chore: remove datetime package dependencies to lodash

[PetrusAsikainen]

Checklist

• Includes tests (well, seems to pass existing ones)
• Update documentation

Changes proposed in this pull request:

I noticed that @blueprintjs/datetime depends on lodash for two extremely trivial use cases. I've changed those as such:

• getCurrentTimezone, a function without arguments, used memoize.

  I've replaced it with a global variable - while this is a new global let, the previous one was a mutable object stored in a const, so it's essentially the same.

  The function was also declared as () => string, meaning there was no official way to access its lodash cache property either.

• timezoneUtils used isEmpty on a variable declared as string | null | undefined, out of which null and undefined were already checked for. I replaced this with a simple manual check

Additionally, @blueprintjs/datetime2 depended on @types/lodash without using it for anything, so I've removed it as well.

This effectively means you can build a Blueprint app without depending transitively on lodash.

Reviewers should focus on:

Whether there are edge cases that might break from these changes.

[changelog-app]

Generate changelog in packages/datetime/changelog/@unreleased

What do the change types mean?

• feature: A new feature of the service.
• improvement: An incremental improvement in the functionality or operation of the service.
• fix: Remedies the incorrect behaviour of a component of the service in a backwards-compatible way.
• break: Has the potential to break consumers of this service's API, inclusive of both Palantir services
  and external consumers of the service's API (e.g. customer-written software or integrations).
• deprecation: Advertises the intention to remove service functionality without any change to the
  operation of the service itself.
• manualTask: Requires the possibility of manual intervention (running a script, eyeballing configuration,
  performing database surgery, ...) at the time of upgrade for it to succeed.
• migration: A fully automatic upgrade migration task with no engineer input required.

Note: only one type should be chosen.

How are new versions calculated?

• ❗The break and manual task changelog types will result in a major release!
• 🐛 The fix changelog type will result in a minor release in most cases, and a patch release version for patch branches. This behaviour is configurable in autorelease.
• ✨ All others will result in a minor version release.

Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

chore: remove datetime package dependencies to lodash

---

Generate changelog in packages/datetime2/changelog/@unreleased

What do the change types mean?

• feature: A new feature of the service.
• improvement: An incremental improvement in the functionality or operation of the service.
• fix: Remedies the incorrect behaviour of a component of the service in a backwards-compatible way.
• break: Has the potential to break consumers of this service's API, inclusive of both Palantir services
  and external consumers of the service's API (e.g. customer-written software or integrations).
• deprecation: Advertises the intention to remove service functionality without any change to the
  operation of the service itself.
• manualTask: Requires the possibility of manual intervention (running a script, eyeballing configuration,
  performing database surgery, ...) at the time of upgrade for it to succeed.
• migration: A fully automatic upgrade migration task with no engineer input required.

Note: only one type should be chosen.

How are new versions calculated?

• ❗The break and manual task changelog types will result in a major release!
• 🐛 The fix changelog type will result in a minor release in most cases, and a patch release version for patch branches. This behaviour is configurable in autorelease.
• ✨ All others will result in a minor version release.

Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

chore: remove datetime package dependencies to lodash

---

Check the box to generate changelog(s)

• Generate changelog entry

[ericjeney]

Thanks! I agree with removing the dep on lodash, especially since it was so light.

[ericjeney]

Suggested change

	if (value === null || value === "") {
	if (value === null || value === "" || typeof value !== "string") {

Can you add a typeof check here to be extra defensive in the event a non-TypeScript consumer is passing in an incorrect value here (such as a number) and expecting to get null returned?

isEmpty evaluates to true on numbers, so I'd like to preserve that behavior to avoid an accidental break.

[PetrusAsikainen]

Seems reasonable. Interesting that here lodash.isEmpty very much doesn't do what it says on the tin:

Checks if value is an empty object, collection, map, or set.

...which a number clearly isn't - handling for primitives isn't specified.