https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71930
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (1) so what? The behavior for - input without -x is the same for all drivers. gfortran -E - will not preprocess as if it is Fortran source, gcj -E - will not preprocess as if it is a Java source (after all, there is no preprocessing for Java), etc. And (2), the fact that -std=c++17 is C++/ObjC++ specific option is not known to the driver, all it knows is that it should pass options starting with -std down to the preprocessor and/or compiler. Why should that affect which preprocessor is used? Should it pick up ObjC++ or C++? There is a standard option to choose the language, and that is -x. If the source has an extension, then the language is generally determined from the file extension (but it can be still overridden). -std= is just about choosing a particular revision of the language.
