Bug#35201901: Server failure of MySQL #3

Some minor refactoring of function find_item_in_list() before the fix.

- Code is generally aligned with coding standard.

- Error handling is separated out, now is is false for success and
  true for error.

- The found item is now an output argument, and a null pointer means
  the item was not found (along with the other two out arguments).

- The report_error argument is removed since it was always used as
  REPORT_EXCEPT_NOT_FOUND.

- A local variable "find_ident" is introduced, since it better
  represents that we are searching for a column reference than having
  separate field_name, table_name and db_name variables.

Item_field::replace_with_derived_expr_ref()

- Redundant tests were removed.

Function resolve_ref_in_select_and_group() has also been changed so
that success/error is now returned as false/true, and the found item
is an out argument.

Function Item_field::fix_fields()

- The value of thd->lex->current_query_block() is cached in a local
  variable.

- Since single resolving was introduced, a test for "field" equal to
  nullptr was redundant and could be eliminated, along with the indented
  code block that followed.

- A code block for checking bitmaps if the above test was false could
  also be removed.

Change-Id: I3cd4bd6a23dd07faff773bdf11940bcfd847c903

sql/aggregate_check.cc

@@ -116,6 +116,7 @@ bool Distinct_check::check_query(THD *thd) {
     assert((*order->item)->fixed);
     uint counter;
     enum_resolution_type resolution;
+    Item **res;
     /*
       Search if this expression is equal to one in the SELECT
       list. setup_order()/find_order_in_list() has already done so, but not
@@ -145,12 +146,11 @@ bool Distinct_check::check_query(THD *thd) {
       differ due to white space....).
       Subqueries in ORDER BY are non-standard anyway.
     */
-    Item **const res =
-        find_item_in_list(thd, *order->item, &select->fields, &counter,
-                          REPORT_EXCEPT_NOT_FOUND, &resolution);
-    if (res == nullptr)  // Other error than "not found", my_error() was called
-      return true;       /* purecov: inspected */
-    if (res != not_found_item)  // is in SELECT list
+    if (find_item_in_list(thd, *order->item, &select->fields, &res, &counter,
+                          &resolution)) {
+      return true; /* purecov: inspected */
+    }
+    if (res != nullptr)  // is in SELECT list
       continue;
     /*
       [numbers refer to the function's comment]
@@ -269,13 +269,13 @@ bool Group_check::check_expression(THD *thd, Item *expr, bool in_select_list) {
   if (!in_select_list) {
     uint counter;
     enum_resolution_type resolution;
-    // Search if this expression is equal to one in the SELECT list.
-    Item **const res = find_item_in_list(thd, expr, &select->fields, &counter,
-                                         REPORT_EXCEPT_NOT_FOUND, &resolution);
-    if (res == nullptr)  // Other error than "not found", my_error() was called
-      return true;       /* purecov: inspected */
-    if (res != not_found_item) {
-      // is in SELECT list, which has already been validated.
+    Item **res;
+    // Check if this expression is equal to one in the SELECT list.
+    if (find_item_in_list(thd, expr, &select->fields, &res, &counter,
+                          &resolution)) {
+      return true; /* purecov: inspected */
+    }
+    if (res != nullptr) {  // in SELECT list, which has already been validated.
       return false;
     }
   }