Allow to get both JSON output from Cargo and human output from rust

[matklad]

This definitely has come up before, but I've failed to find an issue, so I am creating one.

The use case in IntelliJ is this: when building package before launching debugger, we need --message-format=json to get paths to the artifacts. At the same time, we need to show usual Cargo/Rustc output to the user.

In IntelliJ, the easy workaround would be just to launch cargo twice: once for human output, and once for JSON. 

[Jascha-N]

I would like to see this feature too. I'm creating a transparent wrapper around cargo and currently I also run the cargo commands twice. The problem is that not all cargo should be run twice, because of possible side effects (documentation opening twice with doc --open, crates being published twice, etc.).

[roblabla]

I would also like this for cargo-travis. The reasoning is similar: we need the --message-format=json to get paths to the test artifacts, but we want to show the usual cargo output anyways. The current solution involves recreating the output ourselves, and that's kinda painful.

[ehuss]

@matklad I think this is now supported via the --message-format=json-render-diagnostics flag hitting stable 1.38 in a few days (docs). Does that sufficiently cover the use case here to close this issue?

[matklad]

Yeah, I think this can be closed now, seems like json-diagnostic-rendered-ansi might even be better for IntelliJ use case cc @mchernyavsky