Added lazy_normalization_consts feature, and removed the -Z flag.

src/librustc_feature/active.rs

@@ -558,6 +558,9 @@ declare_features! (
 
     /// Allow negative trait implementations.
     (active, negative_impls, "1.44.0", Some(68318), None),
+
+    /// Lazily evaluate constants. Which allows constants to depend on type parameters.
+    (active, lazy_normalization_consts, "1.44.0", Some(60471), None),
 
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
@@ -575,4 +578,5 @@ pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::raw_dylib,
     sym::const_trait_impl,
     sym::const_trait_bound_opt_out,
+    sym::lazy_normalization_consts,
 ];

src/librustc_infer/infer/combine.rs

@@ -165,13 +165,13 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
                 return self.unify_const_variable(!a_is_expected, vid, a);
             }
             (ty::ConstKind::Unevaluated(..), _)
-                if self.tcx.sess.opts.debugging_opts.lazy_normalization =>
+                if self.tcx.features().lazy_normalization_consts =>
             {
                 relation.const_equate_obligation(a, b);
                 return Ok(b);
             }
             (_, ty::ConstKind::Unevaluated(..))
-                if self.tcx.sess.opts.debugging_opts.lazy_normalization =>
+                if self.tcx.features().lazy_normalization_consts =>
             {
                 relation.const_equate_obligation(a, b);
                 return Ok(a);
@@ -660,9 +660,7 @@ impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
                     }
                 }
             }
-            ty::ConstKind::Unevaluated(..)
-                if self.tcx().sess.opts.debugging_opts.lazy_normalization =>
-            {
+            ty::ConstKind::Unevaluated(..) if self.tcx().features().lazy_normalization_consts => {
                 Ok(c)
             }
             _ => relate::super_relate_consts(self, c, c),
@@ -671,7 +669,7 @@ impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
 }
 
 pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> {
-    /// Register am obligation that both constants must be equal to each other.
+    /// Register an obligation that both constants must be equal to each other.
     ///
     /// If they aren't equal then the relation doesn't hold.
     fn const_equate_obligation(&mut self, a: &'tcx ty::Const<'tcx>, b: &'tcx ty::Const<'tcx>);

src/librustc_infer/infer/equate.rs

@@ -1,4 +1,4 @@
-use super::combine::{CombineFields, RelationDir, ConstEquateRelation};
+use super::combine::{CombineFields, ConstEquateRelation, RelationDir};
 use super::Subtype;
 
 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};

src/librustc_infer/infer/nll_relate/mod.rs

@@ -997,9 +997,7 @@ where
                     }
                 }
             }
-            ty::ConstKind::Unevaluated(..)
-                if self.tcx().sess.opts.debugging_opts.lazy_normalization =>
-            {
+            ty::ConstKind::Unevaluated(..) if self.tcx().features().lazy_normalization_consts => {
                 Ok(a)
             }
             _ => relate::super_relate_consts(self, a, a),

src/librustc_middle/ty/relate.rs

@@ -431,9 +431,9 @@ pub fn super_relate_tys<R: TypeRelation<'tcx>>(
             let t = relation.relate(&a_t, &b_t)?;
             match relation.relate(&sz_a, &sz_b) {
                 Ok(sz) => Ok(tcx.mk_ty(ty::Array(t, sz))),
-                // FIXME(lazy-normalization) Implement improved diagnostics for mismatched array
+                // FIXME(lazy_normalization_consts) Implement improved diagnostics for mismatched array
                 //  length?
-                Err(err) if relation.tcx().sess.opts.debugging_opts.lazy_normalization => Err(err),
+                Err(err) if relation.tcx().features().lazy_normalization_consts => Err(err),
                 Err(err) => {
                     // Check whether the lengths are both concrete/known values,
                     // but are unequal, for better diagnostics.

src/librustc_session/options.rs

@@ -982,6 +982,4 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "Link native libraries in the linker invocation."),
     src_hash_algorithm: Option<SourceFileHashAlgorithm> = (None, parse_src_file_hash, [TRACKED],
         "hash algorithm of source files in debug info (`md5`, or `sha1`)"),
-    lazy_normalization: bool = (false, parse_bool, [UNTRACKED],
-        "lazily evaluate constants (experimental)"),
 }

src/librustc_span/symbol.rs

@@ -408,6 +408,7 @@ symbols! {
         label_break_value,
         lang,
         lang_items,
+        lazy_normalization_consts,
         let_chains,
         lhs,
         lib,

