Extend the "Use collection expression" suggestion to scenarios requiring the spread operator #75870
Description
Summary
Expand the Roslyn analyzers to suggest using [.. collection] syntax where applicable. This is a more concise and expressive way to initialize collection from elements in existing collections.
Background and Motivation
The IDE currently suggests collection initialization when a spread operator wouldn't be required. The motivation for this feature is the same as the existing suggestions, informing developers of the existence of a more readable syntax. Notably, ReSharper already suggests using collection expressions in these situations. Adding this feature directly to Roslyn would ensure consistency and improve native support for modern C# practices.
Proposed Feature
Before:
List<int> GetNumbers()
{
return new List<int>(Enumerable.Range(1, 10));
}After:
List<int> GetNumbers()
{
return [.. Enumerable.Range(1, 10)];
}Before:
ImmutableArray<string> GetFormattedNumbers(ImmutableArray<int> numbers)
{
return numbers.Select(n => $"Number: {n}").ToImmutableArray();
}After:
ImmutableArray<string> GetFormattedNumbers(ImmutableArray<int> numbers)
{
return [.. numbers.Select(n => $"Number: {n}")];
}Before:
ImmutableArray<string> GetFormattedRange()
{
return ImmutableArray.CreateRange(Enumerable.Range(1, 10).Select(n => $"Item {n}"));
}After:
ImmutableArray<string> GetFormattedRange()
{
return [.. Enumerable.Range(1, 10).Select(n => $"Item {n}")];
}