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, 6 insertions, 6 deletions

diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index 1b539477d51..1e26d668194 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -2053,8 +2053,8 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
     ) -> Node::OutputTy {
         loop {
             return match self.take_first_attr(&mut node) {
-                Some((attr, pos, derives)) => match attr.name_or_empty() {
-                    sym::cfg => {
+                Some((attr, pos, derives)) => match attr.name() {
+                    Some(sym::cfg) => {
                         let (res, meta_item) = self.expand_cfg_true(&mut node, attr, pos);
                         if res {
                             continue;
@@ -2071,7 +2071,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                         }
                         Default::default()
                     }
-                    sym::cfg_attr => {
+                    Some(sym::cfg_attr) => {
                         self.expand_cfg_attr(&mut node, &attr, pos);
                         continue;
                     }
@@ -2144,8 +2144,8 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
     ) {
         loop {
             return match self.take_first_attr(node) {
-                Some((attr, pos, derives)) => match attr.name_or_empty() {
-                    sym::cfg => {
+                Some((attr, pos, derives)) => match attr.name() {
+                    Some(sym::cfg) => {
                         let span = attr.span;
                         if self.expand_cfg_true(node, attr, pos).0 {
                             continue;
@@ -2154,7 +2154,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                         node.expand_cfg_false(self, pos, span);
                         continue;
                     }
-                    sym::cfg_attr => {
+                    Some(sym::cfg_attr) => {
                         self.expand_cfg_attr(node, &attr, pos);
                         continue;
                     }