ty,
             normalized_output_ty,
-            mir_def_id,
             Locations::All(output_span),
             ConstraintCategory::BoringNoLocation,
         ) {
@@ -145,7 +144,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             if let Err(err) = self.eq_opaque_type_and_type(
                 mir_output_ty,
                 user_provided_output_ty,
-                mir_def_id,
                 Locations::All(output_span),
                 ConstraintCategory::BoringNoLocation,
             ) {