C#: Make Assignment extend BinaryOperation.

csharp/ql/lib/semmle/code/csharp/exprs/Assignment.qll

@@ -11,7 +11,7 @@ import Expr
  * (`LocalVariableDeclAndInitExpr`), a simple assignment (`AssignExpr`), or
  * an assignment operation (`AssignOperation`).
  */
-class Assignment extends Operation, @assign_expr {
+class Assignment extends BinaryOperation, @assign_expr {
   Assignment() {
     this instanceof LocalVariableDeclExpr
     implies
@@ -20,6 +20,10 @@ class Assignment extends Operation, @assign_expr {
     expr_parent(_, 0, this)
   }
 
+  override Expr getLeftOperand() { result = this.getChild(1) }
+
+  override Expr getRightOperand() { result = this.getChild(0) }
+
   /** Gets the left operand of this assignment. */
   Expr getLValue() { result = this.getChild(1) }
 

csharp/ql/lib/semmle/code/csharp/exprs/Expr.qll

@@ -233,7 +233,8 @@ class UnaryOperation extends Operation, @un_op {
  * A binary operation. Either a binary arithmetic operation
  * (`BinaryArithmeticOperation`), a binary bitwise operation
  * (`BinaryBitwiseOperation`), a comparison operation (`ComparisonOperation`),
- * or a binary logical operation (`BinaryLogicalOperation`).
+ * a binary logical operation (`BinaryLogicalOperation`), or an
+ * assignment (`Assignment`).
  */
 class BinaryOperation extends Operation, @bin_op {
   /** Gets the left operand of this binary operation. */

csharp/ql/test/library-tests/linq/Linq2.ql

@@ -5,4 +5,5 @@
 import csharp
 
 from BinaryOperation e
+where not e instanceof Assignment
 select e, e.getAnOperand()