C#: Add NamespaceAccess, and make namespaces declarations.

Author: calumgrant

csharp/ql/src/semmle/code/csharp/Namespace.qll

@@ -18,7 +18,7 @@ class TypeContainer extends DotNet::NamedElement, Element, @type_container { }
  * }
  * ```
  */
-class Namespace extends DotNet::Namespace, TypeContainer, @namespace {
+class Namespace extends DotNet::Namespace, TypeContainer, Declaration, @namespace {
   /** Gets the simple name of this namespace, for example `IO` in `System.IO`. */
   override string getName() { namespaces(this, result) }
 
@@ -117,6 +117,10 @@ class Namespace extends DotNet::Namespace, TypeContainer, @namespace {
   NamespaceDeclaration getADeclaration() { result.getNamespace() = this }
 
   override Location getALocation() { result = this.getADeclaration().getALocation() }
+
+  override string toString() { result = DotNet::Namespace.super.toString() }
+
+  override predicate hasQualifiedName(string a, string b) { DotNet::Namespace.super.hasQualifiedName(a, b) }
 }
 
 /**

csharp/ql/src/semmle/code/csharp/exprs/Access.qll

@@ -826,3 +826,12 @@ class ArrayRead extends ArrayAccess, AssignableRead { }
  * ```
  */
 class ArrayWrite extends ArrayAccess, AssignableWrite { }
+
+/**
+ * An access to a namespace, for example `System` in `nameof(System)`.
+ */
+class NamespaceAccess extends Access, @namespace_access_expr {
+  override Namespace getTarget() { expr_access(this, result) }
+
+  override string toString() { result = "access to namespace " + this.getTarget().getName() }
+}

csharp/ql/test/library-tests/regressions/NameOf.expected

@@ -1,2 +1,3 @@
 | Program.cs:62:17:62:35 | nameof(...) | Program.cs:62:24:62:34 | access to method MethodGroup |
 | Program.cs:63:13:63:50 | nameof(...) | Program.cs:63:20:63:49 | access to method MethodGroup |
+| Program.cs:169:16:169:29 | nameof(...) | Program.cs:169:23:169:28 | access to namespace System |