Auto merge of rust-lang#118641 - fee1-dead-contrib:rollup-2qlatcy, r=fee1-dead

Rollup of 8 pull requests

Successful merges:

 - rust-lang#117922 (Tweak unclosed generics errors)
 - rust-lang#117981 (Remove deprecated `--check-cfg` syntax)
 - rust-lang#118471 (Fix typos in README.md)
 - rust-lang#118488 (Change prefetch to avoid deadlock)
 - rust-lang#118605 (Remove `#[rustc_host]`, use internal desugaring)
 - rust-lang#118608 (Use default params until effects in desugaring)
 - rust-lang#118614 (Update books)
 - rust-lang#118637 (rustc_symbol_mangling,rustc_interface,rustc_driver_impl: Enforce `rustc::potential_query_instability` lint)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

README.md

@@ -12,7 +12,7 @@ If you wish to _contribute_ to the compiler, you should read
 [CONTRIBUTING.md](CONTRIBUTING.md) instead.
 
 <details>
-<summary>Table of content</summary>
+<summary>Table of Contents</summary>
 
 - [Quick Start](#quick-start)
 - [Installing from Source](#installing-from-source)

compiler/rustc_ast_lowering/src/item.rs

@@ -561,11 +561,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     .params
                     .iter()
                     .find(|param| {
-                        parent_hir
-                            .attrs
-                            .get(param.hir_id.local_id)
-                            .iter()
-                            .any(|attr| attr.has_name(sym::rustc_host))
+                        matches!(
+                            param.kind,
+                            hir::GenericParamKind::Const { is_host_effect: true, .. }
+                        )
                     })
                     .map(|param| param.def_id);
             }
@@ -1352,27 +1351,17 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let host_param_parts = if let Const::Yes(span) = constness
             && self.tcx.features().effects
         {
-            if let Some(param) =
-                generics.params.iter().find(|x| x.attrs.iter().any(|x| x.has_name(sym::rustc_host)))
-            {
-                // user has manually specified a `rustc_host` param, in this case, we set
-                // the param id so that lowering logic can use that. But we don't create
-                // another host param, so this gives `None`.
-                self.host_param_id = Some(self.local_def_id(param.id));
-                None
-            } else {
-                let param_node_id = self.next_node_id();
-                let hir_id = self.next_id();
-                let def_id = self.create_def(
-                    self.local_def_id(parent_node_id),
-                    param_node_id,
-                    sym::host,
-                    DefKind::ConstParam,
-                    span,
-                );
-                self.host_param_id = Some(def_id);
-                Some((span, hir_id, def_id))
-            }
+            let param_node_id = self.next_node_id();
+            let hir_id = self.next_id();
+            let def_id = self.create_def(
+                self.local_def_id(parent_node_id),
+                param_node_id,
+                sym::host,
+                DefKind::ConstParam,
+                span,
+            );
+            self.host_param_id = Some(def_id);
+            Some((span, hir_id, def_id))
         } else {
             None
         };
@@ -1436,19 +1425,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
             self.children.push((def_id, hir::MaybeOwner::NonOwner(hir_id)));
             self.children.push((anon_const, hir::MaybeOwner::NonOwner(const_id)));
 
-            let attr_id = self.tcx.sess.parse_sess.attr_id_generator.mk_attr_id();
-
-            let attrs = self.arena.alloc_from_iter([Attribute {
-                kind: AttrKind::Normal(P(NormalAttr::from_ident(Ident::new(
-                    sym::rustc_host,
-                    span,
-                )))),
-                span,
-                id: attr_id,
-                style: AttrStyle::Outer,
-            }]);
-            self.attrs.insert(hir_id.local_id, attrs);
-
             let const_body = self.lower_body(|this| {
                 (
                     &[],
@@ -1490,6 +1466,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         hir_id: const_id,
                         body: const_body,
                     }),
+                    is_host_effect: true,
                 },
                 colon_span: None,
                 pure_wrt_drop: false,

compiler/rustc_ast_lowering/src/lib.rs

@@ -2108,7 +2108,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 let default = default.as_ref().map(|def| self.lower_anon_const(def));
                 (
                     hir::ParamName::Plain(self.lower_ident(param.ident)),
-                    hir::GenericParamKind::Const { ty, default },
+                    hir::GenericParamKind::Const { ty, default, is_host_effect: false },
                 )
             }
         }
@@ -2536,22 +2536,14 @@ impl<'hir> GenericArgsCtor<'hir> {
             })
         });
 
