Enable code quality rule CA1851

[shenglol]

The PR enables the .NET code quality rule CA1851: Possible multiple enumerations of IEnumerable collection and fixes the violations in the codebase. This closes https://github.com/Azure/bicep/issues/13521.

Some key learnings:

Avoid if (enumerable.Any())

The practice of using if (enumerable.Any()) { ...enumerable.XXX() } to determine if an IEnumerable is not empty before proceeding with more operations is common in our code base, but it should be avoided. The reason is that Any() might execute an expensive filtering operation, particularly when used with a Where clause. Although Any() is designed to terminate as soon as an item is detected, thus may not iterating through the entire collection, it can still have performance impacts. Besides, this approach is not free from side effects.

There are several ways to address this:

Replace Any() + First() with FirstOrDefault()

• Before

if (enumerable.Any())
{
    DoSomethingWith(enumerable.First());
}

• After

if (enumerable.FirstOrDefault() is { } first)
{
    DoSomethingWith(first);
}

Perform the empty check on a more specific collection type

• Before

if (!enumerable.Any())
{
    return;
}

var array = enumerable.ToArray();

• After

// Utilizing ToArray will yield Array.Empty<T>() in the case of an empty collection, hence no allocation is made.
var array = enumerable.ToArray();

if (enumerable.Length == 0)
{
    return;
}

Bypass Any() through the use of a Boolean variable

• Before

foreach (var item in enumerable)
{
    ...
}

if (enumerable.Any())
{
   ...
}

• After

var hasItem = false;

foreach (var item in enumerable)
{
    hasItem = true;
    ...
}

if (hasItem)
{
   ...
}

Use DefaultIfNotEmpty()

• Before

var max = enumerable.Any() ? enumerable.Max() : 0;

• After

var max = enumerable.DefaultIfEmpty(0).Max();

Addressing Intentional Multiple Enumeration

In scenarios where repeated enumeration of a collection is intentional, alternative strategies can mitigate the direct enumeration of an IEnumerable.

Favor Specific Interfaces like IReadOnlyCollection<T> or IReadOnlyList<T>

• Before

private void Foo(IEnumerable<int> numbers)
{
    var oddNumbers = numbers.Select(x => x % 2 != 0).ToArray();
    var evenNumbers = numbers.Select(x => x % 2 == 0).ToArray();
}

• After

private void Foo(IReadOnlyList<int> numbers)
{
    var oddNumbers = numbers.Select(x => x % 2 != 0).ToArray();
    var evenNumbers = numbers.Select(x => x % 2 == 0).ToArray();
}

Convert to Array or List When the IEnumerable parameter Type Cannot Be Altered

• Before

private void Foo(IEnumerable<int> numbers)
{
    var oddNumbers = numbers.Select(x => x % 2 != 0).ToArray();
    var evenNumbers = numbers.Select(x => x % 2 == 0).ToArray();
}

• After

private void Foo(IEnumerable<int> numbers)
{
    var numbersArray = numbers.ToArray();
    var oddNumbers = numbersArray .Select(x => x % 2 != 0).ToArray();
    var evenNumbers = numbersArray .Select(x => x % 2 == 0).ToArray();
}

[github-actions[bot]]

Test this change out locally with the following install scripts (Action run 8193199706)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 8193199706
  

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 8193199706"
  

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 8193199706
  

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 8193199706"
  

[github-actions[bot]]

Test Results

    65 files   -     34      65 suites   - 34   22m 11s :stopwatch: - 18m 43s 10 677 tests  -     20  10 675 :white_check_mark:  -     20  2 :zzz: ±0  0 :x: ±0  25 244 runs   - 12 618  25 240 :white_check_mark:  - 12 616  4 :zzz:  - 2  0 :x: ±0 

Results for commit 5c04c6e2. ± Comparison against base commit 9fd452ed.

:recycle: This comment has been updated with latest results.