It breaks Make, which does not have a default rule for “*.c++” files, but does have rules both for “*.cpp” files and the older naming custom of “*.C” files.

In modern GNU make it is generally advised to disable default rules anyways. I know some people try to do portable Make, but I am pretty over that idea myself, so if I do use Make, I'm using GNU extensions and GNUmakefile.

GNU Make does not have a rule for “*.c++” files, either.

Do you have a reference to the advice to disable default rules? It sounds counterproductive to me.

There's lots of different opinions on how to use Make, but here's one. https://tech.davis-hansson.com/p/make/

Not very well recieved here on HN a month ago: https://news.ycombinator.com/item?id=32541016

That's a sign that it's good :)

Jokes aside though, the only major complaint people have is about .RECIPEPREFIX, which I also don't follow. I didn't read too many comments, but the top voted comments do not appear to take issue with the advice to disable built-in rules.

I'd be surprised, since it is far from the first time I've heard that advice, and it never seemed very controversial.

Why would you use .c++ instead of the standard .cpp?

I got tired of arguing about .cpp vs. .cc vs. .cxx vs. .C.

So I used the actual name of the language, and it worked fine. :)