Parsing of `ZonedDateTime` is still confusing

Prerequisites

Please put an X between the brackets as you perform the following steps:

• Check that your issue is not already filed:
  https://github.com/leanprover/lean4/issues
• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
• Test your test case against the latest nightly release, for example on
  https://live.lean-lang.org/#project=lean-nightly
  (You can also use the settings there to switch to “Lean nightly”)

Description

Languages like Java have a single function ZonedDateTime.parse which will generally do the right thing for many reasonable things you give it. In Lean, the situation is more compilicated. Prompted by a recent Zulip thread, I played with ZonedDateTime parsing and the experience was suboptimal.

Click here for a live-lean session where you can see me trying to navigate the ZonedDateTime parsing API

Note that the steps that try to access the time zone database fail on live-lean even though they succeed locally.

Expected behavior: The API should make it easy to do the right thing, and hard/impossible to do the wrong thing.

Actual behavior: Everything is about equally difficult right now, both the right things and the wrong things.

Versions

4.22.0-nightly-2025-06-26

Impact

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No source file, test file, or entry point is named. Start with the linked live-lean session and its minimal ZonedDateTime parsing example, then inspect the existing parsing API and related time-zone database behavior. Done means the API makes correct parsing straightforward while making incorrect usage difficult or impossible.