C#: Introduce a collectionType predicate.

csharp/ql/lib/semmle/code/csharp/commons/Collections.qll

@@ -1,6 +1,8 @@
 /** Provides classes for collections. */
 
 import csharp
+import semmle.code.csharp.frameworks.system.Collections
+import semmle.code.csharp.frameworks.system.collections.Generic
 
 private string modifyMethodName() {
   result =
@@ -66,15 +68,13 @@ class CollectionType extends RefType {
   }
 }
 
-/** An IEnumerable type. */
-class IEnumerableType extends RefType {
-  IEnumerableType() {
-    this.hasQualifiedName("System.Collections", "IEnumerable")
-    or
-    this.(ConstructedType)
-        .getUnboundGeneric()
-        .hasQualifiedName("System.Collections.Generic", "IEnumerable<>")
-  }
+/** Holds if `t` is a collection type. */
+predicate isCollectionType(ValueOrRefType t) {
+  not t instanceof StringType and
+  exists(ValueOrRefType base | base = t.getABaseType*() |
+    base instanceof SystemCollectionsGenericIEnumerableTInterface or
+    base instanceof SystemCollectionsIEnumerableInterface
+  )
 }
 
 /** An object creation that creates an empty collection. */

csharp/ql/src/utils/model-generator/ModelGeneratorUtilsSpecific.qll

@@ -70,14 +70,9 @@ private predicate isPrimitiveTypeUsedForBulkData(Type t) {
   t.getName().regexpMatch("byte|char|Byte|Char")
 }
 
-private predicate isContainerType(Type t) {
-  t instanceof CollectionType or
-  t instanceof IEnumerableType
-}
-
 private string parameterAccess(Parameter p) {
   if
-    isContainerType(p.getType()) and
+    isCollectionType(p.getType()) and
     not isPrimitiveTypeUsedForBulkData(p.getType().(ArrayType).getElementType())
   then result = "Argument[" + p.getPosition() + "].Element"
   else result = "Argument[" + p.getPosition() + "]"