Improve S1125: Flexibility in opting in and out constant patterns

[antonioaversa]

The context

After this issue, reported in 2019, was implemented earlier this year, we have got a user request to relax the reporting in presence of constant patterns: https://github.com/SonarSource/sonar-dotnet/issues/8147.

The goal

Provide the user with more flexibility, by allowing to opt in and out:

• ==-based comparisons: == true and == false
• is false comparison
• is true comparison

Possible solutions

From @antonioaversa I think we have four options here:

1. keep the rule as is, and reject the user request: b is false and b is true remain redundant

Or split the rule into two: take out is cases from 1125 and create a new rule for them:

2. with the new rule treating b is true as redundant and b is false as redundant

3. with the new rule treating b is true as redundant and b is false as valid

4. Or keep b is true in S1125 and have the new rule only report on b is false.

From @Tim-Pohlmann

There could be three rules:

1. Use x instead of x == true and x is true.
2. Use !x instead of x == false and x is false.
3. Use x is true/false instead of x == true/false.

Allowed patterns based on enabled rules:

• Only 1: x !x x == false x is false
• 1 + 2: x !x
• Only 3: x !x x is true x is false
• 1 + 3: x !x x is false

In addition to that 3 could also have an effect on != or that could be a separate thing.

[AronGreen]

It would also be nice if the rule is relaxed when the comparison involves checking the run-time type of a boxed value.

A slimmed down example from a WPF IValueConverter implementation where the is true pattern is reported as a code smell, but returning value is not equivalent.

public object Convert(object value)
{
    return value is true;
}

[WarBorg]

hello, any news when this will be done ? we are also struggling to remove the ! and use is false whenever possible in our code but this rule kinda hinders us at the moment

[MaxFmi]

Having is false as a valid option sounds good to me. is true is redundant and should IMHO not be valid

[Tim-Pohlmann]

I increased the priority of this ticket. Maybe we can pick it up in a future hardening sprint.