Fix comments of find_oldest_ancestor_in_same_ctxt

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

Author: xizheyin

compiler/rustc_span/src/lib.rs

@@ -762,10 +762,10 @@ impl Span {
         Some(self)
     }
 
-    /// Recursively walk down the expansion ancestors to find the oldest ancestor span with the same
-    /// [`SyntaxContext`] the initial span.
+    /// Recursively walk up the expansion ancestors to find the oldest ancestor span with the same
+    /// [`SyntaxContext`] as the initial span.
     ///
-    /// This method is suitable for peeling through *local* macro expansions to find the "innermost"
+    /// This method is suitable for peeling through *local* macro expansions to find the "outermost"
     /// span that is still local and shares the same [`SyntaxContext`]. For example, given
     ///
     /// ```ignore (illustrative example, contains type error)
@@ -787,8 +787,8 @@ impl Span {
     ///  }
     /// ```
     ///
-    /// if provided the initial span of `outer!(x)` inside `bar`, this method will recurse
-    /// the parent callsites until we reach `format!("error: {}", $x)`, at which point it is the
+    /// if provided the initial span of `format!("error: {}", $x)` inside the expansion, this method will recurse
+    /// up the parent callsites until we reach `outer!(x)` in `bar`, at which point it is the
     /// oldest ancestor span that is both still local and shares the same [`SyntaxContext`] as the
     /// initial span.
     pub fn find_oldest_ancestor_in_same_ctxt(self) -> Span {