The grammar lacks support for named parameters in mapping types

[vquelque]

Solidity v0.8.18 enables named parameters in mapping types. The current grammar does not support that. This results in errors when trying to parse source units that contain mappings with named parameters.

For example, this minimal contract will throw an error when parsed:

pragma solidity >=0.8.18;

contract TestParse {
    mapping(address account => uint256 balance) public balances;
}

The grammar would need to be fixed to allow for identifiers in mapping types
It could probably be fixed by adding optional identifiers to the mapping parsing expression:

mapping
  : 'mapping' '(' elementaryTypeName identifier? '=>' typeName identifier? ')' ;