README.md

Test Contracts - Error Cases

This directory contains test contracts that test common compilation errors that were hard to understand in Aztec contracts. These tests are based on the private_token_contract example, with modifications to trigger specific error scenarios.

Test Cases

1. private_token_contract_storage_macro - Missing #[storage] Attribute

Modification: Removed the #[storage] attribute from the Storage struct.

Original Code:

#[storage]
struct Storage<Context> {
    balances: Map<AztecAddress, EasyPrivateUint<Context>, Context>,
}

Modified Code:

struct Storage<Context> {
    balances: Map<AztecAddress, EasyPrivateUint<Context>, Context>,
}

2. private_token_contract_struct_as_arg - Invalid Function Parameter Type

Modification: Added and empty Arbitrary struct. Changed the mint function parameter from u64 to a custom Arbitrary struct.

Original Code:

fn mint(amount: u64, owner: AztecAddress) {
    let balances = storage.balances;
    balances.at(owner).add(amount, owner);
}

Modified Code:

pub struct Arbitrary {}

fn mint(amount: Arbitrary, owner: AztecAddress) {
    //let balances = storage.balances;
    //balances.at(owner).add(amount, owner);
}

Expected Errors:

• No matching impl found for Arbitrary: Serialize<N = _> - The custom struct doesn't implement the Serialize trait required for function parameters
• Type annotation needed - Generic type inference fails due to the serialization error

Purpose: The reason we see this error is function arguments need to be serialized. We need to define Serialize/Deserialize trait implementation for the new struct,

3. private_token_contract_private_struct - Private Struct in Function

Modification: Added a private struct Arbitrary and used it as a function parameter in a #[private] function.

Original Code:

#[private]
fn mint(amount: u64, owner: AztecAddress) {
    let balances = storage.balances;
    balances.at(owner).add(amount, owner);
}

Modified Code:

#[derive(Serialize, Deserialize)]
struct Arbitrary {
    value: u64,
}

#[private]
fn mint(amount: Arbitrary, owner: AztecAddress) {
    //let balances = storage.balances;
    //balances.at(owner).add(amount, owner);
}

Expected Errors:

• Type Arbitrary is more private than item mint_parameters::amount
• Type Arbitrary is more private than item mint

Purpose: It might be confusing to see mint function labelled as #[private], but got error Type Arbitrary is more private than item mint

4. private_token_contract_utility_macro - Missing #[utility] Attribute

Modification: Removed the #[utility] attribute from the get_balance function.

Original Code:

#[utility]
unconstrained fn get_balance(owner: AztecAddress) -> Field {
    storage.balances.at(owner).get_value()
}

Modified Code:

unconstrained fn get_balance(owner: AztecAddress) -> Field {
    storage.balances.at(owner).get_value()
}

Expected Errors:

• Function get_balance must be marked as either #[private], #[public], #[utility], #[contract_library_method], or #[test]

Running the Tests

These test contracts are designed to fail compilation and capture the error output. To run the tests:

./scripts/test.sh

The script will:

1. Compile each test contract (expecting failures)
2. Capture the error output
3. Compare against expected error messages
4. Report whether the error messages match expectations