FIXUP of assign operation implementation.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/Assignable.qll

@@ -292,7 +292,8 @@ module AssignableInternal {
     newtype TAssignableDefinition =
       TAssignmentDefinition(Assignment a) {
         not a.getLValue() instanceof TupleExpr and
-        not a instanceof AssignOperation
+        not a instanceof AssignCompoundOperation and
+        not a instanceof AssignCoalesceExpr
       } or
       TTupleAssignmentDefinition(AssignExpr ae, Expr leaf) { tupleAssignmentDefinition(ae, leaf) } or
       TOutRefDefinition(AssignableAccess aa) {
@@ -317,7 +318,10 @@ module AssignableInternal {
       } or
       TAddressOfDefinition(AddressOfExpr aoe) or
       TPatternDefinition(TopLevelPatternDecl tlpd) or
-      TAssignOperationDefinition(AssignOperation ao)
+      TAssignOperationDefinition(AssignOperation ao) {
+        ao instanceof AssignCompoundOperation or
+        ao instanceof AssignCoalesceExpr
+      }
 
     /**
      * Gets the source expression assigned in tuple definition `def`, if any.

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

@@ -63,7 +63,7 @@ class AssignExpr extends Assignment, @simple_assign_expr {
  * (`AssignArithmeticOperation`), a bitwise assignment operation or
  * (`AssignBitwiseOperation`).
  */
-class AssignOperation extends Assignment, OperatorCall, @assign_op_expr {
+class AssignOperation extends Assignment, @assign_op_expr {
   override string getOperator() { none() }
 
   /**
@@ -79,14 +79,21 @@ class AssignOperation extends Assignment, OperatorCall, @assign_op_expr {
   override string toString() { result = "... " + this.getOperator() + " ..." }
 }
 
+/**
+ * An assignment operation that corresponds to an operator call, for example `x += y` corresponds to `x = x + y`.
+ */
+class AssignCompoundOperation extends AssignOperation, OperatorCall, @assign_op_call_expr {
+  override string toString() { result = "... " + this.getOperator() + " ..." }
+}
+
 /**
  * An arithmetic assignment operation. Either an addition assignment operation
  * (`AssignAddExpr`), a subtraction assignment operation (`AssignSubExpr`), a
  * multiplication assignment operation (`AssignMulExpr`), a division assignment
  * operation (`AssignDivExpr`), or a remainder assignment operation
  * (`AssignRemExpr`).
  */
-class AssignArithmeticOperation extends AssignOperation, @assign_arith_expr { }
+class AssignArithmeticOperation extends AssignCompoundOperation, @assign_arith_expr { }
 
 /**
  * An addition assignment operation, for example `x += y`.
@@ -142,7 +149,7 @@ class AssignRemExpr extends AssignArithmeticOperation, @assign_rem_expr {
  * operation (`AssignRightShiftExpr`), or an unsigned right-shift assignment
  * operation (`AssignUnsignedRightShiftExpr`).
  */
-class AssignBitwiseOperation extends AssignOperation, @assign_bitwise_expr { }
+class AssignBitwiseOperation extends AssignCompoundOperation, @assign_bitwise_expr { }
 
 /**
  * A bitwise-and assignment operation, for example `x &= y`.
@@ -207,7 +214,7 @@ deprecated class AssignUnsighedRightShiftExpr = AssignUnsignedRightShiftExpr;
  * An event assignment. Either an event addition (`AddEventExpr`) or an event
  * removal (`RemoveEventExpr`).
  */
-class AddOrRemoveEventExpr extends Assignment, @assign_event_expr {
+class AddOrRemoveEventExpr extends AssignOperation, @assign_event_expr {
   override string getOperator() { none() }
 
   /** Gets the event targeted by this event assignment. */