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CA2020: Prevent behavioral change caused by built-in operators of IntPtr/UIntPtr

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Property Value
Rule ID CA2020
Title Prevent behavioral change caused by built-in operators of IntPtr/UIntPtr
Category Reliability
Fix is breaking or non-breaking Non-breaking
Enabled by default in .NET 8 As suggestion

Cause

This rule fires when it detects a behavioral change between .NET 6 and .NET 7 introduced by the new built-in operators of IntPtr and UIntPtr.

Rule description

With the numeric IntPtr feature, IntPtr and UIntPtr gained built-in operators for conversions, unary operations, and binary operations. These operators might throw when overflowing within checked context or may not throw in unchecked context compared to the previous user-defined operators in .NET 6 and earlier versions. You might encounter this behavioral change when upgrading to .NET 7.

List of APIs affected

Operator Context In .NET 7 In .NET 6 and earlier Example
operator +(IntPtr, int) checked Throws when overflows Doesn't throw when overflows checked(intPtrVariable + 2);
operator -(IntPtr, int) checked Throws when overflows Doesn't throw when overflows checked(intPtrVariable - 2);
explicit operator IntPtr(long) unchecked Doesn't throw when overflows Can throw in 32-bit contexts (IntPtr)longVariable;
explicit operator void*(IntPtr) checked throws when overflows Doesn't throw when overflows checked((void*)intPtrVariable);
explicit operator IntPtr(void*) checked throws when overflows Doesn't throw when overflows checked((IntPtr)voidPtrVariable);
explicit operator int(IntPtr) unchecked Doesn't throw when overflows Can throw in 64-bit contexts (int)intPtrVariable;
operator +(UIntPtr, int) checked Throws when overflows Doesn't throw when overflows checked(uintPtrVariable + 2);
operator -(UIntPtr, int) checked Throws when overflows Doesn't throw when overflows checked(uintPtrVariable - 2);
explicit operator UIntPtr(ulong) unchecked Doesn't throw when overflows Can throw in 32-bit contexts (UIntPtr)uLongVariable
explicit operator uint(UIntPtr) unchecked Doesn't throw when overflows Can throw in 64-bit contexts (uint)uintPtrVariable

How to fix violations

Examine your code to determine if the flagged expression could cause a behavioral change, and choose an appropriate way to fix the diagnostic from the following options:

Fix options:

  • If the expression would not cause a behavioral change:
    • If the IntPtr or UIntPtr type is used as a native int or uint, change the type to nint or nuint.
    • If the IntPtr or UIntPtr type is used as a native pointer, change the type to the corresponding native pointer type.
    • If you can't change the type of the variable, suppress the warning.
  • If the expression could cause a behavioral change, wrap it with a checked or unchecked statement to preserve the previous behavior.

Example

Violation:

using System;

public unsafe class IntPtrTest
{
    IntPtr intPtrVariable;
    long longVariable;

    void Test ()
    {
        checked
        {
            IntPtr result = intPtrVariable + 2; // Warns: Starting with .NET 7 the operator '+' will throw when overflowing in a checked context. Wrap the expression with an 'unchecked' statement to restore the .NET 6 behavior.

            result = intPtrVariable - 2; // Starting with .NET 7 the operator '-' will throw when overflowing in a checked context. Wrap the expression with an 'unchecked' statement to restore the .NET 6 behavior.

            void* voidPtrVariable = (void*)intPtrVariable; // Starting with .NET 7 the explicit conversion '(void*)IntPtr' will throw when overflowing in a checked context. Wrap the expression with an 'unchecked' statement to restore the .NET 6 behavior.

            result = (IntPtr)voidPtrVariable; // Starting with .NET 7 the explicit conversion '(IntPtr)void*' will throw when overflowing in a checked context. Wrap the expression with an 'unchecked' statement to restore the .NET 6 behavior.
        }

        intPtrVariable = (IntPtr)longVariable; // Starting with .NET 7 the explicit conversion '(IntPtr)Int64' will not throw when overflowing in an unchecked context. Wrap the expression with a 'checked' statement to restore the .NET 6 behavior.

        int a = (int)intPtrVariable; // Starting with .NET 7 the explicit conversion '(Int32)IntPtr' will not throw when overflowing in an unchecked context. Wrap the expression with a 'checked' statement to restore the .NET 6 behavior.
    }
}

Fix:

  • If the expression would not cause a behavioral change and the IntPtr or UIntPtr type is used as a native int or uint, change the type to nint or nuint.
using System;

public unsafe class IntPtrTest
{
    nint intPtrVariable; // type changed to nint
    long longVariable;

    void Test ()
    {
        checked
        {
            nint result = intPtrVariable + 2; // no warning

            result = intPtrVariable - 2;

            void* voidPtrVariable = (void*)intPtrVariable;

            result = (nint)voidPtrVariable;
        }

        intPtrVariable = (nint)longVariable;

        int a = (int)intPtrVariable;
    }
}
  • If the expression could cause a behavioral change, wrap it with a checked or unchecked statement to preserve the previous behavior.
using System;

public unsafe class IntPtrTest
{
    IntPtr intPtrVariable;
    long longVariable;

    void Test ()
    {
        checked
        {
            IntPtr result = unchecked(intPtrVariable + 2); // wrap with unchecked

            result = unchecked(intPtrVariable - 2);

            void* voidPtrVariable = unchecked((void*)intPtrVariable);

            result = unchecked((IntPtr)voidPtrVariable);
        }

        intPtrVariable = checked((IntPtr)longVariable); // wrap with checked

        int a = checked((int)intPtrVariable);
    }
}

When to suppress warnings

If the expression would not cause a behavioral change, it's safe to suppress a warning from this rule.

See also