Auto merge of rust-lang#88369 - lcnr:cec-rename, r=oli-obk

update const generics feature gates

**tl;dr: split const generics into three features: `adt_const_params`, `const_generics_defaults` and `generic_const_exprs`**

continuing the work of `@BoxyUwU` in rust-lang#88324, this PR
- renames `feature(const_evaluatable_checked)` to `feature(generic_const_exprs)` which now doesn't need any other feature gate to work. Previously `feature(const_evaluatable_checked)` was only useful in combination with `feature(const_generics)`.
- completely removes `feature(lazy_normalization_consts)`. This feature only supplied the parents generics to anonymous constants, which is pretty useless as generic anon consts are only allowed with `feature(generic_const_exprs)` anyways.
- moves the ability to use additional const param types from `feature(const_generics)` into `feature(adt_const_params)`. As `feature(const_generics)` is now mostly useless without `feature(generic_const_exprs)` we also remove that feature flag.
- updates tests, removing duplicates and unnecessary revisions in some cases and also deletes all unused `*.stderr` files.

I not also remove the ordering restriction for const and type parameters if any of the three const generics features is active.
This ordering restriction feels like the only "real" use of the current `feature(const_generics)` right now so this change isn't a perfect solution, but as I intend to stabilize the ordering - and `feature(const_generics_defaults)` -  in the very near future, I think this is acceptable for now.

---

cc `@rust-lang/project-const-generics` about the new feature names and this change in general.

I don't think we need any external approval for this change but I do intend to publish an update to the const generics tracking issue the day this PR lands, so I don't want this merged yet.

Apologies to whoever ends up reviewing this PR 😅 ❤️

r? rust-lang/project-const-generics

Author: bors

Diff for: compiler/rustc_ast/src/ast.rs

@@ -332,8 +332,8 @@ pub type GenericBounds = Vec<GenericBound>;
 pub enum ParamKindOrd {
     Lifetime,
     Type,
-    // `unordered` is only `true` if `sess.has_features().const_generics`
-    // is active. Specifically, if it's only `min_const_generics`, it will still require
+    // `unordered` is only `true` if `sess.unordered_const_ty_params()`
+    // returns true. Specifically, if it's only `min_const_generics`, it will still require
     // ordering consts after types.
     Const { unordered: bool },
     // `Infer` is not actually constructed directly from the AST, but is implicitly constructed

Diff for: compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1351,7 +1351,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
     }
 
     fn visit_generics(&mut self, generics: &'a Generics) {
-        let cg_defaults = self.session.features_untracked().const_generics_defaults;
+        let cg_defaults = self.session.features_untracked().unordered_const_ty_params();
 
         let mut prev_param_default = None;
         for param in &generics.params {

Diff for: compiler/rustc_ast_passes/src/feature_gate.rs

@@ -687,7 +687,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
     gate_all!(trait_alias, "trait aliases are experimental");
     gate_all!(associated_type_bounds, "associated type bounds are unstable");
     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
-    gate_all!(const_generics, "const generics are unstable");
     gate_all!(decl_macro, "`macro` is experimental");
     gate_all!(box_patterns, "box pattern syntax is experimental");
     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");

Diff for: compiler/rustc_error_codes/src/error_codes/E0671.md

@@ -4,8 +4,6 @@ Const parameters cannot depend on type parameters.
 The following is therefore invalid:
 
 ```compile_fail,E0770
-#![feature(const_generics)]
-
 fn const_id<T, const N: T>() -> T { // error
     N
 }

Diff for: compiler/rustc_error_codes/src/error_codes/E0741.md

@@ -3,7 +3,7 @@ A non-structural-match type was used as the type of a const generic parameter.
 Erroneous code example:
 
 ```compile_fail,E0741
-#![feature(const_generics)]
+#![feature(adt_const_params)]
 
 struct A;
 
@@ -16,7 +16,7 @@ may be used as the types of const generic parameters.
 To fix the previous code example, we derive `PartialEq` and `Eq`:
 
 ```
-#![feature(const_generics)]
+#![feature(adt_const_params)]
 
 #[derive(PartialEq, Eq)] // We derive both traits here.
 struct A;

Diff for: compiler/rustc_error_codes/src/error_codes/E0770.md

@@ -3,7 +3,6 @@ The type of a const parameter references other generic parameters.
 Erroneous code example:
 
