using System;

using System.Collections.Generic;

using System.Linq;

public class E

{

public void Ex1(long[][][] a1, int ix, int len)

{

long[][] a2 = null;

var haveA2 = ix < len && (a2 = a1[ix]) != null;

long[] a3 = null;

var haveA3 = haveA2 && (a3 = a2[ix]) != null; // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

if (haveA3)

a3[0] = 0; // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

}

public void Ex2(bool x, bool y)

{

var s1 = x ? null : "";

var s2 = (s1 == null) ? null : "";

if (s2 == null)

{

s1 = y ? null : "";

s2 = (s1 == null) ? null : "";

}

if (s2 != null)

s1.ToString(); // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

}

public void Ex3(IEnumerable<string> ss)

{

string last = null;

foreach (var s in new string[] { "aa", "bb" })

last = s;

last.ToString(); // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

last = null;

if (ss.Any())

{

foreach (var s in ss)

last = s;

last.ToString(); // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

}

}

public void Ex4(IEnumerable<string> list, int step)

{

int index = 0;

var result = new List<List<string>>();

List<string> slice = null;

var iter = list.GetEnumerator();

while (iter.MoveNext())

{

var str = iter.Current;

if (index % step == 0)

{

slice = new List<string>();

result.Add(slice);

}

slice.Add(str); // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

++index;

}

}

public void Ex5(bool hasArr, int[] arr)

{

int arrLen = 0;

if (hasArr)

arrLen = arr == null ? 0 : arr.Length;

if (arrLen > 0)

arr[0] = 0; // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

}

public const int MY_CONST_A = 1;

public const int MY_CONST_B = 2;

public const int MY_CONST_C = 3;

public void Ex6(int[] vals, bool b1, bool b2)

{

int switchguard;

if (vals != null && b1)

switchguard = MY_CONST_A;

else if (vals != null && b2)

switchguard = MY_CONST_B;

else

switchguard = MY_CONST_C;

switch (switchguard)

{

case MY_CONST_A:

vals[0] = 0; // GOOD

break;

case MY_CONST_C:

break;

case MY_CONST_B:

vals[0] = 0; // GOOD

break;

default:

throw new Exception();

}

}

public void Ex7(int[] arr1)

{

int[] arr2 = null;

if (arr1.Length > 0)

arr2 = new int[arr1.Length];

for (var i = 0; i < arr1.Length; i++)

arr2[i] = arr1[i]; // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

}

public void Ex8(int x, int lim)

{

bool stop = x < 1;

int i = 0;

var obj = new object();

while (!stop)

{

int j = 0;

while (!stop && j < lim)

{

int step = (j * obj.GetHashCode()) % 10; // GOOD

if (step == 0)

{

obj.ToString(); // GOOD

i += 1;

stop = i >= x;

if (!stop)

{

obj = new object();

}

else

{

obj = null;

}

continue;

}

j += step;

}

}

}

public void Ex9(bool cond, object obj1)

{

if (cond)

{

return;

}

object obj2 = obj1;

if (obj2 != null && obj2.GetHashCode() % 5 > 2)

{

obj2.ToString(); // GOOD

cond = true;

}

if (cond)

obj2.ToString(); // GOOD

}

public void Ex10(int[] a)

{

int n = a == null ? 0 : a.Length;

for (var i = 0; i < n; i++)

{

int x = a[i]; // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

if (x > 7)

a = new int[n];

}

}

public void Ex11(object obj, bool b1)

{

bool b2 = obj == null ? false : b1;

if (b2 == null)

{

obj.ToString(); // GOOD

}

if (obj == null)

{

b1 = true;

}

if (b1 == null)

{

obj.ToString(); // GOOD

}

}

public void Ex12(object o)

{

var i = o.GetHashCode(); // $ Alert[cs/dereferenced-value-may-be-null]

var s = o?.ToString();

}

public void Ex13(bool b)

{

var o = b ? null : "";

o.M1(); // GOOD (because M1 doesn't deref o)

if (b)

o.M2(); // $ Alert[cs/dereferenced-value-may-be-null]

else

o.Select(x => x); // GOOD

}

public int Ex14(string s)

{

if (s is string)

return s.Length;

return s.GetHashCode(); // $ Alert[cs/dereferenced-value-is-always-null]

}

public void Ex15(bool b)

{

var x = "";

if (b)

x = null;

x.ToString(); // $ Alert[cs/dereferenced-value-may-be-null]

if (b)

x.ToString(); // dominated by prior deref, i.e. not reported

}

public void Ex16(bool b)

{

var x = "";

if (b)

x = null;

if (b)

x.ToString(); // $ Alert[cs/dereferenced-value-may-be-null]

x.ToString(); // "dominated" by prior deref, i.e. not reported

}

public int Ex17(int? i)

{

return i.Value; // $ Alert[cs/dereferenced-value-may-be-null]

