NET-2375 New Rule Idea: Use GetRequiredService<T>() instead of the pattern GetService<T>()! (in case of NRT)

[ndsvw]

Description

I found this in my code (Nullable reference types enabled) multiple times and fixed it, but thought, this could be a good rule.

When dealing with the ServiceCollection and ServiceProvider in .Net, there are the extension methods GetRequiredService<T>() and GetService<T>() (defined in ServiceProviderServiceExtensions).

I used GetService<T>() in cases when constructor injection was not an option and appended the null-forgiving operator, because I forgot that the other method exists.

But when there is the pattern GetService<T>()! used in the code, I think, it's always better to replace it with GetRequiredService<T>().

Reason: If the service does not exist in the collection, you get a NullReferenceException in case of GetService<T>()!, but a more useful InvalidOperationException with a clear message There is no service of type serviceType. in the other case.

Noncompliant code snippet

IServiceProvider sp = GetServiceProvider();
var instance = sp.GetService<ISomeInterface>()!;

Compliant code snippet

IServiceProvider sp = GetServiceProvider();
var instance = sp.GetRequiredService<ISomeInterface>();

[github-actions]

Internal ticket NET-2375

[martin-strecker-sonarsource]

Hello @ndsvw

thank you for this rule idea and I think the rule makes sense. I created an internal ticket to track work on such a rule. A few notes about the rule:

• This rule might need to be embedded in a broader set of rules which implement the recommendations given in the Microsoft documentation. This would also mean to discourage the use of IServiceProvider (service locator pattern) entirely, so you have to actively suppress the violation in SonarQube with a reasoning why the service locator pattern was used (often because there is no other option available).
• ServiceProviderServiceExtensions.GetRequiredService is in the Microsoft.Extensions.DependencyInjection.Abstractions package while IServiceProvider is in .netstandard2.0. Therefore GetRequiredService() is not always available where GetService() is. We need to avoid False Positives, when Microsoft.Extensions.DependencyInjection.Abstractions isn't referenced by the compilation.