A patch for Bug#11763166 (55847: SHOW WARNINGS returns empty

result set when SQLEXCEPTION is active.

The problem was in a hackish THD::no_warnings_for_error attribute.
When it was set, an error was not written to Warning_info -- only
Diagnostics_area state was changed. That means, Diagnostics_area
might contain error state, which is not present in Warning_info.

The user-visible problem was that in some cases SHOW WARNINGS
returned empty result set (i.e. there were no warnings) while
the previous SQL statement failed. According to the MySQL
protocol errors must be presented in warning list.

The main idea of this patch is to remove THD::no_warnings_for_error.
There were few places where it was used:
  - sql_admin.cc, handling of REPAIR TABLE USE_FRM.
  - sql_show.cc, when calling fill_schema_table_from_frm().
  - sql_show.cc, when calling fill_table().
The fix is to either use internal-error-handlers, or to use
temporary Warning_info storing warnings, which might be ignored.

This patch is needed to fix Bug 11763162 (55843).

1 files changed, 144 insertions, 9 deletions

diff --git a/sql/sql_show.cc b/sql/sql_show.cc
index 464b966e4be..9e9de5e3524 100644
--- a/sql/sql_show.cc
+++ b/sql/sql_show.cc
@@ -3416,6 +3416,45 @@ end:
 
 
 /**
+  Trigger_error_handler is intended to intercept and silence SQL conditions
+  that might happen during trigger loading for SHOW statements.
+  The potential SQL conditions are:
+
+    - ER_PARSE_ERROR -- this error is thrown if a trigger definition file
+      is damaged or contains invalid CREATE TRIGGER statement. That should
+      not happen in normal life.
+
+    - ER_TRG_NO_DEFINER -- this warning is thrown when we're loading a
+      trigger created/imported in/from the version of MySQL, which does not
+      support trigger definers.
+
+    - ER_TRG_NO_CREATION_CTX -- this warning is thrown when we're loading a
+      trigger created/imported in/from the version of MySQL, which does not
+      support trigger creation contexts.
+*/
+
+class Trigger_error_handler : public Internal_error_handler
+{
+public:
+  bool handle_condition(THD *thd,
+                        uint sql_errno,
+                        const char* sqlstate,
+                        MYSQL_ERROR::enum_warning_level level,
+                        const char* msg,
+                        MYSQL_ERROR ** cond_hdl)
+  {
+    if (sql_errno == ER_PARSE_ERROR ||
+        sql_errno == ER_TRG_NO_DEFINER ||
+        sql_errno == ER_TRG_NO_CREATION_CTX)
+      return true;
+
+    return false;
+  }
+};
+
+
+
+/**
   @brief          Fill I_S tables whose data are retrieved
                   from frm files and storage engine
 
@@ -3570,7 +3609,6 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
         acl_get(sctx->host, sctx->ip, sctx->priv_user, db_name->str, 0))
 #endif
     {
-      thd->no_warnings_for_error= 1;
       List<LEX_STRING> table_names;
       int res= make_table_name_list(thd, &table_names, lex,
                                     &lookup_field_vals,
@@ -3619,9 +3657,24 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
             if (!(table_open_method & ~OPEN_FRM_ONLY) &&
                 !with_i_schema)
             {
-              if (!fill_schema_table_from_frm(thd, tables, schema_table, db_name,
-                                              table_name, schema_table_idx,
-                                              can_deadlock))
+              /*
+                Here we need to filter out warnings, which can happen
+                during loading of triggers in fill_schema_table_from_frm(),
+                because we don't need those warnings to pollute output of
+                SELECT from I_S / SHOW-statements.
+              */
+
+              Trigger_error_handler err_handler;
+              thd->push_internal_handler(&err_handler);
+
+              int res= fill_schema_table_from_frm(thd, tables, schema_table,
+                                                  db_name, table_name,
+                                                  schema_table_idx,
+                                                  can_deadlock);
+
+              thd->pop_internal_handler();
+
+              if (!res)
                 continue;
             }
 
@@ -3631,7 +3684,6 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
               Set the parent lex of 'sel' because it is needed by
               sel.init_query() which is called inside make_table_list.
             */
-            thd->no_warnings_for_error= 1;
             sel.parent_lex= lex;
             if (make_table_list(thd, &sel, db_name, table_name))
               goto err;
@@ -6675,6 +6727,92 @@ int make_schema_select(THD *thd, SELECT_LEX *sel,
 }
 
