Rollup merge of #111215 - BoxyUwU:resolve_anon_consts_differently, r=cjgillot

Various changes to name resolution of anon consts

Sorry this PR is kind of all over the place ^^'

Fixes #111012

- Rewrites anon const nameres to all go through `fn resolve_anon_const` explicitly instead of `visit_anon_const` to ensure that we do not accidentally resolve anon consts as if they are allowed to use generics when they aren't. Also means that we dont have bits of code for resolving anon consts that will get out of sync (i.e. legacy const generics and resolving path consts that were parsed as type arguments)
- Renames two of the `LifetimeRibKind`, `AnonConst -> ConcreteAnonConst` and `ConstGeneric -> ConstParamTy`
- Noticed while doing this that under `generic_const_exprs` all lifetimes currently get resolved to errors without any error being emitted which was causing a bunch of tests to pass without their bugs having been fixed, incidentally fixed that in this PR and marked those tests as `// known-bug:`. I'm fine to break those since `generic_const_exprs` is a very unstable incomplete feature and this PR _does_ make generic_const_exprs "less broken" as a whole, also I can't be assed to figure out what the underlying causes of all of them are. This PR reopens #77357 #83993
- Changed `generics_of` to stop providing generics and predicates to enum variant discriminant anon consts since those are not allowed to use generic parameters
- Updated the error for non 'static lifetime in const arguments and the error for non 'static lifetime in const param tys to use `derive(Diagnostic)`

I have a vague idea why const-arg-in-const-arg.rs, in-closure.rs and simple.rs have started failing which is unfortunate since these were deliberately made to work, I think lifetime resolution being broken just means this regressed at some point and nobody noticed because the tests were not testing anything :( I'm fine breaking these too for the same reason as the tests for #77357 #83993. I couldn't get `// known-bug` to work for these ICEs and just kept getting different stderr between CI and local `--bless` so I just removed them and will create an issue to track re-adding (and fixing) the bugs if this PR lands.

r? `@cjgillot` cc `@compiler-errors`

Author: matthiaskrgr

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,
+}