JS: Add toDataFlowNode() and use more consistently

Author: asgerf

javascript/ql/lib/semmle/javascript/dataflow/internal/CallGraphs.qll

@@ -14,7 +14,7 @@ module CallGraph {
   Function getAFunctionValue(AnalyzedNode node) {
     result = node.getAValue().(AbstractCallable).getFunction()
     or
-    node = DataFlow::valueNode(NameResolution::trackFunctionValue(result))
+    node = NameResolution::trackFunctionValue(result).toDataFlowNode().(DataFlow::SourceNode)
   }
 
   /** Holds if the type inferred for `node` is indefinite due to global flow. */

javascript/ql/lib/semmle/javascript/dataflow/internal/FlowSteps.qll

@@ -336,27 +336,17 @@ private module CachedSteps {
     // TODO: Ensure name resolution has good enough support for NodeJS and AMD
     exists(NameResolution::Node node1, NameResolution::Node node2 |
       NameResolution::ValueFlow::resolvedReadStep(node1, node2) and
-      pred = DataFlow::valueNode(node1) and
-      succ = getNodeFromNameResolutionNode(node2)
+      pred = node1.toDataFlowNode() and
+      succ = node2.toDataFlowNode()
     )
     or
     exists(Import imprt, Module mod |
       imprt.getImportedModule() = mod and
-      pred = DataFlow::valueNode(NameResolution::getModuleBulkExport(mod)) and
+      pred = NameResolution::getModuleBulkExport(mod).toDataFlowNode() and
       succ = imprt.getImportedModuleNodeStrict()
     )
   }
 
-  pragma[inline]
-  private DataFlow::Node getNodeFromNameResolutionNode(NameResolution::Node node) {
-    result = DataFlow::valueNode(node)
-    or
-    exists(ImportSpecifier spec |
-      node = spec.getLocal() and
-      result = DataFlow::valueNode(spec)
-    )
-  }
-
   /**
    * Gets a node whose value is assigned to `gv` in `f`.
    */

javascript/ql/lib/semmle/javascript/internal/NameResolution.qll

@@ -34,6 +34,16 @@ module NameResolution {
       or
       result = this.(JSDocTypeExpr).getLocation()
     }
+
+    DataFlow::Node toDataFlowNode() {
+      result = DataFlow::valueNode(this)
+      or
+      // TODO: refactor graph to avoid the need for this
+      exists(ImportSpecifier spec |
+        this = spec.getLocal() and
+        result = DataFlow::valueNode(spec)
+      )
+    }
   }
 
   private signature predicate nodeSig(Node node);