C#: Implement library support for unsigned right shift.

Author: michaelnebel

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

@@ -151,7 +151,8 @@ class AssignRemExpr extends AssignArithmeticOperation, @assign_rem_expr {
  * operation (`AssignOrExpr`), a bitwise exclusive-or assignment
  * operation (`AssignXorExpr`), a left-shift assignment
  * operation (`AssignLeftShiftExpr`), or a right-shift assignment
- * operation (`AssignRightShiftExpr`).
+ * operation (`AssignRightShiftExpr`), or an unsigned right-shift assignment
+ * operation (`AssignUnsignedRightShiftExpr`).
  */
 class AssignBitwiseOperation extends AssignOperation, @assign_bitwise_expr { }
 
@@ -206,6 +207,15 @@ class AssignRightShiftExpr extends AssignBitwiseOperation, @assign_rshift_expr {
 /** DEPRECATED: Alias for AssignRightShiftExpr. */
 deprecated class AssignRShiftExpr = AssignRightShiftExpr;
 
+/**
+ * An unsigned right-shift assignment operation, for example `x >>>= y`.
+ */
+class AssignUnsighedRightShiftExpr extends AssignBitwiseOperation, @assign_urshift_expr {
+  override string getOperator() { result = ">>>=" }
+
+  override string getAPrimaryQlClass() { result = "AssignUnsighedRightShiftExpr" }
+}
+
 /**
  * An event assignment. Either an event addition (`AddEventExpr`) or an event
  * removal (`RemoveEventExpr`).

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

@@ -31,7 +31,8 @@ class ComplementExpr extends UnaryBitwiseOperation, @bit_not_expr {
  * A binary bitwise operation. Either a bitwise-and operation
  * (`BitwiseAndExpr`), a bitwise-or operation (`BitwiseOrExpr`),
  * a bitwise exclusive-or operation (`BitwiseXorExpr`), a left-shift
- * operation (`LeftShiftExpr`), or a right-shift operation (`RightShiftExpr`).
+ * operation (`LeftShiftExpr`), a right-shift operation (`RightShiftExpr`),
+ * or an unsigned right-shift operation (`UnsignedRightShiftExpr`).
  */
 class BinaryBitwiseOperation extends BitwiseOperation, BinaryOperation, @bin_bit_op_expr {
   override string getOperator() { none() }
@@ -61,6 +62,15 @@ class RightShiftExpr extends BinaryBitwiseOperation, @rshift_expr {
 /** DEPRECATED: Alias for RightShiftExpr. */
 deprecated class RShiftExpr = RightShiftExpr;
 
+/**
+ * An unsigned right-shift operation, for example `x >>> y`.
+ */
+class UnsignedRightShiftExpr extends BinaryBitwiseOperation, @urshift_expr {
+  override string getOperator() { result = ">>>" }
+
+  override string getAPrimaryQlClass() { result = "UnsignedRightShiftExpr" }
+}
+
 /**
  * A bitwise-and operation, for example `x & y`.
  */