[WIP] mgca: Add ConstArg representation for const items

compiler/rustc_ast/src/ast.rs

@@ -3753,10 +3753,29 @@ pub struct ConstItem {
     pub ident: Ident,
     pub generics: Generics,
     pub ty: Box<Ty>,
-    pub expr: Option<Box<Expr>>,
+    pub body: Option<ConstItemRhs>,
     pub define_opaque: Option<ThinVec<(NodeId, Path)>>,
 }
 
+#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
+pub enum ConstItemRhs {
+    TypeConst(AnonConst),
+    Body(Box<Expr>),
+}
+
+impl ConstItemRhs {
+    pub fn span(&self) -> Span {
+        self.expr().span
+    }
+
+    pub fn expr(&self) -> &Expr {
+        match self {
+            ConstItemRhs::TypeConst(anon_const) => &anon_const.value,
+            ConstItemRhs::Body(expr) => expr,
+        }
+    }
+}
+
 // Adding a new variant? Please update `test_item` in `tests/ui/macros/stringify.rs`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum ItemKind {

compiler/rustc_ast/src/visit.rs

@@ -422,6 +422,7 @@ macro_rules! common_visitor_and_walkers {
             Closure,
             Const,
             ConstItem,
+            ConstItemRhs,
             Defaultness,
             Delegation,
             DelegationMac,

compiler/rustc_ast_lowering/src/item.rs

@@ -172,37 +172,41 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }
             ItemKind::Static(box ast::StaticItem {
                 ident,
-                ty: t,
+                ty,
                 safety: _,
                 mutability: m,
                 expr: e,
                 define_opaque,
             }) => {
                 let ident = self.lower_ident(*ident);
-                let (ty, body_id) =
-                    self.lower_const_item(t, span, e.as_deref(), ImplTraitPosition::StaticTy);
+                let ty =
+                    self.lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::StaticTy));
+                let body_id = self.lower_const_body(span, e.as_deref());
                 self.lower_define_opaque(hir_id, define_opaque);
                 hir::ItemKind::Static(*m, ident, ty, body_id)
             }
             ItemKind::Const(box ast::ConstItem {
                 ident,
                 generics,
                 ty,
-                expr,
+                body,
                 define_opaque,
                 ..
             }) => {
                 let ident = self.lower_ident(*ident);
-                let (generics, (ty, body_id)) = self.lower_generics(
+                let (generics, (ty, body)) = self.lower_generics(
                     generics,
                     id,
                     ImplTraitContext::Disallowed(ImplTraitPosition::Generic),
                     |this| {
-                        this.lower_const_item(ty, span, expr.as_deref(), ImplTraitPosition::ConstTy)
+                        let ty = this
+                            .lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy));
+                        let body = this.lower_const_item_rhs(attrs, body.as_ref(), span);
+                        (ty, body)
                     },
                 );
                 self.lower_define_opaque(hir_id, &define_opaque);
-                hir::ItemKind::Const(ident, generics, ty, body_id)
+                hir::ItemKind::Const(ident, generics, ty, body)
             }
             ItemKind::Fn(box Fn {
                 sig: FnSig { decl, header, span: fn_sig_span },
@@ -463,17 +467,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }
     }
 
-    fn lower_const_item(
-        &mut self,
-        ty: &Ty,
-        span: Span,
-        body: Option<&Expr>,
-        impl_trait_position: ImplTraitPosition,
-    ) -> (&'hir hir::Ty<'hir>, hir::BodyId) {
-        let ty = self.lower_ty(ty, ImplTraitContext::Disallowed(impl_trait_position));
-        (ty, self.lower_const_body(span, body))
-    }
-
     #[instrument(level = "debug", skip(self))]
     fn lower_use_tree(
         &mut self,
@@ -808,7 +801,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ident,
                 generics,
                 ty,
-                expr,
+                body,
                 define_opaque,
                 ..
             }) => {
@@ -819,14 +812,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     |this| {
                         let ty = this
                             .lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy));
-                        let body = expr.as_ref().map(|x| this.lower_const_body(i.span, Some(x)));
-
+                        let body = body
+                            .as_ref()
+                            .map(|body| this.lower_const_item_rhs(attrs, Some(body), i.span));
                         hir::TraitItemKind::Const(ty, body)
                     },
                 );
 
                 if define_opaque.is_some() {
-                    if expr.is_some() {
+                    if body.is_some() {
                         self.lower_define_opaque(hir_id, &define_opaque);
                     } else {
                         self.dcx().span_err(
@@ -836,7 +830,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     }
                 }
 
