Rename Cursor/CursorRef as TokenTreeCursor/RefTokenTreeCursor.

This makes it clear they return token trees, and makes for a nice
comparison against `TokenCursor` which returns tokens.

compiler/rustc_ast/src/tokenstream.rs

@@ -389,12 +389,12 @@ impl TokenStream {
         self.0.len()
     }
 
-    pub fn trees(&self) -> CursorRef<'_> {
-        CursorRef::new(self)
+    pub fn trees(&self) -> RefTokenTreeCursor<'_> {
+        RefTokenTreeCursor::new(self)
     }
 
-    pub fn into_trees(self) -> Cursor {
-        Cursor::new(self)
+    pub fn into_trees(self) -> TokenTreeCursor {
+        TokenTreeCursor::new(self)
     }
 
     /// Compares two `TokenStream`s, checking equality without regarding span information.
@@ -552,16 +552,17 @@ impl TokenStream {
     }
 }
 
-/// By-reference iterator over a [`TokenStream`].
+/// By-reference iterator over a [`TokenStream`], that produces `&TokenTree`
+/// items.
 #[derive(Clone)]
-pub struct CursorRef<'t> {
+pub struct RefTokenTreeCursor<'t> {
     stream: &'t TokenStream,
     index: usize,
 }
 
-impl<'t> CursorRef<'t> {
+impl<'t> RefTokenTreeCursor<'t> {
     fn new(stream: &'t TokenStream) -> Self {
-        CursorRef { stream, index: 0 }
+        RefTokenTreeCursor { stream, index: 0 }
     }
 
     pub fn look_ahead(&self, n: usize) -> Option<&TokenTree> {
@@ -569,7 +570,7 @@ impl<'t> CursorRef<'t> {
     }
 }
 
-impl<'t> Iterator for CursorRef<'t> {
+impl<'t> Iterator for RefTokenTreeCursor<'t> {
     type Item = &'t TokenTree;
 
     fn next(&mut self) -> Option<&'t TokenTree> {
@@ -580,15 +581,16 @@ impl<'t> Iterator for CursorRef<'t> {
     }
 }
 
-/// Owning by-value iterator over a [`TokenStream`].
+/// Owning by-value iterator over a [`TokenStream`], that produces `TokenTree`
+/// items.
 // FIXME: Many uses of this can be replaced with by-reference iterator to avoid clones.
 #[derive(Clone)]
-pub struct Cursor {
+pub struct TokenTreeCursor {
     pub stream: TokenStream,
     index: usize,
 }
 
-impl Iterator for Cursor {
+impl Iterator for TokenTreeCursor {
     type Item = TokenTree;
 
     fn next(&mut self) -> Option<TokenTree> {
@@ -599,9 +601,9 @@ impl Iterator for Cursor {
     }
 }
 
-impl Cursor {
+impl TokenTreeCursor {
     fn new(stream: TokenStream) -> Self {
-        Cursor { stream, index: 0 }
+        TokenTreeCursor { stream, index: 0 }
     }
 
     #[inline]