d3cfe19d7e
Co-authored-by: Marco Borgeaud <89914223+marco-antognini-sonarsource@users.noreply.github.com>
104 lines
3.3 KiB
Plaintext
104 lines
3.3 KiB
Plaintext
== Why is this an issue?
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Unnecessary `using` directives refer to importing namespaces, types or creating aliases that are not used or referenced anywhere in the code.
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include::../description.adoc[]
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Starting with C# 10, it's possible to define https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-directive#global-modifier[global usings] for an entire project. They reduce the need for repetitive namespace inclusions, but can also mask which namespaces are truly necessary for the code at hand. Over-relying on them can lead to less transparent code dependencies, especially for newcomers to the project.
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=== Exceptions
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The rule will not raise a warning for `global using` directives, even if none of the types of that namespace are used in the project:
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[source,csharp]
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----
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global using System.Net.Sockets; // Compliant by exception
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----
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Unnecessary `using` directives are ignored in ASP.NET Core projects in the following files:
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* ``++_Imports.razor++``
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* ``++_ViewImports.cshtml++``
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== How to fix it
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While it's not difficult to remove these unneeded lines manually, modern code editors support the removal of every unnecessary `using` directive with a single click from every file of the project.
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=== Code examples
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==== Noncompliant code example
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[source,csharp,diff-id=1,diff-type=noncompliant]
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----
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using System.IO;
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using System.Linq;
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using System.Collections.Generic; // Noncompliant - no types are used from this namespace
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using MyApp.Helpers; // Noncompliant - FileHelper is in the same namespace
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using MyCustomNamespace; // Noncompliant - no types are used from this namespace
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namespace MyApp.Helpers
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{
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public class FileHelper
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{
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public static string ReadFirstLine(string filePath) =>
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File.ReadAllLines(filePath).First();
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}
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}
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----
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==== Compliant solution
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[source,csharp,diff-id=1,diff-type=compliant]
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----
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using System.IO;
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using System.Linq;
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namespace MyApp.Helpers
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{
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public class FileHelper
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{
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public static string ReadFirstLine(string filePath) =>
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File.ReadAllLines(filePath).First();
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}
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}
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----
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== Resources
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=== Documentation
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* https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-directive[MSDN - using directives]
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* https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/namespace[MSDN - namespaces]
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=== Related rules
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* S1144 - Unused private types or members should be removed
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* S1481 - Unused local variables should be removed
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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* Remove this unnecessary 'using'.
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'''
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== Comments And Links
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(visible only on this page)
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include::../comments-and-links.adoc[]
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=== on 23 Sep 2019, 16:37:14 Nicolas Harraudeau wrote:
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*OUT OF SCOPE*
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Duplicate imports are out of scopes as Roslyn already raises an issue in this case. As Roslyn issues are enabled by default this would simply create duplicates.
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=== on 18 Dec 2020, 10:06:15 Andrei Epure wrote:
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We are removing this rule from SonarWay due to its performance issues. After the rule gets re-designed to avoid perf issues, (see https://github.com/SonarSource/sonar-dotnet/issues/3761[#3761]), we should bring it back to SonarWay.
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endif::env-github,rspecator-view[]
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