Python: Move ModificationOfParameterWithDefault to new dataflow API

Author: RasmusWL

python/ql/src/Functions/ModificationOfParameterWithDefault.ql

@@ -13,11 +13,11 @@
 
 import python
 import semmle.python.functions.ModificationOfParameterWithDefault
-import DataFlow::PathGraph
+import ModificationOfParameterWithDefault::Flow::PathGraph
 
 from
-  ModificationOfParameterWithDefault::Configuration config, DataFlow::PathNode source,
-  DataFlow::PathNode sink
-where config.hasFlowPath(source, sink)
+  ModificationOfParameterWithDefault::Flow::PathNode source,
+  ModificationOfParameterWithDefault::Flow::PathNode sink
+where ModificationOfParameterWithDefault::Flow::flowPath(source, sink)
 select sink.getNode(), source, sink, "This expression mutates a $@.", source.getNode(),
   "default value"

python/ql/src/semmle/python/functions/ModificationOfParameterWithDefault.qll

@@ -16,9 +16,11 @@ module ModificationOfParameterWithDefault {
   import ModificationOfParameterWithDefaultCustomizations::ModificationOfParameterWithDefault
 
   /**
+   * DEPRECATED: Use `Flow` module instead.
+   *
    * A data-flow configuration for detecting modifications of a parameters default value.
    */
-  class Configuration extends DataFlow::Configuration {
+  deprecated class Configuration extends DataFlow::Configuration {
     /** Record whether the default value being tracked is non-empty. */
     boolean nonEmptyDefault;
 
@@ -43,4 +45,33 @@ module ModificationOfParameterWithDefault {
       nonEmptyDefault = false and node instanceof MustBeNonEmpty
     }
   }
+
+  private module Config implements DataFlow::StateConfigSig {
+    class FlowState = boolean;
+
+    predicate isSource(DataFlow::Node source, FlowState state) {
+      source.(Source).isNonEmpty() = state
+    }
+
+    predicate isSink(DataFlow::Node sink) { sink instanceof Sink }
+
+    predicate isSink(DataFlow::Node sink, FlowState state) {
+      // dummy implementation since this predicate is required, but actual logic is in
+      // the predicate above.
+      none()
+    }
+
+    predicate isBarrier(DataFlow::Node node, FlowState state) {
+      // if we are tracking a non-empty default, then it is ok to modify empty values,
+      // so our tracking ends at those.
+      state = true and node instanceof MustBeEmpty
+      or
+      // if we are tracking a empty default, then it is ok to modify non-empty values,
+      // so our tracking ends at those.
+      state = false and node instanceof MustBeNonEmpty
+    }
+  }
+
+  /** Global data-flow for detecting modifications of a parameters default value. */
+  module Flow = DataFlow::GlobalWithState<Config>;
 }

python/ql/test/query-tests/Functions/ModificationOfParameterWithDefault/test.ql

@@ -8,7 +8,7 @@ module ModificationOfParameterWithDefaultTest implements TestSig {
   string getARelevantTag() { result = "modification" }
 
   private predicate relevant_node(DataFlow::Node sink) {
-    exists(ModificationOfParameterWithDefault::Configuration cfg | cfg.hasFlowTo(sink))
+    ModificationOfParameterWithDefault::Flow::flowTo(sink)
   }
 
   predicate hasActualResult(Location location, string element, string tag, string value) {