 ```compile_fail,E0770
-#![feature(const_generics)]
 fn foo<T, const N: T>() {} // error!
 ```
 

Diff for: compiler/rustc_error_codes/src/error_codes/E0771.md

@@ -4,7 +4,7 @@ allowed.
 Erroneous code example:
 
 ```compile_fail,E0771
-#![feature(const_generics)]
+#![feature(adt_const_params)]
 
 fn function_with_str<'a, const STRING: &'a str>() {} // error!
 ```
@@ -13,7 +13,7 @@ To fix this issue, the lifetime in the const generic need to be changed to
 `'static`:
 
 ```
-#![feature(const_generics)]
+#![feature(adt_const_params)]
 
 fn function_with_str<const STRING: &'static str>() {} // ok!
 ```

Diff for: compiler/rustc_feature/src/accepted.rs

@@ -273,7 +273,7 @@ declare_features! (
     /// Allows patterns with concurrent by-move and by-ref bindings.
     /// For example, you can write `Foo(a, ref b)` where `a` is by-move and `b` is by-ref.
     (accepted, move_ref_pattern, "1.49.0", Some(68354), None),
-    /// The smallest useful subset of `const_generics`.
+    /// The smallest useful subset of const generics.
     (accepted, min_const_generics, "1.51.0", Some(74878), None),
     /// The `unsafe_op_in_unsafe_fn` lint (allowed by default): no longer treat an unsafe function as an unsafe block.
     (accepted, unsafe_block_in_unsafe_fn, "1.52.0", Some(71668), None),

Diff for: compiler/rustc_feature/src/active.rs

@@ -71,7 +71,7 @@ macro_rules! declare_features {
             }
 
             pub fn unordered_const_ty_params(&self) -> bool {
-                self.const_generics || self.const_generics_defaults
+                self.const_generics_defaults || self.generic_const_exprs || self.adt_const_params
             }
 
             /// Some features are known to be incomplete and using them is likely to have
@@ -453,9 +453,6 @@ declare_features! (
     /// Allows using `#[ffi_returns_twice]` on foreign functions.
     (active, ffi_returns_twice, "1.34.0", Some(58314), None),
 
-    /// Allows const generic types (e.g. `struct Foo<const N: usize>(...);`).
-    (incomplete, const_generics, "1.34.0", Some(44580), None),
-
     /// Allows using `#[optimize(X)]`.
     (active, optimize_attribute, "1.34.0", Some(54882), None),
 
@@ -545,15 +542,9 @@ declare_features! (
     /// Allows capturing variables in scope using format_args!
     (active, format_args_capture, "1.46.0", Some(67984), None),
 
-    /// Lazily evaluate constants. This allows constants to depend on type parameters.
-    (incomplete, lazy_normalization_consts, "1.46.0", Some(72219), None),
-
     /// Allows `if let` guard in match arms.
     (active, if_let_guard, "1.47.0", Some(51114), None),
 
-    /// Allows non-trivial generic constants which have to be manually propagated upwards.
-    (incomplete, const_evaluatable_checked, "1.48.0", Some(76560), None),
-
     /// Allows basic arithmetic on floating point types in a `const fn`.
     (active, const_fn_floating_point_arithmetic, "1.48.0", Some(57241), None),
 
@@ -679,6 +670,12 @@ declare_features! (
     /// Allows using doc(primitive) without a future-incompat warning
     (active, doc_primitive, "1.56.0", Some(88070), 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 additional const parameter types, such as `&'static str` or user defined types
+    (incomplete, adt_const_params, "1.56.0", Some(44580), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

Diff for: compiler/rustc_feature/src/removed.rs

@@ -102,6 +102,9 @@ declare_features! (
     (removed, extern_in_paths, "1.33.0", Some(55600), None,
      Some("subsumed by `::foo::bar` paths")),
     (removed, quote, "1.33.0", Some(29601), None, None),
+    /// Allows const generic types (e.g. `struct Foo<const N: usize>(...);`).
+    (removed, const_generics, "1.34.0", Some(44580), None,
+     Some("removed in favor of `#![feature(adt_const_params]` and `#![feature(generic_const_exprs)]`")),
     /// Allows `[x; N]` where `x` is a constant (RFC 2203).
     (removed, const_in_array_repeat_expressions,  "1.37.0", Some(49147), None,
      Some("removed due to causing promotable bugs")),
@@ -128,9 +131,13 @@ declare_features! (
      Some("Removed in favor of `~const` bound in #![feature(const_trait_impl)]")),
     /// Allows `#[no_debug]`.
     (removed, no_debug, "1.43.0", Some(29721), None, Some("removed due to lack of demand")),
+    /// Lazily evaluate constants. This allows constants to depend on type parameters.