src/librustc_trait_selection/traits/project.rs

@@ -387,7 +387,7 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
     }
 
     fn fold_const(&mut self, constant: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
-        if self.selcx.tcx().sess.opts.debugging_opts.lazy_normalization {
+        if self.selcx.tcx().features().lazy_normalization_consts {
             constant
         } else {
             constant.eval(self.selcx.tcx(), self.param_env)

src/librustc_typeck/collect.rs

@@ -1181,12 +1181,7 @@ fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::Generics {
             Some(tcx.hir().local_def_id(parent_id))
         }
         Node::AnonConst(_) => {
-            // HACK(skinny121) Provide correct generics if `feature(const_generics)` is enabled, in
-            // addition to when the '-Z lazy-normalization' flag is used, so that trait
-            // implementations that have const generic parameters within the standard library still
-            // work. The feature check won't be necessary when lazy normalization is enabled by
-            // default.
-            if tcx.sess.opts.debugging_opts.lazy_normalization || tcx.features().const_generics {
+            if tcx.features().lazy_normalization_consts {
                 let parent_id = tcx.hir().get_parent_item(hir_id);
                 Some(tcx.hir().local_def_id(parent_id))
             } else {

src/test/ui/const-generics/array-size-in-generic-struct-param.rs

@@ -1,5 +1,7 @@
 #![feature(const_generics)]
 //~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+#![feature(lazy_normalization_consts)]
+//~^ WARN the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
 
 #[allow(dead_code)]
 struct ArithArrayLen<const N: usize>([u32; 0 + N]);

src/test/ui/const-generics/array-size-in-generic-struct-param.stderr

@@ -6,16 +6,22 @@ LL | #![feature(const_generics)]
    |
    = note: `#[warn(incomplete_features)]` on by default
 
+warning: the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
+  --> $DIR/array-size-in-generic-struct-param.rs:3:12
+   |
+LL | #![feature(lazy_normalization_consts)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error: constant expression depends on a generic parameter
-  --> $DIR/array-size-in-generic-struct-param.rs:5:38
+  --> $DIR/array-size-in-generic-struct-param.rs:7:38
    |
 LL | struct ArithArrayLen<const N: usize>([u32; 0 + N]);
    |                                      ^^^^^^^^^^^^
    |
    = note: this may fail depending on what value the parameter takes
 
 error: constant expression depends on a generic parameter
-  --> $DIR/array-size-in-generic-struct-param.rs:14:5
+  --> $DIR/array-size-in-generic-struct-param.rs:16:5
    |
 LL |     arr: [u8; CFG.arr_size],
    |     ^^^^^^^^^^^^^^^^^^^^^^^

src/test/ui/const-generics/issues/issue-61336-1.rs

@@ -1,5 +1,7 @@
 #![feature(const_generics)]
 //~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+#![feature(lazy_normalization_consts)]
+//~^ WARN the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
 
 // build-pass
 

src/test/ui/const-generics/issues/issue-61336-1.stderr

@@ -6,3 +6,8 @@ LL | #![feature(const_generics)]
    |
    = note: `#[warn(incomplete_features)]` on by default
 
+warning: the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-61336-1.rs:3:12
+   |
+LL | #![feature(lazy_normalization_consts)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^

src/test/ui/const-generics/issues/issue-61336-2.rs

@@ -1,5 +1,7 @@
 #![feature(const_generics)]
 //~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+#![feature(lazy_normalization_consts)]
+//~^ WARN the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
 
 fn f<T: Copy, const N: usize>(x: T) -> [T; N] {
     [x; { N }]

src/test/ui/const-generics/issues/issue-61336-2.stderr

@@ -6,6 +6,12 @@ LL | #![feature(const_generics)]
    |
    = note: `#[warn(incomplete_features)]` on by default
 
+warning: the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-61336-2.rs:3:12
+   |
+LL | #![feature(lazy_normalization_consts)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error[E0277]: the trait bound `T: std::marker::Copy` is not satisfied
   --> $DIR/issue-61336-2.rs:9:5
    |

src/test/ui/const-generics/issues/issue-61336.rs

@@ -1,5 +1,7 @@
 #![feature(const_generics)]
 //~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+#![feature(lazy_normalization_consts)]
+//~^ WARN the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
 
 fn f<T: Copy, const N: usize>(x: T) -> [T; N] {
     [x; N]

src/test/ui/const-generics/issues/issue-61336.stderr

@@ -6,6 +6,12 @@ LL | #![feature(const_generics)]
    |
    = note: `#[warn(incomplete_features)]` on by default
 
