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, 2 insertions, 3 deletions

diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index b9197be4442..d9aac54ee73 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -527,15 +527,14 @@ impl<'a> TraitDef<'a> {
                     item.attrs
                         .iter()
                         .filter(|a| {
-                            [
+                            a.has_any_name(&[
                                 sym::allow,
                                 sym::warn,
                                 sym::deny,
                                 sym::forbid,
                                 sym::stable,
                                 sym::unstable,
-                            ]
-                            .contains(&a.name_or_empty())
+                            ])
                         })
                         .cloned(),
                 );