proposal: Consider adding new avoid_shrink_wrap_in_lists lint

[gabrielaraujoz]

Describe the rule you'd like to see implemented
This would be a nice lint for Flutter.

According to the Flutter documentation, using shrinkWrap in lists is expensive performance-wise and should be avoided, since using slivers is significantly cheaper and achieves the same or even better results.

ShrinkWrap is usually needed when you have a list inside another list, or a list that should not be scrollable inside a Column or roll. From the docs, it is described as: Whether the extent of the scroll view in the scrollDirection should be determined by the contents being viewed.

I then would like to propose that the team considers adding this performance lint to Dart/Flutter first as optional, but it could eventually even be recommended since it helps with Flutter's performance directly and it's use case is not uncommon.

It could ignore if a list is not contained inside another list, column or row (in this case, slivers would not be needed anyways).

Additional context
Flutter shrinkWrap doc link - Video explaining the difference and performance disparity

Bad Example

Column(
      children: [
        Expanded(
          child: ListView(
            shrinkWrap: true,
            physics: const NeverScrollableScrollPhysics(),
            children: [],
            ),
       ),
  ],
),

Good Example

CustomScrollView(
  slivers: [
    SliverList(
      delegate: SliverChildBuilderDelegate(
        (context, index) {
          return Container();
        },
        childCount: someObject.length,
      ),
    ),
  ],
),

[bwilkerson]

@goderbauer

[goderbauer]

@dnfield @Piinks Did we write down some learnings from our recent discussion on this somewhere? I seem to remember we identified some valid use cases for shrink wrap, which may make a general "avoid shrink wrap" lint a little too broad. However, if we can instead target certain known bad use cases with it (like using shrink wrap to place a list inside another list), this could be helpful.

[dnfield]

flutter/flutter#103068 and flutter/flutter#103085

[douglasiacovelli]

Even though there are valid use cases, shrinkWrap is not recommended because of performance impact when it's easily avoidable with SliverLists. I wouldn't see an issue to add an ignore comment in case it is really needed so we are at least well aware of it. Also it could be more of a warning than an error itself.

[gabrielaraujoz]

@goderbauer I totally agree with you there, this could be pretty useful for performance house-keeping if we focus on the known bad use cases! nowadays when we face this problem, shrinkwrapping is the easiest way out instead of changing your widget tree to use slivers. I see we have already removed the suggestion for using shrinkWrap when we get the unbounded height/width UI errors, maybe we could then suggest the use of slivers in this case as well?