path: root/Test/dafny0/SmallTests.dfy

class Node {
  var next: Node;

  function IsList(r: set<Node>): bool
    reads r;
  {
    this in r &&
    (next != null  ==>  next.IsList(r - {this}))
  }

  method Test(n: Node, nodes: set<Node>)
  {
    assume nodes == nodes - {n};
    // the next line needs the Set extensionality axiom, the antecedent of
    // which is supplied by the previous line
    assert IsList(nodes) == IsList(nodes - {n});
  }

  method Create()
    modifies this;
  {
    next := null;
    var tmp: Node;
    tmp := new Node;
    assert tmp != this;  // was once a bug in the Dafny checker
  }

  method SequenceUpdateOutOfBounds(s: seq<set<int>>, j: int) returns (t: seq<set<int>>)
  {
    t := s[j := {}];  // error: j is possibly out of bounds
  }

  method Sequence(s: seq<bool>, j: int, b: bool, c: bool) returns (t: seq<bool>)
    requires 10 <= |s|;
    requires 8 <= j && j < |s|;
    ensures |t| == |s|;
    ensures t[8] == s[8] || t[9] == s[9];
    ensures t[j] == b;
  {
    if (c) {
      t := s[j := b];
    } else {
      t := s[..j] + [b] + s[j+1..];
    }
  }

  method Max0(x: int, y: int) returns (r: int)
    ensures r == (if x < y then y else x);
  {
    if (x < y) { r := y; } else { r := x; }
  }

  method Max1(x: int, y: int) returns (r: int)
    ensures r == x || r == y;
    ensures x <= r && y <= r;
  {
    r := if x < y then y else x;
  }

  function PoorlyDefined(x: int): int
    requires if next == null then 5/x < 20 else true;  // error: ill-defined then branch
    requires if next == null then true else 0 <= 5/x;  // error: ill-defined then branch
    requires if next.next == null then true else true;  // error: ill-defined guard
    requires 10/x != 8;  // this is well-defined, because we get here only if x is non-0
    reads this;
  {
    12
  }
}

// ------------------ modifies clause tests ------------------------

class Modifies {
  var x: int;
  var next: Modifies;

  method A(p: Modifies)
    modifies this, p;
  {
    x := x + 1;
    while (p != null && p.x < 75)
      decreases 75 - p.x;  // error: not defined (null deref) at top of each iteration (there's good reason
    {                      // to insist on this; for example, the decrement check could not be performed
      p.x := p.x + 1;      // at the end of the loop body if p were set to null in the loop body)
    }
  }

  method Aprime(p: Modifies)
    modifies this, p;
  {
    x := x + 1;
    while (p != null && p.x < 75)
      decreases if p != null then 75 - p.x else 0;  // given explicitly (but see Adoubleprime below)
    {
      p.x := p.x + 1;
    }
  }

  method Adoubleprime(p: Modifies)
    modifies this, p;
  {
    x := x + 1;
    while (p != null && p.x < 75)  // here, the decreases clause is heuristically inferred (to be the
    {                              // same as the one in Aprime above)
      p.x := p.x + 1;
    }
  }

  method B(p: Modifies)
    modifies this;
  {
    A(this);
    if (p == this) {
      p.A(p);
    }
    A(p);  // error: may violate modifies clause
  }

  method C(b: bool)
    modifies this;
    ensures !b ==> x == old(x) && next == old(next);
  {
  }

  method D(p: Modifies, y: int)
    requires p != null;
  {
    if (y == 3) {
      p.C(true);  // error: may violate modifies clause
    } else {
      p.C(false);  // error: may violation modifies clause (the check is done without regard
                        // for the postcondition, which also makes sense, since there may, in
                        // principle, be other fields of the object that are not constrained by the
                        // postcondition)
    }
  }

  method E()
    modifies this;
  {
    A(null);  // allowed
  }

  method F(s: set<Modifies>)
    modifies s;
  {
    forall m | m in s && m != null && 2 <= m.x {
      m.x := m.x + 1;
    }
    if (this in s) {
      x := 2 * x;
    }
  }

  method G(s: set<Modifies>)
    modifies this;
  {
    var m := 3;  // this is a different m

    forall m | m in s && m == this {
      m.x := m.x + 1;
    }
    if (s <= {this}) {
      forall (m | m in s) {
        m.x := m.x + 1;
      }
      F(s);
    }
    forall (m | m in s) ensures true; { assert m == null || m.x < m.x + 10; }
    forall (m | m != null && m in s) {
      m.x := m.x + 1;  // error: may violate modifies clause
    }
  }

  method SetConstruction() {
    var s := {1};
    assert s != {};
    if (*) {
      assert s != {0,1};
    } else {
      assert s != {1,0};
    }
  }
}

