Ruby: fix handling of namespaces with no 'self'

ruby/ql/lib/codeql/ruby/dataflow/internal/DataFlowPrivate.qll

@@ -262,6 +262,9 @@ private module Cached {
       )
     } or
     TSsaDefinitionNode(Ssa::Definition def) or
+    TRawNamespaceSelf(Namespace ns) {
+      not exists(Ssa::SelfDefinition def | def.getSourceVariable() = ns.getModuleSelfVariable())
+    } or
     TNormalParameterNode(Parameter p) {
       p instanceof SimpleParameter or
       p instanceof OptionalParameter or
@@ -402,6 +405,8 @@ private module Cached {
     or
     // Needed for stores in type tracking
     TypeTrackerSpecific::storeStepIntoSourceNode(_, n, _)
+    or
+    n instanceof TRawNamespaceSelf
   }
 
   cached
@@ -523,6 +528,38 @@ class SsaSelfDefinitionNode extends LocalSourceNode, SsaDefinitionNode {
   Scope getSelfScope() { result = self.getDeclaringScope() }
 }
 
+/**
+ * A representative for the created or re-opened class/module in a `Namespace` that does
+ * not have an SSA definition for `self`.
+ */
+class RawNamespaceSelf extends NodeImpl, TRawNamespaceSelf {
+  private Namespace namespace;
+
+  RawNamespaceSelf() { this = TRawNamespaceSelf(namespace) }
+
+  /** Gets the namespace for which this represents the created or re-opened class/module. */
+  Namespace getNamespace() { result = namespace }
+
+  override CfgScope getCfgScope() { result = namespace.getCfgScope() }
+
+  override Location getLocationImpl() { result = namespace.getLocation() }
+
+  override string toStringImpl() { result = namespace.toString() }
+}
+
+/**
+ * Gets a representative for the created or re-opened class/module in a `Namespace`.
+ *
+ * This is usually the SSA definition for `self`, but if this node does not exist due to lack of liveness,
+ * it is the `RawNamespaceSelf` node.
+ */
+LocalSourceNode getNamespaceSelf(Namespace namespace) {
+  result.(SsaDefinitionNode).getDefinition().(Ssa::SelfDefinition).getSourceVariable() =
+    namespace.getModuleSelfVariable()
+  or
+  result = TRawNamespaceSelf(namespace)
+}
+
 /**
  * A value returning statement, viewed as a node in a data flow graph.
  *

ruby/ql/lib/codeql/ruby/dataflow/internal/DataFlowPublic.qll

@@ -1113,9 +1113,7 @@ private LocalSourceNode getConstantAccessNode(ConstantAccess access) {
   // Namespaces don't evaluate to the constant being accessed, they return the value of their last statement.
   // Use the definition of 'self' in the namespace as the representative in this case.
   if access instanceof Namespace
-  then
-    result.(SsaDefinitionNode).getDefinition().(Ssa::SelfDefinition).getSourceVariable() =
-      access.(Namespace).getModuleSelfVariable()
+  then result = getNamespaceSelf(access)
   else result.asExpr().getExpr() = access
 }