}

public int Ex18(int? i)

{

return (int)i; // $ Alert[cs/dereferenced-value-may-be-null]

}

public int Ex19(int? i)

{

if (i.HasValue)

return i.Value; // GOOD

return -1;

}

public int Ex20(int? i)

{

if (i != null)

return i.Value; // GOOD

return -1;

}

public int Ex21(int? i)

{

if (i == null)

i = 0;

return i.Value; // GOOD

}

public void Ex22()

{

object o = null;

try

{

o = Make();

o.ToString(); // GOOD

}

finally

{

if (o != null)

o.ToString(); // GOOD

}

}

public void Ex23(bool b)

{

if (b)

b.ToString();

var o = Make();

o?.ToString();

o.ToString(); // $ Alert[cs/dereferenced-value-may-be-null]

if (b)

b.ToString();

}

public void Ex24(bool b)

{

string s = b ? null : "";

if (s?.M2() == 0)

{

s.ToString(); // GOOD

}

}

public void Ex25(object o)

{

var s = o as string;

s.ToString(); // $ Alert[cs/dereferenced-value-may-be-null]

}

private long? l;

public long Long { get => l ?? 0; set { l = value; } }

public void Ex26(E e)

{

if (l.HasValue)

{

e.Long = l.Value; // GOOD

}

return;

}

public bool Field;

string Make() => Field ? null : "";

static void Ex27(string s1, string s2)

{

if ((s1 ?? s2) is null)

{

s1.ToString(); // $ Alert[cs/dereferenced-value-is-always-null]

s2.ToString(); // $ Alert[cs/dereferenced-value-is-always-null]

}

}

static void Ex28()

{

var x = (string)null ?? null;

x.ToString(); // $ Alert[cs/dereferenced-value-is-always-null]

}

static void Ex29(string s)

{

var x = s ?? "";

x.ToString(); // GOOD

}

static void Ex30(string s, object o)

{

var x = s ?? o as string;

x.ToString(); // $ Alert[cs/dereferenced-value-may-be-null]

}

static void Ex31(string s, object o)

{

dynamic x = s ?? o as string;

x.ToString(); // $ Alert[cs/dereferenced-value-may-be-null]

}

static void Ex32(string s, object o)

{

dynamic x = s ?? o as string;

if (x != null)

x.ToString(); // GOOD

}

static void Ex33(string s, object o)

{

var x = s ?? o as string;

if (x != (string)null)

x.ToString(); // GOOD

}

static int Ex34(string s = null) => s.Length; // $ Alert[cs/dereferenced-value-may-be-null]

static int Ex35(string s = "null") => s.Length; // GOOD

static int Ex36(object o)

{

if (o is string)

{

var s = o as string;

return s.Length; // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

}

return -1;

}

static bool Ex37(E e1, E e2)

{

if ((e1 == null && e2 != null) || (e1 != null && e2 == null))

return false;

if (e1 == null && e2 == null)

return true;

return e1.Long == e2.Long; // GOOD

}

int Ex38(int? i)

{

i ??= 0;

return i.Value; // GOOD

}

System.Drawing.Color Ex39(System.Drawing.Color? color)

{

color ??= System.Drawing.Color.White;

return color.Value; // GOOD

}

int Ex40()

{

int? i = null;

i ??= null;

return i.Value; // $ Alert[cs/dereferenced-value-is-always-null]

}

int Ex41()

{

int? i = 1;

i ??= null;

return i.Value; // GOOD

}

static bool Ex42(int? i, IEnumerable<int> @is)

{

return @is.Any(j => j == i.Value); // $ Alert[cs/dereferenced-value-may-be-null]

}

static bool Ex43(int? i, IEnumerable<int> @is)

{

if (i.HasValue)

return @is.Any(j => j == i.Value); // $ SPURIOUS (false positive): Alert[cs/dereferenced-value-may-be-null]

return false;

}

static bool Ex44(int? i, IEnumerable<int> @is)

{

if (i.HasValue)

@is = @is.Where(j => j == i.Value); // $ Alert[cs/dereferenced-value-may-be-null]

i = null;

return @is.Any();

}

static void Ex45(string s, int i)

{

if (i == 0 && s is null)

{

s.ToString(); // $ Alert[cs/dereferenced-value-is-always-null]

}

if (i == 1 && s is not not null)

{

s.ToString(); // $ Alert[cs/dereferenced-value-may-be-null] MISSING: Alert[cs/dereferenced-value-is-always-null]

}

if (i == 2 && s is not null)

{

s.ToString(); // GOOD

}

if (i == 3 && s is object)

{

s.ToString(); // GOOD

}

if (s is not object)

{

s.ToString(); // $ Alert[cs/dereferenced-value-may-be-null]

}

else

{

s.ToString(); // GOOD

}

}

}

public static class Extensions

{

public static void M1(this string s) { }

public static int M2(this string s) => s.Length;

}