Analysis of integer values in C#

JetBrains Fleet can track the flow of integer values through your code and report redundant or possibly erroneous statements. It supports all C# integral numeric types — int, uint, byte, sbyte, short, ushort, long, and ulong — and warns you about the following issues:

relational/equality operators that always evaluate to true or false,
unreachable switch cases checking int values,
meaningless arithmetic operations, such as multiplication by 1 or addition of 0 (except literals or constants: JetBrains Fleet assumes that expressions like x + 0 are intentional),
possible int overflows,
possible division by 0,
possible errors in invocations of System.Math methods,
the above issues in enumeration types with the corresponding underlying types.

How it works

JetBrains Fleet narrows down the possible range of values for each integer according to possible outcomes of all statements and expressions that can produce or affect that integer. Let's consider some examples.

JetBrains Fleet can deduce that temp < 0 in the example below will always evaluate to false because Math.Abs always returns a non-negative value.

        void TestInput(int input)
        {
            var temp = Math.Abs(input);
            // do something
            if(temp < 0) // Expression is always false
                Console.WriteLine("Some output");
        }

        

In the following example, JetBrains Fleet infers that by the last return, the value of input is in the range of -100 ... 100, and when divided by a larger divider, it will be truncated towards zero.

        int TestDivision(int input, int delta)
        {
            const int divider = 500;
            if(input < -100 || input > 100)
                return input;
            input = input / divider;
            // do something
            return delta + input; // Addition of 0
        }

        

Refine analysis with annotations

There are two JetBrains.Annotations attributes ([NonNegativeValue] and [ValueRange(from, to)]) for analysis of integer values.

You can use these attributes with type members returning int and with int parameters to specify known constraints and thus improve analysis precision.

Here is an example of annotating the method parameter with [NonNegativeValueAttribute] to refine the analysis within the method body. Knowing that the parameter is non-negative, JetBrains Fleet can report all redundant operations on that parameter:

        void TestSwitch([NonNegativeValue] int input)
        {
            var newValue = input switch
            {
                0 => 1,
                -1 => 0, // Case is heuristically unreachable
                _ => input,
            };

            if (input < 0) // Expression is always false
                Console.WriteLine("some output");
        }

            

The following example demonstrates how annotating a method can help find redundant checks around its usages:

        [ValueRange(1,6)]
        int RollDice() => // my random generator

        void Play()
        {
            var firstRoll = RollDice();
            if (firstRoll < 1 || firstRoll > 6) // Expression is always false
                throw new ArgumentOutOfRangeException();
            // roll again
        }

        

Last modified: 30 September 2024