Auto merge of rust-lang#98279 - cjgillot:all-fresh-nofn, r=petrochenkov

Create elided lifetime parameters for function-like types

Split from rust-lang#97720

This PR refactor lifetime generic parameters in bare function types and parenthesized traits to introduce the additional required lifetimes as fresh parameters in a `for<>` bound.

This PR does the same to lifetimes appearing in closure signatures, and as-if introducing `for<>` bounds on closures (without the associated change in semantics).

r? `@petrochenkov`

Author: bors

compiler/rustc_ast_lowering/src/expr.rs

@@ -165,6 +165,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     if let Async::Yes { closure_id, .. } = asyncness {
                         self.lower_expr_async_closure(
                             capture_clause,
+                            e.id,
                             closure_id,
                             decl,
                             body,
@@ -173,6 +174,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     } else {
                         self.lower_expr_closure(
                             capture_clause,
+                            e.id,
                             movability,
                             decl,
                             body,
@@ -604,6 +606,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // `static |_task_context| -> <ret_ty> { body }`:
         let generator_kind = hir::ExprKind::Closure {
             capture_clause,
+            bound_generic_params: &[],
             fn_decl,
             body,
             fn_decl_span: self.lower_span(span),
@@ -828,6 +831,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_expr_closure(
         &mut self,
         capture_clause: CaptureBy,
+        closure_id: NodeId,
         movability: Movability,
         decl: &FnDecl,
         body: &Expr,
@@ -848,16 +852,19 @@ impl<'hir> LoweringContext<'_, 'hir> {
             (body_id, generator_option)
         });
 
-        // Lower outside new scope to preserve `is_in_loop_condition`.
-        let fn_decl = self.lower_fn_decl(decl, None, FnDeclKind::Closure, None);
-
-        hir::ExprKind::Closure {
-            capture_clause,
-            fn_decl,
-            body,
-            fn_decl_span: self.lower_span(fn_decl_span),
-            movability: generator_option,
-        }
+        self.with_lifetime_binder(closure_id, &[], |this, bound_generic_params| {
+            // Lower outside new scope to preserve `is_in_loop_condition`.
+            let fn_decl = this.lower_fn_decl(decl, None, FnDeclKind::Closure, None);
+
+            hir::ExprKind::Closure {
+                capture_clause,
+                bound_generic_params,
+                fn_decl,
+                body,
+                fn_decl_span: this.lower_span(fn_decl_span),
+                movability: generator_option,
+            }
+        })
     }
 
     fn generator_movability_for_fn(
@@ -897,6 +904,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         &mut self,
         capture_clause: CaptureBy,
         closure_id: NodeId,
+        inner_closure_id: NodeId,
         decl: &FnDecl,
         body: &Expr,
         fn_decl_span: Span,
@@ -927,7 +935,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     if let FnRetTy::Ty(ty) = &decl.output { Some(ty.clone()) } else { None };
                 let async_body = this.make_async_expr(
                     capture_clause,
-                    closure_id,
+                    inner_closure_id,
                     async_ret_ty,
                     body.span,
                     hir::AsyncGeneratorKind::Closure,
@@ -938,18 +946,21 @@ impl<'hir> LoweringContext<'_, 'hir> {
             body_id
         });
 
-        // We need to lower the declaration outside the new scope, because we
-        // have to conserve the state of being inside a loop condition for the
-        // closure argument types.
-        let fn_decl = self.lower_fn_decl(&outer_decl, None, FnDeclKind::Closure, None);
-
-        hir::ExprKind::Closure {
-            capture_clause,
-            fn_decl,
-            body,
-            fn_decl_span: self.lower_span(fn_decl_span),
-            movability: None,
-        }
+        self.with_lifetime_binder(closure_id, &[], |this, bound_generic_params| {
+            // We need to lower the declaration outside the new scope, because we
+            // have to conserve the state of being inside a loop condition for the
+            // closure argument types.
+            let fn_decl = this.lower_fn_decl(&outer_decl, None, FnDeclKind::Closure, None);
+
+            hir::ExprKind::Closure {
+                capture_clause,
+                bound_generic_params,
+                fn_decl,
+                body,
+                fn_decl_span: this.lower_span(fn_decl_span),
+                movability: None,
+            }
+        })
     }
 
