2.1.84. ‑‑[no_]nonstd_qualifier_deduction
This option controls whether or not nonstandard template argument deduction is to be performed in the qualifier portion of a qualified name in C++.
With this feature enabled, a template argument for the template parameter T can be deduced in contexts like A<T>::B or T::B. The standard deduction mechanism treats these as non deduced contexts that use the values of template parameters that were either explicitly specified or deduced elsewhere.
Note
The option --nonstd_qualifier_deduction is provided only as a migration aid for legacy source code that does not conform to the C++ standard. Its use is not recommended.
This option is effective only if the source language is C++.
The default is ‑‑no_nonstd_qualifier_deduction.