API: Refactor: Register/unregister created/destroyed buffers

- Add the 'handle' field to `buf_T`
- Add declare/implement functions for registering/unregistering/retrieving
  buffers
- Register/unregister buffers when they are created/destroyed.

src/nvim/api/private/handle.c

@@ -26,6 +26,11 @@
     map_del(uint64_t)(name##_handles, name->handle);                          \
   }
 
+static uint64_t next_handle = 1;
+
+HANDLE_IMPL(buf_T, buffer)
+
 void handle_init()
 {
+  HANDLE_INIT(buffer);
 }

src/nvim/api/private/handle.h

@@ -2,13 +2,17 @@
 #define NVIM_API_HANDLE_H
 
 #include "nvim/vim.h"
+#include "nvim/buffer_defs.h"
 
 #define HANDLE_DECLS(type, name)                                              \
   type *handle_get_##name(uint64_t handle);                                   \
   void handle_register_##name(type *name);                                    \
   void handle_unregister_##name(type *name);
 
+HANDLE_DECLS(buf_T, buffer)
+
 void handle_init(void);
 
+
 #endif  // NVIM_API_HANDLE_H
 

src/nvim/buffer.c

@@ -26,6 +26,7 @@
 
 #include <string.h>
 
+#include "nvim/api/private/handle.h"
 #include "nvim/vim.h"
 #include "nvim/buffer.h"
 #include "nvim/charset.h"
@@ -538,6 +539,7 @@ void buf_freeall(buf_T *buf, int flags)
  */
 static void free_buffer(buf_T *buf)
 {
+  handle_unregister_buffer(buf);
   free_buffer_stuff(buf, TRUE);
   unref_var_dict(buf->b_vars);
   aubuflocal_remove(buf);
@@ -1362,6 +1364,7 @@ buflist_new (
   }
   if (buf != curbuf || curbuf == NULL) {
     buf = xcalloc(1, sizeof(buf_T));
+    handle_register_buffer(buf);
     /* init b: variables */
     buf->b_vars = dict_alloc();
     init_var_dict(buf->b_vars, &buf->b_bufvar, VAR_SCOPE);

src/nvim/buffer_defs.h

@@ -401,6 +401,7 @@ typedef struct {
  */
 
 struct file_buffer {
+  uint64_t handle;              // unique identifier for the buffer
   memline_T b_ml;               /* associated memline (also contains line
                                    count) */