python: model XPathEvaluator

Author: yoff

python/ql/lib/semmle/python/frameworks/Lxml.qll

@@ -70,4 +70,19 @@ private module Lxml {
 
     override string getName() { result = "lxml.etree" }
   }
+
+  class XPathEvaluatorCall extends XPathExecution::Range, DataFlow::CallCfgNode {
+    XPathEvaluatorCall() {
+      this =
+        API::moduleImport("lxml")
+            .getMember("etree")
+            .getMember("XPathEvaluator")
+            .getReturn()
+            .getACall()
+    }
+
+    override DataFlow::Node getXPath() { result = this.getArg(0) }
+
+    override string getName() { result = "lxml.etree" }
+  }
 }

python/ql/test/library-tests/frameworks/lxml/test.py

@@ -18,4 +18,4 @@ def test_ETXpath_class():
 def test_XPathEvaluator_class():
     root = etree.XML("<root><a>TEXT</a></root>")
     search_root = etree.XPathEvaluator(root)
-    text = search_root("path")[0]  # $ MISSING: getXPath="path"
+    text = search_root("path")[0]  # $ getXPath="path"