MDEV-5816: Stored programs: validation of stored program statements

This patch is the second part of implementation for cursor's statement
re-parsing. The patch does the following changes:
  - on re-parsing a failed SP instruction that does need to get access
    to LEX a new lex is instantiated for every SP instruction except
    cursor relating SP instructions.
  - items created on re-parsing a cursor relating statement are moved
    to the free_list of sp_lex_cursor.

sql/sp_instr.cc

@@ -363,34 +363,55 @@ sp_lex_keeper::reset_lex_and_exec_core(THD *thd, uint *nextp,
 
 void sp_lex_keeper::free_lex(THD *thd)
 {
+  /*
+    Currently, m_lex_resp == false for sp_instr_cursor_copy_struct instructions
+    and in some cases for sp_instr_set instructions. For these classes
+    free_lex() returns control flow immediately and doesn't change m_lex.
+  */
   if (!m_lex_resp || !m_lex) return;
 
   /* Prevent endless recursion. */
   m_lex->sphead= nullptr;
   lex_end(m_lex);
 
-  delete (st_lex_local *)m_lex;
+  sp_lex_cursor* cursor_lex= m_lex->get_lex_for_cursor();
+  if (cursor_lex == nullptr)
+  {
+    delete (st_lex_local *)m_lex;
+    /*
+      In case it is not sp_lex_cursor set thd->lex to the null value
+      if it points to a LEX object we just deleted in order to avoid
+      dangling pointers problem.
+    */
+    if (thd->lex == m_lex)
+      thd->lex= nullptr;
 
-  /*
-    Set thd->lex to the null value in case it points to a LEX object
-    we just deleted in order to avoid dangling pointer problem
-  */
-  if (thd->lex == m_lex)
-    thd->lex= nullptr;
+    m_lex= nullptr;
+    m_lex_resp= false;
+  }
+  else
+  {
+    /*
+      sp_lex_cursor has references to items allocated on parsing a cursor
+      declaration statement. These items are deleted on re-parsing a failing
+      cursor declaration statement at the method
+        sp_lex_instr::cleanup_before_parsing.
+      Remove the reference to items that will be deleted from sp_lex_cursor
+      in order to avoid dangling pointers problem.
+    */
+    cleanup_items(cursor_lex->free_list);
+    cursor_lex->free_list= nullptr;
+  }
 
-  m_lex= nullptr;
-  m_lex_resp= false;
   lex_query_tables_own_last= nullptr;
 }
 
 
-void sp_lex_keeper::set_lex(LEX *lex, bool is_lex_owner)
+void sp_lex_keeper::set_lex(LEX *lex)
 {
   m_lex= lex;
-  m_lex_resp= is_lex_owner;
-
-  if (m_lex)
-    m_lex->sp_lex_in_use= true;
+  m_lex_resp= true;
+  m_lex->sp_lex_in_use= true;
 }
 
 
@@ -406,11 +427,15 @@ int sp_lex_keeper::validate_lex_and_exec_core(THD *thd, uint *nextp,
     {
       thd->clear_error();
       free_lex(thd);
-      LEX *lex= instr->parse_expr(thd, thd->spcont->m_sp);
+      LEX *lex= instr->parse_expr(thd, thd->spcont->m_sp, m_lex);
 
       if (!lex) return true;
 
-      set_lex(lex, true);
+      /*
+        m_lex != nullptr in case it points to sp_lex_cursor.
+      */
+      if (m_lex == nullptr)
+        set_lex(lex);
 
       m_first_execution= true;
     }
@@ -608,7 +633,7 @@ bool sp_lex_instr::setup_table_fields_for_trigger(
   return result;
 }
 
-LEX* sp_lex_instr::parse_expr(THD *thd, sp_head *sp)
+LEX* sp_lex_instr::parse_expr(THD *thd, sp_head *sp, LEX *sp_instr_lex)
 {
   String sql_query;
 
@@ -637,17 +662,11 @@ LEX* sp_lex_instr::parse_expr(THD *thd, sp_head *sp)
     saved_ptr_to_next_trg_items_list=
       m_cur_trigger_stmt_items.first->next_trig_field_list;
 
+  /*
+    Clean up items owned by this SP instruction.
+  */
   cleanup_before_parsing(sp->m_handler->type());
 
-  Parser_state parser_state;
-
-  if (parser_state.init(thd, sql_query.c_ptr(), sql_query.length()))
-    return nullptr;
-
-  // Create a new LEX and initialize it.
-
-  LEX *lex_saved= thd->lex;
-
   DBUG_ASSERT(mem_root != thd->mem_root);
   /*
     Back up the current free_list pointer and reset it to nullptr.
@@ -668,7 +687,40 @@ LEX* sp_lex_instr::parse_expr(THD *thd, sp_head *sp)
   thd->set_n_backup_active_arena(this, &backup);
   thd->free_list= nullptr;
 