-        let attr_id = lcx.tcx.sess.parse_sess.attr_id_generator.mk_attr_id();
-        let attr = lcx.arena.alloc(Attribute {
-            kind: AttrKind::Normal(P(NormalAttr::from_ident(Ident::new(sym::rustc_host, span)))),
-            span,
-            id: attr_id,
-            style: AttrStyle::Outer,
-        });
-        lcx.attrs.insert(hir_id.local_id, std::slice::from_ref(attr));
-
         let def_id = lcx.create_def(
             lcx.current_hir_id_owner.def_id,
             id,
             kw::Empty,
             DefKind::AnonConst,
             span,
         );
+
         lcx.children.push((def_id, hir::MaybeOwner::NonOwner(hir_id)));
         self.args.push(hir::GenericArg::Const(hir::ConstArg {
             value: hir::AnonConst { def_id, hir_id, body },

compiler/rustc_driver_impl/src/lib.rs

@@ -13,7 +13,6 @@
 #![feature(let_chains)]
 #![feature(panic_update_hook)]
 #![recursion_limit = "256"]
-#![allow(rustc::potential_query_instability)]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
 

compiler/rustc_feature/src/builtin_attrs.rs

@@ -719,12 +719,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         and it is only intended to be used in `alloc`."
     ),
 
-    rustc_attr!(
-        rustc_host, AttributeType::Normal, template!(Word), ErrorFollowing,
-        "#[rustc_host] annotates const generic parameters as the `host` effect param, \
-        and it is only intended for internal use and as a desugaring."
-    ),
-
     BuiltinAttribute {
         name: sym::rustc_diagnostic_item,
         // FIXME: This can be `true` once we always use `tcx.is_diagnostic_item`.

compiler/rustc_hir/src/hir.rs

@@ -487,6 +487,7 @@ pub enum GenericParamKind<'hir> {
         ty: &'hir Ty<'hir>,
         /// Optional default value for the const generic param
         default: Option<AnonConst>,
+        is_host_effect: bool,
     },
 }
 

compiler/rustc_hir/src/intravisit.rs

@@ -874,7 +874,7 @@ pub fn walk_generic_param<'v, V: Visitor<'v>>(visitor: &mut V, param: &'v Generi
     match param.kind {
         GenericParamKind::Lifetime { .. } => {}
         GenericParamKind::Type { ref default, .. } => walk_list!(visitor, visit_ty, default),
-        GenericParamKind::Const { ref ty, ref default } => {
+        GenericParamKind::Const { ref ty, ref default, is_host_effect: _ } => {
             visitor.visit_ty(ty);
             if let Some(ref default) = default {
                 visitor.visit_const_param_default(param.hir_id, default);

compiler/rustc_hir_analysis/src/astconv/generics.rs

@@ -243,6 +243,31 @@ pub fn create_args_for_parent_generic_args<'tcx, 'a>(
             match (args_iter.peek(), params.peek()) {
                 (Some(&arg), Some(&param)) => {
                     match (arg, &param.kind, arg_count.explicit_late_bound) {
+                        (
+                            GenericArg::Const(hir::ConstArg {
+                                is_desugared_from_effects: true,
+                                ..
+                            }),
+                            GenericParamDefKind::Const { is_host_effect: false, .. }
+                            | GenericParamDefKind::Type { .. }
+                            | GenericParamDefKind::Lifetime,
+                            _,
+                        ) => {
+                            // SPECIAL CASE FOR DESUGARED EFFECT PARAMS
+                            // This comes from the following example:
+                            //
+                            // ```
+                            // #[const_trait]
+                            // pub trait PartialEq<Rhs: ?Sized = Self> {}
+                            // impl const PartialEq for () {}
+                            // ```
+                            //
+                            // Since this is a const impl, we need to insert `<false>` at the end of
+                            // `PartialEq`'s generics, but this errors since `Rhs` isn't specified.
+                            // To work around this, we infer all arguments until we reach the host param.
+                            args.push(ctx.inferred_kind(Some(&args), param, infer_args));
+                            params.next();
+                        }
                         (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime, _)
                         | (
                             GenericArg::Type(_) | GenericArg::Infer(_),

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -859,7 +859,7 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) -> Result<(),
         hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => Ok(()),
 
         // Const parameters are well formed if their type is structural match.
-        hir::GenericParamKind::Const { ty: hir_ty, default: _ } => {
+        hir::GenericParamKind::Const { ty: hir_ty, default: _, is_host_effect: _ } => {
             let ty = tcx.type_of(param.def_id).instantiate_identity();
 
             if tcx.features().adt_const_params {

compiler/rustc_hir_analysis/src/collect.rs

@@ -1383,7 +1383,7 @@ fn impl_trait_ref(
                 let last_segment = path_segments.len() - 1;
                 let mut args = *path_segments[last_segment].args();
                 let last_arg = args.args.len() - 1;
-                assert!(matches!(args.args[last_arg], hir::GenericArg::Const(anon_const) if tcx.has_attr(anon_const.value.def_id, sym::rustc_host)));
+                assert!(matches!(args.args[last_arg], hir::GenericArg::Const(anon_const) if anon_const.is_desugared_from_effects));
                 args.args = &args.args[..args.args.len() - 1];
                 path_segments[last_segment].args = Some(&args);
                 let path = hir::Path {