Various changes to name resolution of anon consts

compiler/rustc_ast/src/ast.rs

@@ -120,6 +120,12 @@ impl Path {
     pub fn is_global(&self) -> bool {
         !self.segments.is_empty() && self.segments[0].ident.name == kw::PathRoot
     }
+
+    /// If this path is a single identifier with no arguments, does not ensure
+    /// that the path resolves to a const param, the caller should check this.
+    pub fn is_potential_trivial_const_arg(&self) -> bool {
+        self.segments.len() == 1 && self.segments[0].args.is_none()
+    }
 }
 
 /// A segment of a path: an identifier, an optional lifetime, and a set of types.
@@ -1154,7 +1160,9 @@ impl Expr {
     ///
     /// If this is not the case, name resolution does not resolve `N` when using
     /// `min_const_generics` as more complex expressions are not supported.
-    pub fn is_potential_trivial_const_param(&self) -> bool {
+    ///
+    /// Does not ensure that the path resolves to a const param, the caller should check this.
+    pub fn is_potential_trivial_const_arg(&self) -> bool {
         let this = if let ExprKind::Block(block, None) = &self.kind
             && block.stmts.len() == 1
             && let StmtKind::Expr(expr) = &block.stmts[0].kind
@@ -1165,8 +1173,7 @@ impl Expr {
         };
 
         if let ExprKind::Path(None, path) = &this.kind
-            && path.segments.len() == 1
-            && path.segments[0].args.is_none()
+            && path.is_potential_trivial_const_arg()
         {
             true
         } else {

compiler/rustc_ast/src/visit.rs

@@ -188,6 +188,9 @@ pub trait Visitor<'ast>: Sized {
     fn visit_variant(&mut self, v: &'ast Variant) {
         walk_variant(self, v)
     }
+    fn visit_variant_discr(&mut self, discr: &'ast AnonConst) {
+        self.visit_anon_const(discr);
+    }
     fn visit_label(&mut self, label: &'ast Label) {
         walk_label(self, label)
     }
@@ -380,7 +383,7 @@ where
     visitor.visit_ident(variant.ident);
     visitor.visit_vis(&variant.vis);
     visitor.visit_variant_data(&variant.data);
-    walk_list!(visitor, visit_anon_const, &variant.disr_expr);
+    walk_list!(visitor, visit_variant_discr, &variant.disr_expr);
     walk_list!(visitor, visit_attribute, &variant.attrs);
 }
 

compiler/rustc_ast_lowering/src/lib.rs

@@ -1190,13 +1190,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     // parsing. We try to resolve that ambiguity by attempting resolution in both the
                     // type and value namespaces. If we resolved the path in the value namespace, we
                     // transform it into a generic const argument.
-                    TyKind::Path(qself, path) => {
+                    TyKind::Path(None, path) => {
                         if let Some(res) = self
                             .resolver
                             .get_partial_res(ty.id)
                             .and_then(|partial_res| partial_res.full_res())
                         {
-                            if !res.matches_ns(Namespace::TypeNS) {
+                            if !res.matches_ns(Namespace::TypeNS)
+                                && path.is_potential_trivial_const_arg()
+                            {
                                 debug!(
                                     "lower_generic_arg: Lowering type argument as const argument: {:?}",
                                     ty,
@@ -1218,7 +1220,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                                 let path_expr = Expr {
                                     id: ty.id,
-                                    kind: ExprKind::Path(qself.clone(), path.clone()),
+                                    kind: ExprKind::Path(None, path.clone()),
                                     span,
                                     attrs: AttrVec::new(),
                                     tokens: None,

compiler/rustc_error_codes/src/error_codes/E0771.md

@@ -1,9 +1,11 @@
+#### Note: this error code is no longer emitted by the compiler
+
 A non-`'static` lifetime was used in a const generic. This is currently not
 allowed.
 
 Erroneous code example:
 
-```compile_fail,E0771
+```compile_fail,E0770
 #![feature(adt_const_params)]
 
 fn function_with_str<'a, const STRING: &'a str>() {} // error!