-  thd->lex= new (thd->mem_root) st_lex_local;
+  Parser_state parser_state;
+
+  if (parser_state.init(thd, sql_query.c_ptr(), sql_query.length()))
+    return nullptr;
+
+  // Create a new LEX and initialize it.
+
+  LEX *lex_saved= thd->lex;
+  Item **cursor_free_list= nullptr;
+
+  /*
+    sp_instr_lex != nullptr for cursor relating SP instructions (sp_instr_cpush,
+    sp_instr_cursor_copy_struct) and in some cases for sp_instr_set.
+  */
+  if (sp_instr_lex == nullptr)
+    thd->lex= new (thd->mem_root) st_lex_local;
+  else
+  {
+    sp_lex_cursor* cursor_lex= sp_instr_lex->get_lex_for_cursor();
+    /*
+      In case sp_instr_cursor_copy_struct instruction being re-parsed
+      the items stored in free_list of sp_lex_cursor are not cleaned up
+      since the class sp_instr_cursor_copy_struct don't pass ownership of
+      lex object to sp_lex_keeper. So, clean up items stored in free_list of
+      sp_lex_cursor explicitly. For sp_instr_cpush instruction items stored
+      in free_list of sp_lex_cursor are cleaned up in the method free_lex()
+      since sp_instr_cpush owns a lex object stored in its sp_lex_keeper
+      data member. So, for the sp_instr_cpush instruction by the time we reach
+      this block cursor_lex->free_list is already empty.
+    */
+    cleanup_items(cursor_lex->free_list);
+    cursor_free_list= &cursor_lex->free_list;
+    DBUG_ASSERT(thd->lex == sp_instr_lex);
+  }
 
   lex_start(thd);
 
@@ -709,13 +761,21 @@ LEX* sp_lex_instr::parse_expr(THD *thd, sp_head *sp)
       setup_table_fields_for_trigger(thd, sp,
                                      saved_ptr_to_next_trg_items_list);
 
-    /*
-      Assign the list of items created on parsing to the current
-      stored routine instruction.
-    */
-    free_list= thd->free_list;
+    if (cursor_free_list)
+      /*
+        Update sp_lex_cursor::free_list to point to a list of items
+        just created on re-parsing the cursor's statement.
+      */
+      *cursor_free_list= thd->free_list;
+    else
+      /*
+        Assign the list of items created on re-parsing the statement to
+        the current stored routine's instruction.
+      */
+      free_list= thd->free_list;
+
     thd->free_list= nullptr;
-   }
+  }
 
   Query_arena old;
   thd->restore_active_arena(&old, &backup);

sql/sp_instr.h

@@ -76,6 +76,11 @@ class sp_lex_cursor: public sp_lex_local, public Query_arena
     return m_expr_str;
   }
 
+  sp_lex_cursor* get_lex_for_cursor() override
+  {
+    return this;
+  }
+
 private:
   LEX_CSTRING m_expr_str;
 };
@@ -316,11 +321,8 @@ class sp_lex_keeper final
     Set LEX object.
 
     @param lex           LEX-object
-    @param is_lex_owner  this flag specifies whether this LEX object is owned
-                         by the sp_lex_keeper and so should deleted when
-                         needed.
   */
-  void set_lex(LEX *lex, bool is_lex_owner);
+  void set_lex(LEX *lex);
 
 private:
   LEX *m_lex;
@@ -386,10 +388,11 @@ class sp_lex_instr : public sp_instr
 
     @param thd  Thread context.
     @param sp   The stored program.
+    @param lex  SP instruction's lex
 
     @return new LEX-object or NULL in case of failure.
   */
-  LEX *parse_expr(THD *thd, sp_head *sp);
+  LEX *parse_expr(THD *thd, sp_head *sp, LEX *lex);
 
   SQL_I_List<Item_trigger_field>* get_instr_trig_field_list() override
   {

sql/sql_lex.h

@@ -3213,6 +3213,8 @@ class Lex_grant_privilege: public Grant_privilege, public Sql_alloc
 };
 
 
+class sp_lex_cursor;
+
 struct LEX: public Query_tables_list
 {
   SELECT_LEX_UNIT unit;                         /* most upper unit */
@@ -4923,6 +4925,11 @@ struct LEX: public Query_tables_list
   {
     return query_tables != nullptr || sroutines.records > 0;
   }
+
+  virtual sp_lex_cursor* get_lex_for_cursor()
+  {
+    return nullptr;
+  }
 };