add debugPrintDot

ConflictSet.cpp

@@ -86,6 +86,77 @@ void destroyNode(Node *node) {
   assert(node->child[1] == nullptr);
   free(node);
 }
+
+// Return a pointer to the node whose key immediately follows `n`'s key (if
+// `dir` is false, precedes). Return nullptr if none exists.
+[[maybe_unused]] Node *next(Node *n, bool dir) {
+  // Traverse left spine of right child (when moving right, i.e. dir = true)
+  if (n->child[dir]) {
+    n = n->child[dir];
+    while (n->child[!dir]) {
+      n = n->child[!dir];
+    }
+  } else {
+    // Search upward for a node such that we're the left child (when moving
+    // right, i.e. dir = true)
+    while (n->parent && n == n->parent->child[dir]) {
+      n = n->parent;
+    }
+    n = n->parent;
+  }
+  return n;
+}
+
+// Return a pointer to the node whose key is greatest among keys in the tree
+// rooted at `n` (if dir = false, least). Return nullptr if none exists (i.e.
+// `n` is null).
+[[maybe_unused]] Node *extrema(Node *n, bool dir) {
+  if (n == nullptr) {
+    return nullptr;
+  }
+  while (n->child[dir] != nullptr) {
+    n = n->child[dir];
+  }
+  return n;
+}
+
+[[maybe_unused]] void debugPrintDot(FILE *file, Node *node) {
+
+  struct DebugDotPrinter {
+
+    explicit DebugDotPrinter(FILE *file) : file(file) {}
+
+    void print(Node *node) {
+      for (int i = 0; i < 2; ++i) {
+        if (node->child[0] != nullptr) {
+          fprintf(file, " _%.*s -> _%.*s;\n", node->len,
+                  (const char *)(node + 1), node->child[0]->len,
+                  (const char *)(node->child[0] + 1));
+          print(node->child[0]);
+        } else {
+          fprintf(file, " _%.*s -> null%d;\n", node->len,
+                  (const char *)(node + 1), id);
+          fprintf(file, " null%d [shape=point];\n", id);
+          ++id;
+        }
+      }
+    }
+    int id = 0;
+    FILE *file;
+  };
+
+  fprintf(file, "digraph TreeSet {\n");
+  fprintf(file, " node [fontname=\"Scientifica\"];\n");
+  for (auto iter = extrema(node, false); iter != nullptr;
+       iter = next(iter, true)) {
+    fprintf(file, " _%.*s;\n", node->len, (const char *)(node + 1));
+  }
+  if (node != nullptr) {
+    DebugDotPrinter{file}.print(node);
+  }
+  fprintf(file, "}\n");
+}
+
 } // namespace
 
 struct ConflictSet::Impl {
@@ -151,5 +222,8 @@ ConflictSet &ConflictSet::operator=(ConflictSet &&other) noexcept {
 }
 
 #ifdef ENABLE_TESTS
-int main(void) { ConflictSet cs{0}; }
+int main(void) {
+  ConflictSet::Impl cs{0};
+  debugPrintDot(stdout, cs.root);
+}
 #endif