C#: Use the NullCoalescingOperation class where needed (now that assignments are no longer expanded).

Author: michaelnebel

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

@@ -292,11 +292,7 @@ private module LogicInput implements GuardsImpl::LogicInputSig {
     v1.isNonNullValue() and
     v2 = v1
     or
-    g2 = g1.(NullCoalescingExpr).getAnOperand() and
-    v1.isNullValue() and
-    v2 = v1
-    or
-    g2 = g1.(AssignCoalesceExpr).getAnOperand() and
+    g2 = g1.(NullCoalescingOperation).getAnOperand() and
     v1.isNullValue() and
     v2 = v1
     or
@@ -844,18 +840,14 @@ module Internal {
     or
     e1 = e2.(Cast).getExpr()
     or
-    e2 = e1.(NullCoalescingExpr).getAnOperand()
-    or
-    e2 = e1.(AssignCoalesceExpr).getAnOperand()
+    e2 = e1.(NullCoalescingOperation).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())
+    e3 = any(NullCoalescingOperation no | e1 = no.getLeftOperand() and e2 = no.getRightOperand())
   }
 
   predicate nullValueImplied(Expr e) {
@@ -932,8 +924,7 @@ module Internal {
   predicate nonNullValueImpliedUnary(Expr e1, Expr e2) {
     e1 = e2.(CastExpr).getExpr() or
     e1 = e2.(AssignExpr).getRValue() or
-    e1 = e2.(NullCoalescingExpr).getAnOperand() or
-    e1 = e2.(AssignCoalesceExpr).getAnOperand()
+    e1 = e2.(NullCoalescingOperation).getAnOperand()
   }
 
   /**

csharp/ql/lib/semmle/code/csharp/controlflow/internal/Completion.qll

@@ -447,7 +447,7 @@ private predicate inBooleanContext(Expr e) {
     e in [ce.getThen(), ce.getElse()]
   )
   or
-  e = any(NullCoalescingExpr nce | inBooleanContext(nce)).getAnOperand()
+  e = any(NullCoalescingOperation nce | inBooleanContext(nce)).getAnOperand()
   or
   e = any(SwitchExpr se | inBooleanContext(se)).getACase()
   or
@@ -467,13 +467,13 @@ private predicate mustHaveNullnessCompletion(Expr e) {
  * that `e` evaluates to determines a `null`/non-`null` branch successor.
  */
 private predicate inNullnessContext(Expr e) {
-  e = any(NullCoalescingExpr nce).getLeftOperand()
+  e = any(NullCoalescingOperation nce).getLeftOperand()
   or
   exists(QualifiableExpr qe | qe.isConditional() | e = qe.getChildExpr(-1))
   or
   exists(ConditionalExpr ce | inNullnessContext(ce) | (e = ce.getThen() or e = ce.getElse()))
   or
-  exists(NullCoalescingExpr nce | inNullnessContext(nce) | e = nce.getRightOperand())
+  exists(NullCoalescingOperation nce | inNullnessContext(nce) | e = nce.getRightOperand())
   or
   e = any(SwitchExpr se | inNullnessContext(se)).getACase()
   or

csharp/ql/lib/semmle/code/csharp/controlflow/internal/ControlFlowGraphImpl.qll

@@ -504,7 +504,7 @@ module Expressions {
       not this instanceof LogicalNotExpr and
       not this instanceof LogicalAndExpr and
       not this instanceof LogicalOrExpr and
-      not this instanceof NullCoalescingExpr and
+      not this instanceof NullCoalescingOperation and
       not this instanceof ConditionalExpr and
       not this instanceof ConditionallyQualifiedExpr and
       not this instanceof ThrowExpr and
@@ -734,7 +734,8 @@ module Expressions {
     }
   }
 
