Add lint of a null check then spread or expand other lint

[parlough]

Name

Some options:

• verbose_conditional_collection_spread
• unnecessary_null_check_and_spread
  • Matches the naming scheme of other lints and diagnostics
• prefer_null_aware_spread_operator

Description

The analyzer produces this diagnostic when a list is added to a collection literal with a spread operator after checking if it's not null.

Categories

style, languageFeatureUsage

Bad examples

final list = [
  itemOne,
  itemTwo,
  if (extraItems != null) ...extraItems,
];

Good examples

final list = [
  itemOne,
  itemTwo,
  ...?extraItems,
];

Fix discussion

A widely applicable fix should be possible. If the lint isn't seen as valuable enough to many, just the assist would still be valuable.

Alternative(s)

Expand prefer_null_aware_operators to cover these cases as it covers other conditional checks then usages.

prefer_spread_collections could also work as it already covers some null-aware cases, and I imagine if one wants that, they'd almost always prefer to use it here too.

[srawlins]

I'd be in favor of enhancing prefer_spread_collections.