     /// Destructure the LHS of complex assignments.

compiler/rustc_ast_lowering/src/item.rs

@@ -1386,16 +1386,19 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
         let mut params: SmallVec<[hir::GenericParam<'hir>; 4]> =
             self.lower_generic_params_mut(&generics.params).collect();
+
+        // Introduce extra lifetimes if late resolution tells us to.
+        let extra_lifetimes = self.resolver.take_extra_lifetime_params(parent_node_id);
+        params.extend(extra_lifetimes.into_iter().filter_map(|(ident, node_id, res)| {
+            self.lifetime_res_to_generic_param(ident, node_id, res)
+        }));
+
         let has_where_clause_predicates = !generics.where_clause.predicates.is_empty();
         let where_clause_span = self.lower_span(generics.where_clause.span);
         let span = self.lower_span(generics.span);
         let res = f(self);
 
-        let extra_lifetimes = self.resolver.take_extra_lifetime_params(parent_node_id);
         let impl_trait_defs = std::mem::take(&mut self.impl_trait_defs);
-        params.extend(extra_lifetimes.into_iter().filter_map(|(ident, node_id, res)| {
-            self.lifetime_res_to_generic_param(ident, node_id, res)
-        }));
         params.extend(impl_trait_defs.into_iter());
 
         let impl_trait_bounds = std::mem::take(&mut self.impl_trait_bounds);

compiler/rustc_ast_lowering/src/lib.rs

@@ -223,6 +223,12 @@ impl ResolverAstLoweringExt for ResolverAstLowering {
     }
 
     /// Obtain the list of lifetimes parameters to add to an item.
+    ///
+    /// Extra lifetime parameters should only be added in places that can appear
+    /// as a `binder` in `LifetimeRes`.
+    ///
+    /// The extra lifetimes that appear from the parenthesized `Fn`-trait desugaring
+    /// should appear at the enclosing `PolyTraitRef`.
     fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
         self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
     }
@@ -721,6 +727,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     }
 
