Replace infallible `name_or_empty` methods with fallible `name` methods.

I'm removing empty identifiers everywhere, because in practice they
always mean "no identifier" rather than "empty identifier". (An empty
identifier is impossible.) It's better to use `Option` to mean "no
identifier" because you then can't forget about the "no identifier"
possibility.

Some specifics:
- When testing an attribute for a single name, the commit uses the
  `has_name` method.
- When testing an attribute for multiple names, the commit uses the new
  `has_any_name` method.
- When using `match` on an attribute, the match arms now have `Some` on
  them.

In the tests, we now avoid printing empty identifiers by not printing
the identifier in the `error:` line at all, instead letting the carets
point out the problem.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_mir_build/src/builder/mod.rs b/compiler/rustc_mir_build/src/builder/mod.rs
index 8ca9ab58e45..59a52ae67cb 100644
--- a/compiler/rustc_mir_build/src/builder/mod.rs
+++ b/compiler/rustc_mir_build/src/builder/mod.rs
@@ -485,7 +485,7 @@ fn construct_fn<'tcx>(
     };
 
     if let Some(custom_mir_attr) =
-        tcx.hir_attrs(fn_id).iter().find(|attr| attr.name_or_empty() == sym::custom_mir)
+        tcx.hir_attrs(fn_id).iter().find(|attr| attr.has_name(sym::custom_mir))
     {
         return custom::build_custom_mir(
             tcx,