Analyzer: change Enumerable.Concat with single element arrays into Append or Prepend

[huoyaoyuan]

Since Append and Prepend comes much later than Enumerable.Concat, there are many old code using Concat with single-element array:

values.Concat(new[] { moreValue })

which can be converted into:

values.Append(moreValue)

Prepend is less common, and changes the order of two elements in code, but it would be more natural.

Category: Performance Severity: Info

[ghost]

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Issue Details

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Since `Append` and `Prepend` comes much later than `Enumerable.Concat`, there are many old code using `Concat` with single-element array: ```csharp values.Concat(new[] { moreValue }) ``` which can be converted into: ```csharp values.Append(moreValue) ``` `Prepend` is less common, and changes the order of two elements in code, but it would be more natural. Category: Performance Severity: Info

Author:	huoyaoyuan
Assignees:	-
Labels:	`api-suggestion`, `area-System.Linq`, `code-analyzer`, `code-fixer`
Milestone:	-

[campersau]

Note that Enumerable.Append is not directly supported in net47 or older. https://apisof.net/catalog/6ae58543-a1b1-3617-8780-227339489ae8

[huoyaoyuan]

Note that Enumerable.Append is not directly supported in net47 or older.

Yes, it needs extra attention for netstandard2.0, since it requires a shim on net461-net47. For non-netstandard platforms, just detecting the existence of the methods should be sufficient.

[huoyaoyuan]

With collection expressions, there are actually additional options with spread: [..values, morevalue]. But maybe there are ones still prefer method call.