+warning: the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-61336.rs:3:12
+   |
+LL | #![feature(lazy_normalization_consts)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error[E0277]: the trait bound `T: std::marker::Copy` is not satisfied
   --> $DIR/issue-61336.rs:9:5
    |

src/test/ui/const-generics/issues/issue-61747.rs

@@ -2,6 +2,8 @@
 
 #![feature(const_generics)]
 //~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+#![feature(lazy_normalization_consts)]
+//~^ WARN the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
 
 struct Const<const N: usize>;
 

src/test/ui/const-generics/issues/issue-61747.stderr

@@ -6,3 +6,9 @@ LL | #![feature(const_generics)]
    |
    = note: `#[warn(incomplete_features)]` on by default
 
+warning: the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-61747.rs:5:12
+   |
+LL | #![feature(lazy_normalization_consts)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^
+

src/test/ui/const-generics/issues/issue-61935.rs

@@ -1,8 +1,9 @@
 // check-pass
-// compile-flags: -Z lazy-normalization
 
 #![feature(const_generics)]
 //~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+#![feature(lazy_normalization_consts)]
+//~^ WARN the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
 
 trait Foo {}
 

src/test/ui/const-generics/issues/issue-61935.stderr

@@ -1,8 +1,14 @@
 warning: the feature `const_generics` is incomplete and may cause the compiler to crash
-  --> $DIR/issue-61935.rs:4:12
+  --> $DIR/issue-61935.rs:3:12
    |
 LL | #![feature(const_generics)]
    |            ^^^^^^^^^^^^^^
    |
    = note: `#[warn(incomplete_features)]` on by default
 
+warning: the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-61935.rs:5:12
+   |
+LL | #![feature(lazy_normalization_consts)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^
+

src/test/ui/const-generics/issues/issue-66205.rs

@@ -2,6 +2,7 @@
 
 #![allow(incomplete_features, dead_code, unconditional_recursion)]
 #![feature(const_generics)]
+#![feature(lazy_normalization_consts)]
 
 fn fact<const N: usize>() {
     fact::<{ N - 1 }>();

src/test/ui/const-generics/issues/issue-67185-1.rs

@@ -1,8 +1,9 @@
 // check-pass
-// compile-flags: -Z lazy-normalization
 
 #![feature(const_generics)]
 //~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+#![feature(lazy_normalization_consts)]
+//~^ WARN the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
 
 trait Baz {
     type Quaks;

src/test/ui/const-generics/issues/issue-67185-1.stderr

@@ -1,8 +1,14 @@
 warning: the feature `const_generics` is incomplete and may cause the compiler to crash
-  --> $DIR/issue-67185-1.rs:4:12
+  --> $DIR/issue-67185-1.rs:3:12
    |
 LL | #![feature(const_generics)]
    |            ^^^^^^^^^^^^^^
    |
    = note: `#[warn(incomplete_features)]` on by default
 
+warning: the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-67185-1.rs:5:12
+   |
+LL | #![feature(lazy_normalization_consts)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^
+

src/test/ui/const-generics/issues/issue-67185-2.rs

@@ -1,7 +1,7 @@
-// compile-flags: -Z lazy-normalization
-
 #![feature(const_generics)]
 //~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+#![feature(lazy_normalization_consts)]
+//~^ WARN the feature `lazy_normalization_consts` is incomplete and may cause the compiler to crash
 
 trait Baz {
     type Quaks;
@@ -14,7 +14,8 @@ trait Bar {}
 impl Bar for [u16; 4] {}
 impl Bar for [[u16; 3]; 3] {}
 
-trait Foo  //~ ERROR mismatched types
+trait Foo  //~ ERROR the trait bound `[u16; 3]: Bar` is not satisfied [E0277]
+           //~^ ERROR the trait bound `[[u16; 3]; 2]: Bar` is not satisfied [E0277]
     where
         [<u8 as Baz>::Quaks; 2]: Bar,
         <u8 as Baz>::Quaks: Bar,
@@ -24,12 +25,12 @@ trait Foo  //~ ERROR mismatched types
 struct FooImpl;
 
 impl Foo for FooImpl {}
-//~^ ERROR mismatched types
-//~^^ ERROR mismatched types
+//~^ ERROR the trait bound `[u16; 3]: Bar` is not satisfied [E0277]
+//~^^ ERROR the trait bound `[[u16; 3]; 2]: Bar` is not satisfied [E0277]
 
 fn f(_: impl Foo) {}
-//~^ ERROR mismatched types
-//~^^ ERROR mismatched types
+//~^ ERROR the trait bound `[u16; 3]: Bar` is not satisfied [E0277]
+//~^^ ERROR the trait bound `[[u16; 3]; 2]: Bar` is not satisfied [E0277]
 
 fn main() {
     f(FooImpl)