Rollup merge of #107489 - compiler-errors:non_lifetime_binders, r=cjgillot

Implement partial support for non-lifetime binders

This implements support for non-lifetime binders. It's pretty useless currently, but I wanted to put this up so the implementation can be discussed.

Specifically, this piggybacks off of the late-bound lifetime collection code in `rustc_hir_typeck::collect::lifetimes`. This seems like a necessary step given the fact we don't resolve late-bound regions until this point, and binders are sometimes merged.

Q: I'm not sure if I should go along this route, or try to modify the earlier nameres code to compute the right bound var indices for type and const binders eagerly... If so, I'll need to rename all these queries to something more appropriate (I've done this for `resolve_lifetime::Region` -> `resolve_lifetime::ResolvedArg`)

cc rust-lang/types-team#81

r? `@ghost`

Author: matthiaskrgr

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_re_late_bound(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_re_early_bound(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_re_free(scope, ty::BrNamed(id, name))
 
@@ -1607,7 +1607,7 @@ 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(|| {
@@ -2600,6 +2600,7 @@ 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();
@@ -2663,11 +2664,25 @@ 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.
@@ -2870,27 +2885,50 @@ 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);
@@ -3346,3 +3384,24 @@ 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);
                 }
             }