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -51,7 +51,15 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 // of a const parameter type, e.g. `struct Foo<const N: usize, const M: [u8; N]>` is not allowed.
                 None
             } else if tcx.lazy_normalization() {
-                if let Some(param_id) = tcx.hir().opt_const_param_default_param_def_id(hir_id) {
+                let parent_node = tcx.hir().get_parent(hir_id);
+                if let Node::Variant(Variant { disr_expr: Some(constant), .. }) = parent_node
+                    && constant.hir_id == hir_id
+                {
+                    // enum variant discriminants are not allowed to use any kind of generics
+                    None
+                } else if let Some(param_id) =
+                    tcx.hir().opt_const_param_default_param_def_id(hir_id)
+                {
                     // If the def_id we are calling generics_of on is an anon ct default i.e:
                     //
                     // struct Foo<const N: usize = { .. }>;
@@ -94,15 +102,15 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                         has_self: generics.has_self,
                         has_late_bound_regions: generics.has_late_bound_regions,
                     };
+                } else {
+                    // HACK(eddyb) this provides the correct generics when
+                    // `feature(generic_const_expressions)` is enabled, so that const expressions
+                    // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
+                    //
+                    // Note that we do not supply the parent generics when using
+                    // `min_const_generics`.
+                    Some(parent_def_id.to_def_id())
                 }
-
-                // HACK(eddyb) this provides the correct generics when
-                // `feature(generic_const_expressions)` is enabled, so that const expressions
-                // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
-                //
-                // Note that we do not supply the parent generics when using
-                // `min_const_generics`.
-                Some(parent_def_id.to_def_id())
             } else {
                 let parent_node = tcx.hir().get_parent(hir_id);
                 match parent_node {
@@ -115,11 +123,6 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                     {
                         Some(parent_def_id.to_def_id())
                     }
-                    Node::Variant(Variant { disr_expr: Some(constant), .. })
-                        if constant.hir_id == hir_id =>
-                    {
-                        Some(parent_def_id.to_def_id())
-                    }
                     Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) => {
                         Some(tcx.typeck_root_def_id(def_id.to_def_id()))
                     }

compiler/rustc_resolve/messages.ftl

@@ -145,6 +145,15 @@ resolve_param_in_ty_of_const_param =
     the type of const parameters must not depend on other generic parameters
     .label = the type must not depend on the parameter `{$name}`
 
+resolve_type_param_in_ty_of_const_param =
+    type parameters may not be used in the type of const parameters
+
+resolve_const_param_in_ty_of_const_param =
+    const parameters may not be used in the type of const parameters
+
+resolve_lifetime_param_in_ty_of_const_param =
+    lifetime parameters may not be used in the type of const parameters
+
 resolve_self_in_generic_param_default =
     generic parameters cannot use `Self` in their defaults
     .label = `Self` in generic parameter default
@@ -156,12 +165,15 @@ resolve_param_in_non_trivial_anon_const =
 resolve_param_in_non_trivial_anon_const_help =
     use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
-resolve_param_in_non_trivial_anon_const_sub_type =
+resolve_type_param_in_non_trivial_anon_const =
     type parameters may not be used in const expressions
 
-resolve_param_in_non_trivial_anon_const_sub_non_type =
+resolve_const_param_in_non_trivial_anon_const =
     const parameters may only be used as standalone arguments, i.e. `{$name}`
 
+resolve_lifetime_param_in_non_trivial_anon_const =
+    lifetime parameters may not be used in const expressions
+
 resolve_unreachable_label =
     use of unreachable label `{$name}`
     .label = unreachable label `{$name}`
@@ -233,3 +245,16 @@ resolve_macro_use_extern_crate_self = `#[macro_use]` is not supported on `extern
 
 resolve_accessible_unsure = not sure whether the path is accessible or not
     .note = the type may have associated items, but we are currently not checking them
+
+resolve_param_in_enum_discriminant =
+    generic parameters may not be used in enum discriminant values
+    .label = cannot perform const operation using `{$name}`
+
+resolve_type_param_in_enum_discriminant =
+    type parameters may not be used in enum discriminant values
+
+resolve_const_param_in_enum_discriminant =
+    const parameters may not be used in enum discriminant values
+
+resolve_lifetime_param_in_enum_discriminant =
+    lifetime parameters may not be used in enum discriminant values