-                (*ident, generics, kind, expr.is_some())
+                (*ident, generics, kind, body.is_some())
             }
             AssocItemKind::Fn(box Fn {
                 sig, ident, generics, body: None, define_opaque, ..
@@ -1021,7 +1015,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ident,
                 generics,
                 ty,
-                expr,
+                body,
                 define_opaque,
                 ..
             }) => (
@@ -1033,8 +1027,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     |this| {
                         let ty = this
                             .lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy));
-                        let body = this.lower_const_body(i.span, expr.as_deref());
                         this.lower_define_opaque(hir_id, &define_opaque);
+                        let body = this.lower_const_item_rhs(attrs, body.as_ref(), i.span);
                         hir::ImplItemKind::Const(ty, body)
                     },
                 ),

compiler/rustc_ast_lowering/src/lib.rs

@@ -2303,6 +2303,33 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.arena.alloc(hir::ConstArg { hir_id: self.next_id(), kind: ct_kind })
     }
 
+    fn lower_const_item_rhs(
+        &mut self,
+        attrs: &[hir::Attribute],
+        rhs: Option<&ConstItemRhs>,
+        span: Span,
+    ) -> hir::ConstItemRhs<'hir> {
+        match rhs {
+            Some(ConstItemRhs::TypeConst(anon)) => {
+                hir::ConstItemRhs::TypeConst(self.lower_anon_const_to_const_arg(anon))
+            }
+            None if attr::contains_name(attrs, sym::type_const) => {
+                let const_arg = ConstArg {
+                    hir_id: self.next_id(),
+                    kind: hir::ConstArgKind::Error(
+                        DUMMY_SP,
+                        self.dcx().span_delayed_bug(DUMMY_SP, "no block"),
+                    ),
+                };
+                hir::ConstItemRhs::TypeConst(self.arena.alloc(const_arg))
+            }
+            Some(ConstItemRhs::Body(body)) => {
+                hir::ConstItemRhs::Body(self.lower_const_body(span, Some(body)))
+            }
+            None => hir::ConstItemRhs::Body(self.lower_const_body(span, None)),
+        }
+    }
+
     /// See [`hir::ConstArg`] for when to use this function vs
     /// [`Self::lower_anon_const_to_anon_const`].
     fn lower_anon_const_to_const_arg(&mut self, anon: &AnonConst) -> &'hir hir::ConstArg<'hir> {

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1236,9 +1236,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     }
                 });
             }
-            ItemKind::Const(box ConstItem { defaultness, expr, .. }) => {
+            ItemKind::Const(box ConstItem { defaultness, body, .. }) => {
                 self.check_defaultness(item.span, *defaultness);
-                if expr.is_none() {
+                if body.is_none() {
                     self.dcx().emit_err(errors::ConstWithoutBody {
                         span: item.span,
                         replace_span: self.ending_semi_or_hi(item.span),
@@ -1578,7 +1578,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 
         if let AssocCtxt::Impl { .. } = ctxt {
             match &item.kind {
-                AssocItemKind::Const(box ConstItem { expr: None, .. }) => {
+                AssocItemKind::Const(box ConstItem { body: None, .. }) => {
                     self.dcx().emit_err(errors::AssocConstWithoutBody {
                         span: item.span,
                         replace_span: self.ending_semi_or_hi(item.span),

compiler/rustc_ast_pretty/src/pprust/state/item.rs

@@ -213,15 +213,15 @@ impl<'a> State<'a> {
                 ident,
                 generics,
                 ty,
-                expr,
+                body,
                 define_opaque,
             }) => {
                 self.print_item_const(
                     *ident,
                     None,
                     generics,
                     ty,
-                    expr.as_deref(),
+                    body.as_ref().map(|ct| ct.expr()),
                     &item.vis,
                     ast::Safety::Default,
                     *defaultness,
@@ -566,15 +566,15 @@ impl<'a> State<'a> {
                 ident,
                 generics,
                 ty,
-                expr,
+                body,
                 define_opaque,
             }) => {
                 self.print_item_const(
                     *ident,
                     None,
                     generics,
                     ty,
-                    expr.as_deref(),
+                    body.as_ref().map(|ct| ct.expr()),
                     vis,
                     ast::Safety::Default,
                     *defaultness,

compiler/rustc_builtin_macros/src/alloc_error_handler.rs

@@ -43,7 +43,7 @@ pub(crate) fn expand(
 
     // Generate anonymous constant serving as container for the allocator methods.
     let const_ty = ecx.ty(sig_span, TyKind::Tup(ThinVec::new()));
-    let const_body = ecx.expr_block(ecx.block(span, stmts));
+    let const_body = ast::ConstItemRhs::Body(ecx.expr_block(ecx.block(span, stmts)));
     let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
     let const_item = if is_stmt {
         Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))

