SERVER-34396 Fail to compile if io manipulators like std::hex are passed to StringBuilder/str::stream

This includes a partial revert of 80f409d1311eb8d20251d17be474aff382538b84
(SERVER-34307) to address this bug.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/mongo/bson/util/builder.h b/src/mongo/bson/util/builder.h
index f82ffccc3fa..ccf4cd183fd 100644
--- a/src/mongo/bson/util/builder.h
+++ b/src/mongo/bson/util/builder.h
@@ -455,6 +455,14 @@ public:
         return optional ? *this << *optional : *this << "(None)";
     }
 
+    /**
+     * Fail to compile if passed an unevaluated function, rather than allow it to decay and invoke
+     * the bool overload. This catches both passing std::hex (which isn't supported by this type)
+     * and forgetting to add () when doing `stream << someFuntion`.
+     */
+    template <typename R, typename... Args>
+    StringBuilderImpl& operator<<(R (*val)(Args...)) = delete;
+
     void appendDoubleNice(double x) {
         const int prev = _buf.l;
         const int maxSize = 32;