Fix S6605 FP: Should not fire in expressions

[benjiwolff]

Description

As I understand, rule S6605 suggests the use of the collection-specific "Exists" method for performance reasons. It becomes a problem when the "Any" extension method is used in an expression because switching to the "Exists" method changes the expression (e. g. the C# MongoDb Driver supports Any but not Exists). There are also no performance benefits unless the expression is compiled and executed which should not be done anyways when performance is important.

Repro steps

Expression<Func<List<int>, bool>> containsThree = list => list.Any(el => el == 3);

Expected behavior

The rule should not fire.

Actual behavior

The rule fires.

Related information

• C# Plugin version 9.4.0.72892
• JetBrains Rider version 2023.1.1
• MSBuild / dotnet version 7.0.305
• Operating System macOS Ventura 13.4.1

[martin-strecker-sonarsource]

Thank you @DrummingBeb for bringing this up. Linq expressions are indeed a special case and we should not raise in that context as they are almost always not executed but translated.

Note to the implementer: We have the IsInExpressionTree helper methods for that.

[martin-strecker-sonarsource]

See also #7286
@sebastien-marichal is this already fixed by #7332? If so, you may use IsInExpressionTree instead of the custom logic you used.

[sebastien-marichal]

@martin-strecker-sonarsource The fix in #7332 only checks if Any is used within an EntityFramework context.
Using IsInExpressionTree would prevent a broader range of false positives indeed.