Protect Bitvector field of BvExtractExpr when it is immutable.

2 files changed, 23 insertions, 4 deletions

diff --git a/Source/Core/AbsyExpr.cs b/Source/Core/AbsyExpr.cs
index 2427d856..f3a943b8 100644
--- a/Source/Core/AbsyExpr.cs
+++ b/Source/Core/AbsyExpr.cs
@@ -2969,11 +2969,21 @@ namespace Microsoft.Boogie {
   }

 

   public class BvExtractExpr : Expr {

-    // FIXME: Protect these fields

-    public /*readonly--except in StandardVisitor*/ Expr/*!*/ Bitvector;

+    private /*readonly--except in StandardVisitor*/ Expr/*!*/ _Bitvector;

+    public Expr Bitvector {

+      get { 

+        return _Bitvector;

+      }

+      set {

+        if (Immutable)

+          throw new InvalidOperationException("Cannot change BitVector field of an immutable BvExtractExpr");

+        

+        _Bitvector = value;

+      }

+    }

     [ContractInvariantMethod]

     void ObjectInvariant() {

-      Contract.Invariant(Bitvector != null);

+      Contract.Invariant(_Bitvector != null);

     }

 

     public readonly int Start, End;

@@ -2982,7 +2992,7 @@ namespace Microsoft.Boogie {
       : base(tok, immutable) {

       Contract.Requires(tok != null);

       Contract.Requires(bv != null);

-      Bitvector = bv;

+      _Bitvector = bv;

       Start = start;

       End = end;

       if (immutable)

diff --git a/Source/UnitTests/CoreTests/ExprImmutability.cs b/Source/UnitTests/CoreTests/ExprImmutability.cs
index 98e7158f..b83983b6 100644
--- a/Source/UnitTests/CoreTests/ExprImmutability.cs
+++ b/Source/UnitTests/CoreTests/ExprImmutability.cs
@@ -269,6 +269,15 @@ namespace CoreTests
             Assert.IsTrue(concat.Immutable);
             concat.E1 = lhs; // Should throw
         }
+
+        [Test(), ExpectedException(typeof(InvalidOperationException))]
+        public void ProtectedBvExtract()
+        {
+            var bv = new LiteralExpr(Token.NoToken, Microsoft.Basetypes.BigNum.FromInt(0), 32, /*immutable=*/true);
+            var extract = new BvExtractExpr(Token.NoToken, bv, 32, 0, /*immutable=*/true);
+            Assert.IsTrue(extract.Immutable);
+            extract.Bitvector = bv; // Should throw
+        }
     }
 }