const_refs_to_static test and cleanup

compiler/rustc_const_eval/messages.ftl

@@ -399,7 +399,6 @@ const_eval_unwind_past_top =
 
 ## The `front_matter`s here refer to either `const_eval_front_matter_invalid_value` or `const_eval_front_matter_invalid_value_with_path`.
 ## (We'd love to sort this differently to make that more clear but tidy won't let us...)
-const_eval_validation_box_to_static = {$front_matter}: encountered a box pointing to a static variable in a constant
 const_eval_validation_box_to_uninhabited = {$front_matter}: encountered a box pointing to uninhabited type {$ty}
 
 const_eval_validation_const_ref_to_extern = {$front_matter}: encountered reference to `extern` static in `const`
@@ -454,7 +453,6 @@ const_eval_validation_out_of_range = {$front_matter}: encountered {$value}, but
 const_eval_validation_partial_pointer = {$front_matter}: encountered a partial pointer or a mix of pointers
 const_eval_validation_pointer_as_int = {$front_matter}: encountered a pointer, but {$expected}
 const_eval_validation_ptr_out_of_range = {$front_matter}: encountered a pointer, but expected something that cannot possibly fail to be {$in_range}
-const_eval_validation_ref_to_static = {$front_matter}: encountered a reference pointing to a static variable in a constant
 const_eval_validation_ref_to_uninhabited = {$front_matter}: encountered a reference pointing to uninhabited type {$ty}
 const_eval_validation_unaligned_box = {$front_matter}: encountered an unaligned box (required {$required_bytes} byte alignment but found {$found_bytes})
 const_eval_validation_unaligned_ref = {$front_matter}: encountered an unaligned reference (required {$required_bytes} byte alignment but found {$found_bytes})

compiler/rustc_const_eval/src/errors.rs

@@ -640,9 +640,6 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
                 const_eval_validation_ref_to_uninhabited
             }
 
-            PtrToStatic { ptr_kind: PointerKind::Box } => const_eval_validation_box_to_static,
-            PtrToStatic { ptr_kind: PointerKind::Ref(_) } => const_eval_validation_ref_to_static,
-
             PointerAsInt { .. } => const_eval_validation_pointer_as_int,
             PartialPointer => const_eval_validation_partial_pointer,
             ConstRefToMutable => const_eval_validation_const_ref_to_mutable,
@@ -807,7 +804,6 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
                 );
             }
             NullPtr { .. }
-            | PtrToStatic { .. }
             | ConstRefToMutable
             | ConstRefToExtern
             | MutableRefToImmutable

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -438,9 +438,6 @@ pub enum ValidationErrorKind<'tcx> {
         ptr_kind: PointerKind,
         ty: Ty<'tcx>,
     },
-    PtrToStatic {
-        ptr_kind: PointerKind,
-    },
     ConstRefToMutable,
     ConstRefToExtern,
     MutableRefToImmutable,

tests/ui/statics/const_generics.rs

@@ -0,0 +1,26 @@
+//! Check that we lose the information that `BAR` points to `FOO`
+//! when going through a const generic.
+//! This is not an intentional guarantee, it just describes the status quo.
+
+//@ run-pass
+// With optimizations, LLVM will deduplicate the constant `X` whose
+// value is `&42` to just be a reference to the static. This is correct,
+// but obscures the issue we're trying to show.
+//@ revisions: opt noopt
+//@[noopt] compile-flags: -Copt-level=0
+//@[opt] compile-flags: -O
+
+#![feature(const_refs_to_static)]
+#![feature(adt_const_params)]
+#![allow(incomplete_features)]
+
+static FOO: usize = 42;
+const BAR: &usize = &FOO;
+fn foo<const X: &'static usize>() {
+    // Without optimizations, `X` ends up pointing to a copy of `FOO` instead of `FOO` itself.
+    assert_eq!(cfg!(opt), std::ptr::eq(X, &FOO));
+}
+
+fn main() {
+    foo::<BAR>();
+}