Implement partial support for non-lifetime binders

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -294,27 +294,6 @@ impl<'a> AstValidator<'a> {
         }
     }
 
-    fn check_late_bound_lifetime_defs(&self, params: &[GenericParam]) {
-        // Check only lifetime parameters are present and that the lifetime
-        // parameters that are present have no bounds.
-        let non_lt_param_spans: Vec<_> = params
-            .iter()
-            .filter_map(|param| match param.kind {
-                GenericParamKind::Lifetime { .. } => {
-                    if !param.bounds.is_empty() {
-                        let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
-                        self.session.emit_err(ForbiddenLifetimeBound { spans });
-                    }
-                    None
-                }
-                _ => Some(param.ident.span),
-            })
-            .collect();
-        if !non_lt_param_spans.is_empty() {
-            self.session.emit_err(ForbiddenNonLifetimeParam { spans: non_lt_param_spans });
-        }
-    }
-
     fn check_fn_decl(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
         self.check_decl_num_args(fn_decl);
         self.check_decl_cvaradic_pos(fn_decl);
@@ -745,7 +724,6 @@ impl<'a> AstValidator<'a> {
                     )
                     .emit();
                 });
-                self.check_late_bound_lifetime_defs(&bfty.generic_params);
                 if let Extern::Implicit(_) = bfty.ext {
                     let sig_span = self.session.source_map().next_point(ty.span.shrink_to_lo());
                     self.maybe_lint_missing_abi(sig_span, ty.id);
@@ -1318,9 +1296,6 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
         for predicate in &generics.where_clause.predicates {
             match predicate {
                 WherePredicate::BoundPredicate(bound_pred) => {
-                    // A type binding, eg `for<'c> Foo: Send+Clone+'c`
-                    self.check_late_bound_lifetime_defs(&bound_pred.bound_generic_params);
-
                     // This is slightly complicated. Our representation for poly-trait-refs contains a single
                     // binder and thus we only allow a single level of quantification. However,
                     // the syntax of Rust permits quantification in two places in where clauses,
@@ -1396,11 +1371,6 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
         visit::walk_param_bound(self, bound)
     }
 
-    fn visit_poly_trait_ref(&mut self, t: &'a PolyTraitRef) {
-        self.check_late_bound_lifetime_defs(&t.bound_generic_params);
-        visit::walk_poly_trait_ref(self, t);
-    }
-
     fn visit_variant_data(&mut self, s: &'a VariantData) {
         self.with_banned_assoc_ty_bound(|this| visit::walk_struct_def(this, s))
     }
@@ -1437,10 +1407,6 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 .emit();
         }
 
-        if let FnKind::Closure(ClosureBinder::For { generic_params, .. }, ..) = fk {
-            self.check_late_bound_lifetime_defs(generic_params);
-        }
-
         if let FnKind::Fn(
             _,
             _,

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -11,6 +11,8 @@ use rustc_span::symbol::sym;
 use rustc_span::Span;
 use rustc_target::spec::abi;
 
+use crate::errors::ForbiddenLifetimeBound;
+
 macro_rules! gate_feature_fn {
     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $help: expr) => {{
         let (visitor, has_feature, span, name, explain, help) =
@@ -136,6 +138,34 @@ impl<'a> PostExpansionVisitor<'a> {
         }
         ImplTraitVisitor { vis: self }.visit_ty(ty);
     }
+
+    fn check_late_bound_lifetime_defs(&self, params: &[ast::GenericParam]) {
+        // Check only lifetime parameters are present and that the lifetime
+        // parameters that are present have no bounds.
+        let non_lt_param_spans: Vec<_> = params
+            .iter()
+            .filter_map(|param| match param.kind {
+                ast::GenericParamKind::Lifetime { .. } => None,
+                _ => Some(param.ident.span),
+            })
+            .collect();
+        // FIXME: gate_feature_post doesn't really handle multispans...
+        if !non_lt_param_spans.is_empty() && !self.features.non_lifetime_binders {
+            feature_err(
+                &self.sess.parse_sess,
+                sym::non_lifetime_binders,
+                non_lt_param_spans,
+                rustc_errors::fluent::ast_passes_forbidden_non_lifetime_param,
+            )
+            .emit();
+        }
+        for param in params {
+            if !param.bounds.is_empty() {
+                let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
+                self.sess.emit_err(ForbiddenLifetimeBound { spans });
+            }
+        }
+    }
 }
 
