Rust: Create data flow nodes for parameters in the CFG

Before data flow nodes where created for all parameters in the AST. But
some AST parameters does not lead to any data flow (for instance
parameters in function pointer types).

Author: paldepind

rust/ql/lib/codeql/rust/controlflow/CfgNodes.qll

@@ -14,6 +14,14 @@ class AstCfgNode extends CfgNode {
   AstCfgNode() { node = this.getAstNode() }
 }
 
+/** A CFG node that corresponds to a parameter in the AST. */
+class ParamCfgNode extends AstCfgNode {
+  override Param node;
+
+  /** Gets the underlying parameter. */
+  Param getParam() { result = node }
+}
+
 /** A CFG node that corresponds to an expression in the AST. */
 class ExprCfgNode extends AstCfgNode {
   override Expr node;

rust/ql/lib/codeql/rust/dataflow/internal/DataFlowImpl.qll

@@ -152,18 +152,18 @@ module Node {
    * flow graph.
    */
   final class ParameterNode extends Node, TParameterNode {
-    Param parameter;
+    ParamCfgNode parameter;
 
     ParameterNode() { this = TParameterNode(parameter) }
 
-    override CfgScope getCfgScope() { result = parameter.getEnclosingCallable() }
+    override CfgScope getCfgScope() { result = parameter.getParam().getEnclosingCallable() }
 
     override Location getLocation() { result = parameter.getLocation() }
 
     override string toString() { result = parameter.toString() }
 
     /** Gets the parameter in the AST that this node corresponds to. */
-    Param getParameter() { result = parameter }
+    Param getParameter() { result = parameter.getParam() }
   }
 
   final class ArgumentNode = NaNode;
@@ -232,7 +232,7 @@ final class Node = Node::Node;
 module SsaFlow {
   private module Impl = SsaImpl::DataFlowIntegration;
 
-  private Node::ParameterNode toParameterNode(Param p) { result = TParameterNode(p) }
+  private Node::ParameterNode toParameterNode(Param p) { result.getParameter() = p }
 
   /** Converts a control flow node into an SSA control flow node. */
   Impl::Node asNode(Node n) {
@@ -484,7 +484,7 @@ private module Cached {
   cached
   newtype TNode =
     TExprNode(ExprCfgNode n) or
-    TParameterNode(Param p) or
+    TParameterNode(ParamCfgNode p) or
     TSsaNode(SsaImpl::DataFlowIntegration::SsaNode node)
 
   cached