api/lua: add on_detach to nvim_buf_attach

src/nvim/api/buffer.c

@@ -12,6 +12,7 @@
 #include "nvim/api/buffer.h"
 #include "nvim/api/private/helpers.h"
 #include "nvim/api/private/defs.h"
+#include "nvim/lua/executor.h"
 #include "nvim/vim.h"
 #include "nvim/buffer.h"
 #include "nvim/charset.h"
@@ -137,24 +138,38 @@ Boolean nvim_buf_attach(uint64_t channel_id,
     if (is_lua && strequal("on_lines", k.data)) {
       if (v->type != kObjectTypeLuaRef) {
         api_set_error(err, kErrorTypeValidation, "callback is not a function");
-        return false;
+        goto error;
       }
       cb.on_lines = v->data.luaref;
       v->data.integer = LUA_NOREF;
     } else if (is_lua && strequal("on_changedtick", k.data)) {
       if (v->type != kObjectTypeLuaRef) {
         api_set_error(err, kErrorTypeValidation, "callback is not a function");
-        return false;
+        goto error;
       }
       cb.on_changedtick = v->data.luaref;
       v->data.integer = LUA_NOREF;
+    } else if (is_lua && strequal("on_detach", k.data)) {
+      if (v->type != kObjectTypeLuaRef) {
+        api_set_error(err, kErrorTypeValidation, "callback is not a function");
+        goto error;
+      }
+      cb.on_detach = v->data.luaref;
+      v->data.integer = LUA_NOREF;
     } else {
       api_set_error(err, kErrorTypeValidation, "unexpected key: %s", k.data);
-      return false;
+      goto error;
     }
   }
 
   return buf_updates_register(buf, channel_id, cb, send_buffer);
+
+error:
+  // TODO(bfredl): ASAN build should check that the ref table is empty?
+  executor_free_luaref(cb.on_lines);
+  executor_free_luaref(cb.on_changedtick);
+  executor_free_luaref(cb.on_detach);
+  return false;
 }
 
 /// Deactivates buffer-update events on the channel.

src/nvim/buffer_defs.h

@@ -456,8 +456,9 @@ typedef TV_DICTITEM_STRUCT(sizeof("changedtick")) ChangedtickDictItem;
 typedef struct {
   LuaRef on_lines;
   LuaRef on_changedtick;
+  LuaRef on_detach;
 } BufUpdateCallbacks;
-#define BUF_UPDATE_CALLBACKS_INIT { LUA_NOREF, LUA_NOREF }
+#define BUF_UPDATE_CALLBACKS_INIT { LUA_NOREF, LUA_NOREF, LUA_NOREF }
 
 #define BUF_HAS_QF_ENTRY 1
 #define BUF_HAS_LL_ENTRY 2

src/nvim/buffer_updates.c

@@ -143,7 +143,21 @@ void buf_updates_unregister_all(buf_T *buf)
   }
 
   for (size_t i = 0; i < kv_size(buf->update_callbacks); i++) {
-    free_update_callbacks(kv_A(buf->update_callbacks, i));
+    BufUpdateCallbacks cb = kv_A(buf->update_callbacks, i);
+    if (cb.on_detach != LUA_NOREF) {
+      Array args = ARRAY_DICT_INIT;
+      Object items[1];
+      args.size = 1;
+      args.items = items;
+
+      // the first argument is always the buffer handle
+      args.items[0] = BUFFER_OBJ(buf->handle);
+
+      textlock++;
+      executor_exec_lua_cb(cb.on_detach, "detach", args, false);
+      textlock--;
+    }
+    free_update_callbacks(cb);
   }
   kv_destroy(buf->update_callbacks);
   kv_init(buf->update_callbacks);
@@ -237,13 +251,14 @@ void buf_updates_send_changes(buf_T *buf,
       args.items[4] = INTEGER_OBJ(firstline - 1 + num_added);
 
       textlock++;
-      Object res = executor_exec_lua_cb(cb.on_lines, "lines", args);
+      Object res = executor_exec_lua_cb(cb.on_lines, "lines", args, true);
       textlock--;
 
       if (res.type == kObjectTypeBoolean && res.data.boolean == true) {
         free_update_callbacks(cb);
         keep = false;
       }
+      api_free_object(res);
     }
     if (keep) {
       kv_A(buf->update_callbacks, j++) = kv_A(buf->update_callbacks, i);
@@ -276,13 +291,15 @@ void buf_updates_changedtick(buf_T *buf)
       args.items[1] = INTEGER_OBJ(buf_get_changedtick(buf));
 
       textlock++;
-      Object res = executor_exec_lua_cb(cb.on_changedtick, "changedtick", args);
+      Object res = executor_exec_lua_cb(cb.on_changedtick, "changedtick",
+                                        args, true);
       textlock--;
 
       if (res.type == kObjectTypeBoolean && res.data.boolean == true) {
         free_update_callbacks(cb);
         keep = false;
       }
+      api_free_object(res);
     }
     if (keep) {
       kv_A(buf->update_callbacks, j++) = kv_A(buf->update_callbacks, i);

src/nvim/lua/executor.c

@@ -520,7 +520,8 @@ Object executor_exec_lua_api(const String str, const Array args, Error *err)
   return nlua_pop_Object(lstate, false, err);
 }
 
-Object executor_exec_lua_cb(LuaRef ref, const char *name, Array args)
+Object executor_exec_lua_cb(LuaRef ref, const char *name, Array args,
+                            bool retval)
 {
   lua_State *const lstate = nlua_enter();
   nlua_pushref(lstate, ref);
@@ -529,7 +530,7 @@ Object executor_exec_lua_cb(LuaRef ref, const char *name, Array args)
     nlua_push_Object(lstate, args.items[i]);
   }
 
-  if (lua_pcall(lstate, (int)args.size+1, 1, 0)) {
+  if (lua_pcall(lstate, (int)args.size+1, retval ? 1 : 0, 0)) {
     // TODO(bfredl): callbacks:s might not always be msg-safe, for instance
     // lua callbacks for redraw events. Later on let the caller deal with the
     // error instead.
@@ -538,7 +539,11 @@ Object executor_exec_lua_cb(LuaRef ref, const char *name, Array args)
   }
   Error err = ERROR_INIT;
 
-  return nlua_pop_Object(lstate, false, &err);
+  if (retval) {
+    return nlua_pop_Object(lstate, false, &err);
+  } else {
+    return NIL;
+  }
 }
 
 /// Run lua string