Just totally fully deny late-bound consts

compiler/rustc_ast_passes/messages.ftl

@@ -120,6 +120,9 @@ ast_passes_fn_without_body =
 ast_passes_forbidden_bound =
     bounds cannot be used in this context
 
+ast_passes_forbidden_const_param =
+    late-bound const parameters cannot be used currently
+
 ast_passes_forbidden_default =
     `default` is only allowed on items in trait impls
     .label = `default` because of this

compiler/rustc_ast_passes/src/errors.rs

@@ -69,6 +69,13 @@ pub struct ForbiddenBound {
     pub spans: Vec<Span>,
 }
 
+#[derive(Diagnostic)]
+#[diag(ast_passes_forbidden_const_param)]
+pub struct ForbiddenConstParam {
+    #[primary_span]
+    pub const_param_spans: Vec<Span>,
+}
+
 #[derive(Diagnostic)]
 #[diag(ast_passes_fn_param_too_many)]
 pub struct FnParamTooMany {

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -162,6 +162,22 @@ impl<'a> PostExpansionVisitor<'a> {
             crate::fluent_generated::ast_passes_forbidden_non_lifetime_param
         );
 
+        // FIXME(non_lifetime_binders): Const bound params are pretty broken.
+        // Let's keep users from using this feature accidentally.
+        if self.features.non_lifetime_binders {
+            let const_param_spans: Vec<_> = params
+                .iter()
+                .filter_map(|param| match param.kind {
+                    ast::GenericParamKind::Const { .. } => Some(param.ident.span),
+                    _ => None,
+                })
+                .collect();
+
+            if !const_param_spans.is_empty() {
+                self.sess.dcx().emit_err(errors::ForbiddenConstParam { const_param_spans });
+            }
+        }
+
         for param in params {
             if !param.bounds.is_empty() {
                 let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -2094,11 +2094,7 @@ pub fn deny_non_region_late_bound(
             format!("late-bound {what} parameter not allowed on {where_}"),
         );
 
-        let guar = if tcx.features().non_lifetime_binders && first {
+        let guar = diag.emit_unless(!tcx.features().non_lifetime_binders || !first);
-            diag.emit()
-        } else {
-            diag.delay_as_bug()
-        };
 
         first = false;
         *arg = ResolvedArg::Error(guar);

compiler/rustc_resolve/src/late.rs

@@ -2763,7 +2763,11 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
             let res = match kind {
                 RibKind::Item(..) | RibKind::AssocItem => Res::Def(def_kind, def_id.to_def_id()),
                 RibKind::Normal => {
-                    if self.r.tcx.features().non_lifetime_binders {
+                    // FIXME(non_lifetime_binders): Stop special-casing
+                    // const params to error out here.
+                    if self.r.tcx.features().non_lifetime_binders
+                        && matches!(param.kind, GenericParamKind::Type { .. })
+                    {
                         Res::Def(def_kind, def_id.to_def_id())
                     } else {
                         Res::Err

tests/crashes/127009.rs

@@ -1,11 +0,0 @@
-//@ known-bug: #127009
-
-#![feature(non_lifetime_binders)]
-
-fn b()
-where
-    for<const C: usize> [(); C]: Copy,
-{
-}
-
-fn main() {}

tests/ui/closures/binder/const-bound.rs

@@ -3,5 +3,6 @@
 
 fn main()  {
     for<const N: i32> || -> () {};
-    //~^ ERROR late-bound const parameter not allowed on closures
+    //~^ ERROR late-bound const parameters cannot be used currently
+    //~| ERROR late-bound const parameter not allowed on closures
 }

tests/ui/closures/binder/const-bound.stderr

@@ -1,3 +1,9 @@
+error: late-bound const parameters cannot be used currently
+  --> $DIR/const-bound.rs:5:15
+   |
+LL |     for<const N: i32> || -> () {};
+   |               ^
+
 warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/const-bound.rs:1:37
    |
@@ -13,5 +19,5 @@ error: late-bound const parameter not allowed on closures
 LL |     for<const N: i32> || -> () {};
    |         ^^^^^^^^^^^^
 
-error: aborting due to 1 previous error; 1 warning emitted
+error: aborting due to 2 previous errors; 1 warning emitted
 

tests/ui/const-generics/generic_const_exprs/no-entry-found-for-key-ice-gce-nlb-113133.rs

@@ -7,7 +7,8 @@
 pub fn foo()
 where
     for<const N: usize = { const fn bar() {} bar(); 1 }> ():,
-    //~^ ERROR defaults for generic parameters are not allowed in `for<...>` binders
+    //~^ ERROR late-bound const parameters cannot be used currently
+    //~| ERROR defaults for generic parameters are not allowed in `for<...>` binders
 {}
 
 fn main() {}

tests/ui/const-generics/generic_const_exprs/no-entry-found-for-key-ice-gce-nlb-113133.stderr