+    (removed, lazy_normalization_consts, "1.46.0", Some(72219), None, Some("superseded by `generic_const_exprs`")),
     /// Allows comparing raw pointers during const eval.
     (removed, const_compare_raw_pointers, "1.46.0", Some(53020), None,
      Some("cannot be allowed in const eval in any meaningful way")),
+    /// Allows non-trivial generic constants which have to be manually propagated upwards.
+    (removed, const_evaluatable_checked, "1.48.0", Some(76560), None, Some("renamed to `generic_const_exprs`")),
     /// Allows using the `#[link_args]` attribute.
     (removed, link_args, "1.53.0", Some(29596), None,
      Some("removed in favor of using `-C link-arg=ARG` on command line, \

Diff for: compiler/rustc_hir/src/def.rs

@@ -307,7 +307,7 @@ pub enum Res<Id = hir::HirId> {
     /// We do however allow `Self` in repeat expression even if it is generic to not break code
     /// which already works on stable while causing the `const_evaluatable_unchecked` future compat lint.
     ///
-    /// FIXME(lazy_normalization_consts): Remove this bodge once that feature is stable.
+    /// FIXME(generic_const_exprs): Remove this bodge once that feature is stable.
     SelfTy(
         /// Optionally, the trait associated with this `Self` type.
         Option<DefId>,

Diff for: compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -678,7 +678,7 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for QueryTypeRelatingDelegate<'_, 'tcx> {
     fn const_equate(&mut self, _a: &'tcx Const<'tcx>, _b: &'tcx Const<'tcx>) {
         span_bug!(
             self.cause.span(self.infcx.tcx),
-            "lazy_normalization_consts: unreachable `const_equate`"
+            "generic_const_exprs: unreachable `const_equate`"
         );
     }
 

Diff for: compiler/rustc_infer/src/infer/combine.rs

@@ -202,7 +202,7 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
     /// A good example of this is the following:
     ///
     /// ```rust
-    /// #![feature(const_generics)]
+    /// #![feature(generic_const_exprs)]
     ///
     /// fn bind<const N: usize>(value: [u8; N]) -> [u8; 3 + 4] {
     ///     todo!()

Diff for: compiler/rustc_lint/src/builtin.rs

@@ -2340,7 +2340,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
-    /// #![feature(const_generics)]
+    /// #![feature(generic_const_exprs)]
     /// ```
     ///
     /// {{produces}}

Diff for: compiler/rustc_middle/src/ty/context.rs

@@ -1420,8 +1420,8 @@ impl<'tcx> TyCtxt<'tcx> {
     #[inline]
     pub fn lazy_normalization(self) -> bool {
         let features = self.features();
-        // Note: We do not enable lazy normalization for `min_const_generics`.
-        features.const_generics || features.lazy_normalization_consts
+        // Note: We only use lazy normalization for generic const expressions.
+        features.generic_const_exprs
     }
 
     #[inline]

Diff for: compiler/rustc_middle/src/ty/relate.rs

@@ -577,13 +577,13 @@ pub fn super_relate_consts<R: TypeRelation<'tcx>>(
         }
 
         (ty::ConstKind::Unevaluated(au), ty::ConstKind::Unevaluated(bu))
-            if tcx.features().const_evaluatable_checked =>
+            if tcx.features().generic_const_exprs =>
         {
             tcx.try_unify_abstract_consts((au.shrink(), bu.shrink()))
         }
 
         // While this is slightly incorrect, it shouldn't matter for `min_const_generics`
-        // and is the better alternative to waiting until `const_evaluatable_checked` can
+        // and is the better alternative to waiting until `generic_const_exprs` can
         // be stabilized.
         (ty::ConstKind::Unevaluated(au), ty::ConstKind::Unevaluated(bu))
             if au.def == bu.def && au.promoted == bu.promoted =>

Diff for: compiler/rustc_privacy/src/lib.rs

@@ -136,7 +136,7 @@ where
             }
             ty::PredicateKind::RegionOutlives(..) => ControlFlow::CONTINUE,
             ty::PredicateKind::ConstEvaluatable(uv)
-                if self.def_id_visitor.tcx().features().const_evaluatable_checked =>
+                if self.def_id_visitor.tcx().features().generic_const_exprs =>
             {
                 let tcx = self.def_id_visitor.tcx();
                 if let Ok(Some(ct)) = AbstractConst::new(tcx, uv) {
@@ -1809,7 +1809,7 @@ impl SearchInterfaceForPrivateItemsVisitor<'tcx> {
                         self.visit(self.tcx.type_of(param.def_id));
                     }