 
+/**
+  Fill INFORMATION_SCHEMA-table, leave correct Diagnostics_area /
+  Warning_info state after itself.
+
+  This function is a wrapper around ST_SCHEMA_TABLE::fill_table(), which
+  may "partially silence" some errors. The thing is that during
+  fill_table() many errors might be emitted. These errors stem from the
+  nature of fill_table().
+
+  For example, SELECT ... FROM INFORMATION_SCHEMA.xxx WHERE TABLE_NAME = 'xxx'
+  results in a number of 'Table <db name>.xxx does not exist' errors,
+  because fill_table() tries to open the 'xxx' table in every possible
+  database.
+
+  Those errors are cleared (the error status is cleared from
+  Diagnostics_area) inside fill_table(), but they remain in Warning_info
+  (Warning_info is not cleared because it may contain useful warnings).
+
+  This function is responsible for making sure that Warning_info does not
+  contain warnings corresponding to the cleared errors.
+
+  @note: THD::no_warnings_for_error used to be set before calling
+  fill_table(), thus those errors didn't go to Warning_info. This is not
+  the case now (THD::no_warnings_for_error was eliminated as a hack), so we
+  need to take care of those warnings here.
+
+  @param thd            Thread context.
+  @param table_list     I_S table.
+  @param join_table     JOIN/SELECT table.
+
+  @return Error status.
+  @retval TRUE Error.
+  @retval FALSE Success.
+*/
+static bool do_fill_table(THD *thd,
+                          TABLE_LIST *table_list,
+                          JOIN_TAB *join_table)
+{
+  // NOTE: fill_table() may generate many "useless" warnings, which will be
+  // ignored afterwards. On the other hand, there might be "useful"
+  // warnings, which should be presented to the user. Warning_info usually
+  // stores no more than THD::variables.max_error_count warnings.
+  // The problem is that "useless warnings" may occupy all the slots in the
+  // Warning_info, so "useful warnings" get rejected. In order to avoid
+  // that problem we create a Warning_info instance, which is capable of
+  // storing "unlimited" number of warnings.
+  Warning_info wi(thd->query_id, true);
+  Warning_info *wi_saved= thd->warning_info;
+
+  thd->warning_info= &wi;
+
+  bool res= table_list->schema_table->fill_table(
+    thd, table_list, join_table->select_cond);
+
+  thd->warning_info= wi_saved;
+
+  // Pass an error if any.
+
+  if (thd->stmt_da->is_error())
+  {
+    thd->warning_info->push_warning(thd,
+                                    thd->stmt_da->sql_errno(),
+                                    thd->stmt_da->get_sqlstate(),
+                                    MYSQL_ERROR::WARN_LEVEL_ERROR,
+                                    thd->stmt_da->message());
+  }
+
+  // Pass warnings (if any).
+  //
+  // Filter out warnings with WARN_LEVEL_ERROR level, because they
+  // correspond to the errors which were filtered out in fill_table().
+
+
+  List_iterator_fast<MYSQL_ERROR> it(wi.warn_list());
+  MYSQL_ERROR *err;
+
+  while ((err= it++))
+  {
+    if (err->get_level() != MYSQL_ERROR::WARN_LEVEL_ERROR)
+      thd->warning_info->push_warning(thd, err);
+  }
+
+  return res;
+}
+
+
 /*
   Fill temporary schema tables before SELECT
 
@@ -6697,7 +6835,6 @@ bool get_schema_tables_result(JOIN *join,
   bool result= 0;
   DBUG_ENTER("get_schema_tables_result");
 
-  thd->no_warnings_for_error= 1;
   for (JOIN_TAB *tab= join->join_tab; tab < tmp_join_tab; tab++)
   {  
     if (!tab->table || !tab->table->pos_in_table_list)
@@ -6748,8 +6885,7 @@ bool get_schema_tables_result(JOIN *join,
       else
         table_list->table->file->stats.records= 0;
 
-      if (table_list->schema_table->fill_table(thd, table_list,
-                                               tab->select_cond))
+      if (do_fill_table(thd, table_list, tab))
       {
         result= 1;
         join->error= 1;
@@ -6761,7 +6897,6 @@ bool get_schema_tables_result(JOIN *join,
       table_list->schema_table_state= executed_place;
     }
   }
-  thd->no_warnings_for_error= 0;
   DBUG_RETURN(result);
 }