C#: Update guards library as assign operations are not expanded.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/controlflow/Guards.qll

@@ -296,6 +296,10 @@ private module LogicInput implements GuardsImpl::LogicInputSig {
     v1.isNullValue() and
     v2 = v1
     or
+    g2 = g1.(AssignCoalesceExpr).getAnOperand() and
+    v1.isNullValue() and
+    v2 = v1
+    or
     exists(Assertion assert, AssertMethod target, int i |
       assert.getAssertMethod() = target and
       g1 = assert and
@@ -841,13 +845,17 @@ module Internal {
     e1 = e2.(Cast).getExpr()
     or
     e2 = e1.(NullCoalescingExpr).getAnOperand()
+    or
+    e2 = e1.(AssignCoalesceExpr).getAnOperand()
   }
 
   /** Holds if expression `e3` is a `null` value whenever `e1` and `e2` are. */
   predicate nullValueImpliedBinary(Expr e1, Expr e2, Expr e3) {
     e3 = any(ConditionalExpr ce | e1 = ce.getThen() and e2 = ce.getElse())
     or
     e3 = any(NullCoalescingExpr nce | e1 = nce.getLeftOperand() and e2 = nce.getRightOperand())
+    or
+    e3 = any(AssignCoalesceExpr ace | e1 = ace.getLeftOperand() and e2 = ace.getRightOperand())
   }
 
   predicate nullValueImplied(Expr e) {
@@ -922,11 +930,10 @@ module Internal {
 
   /** Holds if expression `e2` is a non-`null` value whenever `e1` is. */
   predicate nonNullValueImpliedUnary(Expr e1, Expr e2) {
-    e1 = e2.(CastExpr).getExpr()
-    or
-    e1 = e2.(AssignExpr).getRValue()
-    or
-    e1 = e2.(NullCoalescingExpr).getAnOperand()
+    e1 = e2.(CastExpr).getExpr() or
+    e1 = e2.(AssignExpr).getRValue() or
+    e1 = e2.(NullCoalescingExpr).getAnOperand() or
+    e1 = e2.(AssignCoalesceExpr).getAnOperand()
   }
 
   /**
@@ -953,10 +960,13 @@ module Internal {
       )
     or
     // In C#, `null + 1` has type `int?` with value `null`
-    exists(BinaryArithmeticOperation bao, Expr o |
-      result = bao and
-      bao.getAnOperand() = e and
-      bao.getAnOperand() = o and
+    exists(BinaryOperation bo, Expr o |
+      bo instanceof BinaryArithmeticOperation or
+      bo instanceof AssignArithmeticOperation
+    |
+      result = bo and
+      bo.getAnOperand() = e and
+      bo.getAnOperand() = o and
       // The other operand must be provably non-null in order
       // for `only if` to hold
       nonNullValueImplied(o) and
@@ -972,10 +982,10 @@ module Internal {
       any(QualifiableExpr qe |
         qe.isConditional() and
         result = qe.getQualifier()
-      )
-    or
+      ) or
     // In C#, `null + 1` has type `int?` with value `null`
-    e = any(BinaryArithmeticOperation bao | result = bao.getAnOperand())
+    e = any(BinaryArithmeticOperation bao | result = bao.getAnOperand()) or
+    e = any(AssignArithmeticOperation aao | result = aao.getAnOperand())
   }
 
   deprecated predicate isGuard(Expr e, GuardValue val) {