compiler/rustc_resolve/src/diagnostics.rs

@@ -864,25 +864,26 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             ResolutionError::ForwardDeclaredGenericParam => {
                 self.tcx.sess.create_err(errs::ForwardDeclaredGenericParam { span })
             }
-            ResolutionError::ParamInTyOfConstParam(name) => {
-                self.tcx.sess.create_err(errs::ParamInTyOfConstParam { span, name })
-            }
-            ResolutionError::ParamInNonTrivialAnonConst { name, is_type } => {
+            ResolutionError::ParamInTyOfConstParam { name, param_kind: is_type } => self
+                .tcx
+                .sess
+                .create_err(errs::ParamInTyOfConstParam { span, name, param_kind: is_type }),
+            ResolutionError::ParamInNonTrivialAnonConst { name, param_kind: is_type } => {
                 self.tcx.sess.create_err(errs::ParamInNonTrivialAnonConst {
                     span,
                     name,
-                    sub_is_type: if is_type {
-                        errs::ParamInNonTrivialAnonConstIsType::AType
-                    } else {
-                        errs::ParamInNonTrivialAnonConstIsType::NotAType { name }
-                    },
+                    param_kind: is_type,
                     help: self
                         .tcx
                         .sess
                         .is_nightly_build()
                         .then_some(errs::ParamInNonTrivialAnonConstHelp),
                 })
             }
+            ResolutionError::ParamInEnumDiscriminant { name, param_kind: is_type } => self
+                .tcx
+                .sess
+                .create_err(errs::ParamInEnumDiscriminant { span, name, param_kind: is_type }),
             ResolutionError::SelfInGenericParamDefault => {
                 self.tcx.sess.create_err(errs::SelfInGenericParamDefault { span })
             }

compiler/rustc_resolve/src/errors.rs

@@ -326,6 +326,18 @@ pub(crate) struct ParamInTyOfConstParam {
     #[label]
     pub(crate) span: Span,
     pub(crate) name: Symbol,
+    #[subdiagnostic]
+    pub(crate) param_kind: Option<ParamKindInTyOfConstParam>,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum ParamKindInTyOfConstParam {
+    #[note(resolve_type_param_in_ty_of_const_param)]
+    Type,
+    #[note(resolve_const_param_in_ty_of_const_param)]
+    Const,
+    #[note(resolve_lifetime_param_in_ty_of_const_param)]
+    Lifetime,
 }
 
 #[derive(Diagnostic)]
@@ -344,7 +356,7 @@ pub(crate) struct ParamInNonTrivialAnonConst {
     pub(crate) span: Span,
     pub(crate) name: Symbol,
     #[subdiagnostic]
-    pub(crate) sub_is_type: ParamInNonTrivialAnonConstIsType,
+    pub(crate) param_kind: ParamKindInNonTrivialAnonConst,
     #[subdiagnostic]
     pub(crate) help: Option<ParamInNonTrivialAnonConstHelp>,
 }
@@ -354,11 +366,13 @@ pub(crate) struct ParamInNonTrivialAnonConst {
 pub(crate) struct ParamInNonTrivialAnonConstHelp;
 
 #[derive(Subdiagnostic)]
-pub(crate) enum ParamInNonTrivialAnonConstIsType {
-    #[note(resolve_param_in_non_trivial_anon_const_sub_type)]
-    AType,
-    #[help(resolve_param_in_non_trivial_anon_const_sub_non_type)]
-    NotAType { name: Symbol },
+pub(crate) enum ParamKindInNonTrivialAnonConst {
+    #[note(resolve_type_param_in_non_trivial_anon_const)]
+    Type,
+    #[help(resolve_const_param_in_non_trivial_anon_const)]
+    Const { name: Symbol },
+    #[note(resolve_lifetime_param_in_non_trivial_anon_const)]
+    Lifetime,
 }
 
 #[derive(Diagnostic)]
@@ -539,3 +553,24 @@ pub(crate) struct CfgAccessibleUnsure {
     #[primary_span]
     pub(crate) span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(resolve_param_in_enum_discriminant)]
+pub(crate) struct ParamInEnumDiscriminant {
+    #[primary_span]
+    #[label]
+    pub(crate) span: Span,
+    pub(crate) name: Symbol,
+    #[subdiagnostic]
+    pub(crate) param_kind: ParamKindInEnumDiscriminant,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum ParamKindInEnumDiscriminant {
+    #[note(resolve_type_param_in_enum_discriminant)]
+    Type,
+    #[note(resolve_const_param_in_enum_discriminant)]
+    Const,
+    #[note(resolve_lifetime_param_in_enum_discriminant)]
+    Lifetime,
+}