Pull Span::find_ancestor_inside loop into its own function.

compiler/rustc_span/src/lib.rs

@@ -597,6 +597,14 @@ impl Span {
         if !expn_data.is_root() { Some(expn_data.call_site) } else { None }
     }
 
+    /// Walk down the expansion ancestors to find a span that's contained within `outer`.
+    pub fn find_ancestor_inside(mut self, outer: Span) -> Option<Span> {
+        while !outer.contains(self) {
+            self = self.parent()?;
+        }
+        Some(self)
+    }
+
     /// Edition of the crate from which this span came.
     pub fn edition(self) -> edition::Edition {
         self.ctxt().edition()

compiler/rustc_typeck/src/check/upvar.rs

@@ -680,15 +680,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         migrated_variables_concat
                     );
 
-                    let mut closure_body_span = self.tcx.hir().span(body_id.hir_id);
-
                     // If the body was entirely expanded from a macro
                     // invocation, i.e. the body is not contained inside the
                     // closure span, then we walk up the expansion until we
                     // find the span before the expansion.
-                    while !closure_body_span.is_dummy() && !closure_span.contains(closure_body_span) {
-                        closure_body_span = closure_body_span.parent().unwrap_or(DUMMY_SP);
-                    }
+                    let closure_body_span = self.tcx.hir().span(body_id.hir_id)
+                        .find_ancestor_inside(closure_span)
+                        .unwrap_or(DUMMY_SP);
 
                     if let Ok(s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
                         let mut lines = s.lines();