 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
@@ -147,7 +177,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             ..
         }) = attr_info
         {
-            gate_feature_fn!(self, has_feature, attr.span, *name, descr);
+            gate_feature_fn!(self, has_feature, attr.span, *name, *descr);
         }
         // Check unstable flavors of the `#[doc]` attribute.
         if attr.has_name(sym::doc) {
@@ -306,6 +336,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             ast::TyKind::BareFn(bare_fn_ty) => {
                 // Function pointers cannot be `const`
                 self.check_extern(bare_fn_ty.ext, ast::Const::No);
+                self.check_late_bound_lifetime_defs(&bare_fn_ty.generic_params);
             }
             ast::TyKind::Never => {
                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
@@ -318,6 +349,19 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         visit::walk_ty(self, ty)
     }
 
+    fn visit_generics(&mut self, g: &'a ast::Generics) {
+        for predicate in &g.where_clause.predicates {
+            match predicate {
+                ast::WherePredicate::BoundPredicate(bound_pred) => {
+                    // A type binding, eg `for<'c> Foo: Send+Clone+'c`
+                    self.check_late_bound_lifetime_defs(&bound_pred.bound_generic_params);
+                }
+                _ => {}
+            }
+        }
+        visit::walk_generics(self, g);
+    }
+
     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
         if let ast::FnRetTy::Ty(output_ty) = ret_ty {
             if let ast::TyKind::Never = output_ty.kind {
@@ -437,12 +481,21 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         visit::walk_pat(self, pattern)
     }
 
+    fn visit_poly_trait_ref(&mut self, t: &'a ast::PolyTraitRef) {
+        self.check_late_bound_lifetime_defs(&t.bound_generic_params);
+        visit::walk_poly_trait_ref(self, t);
+    }
+
     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
         if let Some(header) = fn_kind.header() {
             // Stability of const fn methods are covered in `visit_assoc_item` below.
             self.check_extern(header.ext, header.constness);
         }
 
+        if let FnKind::Closure(ast::ClosureBinder::For { generic_params, .. }, ..) = fn_kind {
+            self.check_late_bound_lifetime_defs(generic_params);
+        }
+
         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
         }

compiler/rustc_attr/src/builtin.rs

@@ -731,7 +731,7 @@ pub fn eval_condition(
                             sess,
                             sym::cfg_target_compact,
                             cfg.span,
-                            &"compact `cfg(target(..))` is experimental and subject to change"
+                            "compact `cfg(target(..))` is experimental and subject to change"
                         ).emit();
                     }
 

compiler/rustc_feature/src/active.rs

@@ -473,6 +473,8 @@ declare_features! (
     (active, no_sanitize, "1.42.0", Some(39699), None),
     /// Allows using the `non_exhaustive_omitted_patterns` lint.
     (active, non_exhaustive_omitted_patterns_lint, "1.57.0", Some(89554), None),
+    /// Allows `for<T>` binders in where-clauses
+    (incomplete, non_lifetime_binders, "CURRENT_RUSTC_VERSION", Some(1), None),
     /// Allows making `dyn Trait` well-formed even if `Trait` is not object safe.
     /// In that case, `dyn Trait: Trait` does not hold. Moreover, coercions and
     /// casts in safe Rust to `dyn Trait` for such a `Trait` is also forbidden.

