This generates a Warning diagnostic:

void Foo(double a, double b)
{
    if (a == b) {...} 

If we are able to make a code fix that will exhibit a snippet like behavior, where the user has to fill the value they want for the ellipsis, then we will also do a code fix, otherwise it will be only a diagnostic.
If it is possible to build the code fix this way, it should look like this:

void Foo(double a, double b)
{
    const float ELLIPSIS = MYELLIPSIS;
    if (Math.Abs(a-b) < ELLIPSIS) {...} 

Where the value MYELLIPSIS is highlighted for the user to fill in his value later.
The diagnostic id is: CC0036

@fholiveira will work on it.