CA1859 false positive with arrays

[JustArchi]

Analyzer

Diagnostic ID: CA1859: Use concrete types when possible for improved performance

Analyzer source

SDK: Built-in CA analyzers in .NET 8 SDK or later

Version: SDK 8.0.100-rc1

Describe the bug

False positive of CA1859 where I don't expect one.

Steps To Reproduce

I got false positive with following code:

	public static async Task<IList<T>> InParallel<T>(IEnumerable<Task<T>> tasks) {
		ArgumentNullException.ThrowIfNull(tasks);

		IList<T> results;

		switch (ASF.GlobalConfig?.OptimizationMode) {
			case GlobalConfig.EOptimizationMode.MinMemoryUsage:
				results = new List<T>();

				foreach (Task<T> task in tasks) {
					results.Add(await task.ConfigureAwait(false));
				}

				break;
			default:
				results = await Task.WhenAll(tasks).ConfigureAwait(false);

				break;
		}

		return results;
	}

Rewritten for easier reproduction to the code that compiles:

	public static async Task<IList<T>> InParallel2<T>(IEnumerable<Task<T>> tasks) {
		ArgumentNullException.ThrowIfNull(tasks);

		IList<T> results;

		switch (DateTime.Now.Year) {
			case 2023:
				results = new List<T>();

				foreach (Task<T> task in tasks) {
					results.Add(await task.ConfigureAwait(false));
				}

				break;
			default:
				results = await Task.WhenAll(tasks).ConfigureAwait(false);

				break;
		}

		return results;
	}

Expected behavior

No CA1859 in above code.

Actual behavior

Here roslyn analyzer suggests me to change IList<T> results into List<T>, but doesn't take into account that Task.WhenAll() returns T[] which is not a List<T>.

Additional context

I reproduced this with clean .NET 8 rc1 which was released yesterday so I believe this issue is recent - please feel free to reproduce and see if it applies.

[pcf0]

I think this is the same problem as in my case? #6904 (value is changed by await)

[JustArchi]

Looks the same, yeah! At least we have confirmation that it still happens on rc1 then.