MDEV-6689: valgrind errors in view.test in 10.1

SHOW COLUMNS and SHOW KEYS commands fill IS_table_read_plan
in a special way - they don't set or use lookup_field_vals
member.

Added a "trivial_show_command" flag that signals that
lookup_field_vals has no valid data, made EXPLAIN code honor it.

1 files changed, 9 insertions, 1 deletions

diff --git a/sql/sql_show.h b/sql/sql_show.h
index 2f1cb26d17a..2b58fc45d4c 100644
--- a/sql/sql_show.h
+++ b/sql/sql_show.h
@@ -192,9 +192,17 @@ typedef struct st_lookup_field_values
 class IS_table_read_plan : public Sql_alloc
 {
 public:
-  IS_table_read_plan() : no_rows(false) {}
+  IS_table_read_plan() : no_rows(false), trivial_show_command(FALSE) {}
 
   bool no_rows;
+  /*
+    For EXPLAIN only: For SHOW KEYS and SHOW COLUMNS, we know which
+    db_name.table_name will be read, however for some reason we don't
+    set the fields in this->lookup_field_vals.
+    In order to not have JOIN::save_explain_data() walking over uninitialized
+    data, we set trivial_show_command=true.
+  */
+  bool trivial_show_command;
 
   LOOKUP_FIELD_VALUES lookup_field_vals;
   Item *partial_cond;