Associate endpoints with their potential endpoint types and check these when determining candidates.

This prevents us from associating a sink candidate with a source type and vice versa.

However, this does not fix the problem of negative characteristics for sink types excluding source candidates.

java/ql/automodel/src/AutomodelApplicationModeCharacteristics.qll

@@ -96,6 +96,18 @@ abstract private class ApplicationModeEndpoint extends TApplicationModeEndpoint
       else none() // if both exist, it would be a summaryModel (not yet supported)
   }
 
+  /**
+   * Gets a potential type of this endpoint to make sure that sources are
+   * associated with source types and sinks with sink types.
+   */
+  AutomodelEndpointTypes::EndpointType getAPotentialType() {
+    this.getExtensibleType() = "sourceModel" and
+    result instanceof AutomodelEndpointTypes::SourceType
+    or
+    this.getExtensibleType() = "sinkModel" and
+    result instanceof AutomodelEndpointTypes::SinkType
+  }
+
   abstract string toString();
 }
 

java/ql/automodel/src/AutomodelFrameworkModeCharacteristics.qll

@@ -90,6 +90,18 @@ abstract class FrameworkModeEndpoint extends TFrameworkModeEndpoint {
 
   abstract string getExtensibleType();
 
+  /**
+   * Gets a potential type of this endpoint to make sure that sources are
+   * associated with source types and sinks with sink types.
+   */
+  AutomodelEndpointTypes::EndpointType getAPotentialType() {
+    this.getExtensibleType() = "sourceModel" and
+    result instanceof AutomodelEndpointTypes::SourceType
+    or
+    this.getExtensibleType() = "sinkModel" and
+    result instanceof AutomodelEndpointTypes::SinkType
+  }
+
   string toString() { result = this.asTop().toString() }
 
   Location getLocation() { result = this.asTop().getLocation() }

java/ql/automodel/src/AutomodelSharedCharacteristics.qll

@@ -16,7 +16,9 @@ signature module CandidateSig {
    * An endpoint is a potential candidate for modeling. This will typically be bound to the language's
    * DataFlow node class, or a subtype thereof.
    */
-  class Endpoint;
+  class Endpoint {
+    EndpointType getAPotentialType();
+  }
 
   /**
    * A related location for an endpoint. This will typically be bound to the supertype of all AST nodes (eg., `Top`).
@@ -122,9 +124,10 @@ module SharedCharacteristics<CandidateSig Candidate> {
    *
    * A candidate is an endpoint that cannot be excluded from `endpointType` based on its characteristics.
    */
-  predicate isCandidate(Candidate::Endpoint candidateSink, Candidate::EndpointType sinkType) {
-    not sinkType instanceof Candidate::NegativeEndpointType and
-    not exists(getAnExcludingCharacteristic(candidateSink, sinkType))
+  predicate isCandidate(Candidate::Endpoint endpoint, Candidate::EndpointType endpointType) {
+    not endpointType instanceof Candidate::NegativeEndpointType and
+    endpointType = endpoint.getAPotentialType() and
+    not exists(getAnExcludingCharacteristic(endpoint, endpointType))
   }
 
   /**