     /// Converts a lifetime into a new generic parameter.
+    #[tracing::instrument(level = "debug", skip(self))]
     fn lifetime_res_to_generic_param(
         &mut self,
         ident: Ident,
@@ -731,7 +738,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             LifetimeRes::Param { .. } => {
                 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
             }
-            LifetimeRes::Fresh { .. } => (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided),
+            LifetimeRes::Fresh { param, .. } => {
+                // Late resolution delegates to us the creation of the `LocalDefId`.
+                let _def_id = self.create_def(
+                    self.current_hir_id_owner,
+                    param,
+                    DefPathData::LifetimeNs(kw::UnderscoreLifetime),
+                );
+                debug!(?_def_id);
+
+                (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
+            }
             LifetimeRes::Static | LifetimeRes::Error => return None,
             res => panic!(
                 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
@@ -777,11 +794,25 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     /// Register a binder to be ignored for lifetime capture.
     #[tracing::instrument(level = "debug", skip(self, f))]
     #[inline]
-    fn with_lifetime_binder<T>(&mut self, binder: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
+    fn with_lifetime_binder<T>(
+        &mut self,
+        binder: NodeId,
+        generic_params: &[GenericParam],
+        f: impl FnOnce(&mut Self, &'hir [hir::GenericParam<'hir>]) -> T,
+    ) -> T {
+        let mut generic_params: Vec<_> = self.lower_generic_params_mut(generic_params).collect();
+        let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
+        debug!(?extra_lifetimes);
+        generic_params.extend(extra_lifetimes.into_iter().filter_map(|(ident, node_id, res)| {
+            self.lifetime_res_to_generic_param(ident, node_id, res)
+        }));
+        let generic_params = self.arena.alloc_from_iter(generic_params);
+        debug!(?generic_params);
+
         if let Some(ctxt) = &mut self.captured_lifetimes {
             ctxt.binders_to_ignore.insert(binder);
         }
-        let ret = f(self);
+        let ret = f(self, generic_params);
         if let Some(ctxt) = &mut self.captured_lifetimes {
             ctxt.binders_to_ignore.remove(&binder);
         }
@@ -1178,15 +1209,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 let lifetime = self.lower_lifetime(&region);
                 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
             }
-            TyKind::BareFn(ref f) => self.with_lifetime_binder(t.id, |this| {
-                hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
-                    generic_params: this.lower_generic_params(&f.generic_params),
-                    unsafety: this.lower_unsafety(f.unsafety),
-                    abi: this.lower_extern(f.ext),
-                    decl: this.lower_fn_decl(&f.decl, None, FnDeclKind::Pointer, None),
-                    param_names: this.lower_fn_params_to_names(&f.decl),
-                }))
-            }),
+            TyKind::BareFn(ref f) => {
+                self.with_lifetime_binder(t.id, &f.generic_params, |this, generic_params| {
+                    hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
+                        generic_params,
+                        unsafety: this.lower_unsafety(f.unsafety),
+                        abi: this.lower_extern(f.ext),
+                        decl: this.lower_fn_decl(&f.decl, None, FnDeclKind::Pointer, None),
+                        param_names: this.lower_fn_params_to_names(&f.decl),
+                    }))
+                })
+            }
             TyKind::Never => hir::TyKind::Never,
             TyKind::Tup(ref tys) => hir::TyKind::Tup(
                 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
@@ -1814,8 +1847,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 }
                 hir::LifetimeName::Param(param, p_name)
             }
-            LifetimeRes::Fresh { mut param, binder } => {
+            LifetimeRes::Fresh { param, binder } => {
                 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
+                let mut param = self.local_def_id(param);
                 if let Some(mut captured_lifetimes) = self.captured_lifetimes.take() {
                     if !captured_lifetimes.binders_to_ignore.contains(&binder) {
                         match captured_lifetimes.captures.entry(param) {
@@ -1952,13 +1986,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         p: &PolyTraitRef,
         itctx: ImplTraitContext,
     ) -> hir::PolyTraitRef<'hir> {
-        let bound_generic_params = self.lower_generic_params(&p.bound_generic_params);
-
-        let trait_ref = self.with_lifetime_binder(p.trait_ref.ref_id, |this| {
-            this.lower_trait_ref(&p.trait_ref, itctx)
-        });
-
-        hir::PolyTraitRef { bound_generic_params, trait_ref, span: self.lower_span(p.span) }
+        self.with_lifetime_binder(
+            p.trait_ref.ref_id,
+            &p.bound_generic_params,
+            |this, bound_generic_params| {
+                let trait_ref = this.lower_trait_ref(&p.trait_ref, itctx);
+                hir::PolyTraitRef { bound_generic_params, trait_ref, span: this.lower_span(p.span) }
+            },
+        )
     }
 
     fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext) -> hir::MutTy<'hir> {

compiler/rustc_ast_lowering/src/path.rs

@@ -191,9 +191,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
                 }
                 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
-                    ParenthesizedGenericArgs::Ok => {
-                        self.lower_parenthesized_parameter_data(segment.id, data)
-                    }
+                    ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
                     ParenthesizedGenericArgs::Err => {
                         let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
                         err.span_label(data.span, "only `Fn` traits may use parentheses");
@@ -351,39 +349,34 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
     fn lower_parenthesized_parameter_data(
         &mut self,
-        id: NodeId,
         data: &ParenthesizedArgs,
     ) -> (GenericArgsCtor<'hir>, bool) {
         // Switch to `PassThrough` mode for anonymous lifetimes; this
         // means that we permit things like `&Ref<T>`, where `Ref` has
         // a hidden lifetime parameter. This is needed for backwards
         // compatibility, even in contexts like an impl header where
         // we generally don't permit such things (see #51008).
-        self.with_lifetime_binder(id, |this| {
-            let ParenthesizedArgs { span, inputs, inputs_span, output } = data;
-            let inputs = this.arena.alloc_from_iter(inputs.iter().map(|ty| {
-                this.lower_ty_direct(
-                    ty,
-                    ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitParam),
-                )
-            }));
-            let output_ty = match output {
-                FnRetTy::Ty(ty) => this
-                    .lower_ty(&ty, ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitReturn)),
-                FnRetTy::Default(_) => this.arena.alloc(this.ty_tup(*span, &[])),
-            };
-            let args = smallvec![GenericArg::Type(this.ty_tup(*inputs_span, inputs))];
-            let binding = this.output_ty_binding(output_ty.span, output_ty);
-            (
-                GenericArgsCtor {
-                    args,
-                    bindings: arena_vec![this; binding],
-                    parenthesized: true,
-                    span: data.inputs_span,
-                },
-                false,
-            )
-        })
+        let ParenthesizedArgs { span, inputs, inputs_span, output } = data;
+        let inputs = self.arena.alloc_from_iter(inputs.iter().map(|ty| {
+            self.lower_ty_direct(ty, ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitParam))
+        }));
+        let output_ty = match output {
+            FnRetTy::Ty(ty) => {
+                self.lower_ty(&ty, ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitReturn))
+            }
+            FnRetTy::Default(_) => self.arena.alloc(self.ty_tup(*span, &[])),
+        };
+        let args = smallvec![GenericArg::Type(self.ty_tup(*inputs_span, inputs))];
+        let binding = self.output_ty_binding(output_ty.span, output_ty);
+        (
+            GenericArgsCtor {
+                args,
+                bindings: arena_vec![self; binding],
+                parenthesized: true,
+                span: data.inputs_span,
+            },
+            false,
+        )
     }
 
     /// An associated type binding `Output = $ty`.

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -254,6 +254,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
     /// *user* has a name for. In that case, we'll be able to map
     /// `fr` to a `Region<'tcx>`, and that region will be one of
     /// named variants.
+    #[tracing::instrument(level = "trace", skip(self))]
     fn give_name_from_error_region(&self, fr: RegionVid) -> Option<RegionName> {
         let error_region = self.to_error_region(fr)?;
 
@@ -290,7 +291,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                     if free_region.bound_region.is_named() {
                         // A named region that is actually named.
                         Some(RegionName { name, source: RegionNameSource::NamedFreeRegion(span) })
-                    } else {
+                    } else if let hir::IsAsync::Async = tcx.asyncness(self.mir_hir_id().owner) {
                         // If we spuriously thought that the region is named, we should let the
                         // system generate a true name for error messages. Currently this can
                         // happen if we have an elided name in an async fn for example: the
@@ -301,6 +302,8 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                             name,
                             source: RegionNameSource::AnonRegionFromAsyncFn(span),
                         })
+                    } else {
+                        None
                     }
                 }
 
@@ -362,6 +365,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
     ///  | fn foo(x: &u32) { .. }
     ///           ------- fully elaborated type of `x` is `&'1 u32`
     /// ```
+    #[tracing::instrument(level = "trace", skip(self))]
     fn give_name_if_anonymous_region_appears_in_arguments(
         &self,
         fr: RegionVid,
@@ -651,6 +655,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
     ///  | let x = Some(&22);
     ///        - fully elaborated type of `x` is `Option<&'1 u32>`
     /// ```
+    #[tracing::instrument(level = "trace", skip(self))]
     fn give_name_if_anonymous_region_appears_in_upvars(&self, fr: RegionVid) -> Option<RegionName> {
         let upvar_index = self.regioncx.get_upvar_index_for_region(self.infcx.tcx, fr)?;
         let (upvar_name, upvar_span) = self.regioncx.get_upvar_name_and_span_for_region(
@@ -670,6 +675,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
     /// must be a closure since, in a free fn, such an argument would
     /// have to either also appear in an argument (if using elision)
     /// or be early bound (named, not in argument).
+    #[tracing::instrument(level = "trace", skip(self))]
     fn give_name_if_anonymous_region_appears_in_output(&self, fr: RegionVid) -> Option<RegionName> {
         let tcx = self.infcx.tcx;
         let hir = tcx.hir();
@@ -801,6 +807,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
         }
     }
 
+    #[tracing::instrument(level = "trace", skip(self))]
     fn give_name_if_anonymous_region_appears_in_yield_ty(
         &self,
         fr: RegionVid,