language server: Option to auto-fill required param keyword for non-null arguments

[micimize]

Wanted to open an issue for discussing a potential flag to the language server / analysis server for automatically filling the required keyword when non-nullable arguments are specified.

As far as I know, this would be the first semantic-source-altering feature for the analysis server. I don't know if there has been an explicit decision to never implement something of the sort.

Discussion of language-level solutions:

• required argument inference: [proposal] non-nullable named parameters required by default language#878 (comment)
• f({ int! param }) syntax alternative: Replace current "@required this.name" in the named parameters with "this.name!" language#1103 (comment)

The auto-fill feature should be discussed first, but as an aside, I think an elegant approach to such a feature would be to have it be bi-directional, so that an editor could toggle between "final source" and "truncated/tersified source." I doubt that would make sense if this is the only syntax rewrite that ever gets implemented though.

[bwilkerson]

I think there are some interesting challenges to implementing something like this in the analysis server, and it isn't clear to me that doing so would be good for the user experience, but we do have another tool (dart fix) that might be a reasonable place for implementing such behavior.

We already have a fix to add the required keyword, but it isn't currently enabled for bulk application. The reason is that there are other equally valid fixes so we can't know which one the user is likely to want to have applied in a given situation. If we had a way for the user to specify which fix to apply for a given diagnostic, then we could apply that fix as part of bulk fixing.

[micimize]

wherever it ends up, as long as it can be applied efficiently on file save it should be fine / satisfy this use-case, but I feel like that might be awkward to do with dart fix unless there are pre-existing plans to expand its API surface area / intended usage.