no-unnecessary-type-assertion: Don't check ! if --strictNullChecks is not enabled

[ghost]

PR checklist

• Addresses an existing issue: #0000
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Doesn't check whether x! is an unnecessary non-null assertion if --strictNullChecks is not enabled.

CHANGELOG.md entry:

[bugfix] no-unnecessary-type-assertion: Don't check x! non-null assertions if --strictNullChecks is not enabled

[ajafff]

@andy-ms what's the motivation for this change? Adding assertions during migration to --strictNullChecks?

[ghost]

With --strictNullChecks on this change is unnecessary. But without --strictNullChecks, the rule currently produces a lot of false positives at x! because it gets a non-null type for x.

[ajafff]

Yeah, I get that. But what's the use case?
There's no reason to use non null assertions without strictNullChecks. The assertion is really unnecessary.
It only makes sense if you are migrating to strictNullChecks.

[ghost]

At least for TypeScript, we annotated our code as best as we could even without having --strictNullChecks enabled. I wouldn't want to have to remove all of those assertions to enable this lint rule, then have to add them all back when enabling --strictNullChecks.

[giladgray]

@andy-ms this change looks good! would you mind merging latest master and resolving merge conflicts?

[NaridaL]

What's the status on this?

[JoshuaKGoldberg]

👋 @andy-ms and @NaridaL! I don't know if this is still relevant or useful to you, but heads up that this is now merged in and will be available in the next TSLint release. Sorry this took so long!