Unable to import types from another canister. Works for a plain "lib" type

saikatdas0790 · September 18, 2022, 4:07am

Here is a minimal reproduction

saikatdas0790/cross_canister_package_import/blob/master/src/caller/src/lib.rs

// use candid::Principal;
// use ic_cdk::api::call;

#[ic_cdk_macros::update]
#[candid::candid_method(update)]
fn greet() {
    let details_1 = callee::UserDetails {
        name: "Alice".to_string(),
        power: 9001,
    };
    let details_2 = utils::UserDetails {
        name: "Bob".to_string(),
        power: 9001,
    };
    // call::call(
    //     Principal::from_text(option_env!("CANISTER_ID_callee").unwrap()).unwrap(),
    //     "greet",
    //     (UserDetails {
    //         name: "Saikat".to_string(),
    //         age: 100,

This file has been truncated. show original

Basically, the issue is I am unable to import from a package that is a canister but can import from a package that contains a normal lib

These lines import from another canister

github.com

saikatdas0790/cross_canister_package_import/blob/d7b495c3888523a9f217d45802aa3457edbab368/src/caller/src/lib.rs#L7-L10


      
          let details_1 = callee::UserDetails {
              name: "Alice".to_string(),
              power: 9001,
          };

These lines import from another package in the workspace

github.com

saikatdas0790/cross_canister_package_import/blob/d7b495c3888523a9f217d45802aa3457edbab368/src/caller/src/lib.rs#L11-L14


      
          let details_2 = utils::UserDetails {
              name: "Bob".to_string(),
              power: 9001,
          };

The first one doesn’t work, the second one does. Can I not import from one canister package into another? Seems like an arbitrary limitation.

Thoughts?

lwshang · September 19, 2022, 8:25pm

Hi @saikatdas0790,

Likely, the constraint comes from following config in callee/Cargo.toml:

[lib]
crate-type = ["cdylib"]

This is crucial for building target wasm. But it also make the crate not a rust lib anymore. Then it cannot be depended by other crates.

For data structures to be used by multiple canisters, it’s better to move them into a non-cdylib crate.
And let each canister crate depend on that crate.

This is indeed what you achieved with the utils crate.

saikatdas0790 · September 20, 2022, 3:27am

Oh well, would have preferred to be able to do that, for the sake of colocating types, but as I read more, I understand this is a Rust limitation, not an IC limitation.

saikatdas0790 · September 20, 2022, 3:49am

I updated the code here to make the compiler happy, but the dfx build step still fails.

Basically, I tried 2 things:

Removing the crate type
Adding “lib” to the “cdylib” for the crate type array

Both of them make the compiler happy but the build fails.

What’s the reason for a canister type to specifically be “cdylib”?

paulyoung · September 20, 2022, 4:47am

You can definitely import from canisters but you might run into duplicate symbols, e.g. `rust-lld: error: duplicate symbol: canister_query http_request` when trying to use `ic-certified-assets` · Issue #304 · dfinity/cdk-rs · GitHub

saikatdas0790 · September 20, 2022, 12:53pm

So, better not to do it and just define things in a shared lib?