quick-fixes for rest statements in map patterns

[pq]

With dart-lang/language#2861, empty maps and rests in maps will become disallowed, presenting some new quick-fix opportunities.

• {...} => Map()
• {'a': a, 'b': b, ...} => {'a': a, 'b': b}
• {} => Map() or Map(isEmpty: true) (2 fixes)

/cc @stereotype441 @munificent @bwilkerson

[stereotype441]

It just occurred to me that Map(isEmpty: true) is only valid in a matching context; in a declaration or assignment context it's illegal. So the quick-fix {} => Map(isEmpty: true) probably should only be offered in a matching context.

[eernstg]

Sounds OK! It's really difficult to justify var {} = myMap; with the old semantics ("throw unless myMap is empty"). It doesn't declare any variables, and if (myMap.isEmpty) throw "something"; is more readable. ;-)

[munificent]

1. {...} => Map()
2. {'a': a, 'b': b, ...} => {'a': a, 'b': b}

Probably not worth doing a quick fix for these since ... will never be supported in a stable version. It exists right now on the bleeding edge, but it will be gone before any significant number of users ever see it.

[bwilkerson]

Definitely lower priority than the other fixes, in my opinion. But if we think that some users might try to use rest patterns, then it might be useful to have a fix if other support is done.

[bwilkerson]

Replacing an empty map pattern is done with https://dart-review.googlesource.com/c/sdk/+/292284.

Reducing the priority to reflect the remaining work to implement "remove rest pattern".

[bwilkerson]

I'm not sure I understand. Are you perhaps confusing "map pattern" with "map literal"? A map pattern is a pattern (new language feature) that can be used to check the type and structure of a map, but does not itself produce a map.

[mraleph]

@bwilkerson it's just an AI generated nonsense answer. ChatGPT most likely.