Add some useful Path/PathSegment equality operations.

They will be used in a subsequent commit.

compiler/rustc_ast/src/ast.rs

@@ -97,12 +97,12 @@ pub struct Path {
     pub tokens: Option<LazyAttrTokenStream>,
 }
 
+// Succeeds if the path has a single segment that is arg-free and matches the given symbol.
 impl PartialEq<Symbol> for Path {
     #[inline]
     fn eq(&self, name: &Symbol) -> bool {
         if let [segment] = self.segments.as_ref()
-            && segment.args.is_none()
+            && segment == name
-            && segment.ident.name == *name
         {
             true
         } else {
@@ -111,6 +111,15 @@ impl PartialEq<Symbol> for Path {
     }
 }
 
+// Succeeds if the path has segments that are arg-free and match the given symbols.
+impl PartialEq<&[Symbol]> for Path {
+    #[inline]
+    fn eq(&self, names: &&[Symbol]) -> bool {
+        self.segments.len() == names.len()
+            && self.segments.iter().zip(names.iter()).all(|(s1, s2)| s1 == s2)
+    }
+}
+
 impl<CTX: rustc_span::HashStableContext> HashStable<CTX> for Path {
     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
         self.segments.len().hash_stable(hcx, hasher);
@@ -166,6 +175,14 @@ pub struct PathSegment {
     pub args: Option<P<GenericArgs>>,
 }
 
+// Succeeds if the path segment is arg-free and matches the given symbol.
+impl PartialEq<Symbol> for PathSegment {
+    #[inline]
+    fn eq(&self, name: &Symbol) -> bool {
+        self.args.is_none() && self.ident.name == *name
+    }
+}
+
 impl PathSegment {
     pub fn from_ident(ident: Ident) -> Self {
         PathSegment { ident, id: DUMMY_NODE_ID, args: None }