Python: Improve usefulness of RemoteFlowSourcesReach meta query

Before, results from `dca` would look something like

    ## + py/meta/alerts/remote-flow-sources-reach

    - django/django@c2250cf_cb8f: tests/messages_tests/urls.py:38:16:38:48
        reachable with taint-tracking from RemoteFlowSource
    - django/django@c2250cf_cb8f: tests/messages_tests/urls.py:38:9:38:12
        reachable with taint-tracking from RemoteFlowSource

now it should make it easier to spot _what_ it is that actually changed,
since we pretty-print the node.

Author: RasmusWL

python/ql/src/meta/alerts/RemoteFlowSourcesReach.ql

@@ -14,6 +14,7 @@ private import semmle.python.dataflow.new.DataFlow
 private import semmle.python.dataflow.new.TaintTracking
 private import semmle.python.dataflow.new.RemoteFlowSources
 private import meta.MetaMetrics
+private import semmle.python.dataflow.new.internal.PrintNode
 
 class RemoteFlowSourceReach extends TaintTracking::Configuration {
   RemoteFlowSourceReach() { this = "RemoteFlowSourceReach" }
@@ -43,4 +44,4 @@ class RemoteFlowSourceReach extends TaintTracking::Configuration {
 
 from RemoteFlowSourceReach cfg, DataFlow::Node reachable
 where cfg.hasFlow(_, reachable)
-select reachable, "reachable with taint-tracking from RemoteFlowSource"
+select reachable, prettyNode(reachable)

python/ql/test/experimental/dataflow/TestUtil/PrintNode.qll renamed to python/ql/src/semmle/python/dataflow/new/internal/PrintNode.qll

@@ -1,6 +1,20 @@
-import python
-import semmle.python.dataflow.new.DataFlow
+/**
+ * INTERNAL: Do not use.
+ *
+ * Provides helper predicates for pretty-printing `DataFlow::Node`s.
+ *
+ * Since these have not been performance optimized, please only use them for
+ * debug-queries or in tests.
+ */
+
+private import python
+private import semmle.python.dataflow.new.DataFlow
 
+/**
+ * INTERNAL: Do not use.
+ *
+ * Gets the pretty-printed version of the Expr `e`.
+ */
 string prettyExpr(Expr e) {
   not e instanceof Num and
   not e instanceof StrConst and
@@ -27,15 +41,19 @@ string prettyExpr(Expr e) {
 }
 
 /**
- * Gets pretty-printed version of the DataFlow::Node `node`
+ * INTERNAL: Do not use.
+ *
+ * Gets the pretty-printed version of the DataFlow::Node `node`
  */
 bindingset[node]
 string prettyNode(DataFlow::Node node) {
   if exists(node.asExpr()) then result = prettyExpr(node.asExpr()) else result = node.toString()
 }
 
 /**
- * Gets pretty-printed version of the DataFlow::Node `node`, that is suitable for use
+ * INTERNAL: Do not use.
+ *
+ * Gets the pretty-printed version of the DataFlow::Node `node`, that is suitable for use
  * with `TestUtilities.InlineExpectationsTest` (that is, no spaces unless required).
  */
 bindingset[node]

python/ql/test/experimental/dataflow/TestUtil/FlowTest.qll

@@ -1,7 +1,7 @@
 import python
 import semmle.python.dataflow.new.DataFlow
 import TestUtilities.InlineExpectationsTest
-import experimental.dataflow.TestUtil.PrintNode
+private import semmle.python.dataflow.new.internal.PrintNode
 
 abstract class FlowTest extends InlineExpectationsTest {
   bindingset[this]

python/ql/test/experimental/dataflow/TestUtil/RoutingTest.qll

@@ -1,7 +1,7 @@
 import python
 import semmle.python.dataflow.new.DataFlow
 import TestUtilities.InlineExpectationsTest
-import experimental.dataflow.TestUtil.PrintNode
+private import semmle.python.dataflow.new.internal.PrintNode
 
 /**
  * A routing test is designed to test that values are routed to the

python/ql/test/experimental/dataflow/method-calls/test.ql

@@ -1,6 +1,6 @@
 import python
 import semmle.python.dataflow.new.DataFlow
-import experimental.dataflow.TestUtil.PrintNode
+private import semmle.python.dataflow.new.internal.PrintNode
 
 query predicate conjunctive_lookup(
   DataFlow::MethodCallNode methCall, string call, string object, string methodName

python/ql/test/experimental/dataflow/tainttracking/TestTaintLib.qll

@@ -1,7 +1,7 @@
 import python
 import semmle.python.dataflow.new.TaintTracking
 import semmle.python.dataflow.new.DataFlow
-import experimental.dataflow.TestUtil.PrintNode
+private import semmle.python.dataflow.new.internal.PrintNode
 
 class TestTaintTrackingConfiguration extends TaintTracking::Configuration {
   TestTaintTrackingConfiguration() { this = "TestTaintTrackingConfiguration" }

python/ql/test/experimental/meta/ConceptsTest.qll

@@ -2,7 +2,7 @@ import python
 import semmle.python.dataflow.new.DataFlow
 import semmle.python.Concepts
 import TestUtilities.InlineExpectationsTest
-import experimental.dataflow.TestUtil.PrintNode
+private import semmle.python.dataflow.new.internal.PrintNode
 
 class SystemCommandExecutionTest extends InlineExpectationsTest {
   SystemCommandExecutionTest() { this = "SystemCommandExecutionTest" }

python/ql/test/experimental/meta/InlineTaintTest.qll

@@ -14,7 +14,7 @@ import semmle.python.dataflow.new.DataFlow
 import semmle.python.dataflow.new.TaintTracking
 import semmle.python.dataflow.new.RemoteFlowSources
 import TestUtilities.InlineExpectationsTest
-import experimental.dataflow.TestUtil.PrintNode
+private import semmle.python.dataflow.new.internal.PrintNode
 
 DataFlow::Node shouldBeTainted() {
   exists(DataFlow::CallCfgNode call |