Importing another contract into the scope prohibits emitting event

[fbielejec]

Description Putting another contract struct into context creates a situation where there isn't enough (type) information to use emit_event :

error[E0284]: type annotations needed
  --> lib.rs:36:24
   |
36 |             self.env().emit_event(ContractACalled { caller });
   |                        ^^^^^^^^^^ cannot infer type for type parameter `C` declared on the trait `EmitEvent`
   |
   = note: cannot satisfy `<_ as ink_lang::reflect::ContractEventBase>::Type == _`

error[E0283]: type annotations needed
  --> lib.rs:36:24
   |
36 |             self.env().emit_event(ContractACalled { caller });
   |                        ^^^^^^^^^^ cannot infer type for type parameter `C` declared on the trait `EmitEvent`
   |
note: multiple `impl`s satisfying `ink_lang::EnvAccess<'_, ink_env::DefaultEnvironment>: ink_lang::codegen::EmitEvent<_>` found
  --> lib.rs:5:1
   |
5  | #[ink::contract]
   | ^^^^^^^^^^^^^^^^
   = note: and another `impl` found in the `contract_b` crate: `impl<'a> ink_lang::codegen::EmitEvent<contract_b::ContractB> for ink_lang::EnvAccess<'a, <contract_b::ContractB as ink_lang::reflect::ContractEnv>::Env>;`
   = note: this error originates in the attribute macro `ink::contract` (in Nightly builds, run with -Z macro-backtrace for more info)

Casting <ContractA as ContractEventBase>::Type could potentially be used to hint the compiler but all the events are behind a (macro-generated) public enum:

pub enum __ink_EventBase {
    ContractACalled(ContractACalled),
}

and Rust won't take __ as an identifier (not a valid syntax).

self.env() is ink_lang::codegen::EmitEvent<ContractA> so some solution is to wrap event emitting in a function such as:

fn emit_event<EE: EmitEvent<Self>>(e: EE) {
   e.emit_event(ContractACalled {});
}

but that is not the most ergonomic.

Additional context Here's a reproducible example: https://github.com/fbielejec/emit_event

[xgreenx]

Duplicate of https://github.com/paritytech/ink/issues/1000