compiler/rustc_builtin_macros/src/global_allocator.rs

@@ -47,7 +47,7 @@ pub(crate) fn expand(
 
     // Generate anonymous constant serving as container for the allocator methods.
     let const_ty = ecx.ty(ty_span, TyKind::Tup(ThinVec::new()));
-    let const_body = ecx.expr_block(ecx.block(span, stmts));
+    let const_body = ast::ConstItemRhs::Body(ecx.expr_block(ecx.block(span, stmts)));
     let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
     let const_item = if is_stmt {
         Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))

compiler/rustc_builtin_macros/src/proc_macro_harness.rs

@@ -385,9 +385,9 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> Box<ast::Item> {
         cx.attr_nested_word(sym::allow, sym::deprecated, span),
     ]);
 
-    let block = cx.expr_block(
+    let block = ast::ConstItemRhs::Body(cx.expr_block(
         cx.block(span, thin_vec![cx.stmt_item(span, krate), cx.stmt_item(span, decls_static)]),
-    );
+    ));
 
     let anon_constant = cx.item_const(
         span,

compiler/rustc_builtin_macros/src/test.rs

@@ -289,7 +289,7 @@ pub(crate) fn expand_test_or_bench(
                     ty: cx.ty(sp, ast::TyKind::Path(None, test_path("TestDescAndFn"))),
                     define_opaque: None,
                     // test::TestDescAndFn {
-                    expr: Some(
+                    body: Some(ast::ConstItemRhs::Body(
                         cx.expr_struct(
                             sp,
                             test_path("TestDescAndFn"),
@@ -371,7 +371,7 @@ pub(crate) fn expand_test_or_bench(
                         field("testfn", test_fn), // }
                     ],
                         ), // }
-                    ),
+                    )),
                 }
                 .into(),
             ),

compiler/rustc_const_eval/src/check_consts/qualifs.rs

@@ -6,7 +6,9 @@
 // having basically only two use-cases that act in different ways.
 
 use rustc_errors::ErrorGuaranteed;
-use rustc_hir::LangItem;
+use rustc_hir::attrs::AttributeKind;
+use rustc_hir::def::DefKind;
+use rustc_hir::{LangItem, find_attr};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, AdtDef, Ty};
@@ -365,8 +367,14 @@ where
         // check performed after the promotion. Verify that with an assertion.
         assert!(promoted.is_none() || Q::ALLOW_PROMOTED);
 
-        // Don't peek inside trait associated constants.
-        if promoted.is_none() && cx.tcx.trait_of_assoc(def).is_none() {
+        // Avoid looking at attrs of anon consts as that will ICE
+        let is_type_const_item =
+            matches!(cx.tcx.def_kind(def), DefKind::Const | DefKind::AssocConst)
+                && find_attr!(cx.tcx.get_all_attrs(def), AttributeKind::TypeConst(_));
+
+        // Don't peak inside trait associated consatnts, also `#[type_const] const` items
+        // don't have bodies so there's nothing to look at
+        if promoted.is_none() && cx.tcx.trait_of_assoc(def).is_none() && !is_type_const_item {
             let qualifs = cx.tcx.at(constant.span).mir_const_qualif(def);
 
             if !Q::in_qualifs(&qualifs) {

compiler/rustc_expand/src/build.rs

@@ -104,6 +104,10 @@ impl<'a> ExtCtxt<'a> {
         }
     }
 
+    pub fn anon_const_block(&self, b: Box<ast::Block>) -> Box<ast::AnonConst> {
+        Box::new(self.anon_const(b.span, ast::ExprKind::Block(b, None)))
+    }
+
     pub fn const_ident(&self, span: Span, ident: Ident) -> ast::AnonConst {
         self.anon_const(span, ast::ExprKind::Path(None, self.path_ident(span, ident)))
     }
@@ -722,7 +726,7 @@ impl<'a> ExtCtxt<'a> {
         span: Span,
         ident: Ident,
         ty: Box<ast::Ty>,
-        expr: Box<ast::Expr>,
+        body: ast::ConstItemRhs,
     ) -> Box<ast::Item> {
         let defaultness = ast::Defaultness::Final;
         self.item(
@@ -735,7 +739,7 @@ impl<'a> ExtCtxt<'a> {
                     // FIXME(generic_const_items): Pass the generics as a parameter.
                     generics: ast::Generics::default(),
                     ty,
-                    expr: Some(expr),
+                    body: Some(body),
                     define_opaque: None,
                 }
                 .into(),