// ------------------ allocated --------------------------------------------------

class AllocatedTests {
  method M(r: AllocatedTests, k: Node, S: set<Node>, d: Lindgren)
  {
    var n := new Node;
    var t := S + {n};
    
    if (*) {
      assert !fresh(n);  // error: n was not allocated in the initial state
    } else {
      assert fresh(n);  // correct
    }

    var U := {k,n};
    if (*) {
      assert !fresh(U);  // error: n was not allocated initially
    } else {
      assert fresh(U);  // correct (note, the assertion does NOT say: everything was unallocated in the initial state)
    }
  }
}

datatype Lindgren =
  Pippi(Node) |
  Longstocking(seq<object>, Lindgren) |
  HerrNilsson;

// --------------------------------------------------

class InitCalls {
  var z: int;
  var p: InitCalls;

  method Init(y: int)
    modifies this;
    ensures z == y;
  {
    z := y;
  }

  method InitFromReference(q: InitCalls)
    requires q != null && 15 <= q.z;
    modifies this;
    ensures p == q;
  {
    p := q;
  }

  method TestDriver()
  {
    var c: InitCalls;
    c := new InitCalls.Init(15);
    var d := new InitCalls.Init(17);
    var e: InitCalls := new InitCalls.Init(18);
    var f: object := new InitCalls.Init(19);
    assert c.z + d.z + e.z == 50;
    // poor man's type cast:
    ghost var g: InitCalls;
    assert f == g ==> g.z == 19;

    // test that the call is done before the assignment to the LHS
    var r := c;
    r := new InitCalls.InitFromReference(r);  // fine, since r.z==15
    r := new InitCalls.InitFromReference(r);  // error, since r.z is unknown
  }
}

// --------------- some tests with quantifiers and ranges ----------------------

method QuantifierRange0<T>(a: seq<T>, x: T, y: T, N: int)
  requires 0 <= N && N <= |a|;
  requires forall k | 0 <= k && k < N :: a[k] != x;
  requires exists k | 0 <= k && k < N :: a[k] == y;
  ensures forall k :: 0 <= k && k < N ==> a[k] != x;  // same as the precondition, but using ==> instead of |
  ensures exists k :: 0 <= k && k < N && a[k] == y;  // same as the precondition, but using && instead of |
{
  assert x != y;
}

method QuantifierRange1<T>(a: seq<T>, x: T, y: T, N: int)
  requires 0 <= N && N <= |a|;
  requires forall k :: 0 <= k && k < N ==> a[k] != x;
  requires exists k :: 0 <= k && k < N && a[k] == y;
  ensures forall k | 0 <= k && k < N :: a[k] != x;  // same as the precondition, but using | instead of ==>
  ensures exists k | 0 <= k && k < N :: a[k] == y;  // same as the precondition, but using | instead of &&
{
  assert x != y;
}

method QuantifierRange2<T(==)>(a: seq<T>, x: T, y: T, N: int)
  requires 0 <= N && N <= |a|;
  requires exists k | 0 <= k && k < N :: a[k] == y;
  ensures forall k | 0 <= k && k < N :: a[k] == y;  // error
{
  assert N != 0;
  if (N == 1) {
    assert forall k | a[if 0 <= k && k < N then k else 0] != y :: k < 0 || N <= k;  // in this case, the precondition holds trivially
  }
  if (forall k | 0 <= k && k < N :: a[k] == x) {
    assert x == y;
  }
}

// ----------------------- tests that involve sequences of boxes --------

ghost method M(zeros: seq<bool>, Z: bool)
  requires 1 <= |zeros| && Z == false;
  requires forall k :: 0 <= k && k < |zeros| ==> zeros[k] == Z;
{
  var x := [Z];
  assert zeros[0..1] == [Z];
}

class SomeType
{
  var x: int;
  method DoIt(stack: seq<SomeType>)
    requires null !in stack;
    modifies stack;
  {
    forall n | n in stack {
      n.x := 10;
    }
  }
}

