Added checker for FirEqualityOperatorCall. It's surfaced as one of the
following diagnostics depending on the PSI structure and types under
comparison:
* INCOMPATIBLE_TYPES(_WARNING)
* EQUALITY_NOT_APPLICABLE(_WARNING)
* INCOMPATIBLE_ENUM_COMPARISON_ERROR
Comparing with FE1.0, the current implementation is more conservative
and only highlights error if the types are known to follow certain
contracts with `equals` method. Otherwise, the checker reports warnings
instead.
However, the current checker is more strict in the following situations:
1. it now rejects incompatible enum types like `Enum<E1>` and
`Enum<E2>`, which was previously accepted
2. it now rejects incompatible class types like `Class<String>` and
`Class<Int>`, which was previously accepted
3. the check now takes smart cast into consideration, so
`if (x is String) x == 3` is now rejected
Previously helpers from checkType.kt was in special package, and
if directive was enabled then test runner (`AbstractDiagnosticTest`)
injected additional imports to test files and removed them after test
was completed.
It's very hard to support such behavior in new test infrastructure so
there was a decision about changing `CHECK_TYPE`:
1. All helpers from `checkType.kt` now stays in default package
2. `CHECK_TYPE` only adds `checkType.kt` to set of analyzed files
and don't modify their content
For test which are written in default package (most of tests actually)
there are no changes. On the other hand if there is a test where dev
want to use checkType functions in testfile with some package then he
should explicitly import functions which he needed (`checkSubtype`,
`checkType`, `_`)
Ivan Kochurkin