feat(codegen): allow defining additional capabilities, closes #8798

[lucasfernog]

Changes the tauri::generate_context proc macro to parse the capabilities attribute:

tauri::generate_context!(
  capabilities = [
    "../capabilities/base.json",
    #[cfg(feature = "beta")]
    "../capabilities/beta.json"
  ]

In this case, the additional capabilities are parsed at runtime (limitation of proc-macro, cannot resolve the #[cfg] attributes :(

Additionally, the tauri-build context codegen method now has a capability method:

fn main() {
  let mut codegen = tauri_build::CodegenContext::new();
  if !cfg!(feature = "custom-protocol") {
    codegen = codegen.dev();
  }

  #[cfg(feature = "admin")]
  codegen = codegen.capability("./capabilities/admin.json");

  tauri_build::try_build(tauri_build::Attributes::new().codegen(codegen))
    .expect("failed to run tauri-build");
}

This API is more powerful since it can resolve the capability at compile time.

[lucasfernog-crabnebula]

RuntimeAuthority::add_capability implements the base API for #8799

[amrbashir]

does this need to be hidden also? and have this internal name? why not just expose it?

[lucasfernog]

not stable yet.. maybe we move it under the unstable feature flag, but I don't like the idea of allowing devs to allow an specific command, they should go through the whole capabilities > permissions folow, this was just added for our examples which can't use a build script so they do not go through our ACL definitions
cc @tweidinger

[lucasfernog]

Needs #8797

[lucasfernog]

I would be ok with removing the option from the generate_context macro too since it leads you into thinking it's resolved at compile time but it isn't (the tauri-build option is much better).

[amrbashir]

In this case, the additional capabilities are parsed at runtime (limitation of proc-macro, cannot resolve the #[cfg] attributes :(

Can't we just provide an option to specify a capability file without #[cfg] and so we can parse this at compile-time? if they want to use #[cfg], they should do so on the whole macro

#[cfg(not(beta))]
let context = tauri::generate_context!(capabilities = ["path/to/capability.json"]);
#[cfg(beta)]
let context = tauri::generate_context!(capabilities = ["path/to/capability-beta.json"]);

[lucasfernog]

Let's roll with that approach for now until Rust supports expanding cfg on the proc macro.