@@ -1,8 +1,14 @@
+error: late-bound const parameters cannot be used currently
+  --> $DIR/no-entry-found-for-key-ice-gce-nlb-113133.rs:9:15
+   |
+LL |     for<const N: usize = { const fn bar() {} bar(); 1 }> ():,
+   |               ^
+
 error: defaults for generic parameters are not allowed in `for<...>` binders
   --> $DIR/no-entry-found-for-key-ice-gce-nlb-113133.rs:9:9
    |
 LL |     for<const N: usize = { const fn bar() {} bar(); 1 }> ():,
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 

tests/ui/traits/non_lifetime_binders/bad-suggestion-on-missing-assoc.rs

@@ -18,7 +18,8 @@ trait TraitC {}
 fn foo<T>()
 where
     for<const N: u8 = { T::A }> T: TraitA<AsA = impl TraitB<AsB = impl TraitC>>,
-    //~^ ERROR defaults for generic parameters are not allowed in `for<...>` binders
+    //~^ ERROR late-bound const parameters cannot be used currently
+    //~| ERROR defaults for generic parameters are not allowed in `for<...>` binders
     //~| ERROR `impl Trait` is not allowed in bounds
 {
 }

tests/ui/traits/non_lifetime_binders/bad-suggestion-on-missing-assoc.stderr

@@ -1,3 +1,9 @@
+error: late-bound const parameters cannot be used currently
+  --> $DIR/bad-suggestion-on-missing-assoc.rs:20:15
+   |
+LL |     for<const N: u8 = { T::A }> T: TraitA<AsA = impl TraitB<AsB = impl TraitC>>,
+   |               ^
+
 warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/bad-suggestion-on-missing-assoc.rs:1:12
    |
@@ -29,6 +35,6 @@ LL |     for<const N: u8 = { T::A }> T: TraitA<AsA = impl TraitB<AsB = impl Trai
    |
    = note: `impl Trait` is only allowed in arguments and return types of functions and methods
 
-error: aborting due to 2 previous errors; 2 warnings emitted
+error: aborting due to 3 previous errors; 2 warnings emitted
 
 For more information about this error, try `rustc --explain E0562`.

tests/ui/traits/non_lifetime_binders/binder-defaults-112547.rs

@@ -4,10 +4,11 @@
 pub fn bar()
 where
     for<const N: usize = {
+    //~^ ERROR late-bound const parameters cannot be used currently
+    //~| ERROR defaults for generic parameters are not allowed in `for<...>` binders
     (||1usize)()
 }> V: IntoIterator
-//~^^^ ERROR defaults for generic parameters are not allowed in `for<...>` binders
+//~^ ERROR cannot find type `V` in this scope
-//~^^ ERROR cannot find type `V` in this scope
 {
 }
 

tests/ui/traits/non_lifetime_binders/binder-defaults-112547.stderr

@@ -1,5 +1,5 @@
 error[E0412]: cannot find type `V` in this scope
-  --> $DIR/binder-defaults-112547.rs:8:4
+  --> $DIR/binder-defaults-112547.rs:10:4
    |
 LL | }> V: IntoIterator
    |    ^ not found in this scope
@@ -9,6 +9,12 @@ help: you might be missing a type parameter
 LL | pub fn bar<V>()
    |           +++
 
+error: late-bound const parameters cannot be used currently
+  --> $DIR/binder-defaults-112547.rs:6:15
+   |
+LL |     for<const N: usize = {
+   |               ^
+
 warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/binder-defaults-112547.rs:1:12
    |
@@ -23,10 +29,12 @@ error: defaults for generic parameters are not allowed in `for<...>` binders
    |
 LL |       for<const N: usize = {
    |  _________^
+LL | |
+LL | |
 LL | |     (||1usize)()
 LL | | }> V: IntoIterator
    | |_^
 
-error: aborting due to 2 previous errors; 1 warning emitted
+error: aborting due to 3 previous errors; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0412`.

tests/ui/traits/non_lifetime_binders/binder-defaults-119489.rs

@@ -5,8 +5,9 @@
 fn fun()
 where
     for<T = (), const N: usize = 1> ():,
-//~^ ERROR defaults for generic parameters are not allowed in `for<...>` binders
+    //~^ ERROR late-bound const parameters cannot be used currently
-//~| ERROR defaults for generic parameters are not allowed in `for<...>` binders
+    //~| ERROR defaults for generic parameters are not allowed in `for<...>` binders
+    //~| ERROR defaults for generic parameters are not allowed in `for<...>` binders
 {}
 
 fn main() {}

tests/ui/traits/non_lifetime_binders/binder-defaults-119489.stderr

@@ -1,3 +1,9 @@
+error: late-bound const parameters cannot be used currently
+  --> $DIR/binder-defaults-119489.rs:7:23
+   |
+LL |     for<T = (), const N: usize = 1> ():,
+   |                       ^
+
 warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/binder-defaults-119489.rs:1:12
    |
@@ -27,5 +33,5 @@ error: defaults for generic parameters are not allowed in `for<...>` binders
 LL |     for<T = (), const N: usize = 1> ():,
    |                 ^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors; 2 warnings emitted
+error: aborting due to 3 previous errors; 2 warnings emitted
 

tests/ui/traits/non_lifetime_binders/late-const-param-wf.rs

@@ -0,0 +1,11 @@
+#![feature(non_lifetime_binders)]
+//~^ WARN the feature `non_lifetime_binders` is incomplete
+
+fn b()
+where
+    for<const C: usize> [(); C]: Copy,
+    //~^ ERROR late-bound const parameters cannot be used currently
+{
+}
+
+fn main() {}

tests/ui/traits/non_lifetime_binders/late-const-param-wf.stderr

@@ -0,0 +1,17 @@
+error: late-bound const parameters cannot be used currently
+  --> $DIR/late-const-param-wf.rs:6:15
+   |
+LL |     for<const C: usize> [(); C]: Copy,
+   |               ^
+
+warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/late-const-param-wf.rs:1:12
+   |
+LL | #![feature(non_lifetime_binders)]
+   |            ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error: aborting due to 1 previous error; 1 warning emitted
+