Implementing control flow collections

[nate-thegrate]

This pull request aims for improved readability, based on issue #146600.

// before
Set<Color> _distinctVisibleColors() {
  final Set<Color> distinctVisibleColors = <Color>{};
  if (top.style != BorderStyle.none) {
    distinctVisibleColors.add(top.color);
  }
  if (right.style != BorderStyle.none) {
    distinctVisibleColors.add(right.color);
  }
  if (bottom.style != BorderStyle.none) {
    distinctVisibleColors.add(bottom.color);
  }
  if (left.style != BorderStyle.none) {
    distinctVisibleColors.add(left.color);
  }
  return distinctVisibleColors;
}


// after
Set<Color> _distinctVisibleColors() {
  return <Color>{
    if (top.style != BorderStyle.none) top.color,
    if (right.style != BorderStyle.none) right.color,
    if (bottom.style != BorderStyle.none) bottom.color,
    if (left.style != BorderStyle.none) left.color,
  };
}

Most of the repo should be covered in this PR (aside from flutter_tools/, since there was a lot going on in there).

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

[goderbauer]

LGTM

Thank you!

[Piinks]

[auto-submit]

auto label is removed for flutter/flutter/146601, due to Pull request flutter/flutter/146601 is not in a mergeable state.

[justinmc]

LGTM 👍 Thanks for making the codebase more readable as always.

[justinmc]

I had to double check the styleguide but looks like this is right. It should be on one line like this (as long as it fits in the line length). https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#prefer-single-line-for-short-collection-if-and-collection-for

[justinmc]

That was a weird one...

[justinmc]

I didn't know about this case syntax.

[rakudrama]

Avoid .cast.
The result checks the value on every read and write, rather than once in constructing the list.
This kind of inefficiency should be avoided in the foundation.

Instead, nest a for-in in the control flow collection to make it equivalent to the original code.

[nate-thegrate]

I had no idea that .cast worked that way, thank you!

[rakudrama]

..._slice.sublist(...) is creating an extra temporary list.
Presumably the original code avoided result.addAll(_slice.sublist(0, _pointer)) for some reason.

I would make this more like the original, i.e.
for (int i = 0; i < _pointer; i++) _slice[i]!,

[nate-thegrate]

Thank you all very much!

It looks like a merge conflict popped up and autosubmit was removed, so if a kind soul is able to re-add it, that would be much appreciated.