Problem: Both `PackChangedPre` and `PackChanged` contain |event-data|
with plugin's `spec`. It looks like a good idea to have all its
triggers contain the same format across all kinds ("install",
"update", "delete"). There are several choices:
- Have it be as verbatim as supplied to `vim.pack.add()`, i.e. can
be either string or table. A bit too ambiguous.
- Have it be table with `src` and `name` inferred. This requires
less work for "install", but more work for "update" and "delete"
(since they use `vim.pack.get()` which already infers default
`version`).
- Have it be table with *all* defaults made explicit. This looks
like the best approach, but requires extra care to only infer
default `version` when needed (i.e. avoid inferring during regular
load) because it is costly in terms of startup time.
This might also introduce inconsistency when dealing with
lockfile(s) as information there should be as close to what user
supplied as possible. Address that when dealing with lockfile.
Solution: Ensure explicit `version` in all events where possible.
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