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -14,7 +14,7 @@ use crate::errors::{
     AmbiguousLifetimeBound, MultipleRelaxedDefaultBounds, TraitObjectDeclaredWithNoTraits,
     TypeofReservedKeywordUsed, ValueOfAssociatedStructAlreadySpecified,
 };
-use crate::middle::resolve_lifetime as rl;
+use crate::middle::resolve_bound_vars as rbv;
 use crate::require_c_abi_if_c_variadic;
 use rustc_ast::TraitObjectSyntax;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
@@ -225,10 +225,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let tcx = self.tcx();
         let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
 
-        match tcx.named_region(lifetime.hir_id) {
-            Some(rl::Region::Static) => tcx.lifetimes.re_static,
+        match tcx.named_bound_var(lifetime.hir_id) {
+            Some(rbv::ResolvedArg::StaticLifetime) => tcx.lifetimes.re_static,
 
-            Some(rl::Region::LateBound(debruijn, index, def_id)) => {
+            Some(rbv::ResolvedArg::LateBound(debruijn, index, def_id)) => {
                 let name = lifetime_name(def_id.expect_local());
                 let br = ty::BoundRegion {
                     var: ty::BoundVar::from_u32(index),
@@ -237,15 +237,15 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 tcx.mk_region(ty::ReLateBound(debruijn, br))
             }
 
-            Some(rl::Region::EarlyBound(def_id)) => {
+            Some(rbv::ResolvedArg::EarlyBound(def_id)) => {
                 let name = tcx.hir().ty_param_name(def_id.expect_local());
                 let item_def_id = tcx.hir().ty_param_owner(def_id.expect_local());
                 let generics = tcx.generics_of(item_def_id);
                 let index = generics.param_def_id_to_index[&def_id];
                 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, index, name }))
             }
 
-            Some(rl::Region::Free(scope, id)) => {
+            Some(rbv::ResolvedArg::Free(scope, id)) => {
                 let name = lifetime_name(id.expect_local());
                 tcx.mk_region(ty::ReFree(ty::FreeRegion {
                     scope,
@@ -1604,7 +1604,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             self.ast_region_to_region(lifetime, None)
         } else {
             self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
-                if tcx.named_region(lifetime.hir_id).is_some() {
+                if tcx.named_bound_var(lifetime.hir_id).is_some() {
                     self.ast_region_to_region(lifetime, None)
                 } else {
                     self.re_infer(None, span).unwrap_or_else(|| {
@@ -2598,6 +2598,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         &self,
         opt_self_ty: Option<Ty<'tcx>>,
         path: &hir::Path<'_>,
+        hir_id: hir::HirId,
         permit_variants: bool,
     ) -> Ty<'tcx> {
         let tcx = self.tcx();
@@ -2661,11 +2662,25 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     }
                 });
 
-                let def_id = def_id.expect_local();
-                let item_def_id = tcx.hir().ty_param_owner(def_id);
-                let generics = tcx.generics_of(item_def_id);
-                let index = generics.param_def_id_to_index[&def_id.to_def_id()];
-                tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id))
+                match tcx.named_bound_var(hir_id) {
+                    Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => {
+                        let name =
+                            tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id.expect_local()));
+                        let br = ty::BoundTy {
+                            var: ty::BoundVar::from_u32(index),
+                            kind: ty::BoundTyKind::Param(def_id, name),
+                        };
+                        tcx.mk_ty(ty::Bound(debruijn, br))
+                    }
+                    Some(rbv::ResolvedArg::EarlyBound(_)) => {
+                        let def_id = def_id.expect_local();
+                        let item_def_id = tcx.hir().ty_param_owner(def_id);
+                        let generics = tcx.generics_of(item_def_id);
+                        let index = generics.param_def_id_to_index[&def_id.to_def_id()];
+                        tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id))
+                    }
+                    arg => bug!("unexpected bound var resolution for {hir_id:?}: {arg:?}"),
+                }
             }
             Res::SelfTyParam { .. } => {
                 // `Self` in trait or type alias.
@@ -2868,27 +2883,50 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             hir::TyKind::BareFn(bf) => {
                 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
 
