rspec/rules/S2291/csharp/rule.adoc

== Why is this an issue?

https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.sum[Enumerable.Sum()] always executes addition in a `checked` context, so an https://learn.microsoft.com/en-us/dotnet/api/system.overflowexception[OverflowException] will be thrown if the value exceeds `MaxValue`, even if an `unchecked` context was specified. Therefore, using this method inside an `unchecked` context will only make the code more confusing, since the behavior will still be `checked`.

This rule raises an issue when an `unchecked` context is specified for a `Sum` on integer types.

=== Exceptions

When the `Sum` call is inside a https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/exceptions/[try-catch block], no issues are reported, since the exception is properly handled.

[source,csharp]
----
void Add(List<int> list)
{
  unchecked 
  {
    try 
    {
      int total = list.Sum();
    } 
    catch (System.OverflowException e) 
    {
      // Exception handling    
    }
  }
}
----


== How to fix it

Remove the `unchecked` operator/statement, and optionally add some exception handling for the `OverflowException`.

=== Code examples

==== Noncompliant code example

[source,csharp,diff-id=1,diff-type=noncompliant]
----
void Add(List<int> list)
{
  int total1 = unchecked(list.Sum());  // Noncompliant

  unchecked 
  {
    int total2 = list.Sum();  // Noncompliant
  }
}
----


==== Compliant solution

[source,csharp,diff-id=1,diff-type=compliant]
----
void Add(List<int> list)
{
  int total1 = list.Sum();

  try 
  {
    int total2 = list.Sum();
  } 
  catch (System.OverflowException e) 
  {
    // Exception handling
  }
}
----

== Resources

=== Documentation

* https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.sum[`Enumerable.Sum` Method]
* https://github.com/microsoft/referencesource/blob/51cf7850defa8a17d815b4700b67116e3fa283c2/System.Core/System/Linq/Enumerable.cs#L1408-L1415[`Enumerable.Sum` implementation]
* https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/statements/checked-and-unchecked[`checked` and `unchecked` statements]
* https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/expressions#12819-the-checked-and-unchecked-operators[`checked` and `unchecked` operators]
* https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/exceptions/[Exceptions and Exception Handling]
* https://learn.microsoft.com/en-us/dotnet/api/system.overflowexception[`OverflowException` Class]
* https://en.wikipedia.org/wiki/Integer_overflow[Integer overflow]

include::../rspecator.adoc[]