tonic_build: option to check for changes

[emilk]

Feature Request

Crates

tonic_build

Motivation

We run tonic_build manually and check in our generated code.
We want to have a CI step to check that the generated code is up-to-date.

Proposal

Add an option to Builder that, when set, will cause the compile_protos invocation to FAIL if the files on disk differs from the generated ones.
The fail could be returning a special error.

   let is_on_ci: bool = …;
   tonic_build::configure()
        .out_dir(output_dir.as_ref())
        .build_client(true)
        .build_server(true)
        .fail_on_diff(is_on_ci) // Turn on "check" mode when we're on CI
        .compile_protos(proto_paths, &[definitions_dir])
        .unwrap(); // will fail if the files require changes on ci

Alternatives

As a user, I can also just run the code-gen and then check for diffs with git - but that is messy.