JS: move isDefensiveInit to DefensiveProgramming.qll

javascript/ql/src/Statements/UselessConditional.ql

@@ -15,29 +15,7 @@
 import javascript
 import semmle.javascript.RestrictedLocations
 import semmle.javascript.dataflow.Refinements
-
-/**
- * Holds if `va` is a defensive truthiness check that may be worth keeping, even if it
- * is strictly speaking useless.
- *
- * We currently recognize three patterns:
- *
- *   - the first `x` in `x || (x = e)`
- *   - the second `x` in `x = (x || e)`
- *   - the second `x` in `var x = x || e`
- */
-predicate isDefensiveInit(VarAccess va) {
-  exists (LogOrExpr o, VarRef va2 |
-    va = o.getLeftOperand().getUnderlyingReference() and va2.getVariable() = va.getVariable() |
-    exists (AssignExpr assgn | va2 = assgn.getTarget() |
-      assgn = o.getRightOperand().stripParens() or
-      o = assgn.getRhs().getUnderlyingValue()
-    ) or
-    exists (VariableDeclarator vd | va2 = vd.getBindingPattern() |
-      o = vd.getInit().getUnderlyingValue()
-    )
-  )
-}
+import semmle.javascript.DefensiveProgramming
 
 /**
  * Holds if variable `v` looks like a symbolic constant, that is, it is assigned
@@ -109,7 +87,7 @@ predicate isConstantBooleanReturnValue(Expr e) {
 predicate whitelist(Expr e) {
   isConstant(e) or
   isConstant(e.(LogNotExpr).getOperand()) or
-  isDefensiveInit(e) or
+  e.flow() instanceof DefensiveInit or
   isInitialParameterUse(e) or
   isConstantBooleanReturnValue(e)
 }

javascript/ql/src/semmle/javascript/DefensiveProgramming.qll

@@ -0,0 +1,27 @@
+import javascript
+
+/**
+ * A defensive truthiness check that may be worth keeping, even if it
+ * is strictly speaking useless.
+ *
+ * We currently recognize three patterns:
+ *
+ *   - the first `x` in `x || (x = e)`
+ *   - the second `x` in `x = (x || e)`
+ *   - the second `x` in `var x = x || e`
+ */
+class DefensiveInit extends DataFlow::ValueNode {
+  DefensiveInit() {
+    exists(VarAccess va, LogOrExpr o, VarRef va2 |
+      va = astNode and
+      va = o.getLeftOperand().stripParens() and va2.getVariable() = va.getVariable() |
+      exists(AssignExpr assgn | va2 = assgn.getTarget() |
+        assgn = o.getRightOperand().stripParens() or
+        o = assgn.getRhs().stripParens()
+      )
+      or
+      exists(VariableDeclarator vd | va2 = vd.getBindingPattern() | o = vd.getInit().stripParens())
+    )
+  }
+
+}