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, 3 insertions, 2 deletions

diff --git a/compiler/rustc_mir_dataflow/src/framework/graphviz.rs b/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
index c436b8c0fb0..144fa8c6fdd 100644
--- a/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
@@ -144,9 +144,10 @@ impl RustcMirAttrs {
         attr: &ast::MetaItemInner,
         mapper: impl FnOnce(Symbol) -> Result<T, ()>,
     ) -> Result<(), ()> {
+        // Unwrapping the name is safe because this is only called when `has_name` has succeeded.
         if field.is_some() {
             tcx.dcx()
-                .emit_err(DuplicateValuesFor { span: attr.span(), name: attr.name_or_empty() });
+                .emit_err(DuplicateValuesFor { span: attr.span(), name: attr.name().unwrap() });
 
             return Err(());
         }
@@ -156,7 +157,7 @@ impl RustcMirAttrs {
             Ok(())
         } else {
             tcx.dcx()
-                .emit_err(RequiresAnArgument { span: attr.span(), name: attr.name_or_empty() });
+                .emit_err(RequiresAnArgument { span: attr.span(), name: attr.name().unwrap() });
             Err(())
         }
     }