FieldSelectorMacros

Scala 3 macro implementations that turn a field selector such as _.userCount into the name of the field, checked at compile time.

They back the selector-based methods of FieldUpdate (increment, decrement, setValue, maxValue, minValue) and the HandlerBuilder.update macro, so that a misspelled field is a compile error and not a runtime failure. The selector must be a lambda that reads a field, such as _.userCount. Only the last field name of the selector is used, so _.stats.userCount gives userCount. A selector that is not a lambda, or that reads no field, such as x => x, is rejected with a compile error.

Field names are mapped to SQL snake_case column names with SqlNameMapper.SnakeCase, for example userCount becomes user_count. The name is worked out at compile time and appears as a string literal in the expanded code, so no reflection happens at runtime.