Index: src/AST/Util.cpp
===================================================================
--- src/AST/Util.cpp	(revision e0069bd332ef5d4206eb128f91629bf8d19b2dcf)
+++ src/AST/Util.cpp	(revision a0b59ed6abbe61cd691f06660beded5ef210e26c)
@@ -102,4 +102,15 @@
 }
 
+/// Check for Floating Nodes:
+/// Every node should be reachable from a root (the TranslationUnit) via a
+/// chain of structural references (tracked with ptr). This cannot check all
+/// of that, it just checks if a given node's field has a strong reference.
+template<typename node_t, typename field_t>
+void noFloatingNode( const node_t * node, field_t node_t::*field_ptr ) {
+	const field_t & field = node->*field_ptr;
+	if ( nullptr == field ) return;
+	assertf( field->isManaged(), "Floating node found." );
+}
+
 struct InvariantCore {
 	// To save on the number of visits: this is a kind of composed core.
@@ -127,7 +138,32 @@
 	}
 
+	void previsit( const VariableExpr * node ) {
+		previsit( (const ParseNode *)node );
+		noFloatingNode( node, &VariableExpr::var );
+	}
+
 	void previsit( const MemberExpr * node ) {
 		previsit( (const ParseNode *)node );
 		memberMatchesAggregate( node );
+	}
+
+	void previsit( const StructInstType * node ) {
+		previsit( (const Node *)node );
+		noFloatingNode( node, &StructInstType::base );
+	}
+
+	void previsit( const UnionInstType * node ) {
+		previsit( (const Node *)node );
+		noFloatingNode( node, &UnionInstType::base );
+	}
+
+	void previsit( const EnumInstType * node ) {
+		previsit( (const Node *)node );
+		noFloatingNode( node, &EnumInstType::base );
+	}
+
+	void previsit( const TypeInstType * node ) {
+		previsit( (const Node *)node );
+		noFloatingNode( node, &TypeInstType::base );
 	}