                 }
-                // FIXME(const_evaluatable_checked): May want to look inside const here
+                // FIXME(generic_const_exprs): May want to look inside const here
                 GenericParamDefKind::Const { .. } => {
                     self.visit(self.tcx.type_of(param.def_id));
                 }

Diff for: compiler/rustc_resolve/src/diagnostics.rs

@@ -506,8 +506,7 @@ impl<'a> Resolver<'a> {
 
                 if self.session.is_nightly_build() {
                     err.help(
-                        "use `#![feature(const_generics)]` and `#![feature(const_evaluatable_checked)]` \
-                        to allow generic const expressions"
+                        "use `#![feature(generic_const_exprs)]` to allow generic const expressions",
                     );
                 }
 

Diff for: compiler/rustc_resolve/src/late/diagnostics.rs

@@ -2245,7 +2245,7 @@ impl<'tcx> LifetimeContext<'_, 'tcx> {
     }
 
     /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
-    /// This function will emit an error if `const_generics` is not enabled, the body identified by
+    /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
     /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
     crate fn maybe_emit_forbidden_non_static_lifetime_error(
         &self,
@@ -2264,7 +2264,7 @@ impl<'tcx> LifetimeContext<'_, 'tcx> {
         if !self.tcx.lazy_normalization() && is_anon_const && !is_allowed_lifetime {
             feature_err(
                 &self.tcx.sess.parse_sess,
-                sym::const_generics,
+                sym::generic_const_exprs,
                 lifetime_ref.span,
                 "a non-static lifetime is not allowed in a `const`",
             )

Diff for: compiler/rustc_resolve/src/late/lifetimes.rs

@@ -2301,7 +2301,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
             match *scope {
                 Scope::Body { id, s } => {
                     // Non-static lifetimes are prohibited in anonymous constants without
-                    // `const_generics`.
+                    // `generic_const_exprs`.
                     self.maybe_emit_forbidden_non_static_lifetime_error(id, lifetime_ref);
 
                     outermost_body = Some(id);

Diff for: compiler/rustc_resolve/src/lib.rs

@@ -2734,10 +2734,7 @@ impl<'a> Resolver<'a> {
                         ConstantItemRibKind(trivial, _) => {
                             let features = self.session.features_untracked();
                             // HACK(min_const_generics): We currently only allow `N` or `{ N }`.
-                            if !(trivial
-                                || features.const_generics
-                                || features.lazy_normalization_consts)
-                            {
+                            if !(trivial || features.generic_const_exprs) {
                                 // HACK(min_const_generics): If we encounter `Self` in an anonymous constant
                                 // we can't easily tell if it's generic at this stage, so we instead remember
                                 // this and then enforce the self type to be concrete later on.
@@ -2809,10 +2806,7 @@ impl<'a> Resolver<'a> {
                         ConstantItemRibKind(trivial, _) => {
                             let features = self.session.features_untracked();
                             // HACK(min_const_generics): We currently only allow `N` or `{ N }`.
-                            if !(trivial
-                                || features.const_generics
-                                || features.lazy_normalization_consts)
-                            {
+                            if !(trivial || features.generic_const_exprs) {
                                 if record_used {
                                     self.report_error(
                                         span,

Diff for: compiler/rustc_span/src/symbol.rs

@@ -284,6 +284,7 @@ symbols! {
         add_assign,
         add_with_overflow,
         address,
+        adt_const_params,
         advanced_slice_patterns,
         adx_target_feature,
         alias,
@@ -662,6 +663,7 @@ symbols! {
         generators,
         generic_arg_infer,
         generic_associated_types,
+        generic_const_exprs,
         generic_param_attrs,
         get_context,
         global_allocator,

