MDEV-7652 - More explanatory ERROR and WARNING messages when loading plugins

            with plugin-load-add that are already registered at mysql.plugin

- issue just one error message, without this extra warning
- don't abuse ER_UDF_EXISTS, instead add a proper error message for plugins
- report started initialization for each plugin source

2 files changed, 14 insertions, 4 deletions

diff --git a/sql/share/errmsg-utf8.txt b/sql/share/errmsg-utf8.txt
index 6954170e86c..5fed6b10425 100644
--- a/sql/share/errmsg-utf8.txt
+++ b/sql/share/errmsg-utf8.txt
@@ -7111,3 +7111,6 @@ ER_SLAVE_SKIP_NOT_IN_GTID
 	eng "When using GTID, @@sql_slave_skip_counter can not be used. Instead, setting @@gtid_slave_pos explicitly can be used to skip to after a given GTID position."
 ER_TABLE_DEFINITION_TOO_BIG
         eng "The definition for table %`s is too big"
+ER_PLUGIN_INSTALLED
+        eng "Plugin '%-.192s' already installed"
+        rus "Плагин '%-.192s' уже установлен"
diff --git a/sql/sql_plugin.cc b/sql/sql_plugin.cc
index dc408703da4..dea224398ea 100644
--- a/sql/sql_plugin.cc
+++ b/sql/sql_plugin.cc
@@ -1049,7 +1049,7 @@ static bool plugin_add(MEM_ROOT *tmp_root,
 
   if (name->str && plugin_find_internal(name, MYSQL_ANY_PLUGIN))
   {
-    report_error(report, ER_UDF_EXISTS, name->str);
+    report_error(report, ER_PLUGIN_INSTALLED, name->str);
     DBUG_RETURN(TRUE);
   }
   /* Clear the whole struct to catch future extensions. */
@@ -1546,6 +1546,9 @@ int plugin_init(int *argc, char **argv, int flags)
   /*
     First we register builtin plugins
   */
+  if (global_system_variables.log_warnings >= 9)
+    sql_print_information("Initializing built-in plugins");
+
   for (builtins= mysql_mandatory_plugins; *builtins || mandatory; builtins++)
   {
     if (!*builtins)
@@ -1627,11 +1630,17 @@ int plugin_init(int *argc, char **argv, int flags)
   {
     I_List_iterator<i_string> iter(opt_plugin_load_list);
     i_string *item;
+    if (global_system_variables.log_warnings >= 9)
+      sql_print_information("Initializing plugins specified on the command line");
     while (NULL != (item= iter++))
       plugin_load_list(&tmp_root, item->ptr);
 
     if (!(flags & PLUGIN_INIT_SKIP_PLUGIN_TABLE))
+    {
+      if (global_system_variables.log_warnings >= 9)
+        sql_print_information("Initializing installed plugins");
       plugin_load(&tmp_root);
+    }
   }
 
   /*
@@ -1772,9 +1781,7 @@ static void plugin_load(MEM_ROOT *tmp_root)
       the mutex here to satisfy the assert
     */
     mysql_mutex_lock(&LOCK_plugin);
-    if (plugin_add(tmp_root, &name, &dl, REPORT_TO_LOG))
-      sql_print_warning("Couldn't load plugin named '%s' with soname '%s'.",
-                        str_name.c_ptr(), str_dl.c_ptr());
+    plugin_add(tmp_root, &name, &dl, REPORT_TO_LOG);
     free_root(tmp_root, MYF(MY_MARK_BLOCKS_FREE));
     mysql_mutex_unlock(&LOCK_plugin);
   }