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, 22 insertions, 11 deletions

diff --git a/compiler/rustc_ast/src/attr/mod.rs b/compiler/rustc_ast/src/attr/mod.rs
index d656d9b0b8a..f104400a572 100644
--- a/compiler/rustc_ast/src/attr/mod.rs
+++ b/compiler/rustc_ast/src/attr/mod.rs
@@ -305,8 +305,8 @@ impl MetaItem {
         if let [PathSegment { ident, .. }] = self.path.segments[..] { Some(ident) } else { None }
     }
 
-    pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or_else(Ident::empty).name
+    pub fn name(&self) -> Option<Symbol> {
+        self.ident().map(|ident| ident.name)
     }
 
     pub fn has_name(&self, name: Symbol) -> bool {
@@ -511,13 +511,14 @@ impl MetaItemInner {
         }
     }
 
-    /// For a single-segment meta item, returns its name; otherwise, returns `None`.
+    /// For a single-segment meta item, returns its identifier; otherwise, returns `None`.
     pub fn ident(&self) -> Option<Ident> {
         self.meta_item().and_then(|meta_item| meta_item.ident())
     }
 
-    pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or_else(Ident::empty).name
+    /// For a single-segment meta item, returns its name; otherwise, returns `None`.
+    pub fn name(&self) -> Option<Symbol> {
+        self.ident().map(|ident| ident.name)
     }
 
     /// Returns `true` if this list item is a MetaItem with a name of `name`.
@@ -738,9 +739,9 @@ pub trait AttributeExt: Debug {
     fn id(&self) -> AttrId;
 
     /// For a single-segment attribute (i.e., `#[attr]` and not `#[path::atrr]`),
-    /// return the name of the attribute, else return the empty identifier.
-    fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or_else(Ident::empty).name
+    /// return the name of the attribute; otherwise, returns `None`.
+    fn name(&self) -> Option<Symbol> {
+        self.ident().map(|ident| ident.name)
     }
 
     /// Get the meta item list, `#[attr(meta item list)]`
@@ -752,7 +753,7 @@ pub trait AttributeExt: Debug {
     /// Gets the span of the value literal, as string, when using `#[attr = value]`
     fn value_span(&self) -> Option<Span>;
 
-    /// For a single-segment attribute, returns its name; otherwise, returns `None`.
+    /// For a single-segment attribute, returns its ident; otherwise, returns `None`.
     fn ident(&self) -> Option<Ident>;
 
     /// Checks whether the path of this attribute matches the name.
@@ -770,6 +771,11 @@ pub trait AttributeExt: Debug {
         self.ident().map(|x| x.name == name).unwrap_or(false)
     }
 
+    #[inline]
+    fn has_any_name(&self, names: &[Symbol]) -> bool {
+        names.iter().any(|&name| self.has_name(name))
+    }
+
     /// get the span of the entire attribute
     fn span(&self) -> Span;
 
@@ -813,8 +819,8 @@ impl Attribute {
         AttributeExt::id(self)
     }
 
-    pub fn name_or_empty(&self) -> Symbol {
-        AttributeExt::name_or_empty(self)
+    pub fn name(&self) -> Option<Symbol> {
+        AttributeExt::name(self)
     }
 
     pub fn meta_item_list(&self) -> Option<ThinVec<MetaItemInner>> {
@@ -846,6 +852,11 @@ impl Attribute {
         AttributeExt::has_name(self, name)
     }
 
+    #[inline]
+    pub fn has_any_name(&self, names: &[Symbol]) -> bool {
+        AttributeExt::has_any_name(self, names)
+    }
+
     pub fn span(&self) -> Span {
         AttributeExt::span(self)
     }