-                tcx.mk_fn_ptr(self.ty_of_fn(
+                let fn_ptr_ty = tcx.mk_fn_ptr(self.ty_of_fn(
                     ast_ty.hir_id,
                     bf.unsafety,
                     bf.abi,
                     bf.decl,
                     None,
                     Some(ast_ty),
-                ))
+                ));
+
+                if let Some(guar) =
+                    deny_non_region_late_bound(tcx, bf.generic_params, "function pointer")
+                {
+                    tcx.ty_error_with_guaranteed(guar)
+                } else {
+                    fn_ptr_ty
+                }
             }
             hir::TyKind::TraitObject(bounds, lifetime, repr) => {
                 self.maybe_lint_bare_trait(ast_ty, in_path);
                 let repr = match repr {
                     TraitObjectSyntax::Dyn | TraitObjectSyntax::None => ty::Dyn,
                     TraitObjectSyntax::DynStar => ty::DynStar,
                 };
-                self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed, repr)
+
+                let object_ty = self.conv_object_ty_poly_trait_ref(
+                    ast_ty.span,
+                    bounds,
+                    lifetime,
+                    borrowed,
+                    repr,
+                );
+
+                if let Some(guar) = bounds.iter().find_map(|trait_ref| {
+                    deny_non_region_late_bound(tcx, trait_ref.bound_generic_params, "trait object")
+                }) {
+                    tcx.ty_error_with_guaranteed(guar)
+                } else {
+                    object_ty
+                }
             }
             hir::TyKind::Path(hir::QPath::Resolved(maybe_qself, path)) => {
                 debug!(?maybe_qself, ?path);
                 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
-                self.res_to_ty(opt_self_ty, path, false)
+                self.res_to_ty(opt_self_ty, path, ast_ty.hir_id, false)
             }
             &hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
                 let opaque_ty = tcx.hir().item(item_id);
@@ -3344,3 +3382,24 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
     }
 }
+
+fn deny_non_region_late_bound(
+    tcx: TyCtxt<'_>,
+    params: &[hir::GenericParam<'_>],
+    where_: &str,
+) -> Option<ErrorGuaranteed> {
+    params.iter().find_map(|bad_param| {
+        let what = match bad_param.kind {
+            hir::GenericParamKind::Type { .. } => "type",
+            hir::GenericParamKind::Const { .. } => "const",
+            hir::GenericParamKind::Lifetime { .. } => return None,
+        };
+
+        let mut diag = tcx.sess.struct_span_err(
+            bad_param.span,
+            format!("late-bound {what} parameter not allowed on {where_} types"),
+        );
+
+        Some(if tcx.features().non_lifetime_binders { diag.emit() } else { diag.delay_as_bug() })
+    })
+}

compiler/rustc_hir_analysis/src/collect.rs

@@ -41,8 +41,8 @@ use std::iter;
 
 mod generics_of;
 mod item_bounds;
-mod lifetimes;
 mod predicates_of;
+mod resolve_bound_vars;
 mod type_of;
 
 ///////////////////////////////////////////////////////////////////////////
@@ -53,7 +53,7 @@ fn collect_mod_item_types(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 }
 
 pub fn provide(providers: &mut Providers) {
-    lifetimes::provide(providers);
+    resolve_bound_vars::provide(providers);
     *providers = Providers {
         opt_const_param_of: type_of::opt_const_param_of,
         type_of: type_of::type_of,

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -1,4 +1,4 @@
-use crate::middle::resolve_lifetime as rl;
+use crate::middle::resolve_bound_vars as rbv;
 use hir::{
     intravisit::{self, Visitor},
     GenericParamKind, HirId, Node,
@@ -394,10 +394,11 @@ fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<S
                 return;
             }
 
-            match self.tcx.named_region(lt.hir_id) {
-                Some(rl::Region::Static | rl::Region::EarlyBound(..)) => {}
-                Some(rl::Region::LateBound(debruijn, _, _)) if debruijn < self.outer_index => {}
-                Some(rl::Region::LateBound(..) | rl::Region::Free(..)) | None => {
+            match self.tcx.named_bound_var(lt.hir_id) {
+                Some(rbv::ResolvedArg::StaticLifetime | rbv::ResolvedArg::EarlyBound(..)) => {}
+                Some(rbv::ResolvedArg::LateBound(debruijn, _, _))
+                    if debruijn < self.outer_index => {}
+                Some(rbv::ResolvedArg::LateBound(..) | rbv::ResolvedArg::Free(..)) | None => {
                     self.has_late_bound_regions = Some(lt.ident.span);
                 }
             }