-  private class NullCoalescingExprTree extends PostOrderTree instanceof NullCoalescingExpr {
+  private class NullCoalescingOperationTree extends PostOrderTree instanceof NullCoalescingOperation
+  {
     final override predicate propagatesAbnormal(AstNode child) {
       child in [super.getLeftOperand(), super.getRightOperand()]
     }

csharp/ql/lib/semmle/code/csharp/controlflow/internal/Splitting.qll

@@ -95,7 +95,7 @@ module ConditionalCompletionSplitting {
         child = parent.(SwitchCaseExpr).getBody()
         or
         parent =
-          any(NullCoalescingExpr nce |
+          any(NullCoalescingOperation nce |
             if childCompletion instanceof NullnessCompletion
             then child = nce.getRightOperand()
             else child = nce.getAnOperand()

csharp/ql/lib/semmle/code/csharp/dataflow/Nullness.qll

@@ -42,7 +42,7 @@ private Expr maybeNullExpr(Expr reason) {
       ce.getElse() = maybeNullExpr(reason)
     )
   or
-  result.(NullCoalescingExpr).getRightOperand() = maybeNullExpr(reason)
+  result.(NullCoalescingOperation).getRightOperand() = maybeNullExpr(reason)
   or
   result =
     any(QualifiableExpr qe |

csharp/ql/lib/semmle/code/csharp/metrics/Complexity.qll

@@ -32,7 +32,7 @@ private predicate branchingExpr(Expr expr) {
   expr instanceof ConditionalExpr or
   expr instanceof LogicalAndExpr or
   expr instanceof LogicalOrExpr or
-  expr instanceof NullCoalescingExpr
+  expr instanceof NullCoalescingOperation
 }
 
 /**

csharp/ql/src/Bad Practices/Control-Flow/ConstantCondition.ql

@@ -43,7 +43,7 @@ module ConstCondImpl = ConstCond::Make<Location, Cfg, ConstCondInput>;
 predicate nullCheck(Expr e, boolean direct) {
   exists(QualifiableExpr qe | qe.isConditional() and qe.getQualifier() = e and direct = true)
   or
-  exists(NullCoalescingExpr nce | nce.getLeftOperand() = e and direct = true)
+  exists(NullCoalescingOperation nce | nce.getLeftOperand() = e and direct = true)
   or
   exists(ConditionalExpr ce | ce.getThen() = e or ce.getElse() = e |
     nullCheck(ce, _) and direct = false
@@ -114,7 +114,7 @@ class ConstantBooleanCondition extends ConstantCondition {
 
   override predicate isWhiteListed() {
     // E.g. `x ?? false`
-    this.(BoolLiteral) = any(NullCoalescingExpr nce).getRightOperand() or
+    this.(BoolLiteral) = any(NullCoalescingOperation nce).getRightOperand() or
     // No need to flag logical operations when the operands are constant
     isConstantCondition(this.(LogicalNotExpr).getOperand(), _) or
     this =

csharp/ql/src/Language Abuse/UselessNullCoalescingExpression.ql

@@ -17,20 +17,20 @@ import semmle.code.csharp.commons.StructuralComparison
 
 pragma[noinline]
 private predicate same(AssignableAccess x, AssignableAccess y) {
-  exists(NullCoalescingExpr nce |
-    x = nce.getLeftOperand() and
-    y = nce.getRightOperand().getAChildExpr*()
+  exists(NullCoalescingOperation nc |
+    x = nc.getLeftOperand() and
+    y = nc.getRightOperand().getAChildExpr*()
   ) and
   sameGvn(x, y)
 }
 
-private predicate uselessNullCoalescingExpr(NullCoalescingExpr nce) {
+private predicate uselessNullCoalescingOperation(NullCoalescingOperation nce) {
   exists(AssignableAccess x |
     nce.getLeftOperand() = x and
     forex(AssignableAccess y | same(x, y) | y instanceof AssignableRead and not y.isRefArgument())
   )
 }
 
-from NullCoalescingExpr nce
-where uselessNullCoalescingExpr(nce)
+from NullCoalescingOperation nce
+where uselessNullCoalescingOperation(nce)
 select nce, "Both operands of this null-coalescing expression access the same variable or property."