Parse generic consts

Author: fmease

compiler/rustc_ast/src/ast.rs

@@ -2942,6 +2942,7 @@ pub struct StaticItem {
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct ConstItem {
     pub defaultness: Defaultness,
+    pub generics: Generics,
     pub ty: P<Ty>,
     pub expr: Option<P<Expr>>,
 }
@@ -3053,6 +3054,7 @@ impl ItemKind {
         match self {
             Self::Fn(box Fn { generics, .. })
             | Self::TyAlias(box TyAlias { generics, .. })
+            | Self::Const(box ConstItem { generics, .. })
             | Self::Enum(_, generics)
             | Self::Struct(_, generics)
             | Self::Union(_, generics)

compiler/rustc_ast/src/mut_visit.rs

@@ -1149,10 +1149,11 @@ pub fn noop_flat_map_assoc_item<T: MutVisitor>(
 }
 
 fn visit_const_item<T: MutVisitor>(
-    ConstItem { defaultness, ty, expr }: &mut ConstItem,
+    ConstItem { defaultness, generics, ty, expr }: &mut ConstItem,
     visitor: &mut T,
 ) {
     visit_defaultness(defaultness, visitor);
+    visitor.visit_generics(generics);
     visitor.visit_ty(ty);
     visit_opt(expr, |expr| visitor.visit_expr(expr));
 }

compiler/rustc_ast/src/visit.rs

@@ -308,8 +308,12 @@ pub fn walk_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a Item) {
     match &item.kind {
         ItemKind::ExternCrate(_) => {}
         ItemKind::Use(use_tree) => visitor.visit_use_tree(use_tree, item.id, false),
-        ItemKind::Static(box StaticItem { ty, mutability: _, expr })
-        | ItemKind::Const(box ConstItem { ty, expr, .. }) => {
+        ItemKind::Static(box StaticItem { ty, mutability: _, expr }) => {
+            visitor.visit_ty(ty);
+            walk_list!(visitor, visit_expr, expr);
+        }
+        ItemKind::Const(box ConstItem { generics, ty, expr, .. }) => {
+            visitor.visit_generics(generics);
             visitor.visit_ty(ty);
             walk_list!(visitor, visit_expr, expr);
         }
@@ -677,7 +681,8 @@ pub fn walk_assoc_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a AssocItem,
     visitor.visit_ident(ident);
     walk_list!(visitor, visit_attribute, attrs);
     match kind {
-        AssocItemKind::Const(box ConstItem { ty, expr, .. }) => {
+        AssocItemKind::Const(box ConstItem { generics, ty, expr, .. }) => {
+            visitor.visit_generics(generics);
             visitor.visit_ty(ty);
             walk_list!(visitor, visit_expr, expr);
         }

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1338,6 +1338,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             self.check_item_named(item.ident, "const");
         }
 
+        // FIXME(generic_consts): Pretty sure we need to visit the generics of consts here, too.
         match &item.kind {
             AssocItemKind::Type(box TyAlias { generics, bounds, ty, .. })
                 if ctxt == AssocCtxt::Trait =>

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -556,6 +556,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
     gate_all!(const_closures, "const closures are experimental");
     gate_all!(builtin_syntax, "`builtin #` syntax is unstable");
     gate_all!(explicit_tail_calls, "`become` expression is experimental");
+    gate_all!(generic_consts, "generic consts are experimental");
 
     if !visitor.features.negative_bounds {
         for &span in spans.get(&sym::negative_bounds).iter().copied().flatten() {

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

@@ -32,7 +32,7 @@ impl<'a> State<'a> {
             }
             ast::ForeignItemKind::Static(ty, mutbl, body) => {
                 let def = ast::Defaultness::Final;
-                self.print_item_const(ident, Some(*mutbl), ty, body.as_deref(), vis, def);
+                self.print_item_const(ident, Some(*mutbl), None, ty, body.as_deref(), vis, def);
             }
             ast::ForeignItemKind::TyAlias(box ast::TyAlias {
                 defaultness,
@@ -67,6 +67,7 @@ impl<'a> State<'a> {
         &mut self,
         ident: Ident,
         mutbl: Option<ast::Mutability>,
+        generics: Option<&ast::Generics>,
         ty: &ast::Ty,
         body: Option<&ast::Expr>,
         vis: &ast::Visibility,
@@ -82,6 +83,9 @@ impl<'a> State<'a> {
         };
         self.word_space(leading);
         self.print_ident(ident);
+        if let Some(generics) = generics {
+            self.print_generic_params(&generics.params);
+        }
         self.word_space(":");
         self.print_type(ty);
         if body.is_some() {
@@ -92,6 +96,9 @@ impl<'a> State<'a> {
             self.word_space("=");
             self.print_expr(body);
         }
+        if let Some(generics) = generics {
+            self.print_where_clause(&generics.where_clause);
+        }
         self.word(";");
         self.end(); // end the outer cbox
     }
@@ -162,16 +169,18 @@ impl<'a> State<'a> {
                 self.print_item_const(
                     item.ident,
                     Some(*mutbl),
+                    None,
                     ty,
                     body.as_deref(),
                     &item.vis,
                     def,
                 );
             }
-            ast::ItemKind::Const(box ast::ConstItem { defaultness, ty, expr }) => {
+            ast::ItemKind::Const(box ast::ConstItem { defaultness, generics, ty, expr }) => {
                 self.print_item_const(
                     item.ident,
                     None,
+                    Some(generics),
                     ty,
                     expr.as_deref(),
                     &item.vis,
@@ -515,8 +524,16 @@ impl<'a> State<'a> {
             ast::AssocItemKind::Fn(box ast::Fn { defaultness, sig, generics, body }) => {
                 self.print_fn_full(sig, ident, generics, vis, *defaultness, body.as_deref(), attrs);
             }
-            ast::AssocItemKind::Const(box ast::ConstItem { defaultness, ty, expr }) => {
-                self.print_item_const(ident, None, ty, expr.as_deref(), vis, *defaultness);
+            ast::AssocItemKind::Const(box ast::ConstItem { defaultness, generics, ty, expr }) => {
+                self.print_item_const(
+                    ident,
+                    None,
+                    Some(generics),
+                    ty,
+                    expr.as_deref(),
+                    vis,
+                    *defaultness,
+                );
             }
             ast::AssocItemKind::Type(box ast::TyAlias {
                 defaultness,