// ----------------------- tests of some theory axioms --------

method TestSequences0()
{
  var s := [0, 2, 4];
  if (*) {
    assert 4 in s;
    assert 0 in s;
    assert 1 !in s;
  } else {
    assert 2 in s;
    assert exists n :: n in s && -3 <= n && n < 2;
  }
  assert 7 in s;  // error
}

// ----------------------- test attributes on methods and constructors --------

method test0()
{
  assert false;  // error
}

method {:verify false} test1()
{
  assert false;
}

function test2() : bool
{
  !test2()  // error
}

function {:verify false} test3() : bool
{
  !test3()
}

class Test {

  method test0()
  {
    assert false;  // error
  }

  method {:verify false} test1()
  {
    assert false;
  }

  constructor init0()
  {
    assert false;  // error
  }

  constructor {:verify false} init1()
  {
    assert false;
  }

  function test2() : bool
  {
    !test2()  // error
  }

  function {:verify false} test3() : bool
  {
    !test3()
  }

}

// ------ an if-then-else regression test

function F(b: bool): int
  // The if-then-else in the following line was once translated incorrectly,
  // incorrectly causing the postcondition to verify
  ensures if b then F(b) == 5 else F(b) == 6;
{
  5
}

// ----------------------- test attributes on method specification constructs (assert, ensures, modifies, decreases, invariant) --------

class AttributeTests {
  var f: int;

  method m0()
  {

  }

  method m1() returns (r: bool)
  {
    r := false;
  }

  function method m2() : bool
  {
    true
  }

  constructor C()
  {

  }

  method testAttributes0() returns (r: AttributeTests)
    ensures {:boolAttr true} true;
    ensures {:boolAttr false} true;
    ensures {:intAttr 0} true;
    ensures {:intAttr 1} true;
    free ensures {:boolAttr true} true;
    free ensures {:boolAttr false} true;
    free ensures {:intAttr 0} true;
    free ensures {:intAttr 1} true;
    modifies {:boolAttr true} this`f;
    modifies {:boolAttr false} this`f;
    modifies {:intAttr 0} this`f;
    modifies {:intAttr 1} this`f;
    modifies {:boolAttr true} this;
    modifies {:boolAttr false} this;
    modifies {:intAttr 0} this;
    modifies {:intAttr 1} this;
    decreases {:boolAttr true} f;
    decreases {:boolAttr false} f;
    decreases {:intAttr 0} f;
    decreases {:intAttr 1} f;
  {
    assert {:boolAttr true} true;
    assert {:boolAttr false} true;
    assert {:intAttr 0} true;
    assert {:intAttr 1} true;

    while (false)
      invariant {:boolAttr true} true;
      invariant {:boolAttr false} true;
      invariant {:intAttr 0} true;
      invariant {:intAttr 1} true;
      free invariant {:boolAttr true} true;
      free invariant {:boolAttr false} true;
      free invariant {:intAttr 0} true;
      free invariant {:intAttr 1} true;
      modifies {:boolAttr true} this`f;
      modifies {:boolAttr false} this`f;
      modifies {:intAttr 0} this`f;
      modifies {:intAttr 1} this`f;
      decreases {:boolAttr true} f;
      decreases {:boolAttr false} f;
      decreases {:intAttr 0} f;
      decreases {:intAttr 1} f;
    {

    }

    m0() {:boolAttr true};
    m0() {:boolAttr false};
    m0() {:intAttr 0};
    m0() {:intAttr 1};

    this.m0() {:boolAttr true};
    this.m0() {:boolAttr false};
    this.m0() {:intAttr 0};
    this.m0() {:intAttr 1};

    var b1 := m1() {:boolAttr true};
    b1 := m1() {:boolAttr false};
    b1 := m1() {:intAttr 0};
    b1 := m1() {:intAttr 1};

    var b2, b2' := m2() {:boolAttr true}, m2() {:boolAttr true};
    b2, b2' := m2() {:boolAttr false}, m2() {:boolAttr false};
    b2, b2' := m2() {:intAttr 0}, m2() {:boolAttr false};
    b2, b2' := m2() {:intAttr 1}, m2() {:boolAttr false};

    var c := new AttributeTests.C() {:boolAttr true};
    c := new AttributeTests.C() {:boolAttr false};
    c := new AttributeTests.C() {:intAttr 0};
    c := new AttributeTests.C() {:intAttr 1};

    if (*) {
      return new AttributeTests.C() {:boolAttr true};
    } else {
      return new AttributeTests.C() {:intAttr 0};
    }
  }
}

