Function compile_fill_expr 

pub fn compile_fill_expr(
    type_name: &str,
    expr_str: &str,
    schema: &SchemaDescriptor,
) -> Result<String, PyQLError>

Compile a PyQL expression string in the context of a named type to a bare SQL expression suitable for use in an UPDATE SET clause.

Pointer references (.name) are emitted without a table alias because UPDATE SET expressions reference the current row directly. Query parameters ($name) are rejected — fill expressions must be literal values or pointer references.