E138: Trait Parameter Used As Parent Prefix

This error occurs when a trait tries to extend a parent type that is derived from the trait's own parameters.

Using a trait parameter as the prefix for a parent type is disallowed to prevent outer-related NullPointerException errors at runtime. The parent class initialization happens before trait parameters are available, which would cause runtime failures.

Note: This error code is typically caught by an earlier compiler phase with a different error message. The TraitParameterUsedAsParentPrefix check in RefChecks serves as a safety net but is rarely triggered in practice because PostTyper catches the same scenarios first.

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