// ----------------------- Pretty printing of !(!expr) --------

static method TestNotNot()
{
  assert !(!true);  // Shouldn't pretty print as "!!true".

  assert !(true == false);

  assert !(if true then false else false);

  assert !if true then false else false;

  assert !if !(!true) then false else false;

  assert true == !(!true);
}

// ----------------------- Assign-such-that statements -------

method AssignSuchThat0(a: int, b: int) returns (x: int, y: int)
  ensures x == a && y == b;
{
  if (*) {
    x, y :| a <= x < a + 1 && b + a <= y + a && y <= b;
  } else {
    var xx, yy :| a <= xx < a + 1 && b + a <= yy + a && yy <= b;
    x, y := xx, yy;
  }
}

method AssignSuchThat1(a: int, b: int) returns (x: int, y: int)
{
  ghost var k :| assume 0 <= k < a - b;  // this acts like an 'assume 0 < a - b;'
  assert b < a;
  k :| k == old(2*k);  // note, the 'old' has no effect on local variables like k
  assert k == 0;
  var S := {2, 4, 7};
  var T :| T <= S;
  assert 3 !in T;
  assert T == {};  // error: T may be larger
}

method AssignSuchThat2(i: int, j: int, ghost S: set<Node>)
  modifies S;
{
  var n := new Node;
  var a := new int[25];
  var t;
  if (0 <= i < j < 25) {
    a[i], t, a[j], n.next, n :| assume true;
  }
  if (n != null && n.next != null) {
    assume n in S && n.next in S;
    n.next.next, n.next :| assume n != null && n.next != null && n.next.next == n.next;  // error: n.next may equal n (thus aliasing n.next.next and n.next)
  } else if (0 <= i < 25 && 0 <= j < 25) {
    t, a[i], a[j] :| assume t < a[i] < a[j];  // error: i may equal j (thus aliasing a[i] and a[j])
  }
}

method AssignSuchThat3()
{
  var n := new Node;
  n, n.next :| assume n.next == n;  // error: RHS is not well defined (RHS is evaluated after the havocking of the LHS)
}

method AssignSuchThat4()
{
  var n := new Node;
  n, n.next :| assume n != null && n.next == n;  // that's the ticket
}

method AssignSuchThat5()
{
  ghost var n := new Node;
  n :| fresh(n);  // fine
  assert false;  // error
}

method AssignSuchThat6()
{
  var n: Node;
  n :| assume n != null && fresh(n);  // there is no non-null fresh object, so this amounts to 'assume false;'
  assert false;  // no problemo
}

method AssignSuchThat7<T>(A: set<T>, x: T) {
  var B :| A <= B;
  assert x in A ==> x in B;
}

// ----------- let-such-that expressions ------------------------

function method LetSuchThat_P(x: int): bool

method LetSuchThat0(ghost g: int)
  requires LetSuchThat_P(g);
{
  var t :| LetSuchThat_P(t);  // assign-such-that statement
  ghost var u := var q :| LetSuchThat_P(q); q + 1;  // let-such-that expression
  if (forall a,b | LetSuchThat_P(a) && LetSuchThat_P(b) :: a == b) {
    assert t < u;
  }
  assert LetSuchThat_P(u-1);  // yes
  assert LetSuchThat_P(u);  // error: no reason to expect this to hold
}

method LetSuchThat1<T>(A: set<T>)
{
  ghost var C := var B :| A <= B; A - B;
  assert C == {};
}

method LetSuchThat2(n: nat)
{
  ghost var x := (var k :| k < n; k) + 3;  // fine, such a k always exists
  assert x < n+3;
  if (*) {
    x := var k :| 0 <= k < n; k;  // error: there may not be such a k
  } else {
    x := var k: nat :| k < n; k;  // error: there may not be such a k
  }
}