Standard method checks should allow out-of-package messages

[jgeewax]

For example

rpc CreateBook(CreateBookRequest) returns (other.package.Book);

This should be allowed (I think), but am not sure if it's covered.

[lukesneeringer]

This actually would be allowed now (we only check the name, not the fully qualified name), although I actually wonder whether it should be disallowed.

[jgeewax]

I'd argue that it's generally bad practice to use other APIs protos in your RPCs input/output types, however "the presence of dots" does not necessarily mean "it belongs to another API" (it might be owned by the same group, etc).

I'll look for a test case for this just to be sure. If there isn't one, we should add one.

In future, we should come up with a different rule that says "Don't copy and use other people's proto files unless you control them or they're considered 'sealed'" and have a lint check for that.

[lukesneeringer]

Sure, but this bug is specifically about the standard methods. And I really can not think of a reason why standard methods would use protos from different packages (other than g.p.Empty, which we explicitly permit) that does not violate our standards.

[lukesneeringer]

This is not coming up in user reports, and we do not agree on whether it should be allowed (it currently is), so going to close this.