[clang] c6a05eb - [Syntax] Disallow invalid Node operations

[Sam McCall via cfe-commits]

Author: Sam McCall
Date: 2020-10-27T08:36:35+01:00
New Revision: c6a05eb62f2ab392eba4e7a056e95c821587ae47

URL: https://github.com/llvm/llvm-project/commit/c6a05eb62f2ab392eba4e7a056e95c821587ae47
DIFF: https://github.com/llvm/llvm-project/commit/c6a05eb62f2ab392eba4e7a056e95c821587ae47.diff

LOG: [Syntax] Disallow invalid Node operations

Copy/move break invariants (move could be fixed).
Node/Tree should have no public constructors, they're abstract.
Destructor is private to enforce arena allocation.

(Making the constructor of all subclasses private doesn't seem worthwhile)

Differential Revision: https://reviews.llvm.org/D90163

Added: 
    

Modified: 
    clang/include/clang/Tooling/Syntax/Tree.h

Removed: 
    


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diff  --git a/clang/include/clang/Tooling/Syntax/Tree.h b/clang/include/clang/Tooling/Syntax/Tree.h
index 5840a86199eb..c6430452a94d 100644
--- a/clang/include/clang/Tooling/Syntax/Tree.h
+++ b/clang/include/clang/Tooling/Syntax/Tree.h
@@ -76,10 +76,20 @@ enum class NodeRole : uint8_t;
 /// A node in a syntax tree. Each node is either a Leaf (representing tokens) or
 /// a Tree (representing language constructrs).
 class Node {
-public:
+protected:
   /// Newly created nodes are detached from a tree, parent and sibling links are
   /// set when the node is added as a child to another one.
   Node(NodeKind Kind);
+  /// Nodes are allocated on Arenas; the destructor is never called.
+  ~Node() = default;
+
+public:
+  /// Nodes cannot simply be copied without violating tree invariants.
+  Node(const Node &) = delete;
+  Node &operator=(const Node &) = delete;
+  /// Idiomatically, nodes are allocated on an Arena and never moved.
+  Node(Node &&) = delete;
+  Node &operator=(Node &&) = delete;
 
   NodeKind getKind() const { return static_cast<NodeKind>(Kind); }
   NodeRole getRole() const { return static_cast<NodeRole>(Role); }
@@ -153,7 +163,6 @@ class Leaf final : public Node {
 /// A node that has children and represents a syntactic language construct.
 class Tree : public Node {
 public:
-  using Node::Node;
   static bool classof(const Node *N);
 
   Node *getFirstChild() { return FirstChild; }
@@ -170,6 +179,7 @@ class Tree : public Node {
   }
 
 protected:
+  using Node::Node;
   /// Find the first node with a corresponding role.
   Node *findChild(NodeRole R);