New rule S2198: Silly mathematical comparisons should not be made

[cristian-ambrosini-sonarsource]

S2198
RSPEC PR: SonarSource/rspec#1534

[gregory-paidis-sonarsource]

Maybe this could be a part of S2437.

Or even better, the other way around, we could merge the rules and have different diagnostics.

[gregory-paidis-sonarsource]

Looking a bit at what this rule covers, as well as some testing:

• comparing a byte with an int or long constant that’s outside the byte range

This is covered by CS0652 for all types of of comparisons (<, <=, >, >=, ==)

• comparing an int with a long constant that’s outside the int range

This is covered by CS0652 for all types of of comparisons (<, <=, >, >=, ==)

• comparing a value guaranteed to be negative with a one that’s guaranteed to be non-negative

This is covered by CS0652 for comparing a uint with a constant negative int. I cannot think of any other usecases.

• comparing aByte <= Byte.MAX_VALUE and aByte >= Byte.MIN_VALUE

Not covered.

• comparing anInt <= Integer.MAX_VALUE and anInt >= Integer.MIN_VALUE

Not covered.

• comparing aLong <= Long.MAX_VALUE and aLong >= Long.MIN_VALLUE

Not covered.

• Additional notes

Maybe we can implement a comparison between float and constant double that is > float.MaxValue.

[gregory-paidis-sonarsource]

We decided to implement only the parts that are NOT covered by CS0652, meaning:

• comparing aByte <= byte.MaxValue and aByte >= byte.MinValue
• comparing anInt <= int.MaxValue and anInt >= int.MinValue
• comparing aLong <= long.MaxValue and aLong >= long.MinValue
• comparing a float with a constant double outside of float's range

Also, to cut branches we will only implement the C# part of the rule, at least at first.

Also, it will indeed be part of S2437.