Implement LowerHex on Scalar to clean up their display in rustdoc

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -697,7 +697,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
                 this.ecx.read_discriminant(op),
                 this.path,
                 err_ub!(InvalidTag(val)) =>
-                    { "{}", val } expected { "a valid enum tag" },
+                    { "{:x}", val } expected { "a valid enum tag" },
                 err_ub!(InvalidUninitBytes(None)) =>
                     { "uninitialized bytes" } expected { "a valid enum tag" },
                 err_unsup!(ReadPointerAsBytes) =>

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

@@ -370,7 +370,7 @@ impl fmt::Display for UndefinedBehaviorInfo<'_> {
             InvalidChar(c) => {
                 write!(f, "interpreting an invalid 32-bit value as a char: 0x{:08x}", c)
             }
-            InvalidTag(val) => write!(f, "enum value has invalid tag: {}", val),
+            InvalidTag(val) => write!(f, "enum value has invalid tag: {:x}", val),
             InvalidFunctionPointer(p) => {
                 write!(f, "using {:?} as function pointer but it does not point to a function", p)
             }

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

@@ -153,7 +153,16 @@ impl<Tag: Provenance> fmt::Display for Scalar<Tag> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Scalar::Ptr(ptr, _size) => write!(f, "pointer to {:?}", ptr),
-            Scalar::Int(int) => write!(f, "{:?}", int),
+            Scalar::Int(int) => write!(f, "{}", int),
+        }
+    }
+}
+
+impl<Tag: Provenance> fmt::LowerHex for Scalar<Tag> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Scalar::Ptr(ptr, _size) => write!(f, "pointer to {:?}", ptr),
+            Scalar::Int(int) => write!(f, "0x{:x}", int),
         }
     }
 }
@@ -456,11 +465,6 @@ impl<'tcx, Tag: Provenance> Scalar<Tag> {
         // Going through `u64` to check size and truncation.
         Ok(Double::from_bits(self.to_u64()?.into()))
     }
-
-    // FIXME: Replace current `impl Display for Scalar` with `impl LowerHex`.
-    pub fn rustdoc_display(&self) -> String {
-        if let Scalar::Int(int) = self { int.to_string() } else { self.to_string() }
-    }
 }
 
 #[derive(Clone, Copy, Eq, PartialEq, TyEncodable, TyDecodable, HashStable, Hash)]
@@ -494,7 +498,7 @@ impl<Tag: Provenance> fmt::Display for ScalarMaybeUninit<Tag> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             ScalarMaybeUninit::Uninit => write!(f, "uninitialized bytes"),
-            ScalarMaybeUninit::Scalar(s) => write!(f, "{}", s),
+            ScalarMaybeUninit::Scalar(s) => write!(f, "{:x}", s),
         }
     }
 }

src/librustdoc/clean/utils.rs

@@ -302,11 +302,7 @@ fn print_const_with_custom_print_scalar(tcx: TyCtxt<'_>, ct: ty::Const<'_>) -> S
     // For all other types, fallback to the original `pretty_print_const`.
     match (ct.val(), ct.ty().kind()) {
         (ty::ConstKind::Value(ConstValue::Scalar(int)), ty::Uint(ui)) => {
-            format!(
-                "{}{}",
-                format_integer_with_underscore_sep(&int.rustdoc_display()),
-                ui.name_str()
-            )
+            format!("{}{}", format_integer_with_underscore_sep(&int.to_string()), ui.name_str())
         }
         (ty::ConstKind::Value(ConstValue::Scalar(int)), ty::Int(i)) => {
             let ty = tcx.lift(ct.ty()).unwrap();