JS: move default parameter values to the DefUse graph

javascript/ql/src/semmle/javascript/DefUse.qll

@@ -12,6 +12,7 @@ import javascript
  * <tr><td><code>x = y</code><td><code>x = y</code><td><code>x</code><td><code>y</code></tr>
  * <tr><td><code>var a = b</code><td><code>var a = b</code><td><code>a</code><td><code>b</code></tr>
  * <tr><td><code>function f { ... }</code><td><code>f</code><td><code>f</code><td><code>function f { ... }</code></tr>
+ * <tr><td><code>function f ( x = y ){ ... }</code><td><code>x</code><td><code>x</code><td><code>y</code></tr>
  * <tr><td><code>class C { ... }</code><td><code>C</code><td><code>C</code><td><code>class C { ... }</code></tr>
  * <tr><td><code>namespace N { ... }</code><td><code>N</code><td><code>N</code><td><code>namespace N { ... }</code></tr>
  * <tr><td><code>enum E { ... }</code><td><code>E</code><td><code>E</code><td><code>enum E { ... }</code></tr>
@@ -42,6 +43,8 @@ private predicate defn(ControlFlowNode def, Expr lhs, AST::ValueNode rhs) {
   exists(EnumMember member | def = member.getIdentifier() |
     lhs = def and rhs = member.getInitializer()
   )
+  or
+  lhs = def and def.(Parameter).getDefault() = rhs
 }
 
 /**

javascript/ql/src/semmle/javascript/RangeAnalysis.qll

@@ -104,7 +104,12 @@ module RangeAnalysis {
   pragma[noinline]
   private predicate hasUniquePredecessor(DataFlow::Node node) {
     isRelevant(node) and
-    strictcount(node.getAPredecessor()) = 1
+    strictcount(node.getAPredecessor()) = 1 and
+    // exclude parameters with default values
+    not exists (Parameter p |
+      DataFlow::parameterNode(p) = node and
+      exists(p.getDefault())
+    )
   }
 
   /**

javascript/ql/src/semmle/javascript/dataflow/internal/VariableTypeInference.qll

@@ -143,7 +143,7 @@ private class AnalyzedParameter extends AnalyzedVarDef, @vardecl {
 
   override DataFlow::AnalyzedNode getRhs() {
     getFunction().argumentPassing(this, result.asExpr()) or
-    result = this.(Parameter).getDefault().analyze()
+    result = AnalyzedVarDef.super.getRhs()
   }
 
   override AbstractValue getAnRhsValue() {