Automatically generate candid from rust sources

roman-kashitsyn · July 16, 2021, 8:44pm

I believe it pays off to have your .did file committed to the repository, documented, and curated manually. This is the face of your canister, the main thing that people who integrate with your canister will care about. It’s a lot like a header file for a C/C++ library or a module interface file in OCaml.

Being able to generate a .did file automatically is still very useful:

You can use it get the first version of the .did file that you can edit by hand afterwards.
You can use it to generate the actual interface of your canister and pipe it to didc subtype as a precommit hook to make sure that the manually curated .did file is not obsolete.

IC governance canister adds a main function that outputs the .did file when compiled in native mode:

github.com

dfinity/ic/blob/40ab84f4fcb9e6c2441e91a59cfaa5acf84fe38d/rs/nns/governance/canister/canister.rs#L742-L756

    
      
          // When run on native this prints the candid service definition of this
          // canister, from the methods annotated with `candid_method` above.
          //
          // Note that `cargo test` calls `main`, and `export_service` (which defines
          // `__export_service` in the current scope) needs to be called exactly once. So
          // in addition to `not(target_arch = "wasm32")` we have a `not(test)` guard here
          // to avoid calling `export_service`, which we need to call in the test below.
          #[cfg(not(any(target_arch = "wasm32", test)))]
          fn main() {
              // The line below generates did types and service definition from the
              // methods annotated with `candid_method` above. The definition is then
              // obtained with `__export_service()`.
              candid::export_service!();
              std::print!("{}", __export_service());
          }

The generated governance.did file is also committed to the repository: ic/governance.did at 40ab84f4fcb9e6c2441e91a59cfaa5acf84fe38d · dfinity/ic · GitHub

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Automatically generate candid from rust sources

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