Diff for: compiler/rustc_trait_selection/src/traits/const_evaluatable.rs

@@ -34,7 +34,7 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
     span: Span,
 ) -> Result<(), NotConstEvaluatable> {
     debug!("is_const_evaluatable({:?})", uv);
-    if infcx.tcx.features().const_evaluatable_checked {
+    if infcx.tcx.features().generic_const_exprs {
         let tcx = infcx.tcx;
         match AbstractConst::new(tcx, uv)? {
             // We are looking at a generic abstract constant.
@@ -537,9 +537,9 @@ pub(super) fn mir_abstract_const<'tcx>(
     tcx: TyCtxt<'tcx>,
     def: ty::WithOptConstParam<LocalDefId>,
 ) -> Result<Option<&'tcx [mir::abstract_const::Node<'tcx>]>, ErrorReported> {
-    if tcx.features().const_evaluatable_checked {
+    if tcx.features().generic_const_exprs {
         match tcx.def_kind(def.did) {
-            // FIXME(const_evaluatable_checked): We currently only do this for anonymous constants,
+            // FIXME(generic_const_exprs): We currently only do this for anonymous constants,
             // meaning that we do not look into associated constants. I(@lcnr) am not yet sure whether
             // we want to look into them or treat them as opaque projections.
             //
@@ -568,7 +568,7 @@ pub(super) fn try_unify_abstract_consts<'tcx>(
         Ok(false)
     })()
     .unwrap_or_else(|ErrorReported| true)
-    // FIXME(const_evaluatable_checked): We should instead have this
+    // FIXME(generic_const_exprs): We should instead have this
     // method return the resulting `ty::Const` and return `ConstKind::Error`
     // on `ErrorReported`.
 }
@@ -656,13 +656,13 @@ pub(super) fn try_unify<'tcx>(
                 // branch should only be taking when dealing with associated constants, at
                 // which point directly comparing them seems like the desired behavior.
                 //
-                // FIXME(const_evaluatable_checked): This isn't actually the case.
+                // FIXME(generic_const_exprs): This isn't actually the case.
                 // We also take this branch for concrete anonymous constants and
                 // expand generic anonymous constants with concrete substs.
                 (ty::ConstKind::Unevaluated(a_uv), ty::ConstKind::Unevaluated(b_uv)) => {
                     a_uv == b_uv
                 }
-                // FIXME(const_evaluatable_checked): We may want to either actually try
+                // FIXME(generic_const_exprs): We may want to either actually try
                 // to evaluate `a_ct` and `b_ct` if they are are fully concrete or something like
                 // this, for now we just return false here.
                 _ => false,

Diff for: compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -794,7 +794,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 )
             }
             SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
-                if !self.tcx.features().const_evaluatable_checked {
+                if !self.tcx.features().generic_const_exprs {
                     let mut err = self.tcx.sess.struct_span_err(
                         span,
                         "constant expression depends on a generic parameter",
@@ -803,7 +803,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     // issue. However, this is currently not actually possible
                     // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
                     //
-                    // Note that with `feature(const_evaluatable_checked)` this case should not
+                    // Note that with `feature(generic_const_exprs)` this case should not
                     // be reachable.
                     err.note("this may fail depending on what value the parameter takes");
                     err.emit();

Diff for: compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -572,7 +572,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
                 ty::PredicateKind::ConstEquate(c1, c2) => {
                     debug!(?c1, ?c2, "equating consts");
                     let tcx = self.selcx.tcx();
-                    if tcx.features().const_evaluatable_checked {
+                    if tcx.features().generic_const_exprs {
                         // FIXME: we probably should only try to unify abstract constants
                         // if the constants depend on generic parameters.
                         //