Add ErrorGuaranteed to ast::LitKind::Err, token::LitKind::Err.

This mostly works well, and eliminates a couple of delayed bugs.

One annoying thing is that we should really also add an
`ErrorGuaranteed` to `proc_macro::bridge::LitKind::Err`. But that's
difficult because `proc_macro` doesn't have access to `ErrorGuaranteed`,
so we have to fake it.

Author: nnethercote

clippy_lints/src/matches/match_same_arms.rs

@@ -295,7 +295,8 @@ impl<'a> NormalizedPat<'a> {
                     LitKind::Char(val) => Self::LitInt(val.into()),
                     LitKind::Int(val, _) => Self::LitInt(val.get()),
                     LitKind::Bool(val) => Self::LitBool(val),
-                    LitKind::Float(..) | LitKind::Err => Self::Wild,
+                    LitKind::Float(..) => Self::Wild,
+                    LitKind::Err(guar) => Self::Err(guar),
                 },
                 _ => Self::Wild,
             },

clippy_lints/src/redundant_type_annotations.rs

@@ -200,7 +200,7 @@ impl LateLintPass<'_> for RedundantTypeAnnotations {
                                 span_lint(cx, REDUNDANT_TYPE_ANNOTATIONS, local.span, "redundant type annotation");
                             }
                         },
-                        LitKind::Err => (),
+                        LitKind::Err(_) => (),
                         LitKind::ByteStr(..) => {
                             // We only lint if the type annotation is an array type (e.g. &[u8; 4]).
                             // If instead it is a slice (e.g. &[u8]) it may not be redundant, so we

clippy_lints/src/utils/author.rs

@@ -279,7 +279,7 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
         match lit.value.node {
             LitKind::Bool(val) => kind!("Bool({val:?})"),
             LitKind::Char(c) => kind!("Char({c:?})"),
-            LitKind::Err => kind!("Err"),
+            LitKind::Err(_) => kind!("Err"),
             LitKind::Byte(b) => kind!("Byte({b})"),
             LitKind::Int(i, suffix) => {
                 let int_ty = match suffix {

clippy_utils/src/consts.rs

@@ -286,7 +286,7 @@ pub fn lit_to_mir_constant<'tcx>(lit: &LitKind, ty: Option<Ty<'tcx>>) -> Constan
             _ => bug!(),
         },
         LitKind::Bool(b) => Constant::Bool(b),
-        LitKind::Err => Constant::Err,
+        LitKind::Err(_) => Constant::Err,
     }
 }