Allow to pass protoc command line arguments via a file or stdin

[sergei-ivanov]

This has been a recurring source of pain on Windows for ages: in large projects with lots of .proto definitions or lots of .proto imports it is pretty easy to reach the command line length limit on Windows, which is ridiculously small. We've developed a number of workarounds for this problem in the Maven plugin, but there are still reports that some projects are struggling.
A simple solution that would have allowed us to solve that issue once and forever would be to pass a file with the actual command line arguments on the command line, or alternatively pipe them in.

[xfxyjwf]

If you have a lot of .proto files, you don't have to invoke protoc on all of them in a single pass. Instead, you can invoke protoc once for each of them.

[sergei-ivanov]

I know, it is one of the workarounds that we either considered or already implemented. It may be less efficient, but it gets things done. I think the latest problem that one of the clients ran into was related to a large number of import paths (-I=xxxxxx), which busts the command line limit. Again, I think we can work around it in some creative way, but it would be much easier if we could run something like protoc @args.tmp where args.tmp would be a text file containing a newline-separated list of command line arguments.

[xfxyjwf]

We actually have this feature internally already.

[sergei-ivanov]

This is amazingly good news. I shall add support to the Maven plugin as soon as it is publicly available in protoc.

[liujisi]

I believe this is already implemented.

[sergei-ivanov]

I've just tested it with protoc 3.5.0, and it appears to work beautifully. Is 3.5.0 the earliest version where this feature has become publicly available?
Many thanks for implementing this.

[xfxyjwf]

@sergei-ivanov Yes, 3.5.0 is the first version with this feature.