Proposed resolution:

This wording is relative to N5001.

1. Modify [time.zone.db.tzdb] as indicated:

   
   const time_zone* locate_zone(string_view tz_name) const;
   

   -2- Returns:

   1. (2.1) — If `zones` contains an element `tz` for which `tz.name() == tz_name`, a pointer to `tz`;
   2. (2.2) — otherwise, if `links` contains an element `tz_l` for which `tz_l.name() == tz_name`, then a pointer to the element `tz` of zones for which `tz.name() == tz_l.target()` the result of `locate_zone(tz_l.target())`. .

   [Note 1: A `time_zone_link` specifies an alternative name for a `time_zone`. — end note]

   -3- Throws: If a `const time_zone*` cannot be found as described in the Returns: element, throws a `runtime_error`.

   [Note 2: On non-exceptional return, the return value is always a pointer to a valid `time_zone`. — end note]

   -?- Remarks: If both `zones` and `links` contain elements that match `tz_name` then it is unspecified whether &tz or locate_zone(tz_l.target()) is returned.

   [Drafting note: This gives flexibility how to implement the lookup in `locate_zone`.]

2. Modify [time.zone.link.overview] as indicated:

   -1- A `time_zone_link` specifies an alternative name for a `time_zone`. `time_zone_links` are constructed when the time zone database is initialized. The name of a `time_zone_link` can be used as an argument to `tzdb::locate_zone` ([time.zone.db.tzdb]). A `time_zone_link` can refer directly to a `time_zone`, or to another `time_zone_link`, forming a chain of links.

3. Modify [time.zone.link.members] as indicated:

   
   string_view name() const noexcept;
   

   -1- Returns: The alternative name for the time zone.

   
   string_view target() const noexcept;
   

   -2- Returns: The name of the `time_zone` for which this `time_zone_link` provides an alternative name or the name of another `time_zone_link`.

   [Note 1: `tzdb::locate_zone` follows a chain of links formed when a link's target is the name of a `time_zone_link`, throwing an exception if the chain of links does not terminate in a `time_zone`. — end note]

Since October 2022 the IANA Time Zone Database's `tzfile` data format allows a Link to refer to another Link, instead of referring directly to a Zone. The zic(8) man page says:

The TARGET field should appear as the NAME field in some zone line or as the LINK-NAME field in some link line. The LINK-NAME field is used as an alternative name for that zone; it has the same syntax as a zone line's NAME field. Links can chain together, although the behavior is unspecified if a chain of one or more links does not terminate in a Zone name.

The `time_zone_link::target()` member function is required to return "The name of the `time_zone` for which this `time_zone_link` provides an alternative name." This doesn't allow returning the name of another `time_zone_link`, which implies that the implementation should flatten a series of links so that the target is a `time_zone`. However, this discards information which is present in the `tzdb`, so that the information exposed to a C++ program does not preserve the original structure of a chain of links.

The standard could be adjusted to support chains of links by allowing `time_zone_link::target()` to refer to another link, and then altering the algorithm used by `tzdb::locate_zone(string_view)` to find a `time_zone` from a name that might be a zone or a link.