Add function for rendering the stack as a DOT graph

src/runtime/stack.c

@@ -475,3 +475,80 @@ void ts_stack_delete(Stack *self) {
   array_delete(&self->heads);
   ts_free(self);
 }
+
+size_t ts_stack__write_dot_graph(Stack *self, char *string, size_t n,
+                                 const char **symbol_names) {
+  char *cursor = string;
+  char **s = n > 0 ? &cursor : &string;
+  cursor += snprintf(*s, n, "digraph stack {\n");
+  cursor += snprintf(*s, n, "rankdir=\"RL\";\n");
+  cursor += snprintf(*s, n, "node_%p [label=\"0:NULL\"];\n", NULL);
+
+  array_clear(&self->pop_paths);
+  for (int i = 0; i < self->heads.size; i++)
+    array_push(&self->pop_paths, ((PopPath){
+      .node = self->heads.contents[i],
+    }));
+
+  bool all_paths_done = false;
+  while (!all_paths_done) {
+    all_paths_done = true;
+
+    for (size_t i = 0; i < self->pop_paths.size; i++) {
+      PopPath *path = &self->pop_paths.contents[i];
+      StackNode *node = path->node;
+
+      if (!node)
+        continue;
+
+      all_paths_done = false;
+
+      cursor += snprintf(*s, n, "node_%p [label=\"%d:%s\"];\n", node,
+                         node->entry.state,
+                         symbol_names[node->entry.tree->symbol]);
+
+      path->node = node->successors[0];
+      cursor += snprintf(*s, n, "node_%p -> node_%p;\n", node, node->successors[0]);
+
+      for (int j = 1; j < node->successor_count; j++) {
+        if (!array_push(&self->pop_paths, *path))
+          goto error;
+        cursor += snprintf(*s, n, "node_%p -> node_%p;\n", node, node->successors[j]);
+
+        PopPath *next_path = array_back(&self->pop_paths);
+        next_path->node = node->successors[j];
+        next_path->is_shared = true;
+      }
+    }
+  }
+
+  cursor += snprintf(*s, n, "}\n");
+
+  return cursor - string;
+
+error:
+  return (size_t)-1;
+}
+
+char *ts_stack_dot_graph(Stack *self, const char **symbol_names) {
+  static char SCRATCH[1];
+  char *result = NULL;
+  size_t size = ts_stack__write_dot_graph(self, SCRATCH, 0, symbol_names) + 1;
+  if (size == -1)
+    goto error;
+
+  result = ts_malloc(size * sizeof(char));
+  if (!result)
+    goto error;
+
+  size = ts_stack__write_dot_graph(self, result, size, symbol_names);
+  if (size == -1)
+    goto error;
+
+  return result;
+
+error:
+  if (result)
+    ts_free(result);
+  return NULL;
+}