compiler/rustc_builtin_macros/src/test.rs

@@ -255,6 +255,7 @@ pub fn expand_test_or_bench(
             ast::ItemKind::Const(
                 ast::ConstItem {
                     defaultness: ast::Defaultness::Final,
+                    generics: ast::Generics::default(),
                     ty: cx.ty(sp, ast::TyKind::Path(None, test_path("TestDescAndFn"))),
                     // test::TestDescAndFn {
                     expr: Some(

compiler/rustc_expand/src/build.rs

@@ -643,7 +643,16 @@ impl<'a> ExtCtxt<'a> {
             span,
             name,
             AttrVec::new(),
-            ast::ItemKind::Const(ast::ConstItem { defaultness, ty, expr: Some(expr) }.into()),
+            ast::ItemKind::Const(
+                ast::ConstItem {
+                    defaultness,
+                    // FIXME(generic_consts): Pass the generics as a parameter.
+                    generics: ast::Generics::default(),
+                    ty,
+                    expr: Some(expr),
+                }
+                .into(),
+            ),
         )
     }
 

compiler/rustc_feature/src/active.rs

@@ -422,6 +422,8 @@ declare_features! (
     (incomplete, generic_associated_types_extended, "1.61.0", Some(95451), None),
     /// Allows non-trivial generic constants which have to have wfness manually propagated to callers
     (incomplete, generic_const_exprs, "1.56.0", Some(76560), None),
+    /// Allows generic parameters and where-clauses on free & associated const items.
+    (incomplete, generic_consts, "CURRENT_RUSTC_VERSION", Some(113521), None),
     /// Allows using `..=X` as a patterns in slices.
     (active, half_open_range_patterns_in_slices, "1.66.0", Some(67264), None),
     /// Allows `if let` guard in match arms.

compiler/rustc_parse/messages.ftl

@@ -690,6 +690,10 @@ parse_single_colon_import_path = expected `::`, found `:`
 parse_single_colon_struct_type = found single colon in a struct field type path
     .suggestion = write a path separator here
 
+parse_static_with_generics = static items may not have generic parameters
+
+parse_static_with_where_clause = static items may not have a where clause
+
 parse_struct_literal_body_without_path =
     struct literal body without path
     .suggestion = you might have forgotten to add the struct literal inside the block
@@ -847,6 +851,12 @@ parse_visibility_not_followed_by_item = visibility `{$vis}` is not followed by a
     .label = the visibility
     .help = you likely meant to define an item, e.g., `{$vis} fn foo() {"{}"}`
 
+parse_where_clause_before_const_body = where clauses are not allowed before const item bodies
+    .label = unexpected where clause
+    .name_label = while parsing this const item
+    .body_label = the item body
+    .suggestion = move the body before the where clause
+
 parse_where_clause_before_tuple_struct_body = where clauses are not allowed before tuple struct bodies
     .label = unexpected where clause
     .name_label = while parsing this tuple struct

compiler/rustc_parse/src/errors.rs

@@ -2692,3 +2692,41 @@ pub(crate) struct ExpectedBuiltinIdent {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(parse_static_with_generics)]
+pub(crate) struct StaticWithGenerics {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_static_with_where_clause)]
+pub(crate) struct StaticWithWhereClause {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_where_clause_before_const_body)]
+pub(crate) struct WhereClauseBeforeConstBody {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[label(parse_name_label)]
+    pub name: Span,
+    #[label(parse_body_label)]
+    pub body: Span,
+    #[subdiagnostic]
+    pub sugg: Option<WhereClauseBeforeConstBodySugg>,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parse_suggestion, applicability = "machine-applicable")]
+pub(crate) struct WhereClauseBeforeConstBodySugg {
+    #[suggestion_part(code = "= {snippet} ")]
+    pub left: Span,
+    pub snippet: String,
+    #[suggestion_part(code = "")]
+    pub right: Span,
+}