C#: Update model generator to exclude models for some collection like types.

Author: michaelnebel

csharp/ql/src/utils/model-generator/internal/CaptureModelsSpecific.qll

@@ -58,6 +58,31 @@ predicate asPartialModel = DataFlowPrivate::Csv::asPartialModel/1;
 
 predicate asPartialNegativeModel = DataFlowPrivate::Csv::asPartialNegativeModel/1;
 
+/**
+ * Holds if `t` is a type that is generally used for bulk data in collection types.
+ * Eg. char[] is roughly equivalent to string and thus a highly
+ * relevant type for model generation.
+ */
+private predicate isPrimitiveTypeUsedForBulkData(CS::Type t) {
+  t instanceof CS::ByteType or
+  t instanceof CS::CharType
+}
+
+/**
+ * Holds if the collection type `ct` is irrelevant for model generation.
+ * Collection types where the type of the elements are
+ * (1) unknown - are considered relevant.
+ * (2) known - at least one the child types should be relevant (a non-simple type
+ * or a type used for bulk data)
+ */
+private predicate irrelevantCollectionType(CS::Type ct) {
+  Collections::isCollectionType(ct) and
+  forex(CS::Type child | child = ct.getAChild() |
+    child instanceof CS::SimpleType and
+    not isPrimitiveTypeUsedForBulkData(child)
+  )
+}
+
 /**
  * Holds for type `t` for fields that are relevant as an intermediate
  * read or write step in the data flow analysis.
@@ -66,7 +91,8 @@ predicate asPartialNegativeModel = DataFlowPrivate::Csv::asPartialNegativeModel/
  */
 predicate isRelevantType(CS::Type t) {
   not t instanceof CS::SimpleType and
-  not t instanceof CS::Enum
+  not t instanceof CS::Enum and
+  not irrelevantCollectionType(t)
 }
 
 /**