typeck: fix ? operator suggestion span

Author: jieyouxu

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -1291,12 +1291,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 ty::TraitRef::new(self.tcx, into_def_id, [expr_ty, expected_ty]),
             ))
         {
-            let mut span = expr.span;
-            while expr.span.eq_ctxt(span)
-                && let Some(parent_callsite) = span.parent_callsite()
-            {
-                span = parent_callsite;
-            }
+            let span = find_local_most_ancestor_suggestable_span(expr.span);
 
             let mut sugg = if expr.precedence().order() >= PREC_POSTFIX {
                 vec![(span.shrink_to_hi(), ".into()".to_owned())]
@@ -1901,12 +1896,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             None => sugg.to_string(),
         };
 
-        err.span_suggestion_verbose(
-            expr.span.shrink_to_hi(),
-            msg,
-            sugg,
-            Applicability::HasPlaceholders,
-        );
+        let span = find_local_most_ancestor_suggestable_span(expr.span);
+        err.span_suggestion_verbose(span.shrink_to_hi(), msg, sugg, Applicability::HasPlaceholders);
         return true;
     }
 
@@ -3180,3 +3171,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 }
+
+/// For suggestion span, recursively try to look for the ancestor span which shares the same syntax
+/// context as the initially provided `span`. This will recursively look into local macros until the
+/// span inside the most ancestor local macro is found. It will stop recursing as soon as the
+/// syntax context of a potential parent callsite changes, such as if the potential parent callsite
+/// is in a foreign macro. This helps to prevent leaking implementation details from upstream
+/// crates and stdlib crates that the user likely have no control over.
+fn find_local_most_ancestor_suggestable_span(initial_span: Span) -> Span {
+    let mut span = initial_span;
+    while initial_span.eq_ctxt(span)
+        && let Some(parent_callsite) = span.parent_callsite()
+    {
+        span = parent_callsite;
+    }
+    span
+}