Auto merge of #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 #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

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

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 {

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");

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
 }

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;

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!
 ```
 

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!
 ```

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),

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
     // -------------------------------------------------------------------------

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, \