A fix and a test case for Bug#24179 "select b into $var" fails with

--cursor_protocol": fix a misleading error message in case of
SELECT .. INTO.


sql/sql_class.cc:
  Implement select_result::check_simple_select hierarchy to 
  support correct error messages in case of SELECT .. INTO and C API 
  cursors.
sql/sql_class.h:
  Set the error message inside the function that checks for the error
  condition (simple_select, renamed to check_simple_select).
sql/sql_prepare.cc:
  Use a new method that now sets the error.
tests/mysql_client_test.c:
  Add a test case for Bug#24179 "select b into $var" fails with 
  --cursor_protocol" (check for the right error message and error code).

sql/sql_class.cc

@@ -885,6 +885,13 @@ void select_result::cleanup()
   /* do nothing */
 }
 
+bool select_result::check_simple_select() const
+{
+  my_error(ER_SP_BAD_CURSOR_QUERY, MYF(0));
+  return TRUE;
+}
+
+
 static String default_line_term("\n",default_charset_info);
 static String default_escaped("\\",default_charset_info);
 static String default_field_term("\t",default_charset_info);
@@ -1553,6 +1560,13 @@ int select_dumpvar::prepare(List<Item> &list, SELECT_LEX_UNIT *u)
 }
 
 
+bool select_dumpvar::check_simple_select() const
+{
+  my_error(ER_SP_BAD_CURSOR_SELECT, MYF(0));
+  return TRUE;
+}
+
+
 void select_dumpvar::cleanup()
 {
   vars.empty();

sql/sql_class.h

@@ -1724,7 +1724,14 @@ class select_result :public Sql_alloc {
   virtual bool initialize_tables (JOIN *join=0) { return 0; }
   virtual void send_error(uint errcode,const char *err);
   virtual bool send_eof()=0;
-  virtual bool simple_select() { return 0; }
+  /**
+    Check if this query returns a result set and therefore is allowed in
+    cursors and set an error message if it is not the case.
+
+    @retval FALSE     success
+    @retval TRUE      error, an error message is set
+  */
+  virtual bool check_simple_select() const;
   virtual void abort() {}
   /*
     Cleanup instance of this class for next execution of a prepared
@@ -1762,7 +1769,7 @@ class select_send :public select_result {
   bool send_fields(List<Item> &list, uint flags);
   bool send_data(List<Item> &items);
   bool send_eof();
-  bool simple_select() { return 1; }
+  virtual bool check_simple_select() const { return FALSE; }
   void abort();
 };
 
@@ -2202,6 +2209,7 @@ class select_dumpvar :public select_result_interceptor {
   int prepare(List<Item> &list, SELECT_LEX_UNIT *u);
   bool send_data(List<Item> &items);
   bool send_eof();
+  virtual bool check_simple_select() const;
   void cleanup();
 };
 

sql/sql_prepare.cc

@@ -2906,10 +2906,9 @@ bool Prepared_statement::execute(String *expanded_query, bool open_cursor)
     in INSERT ... SELECT and similar commands.
   */
 
-  if (open_cursor && lex->result && !lex->result->simple_select())
+  if (open_cursor && lex->result && lex->result->check_simple_select())
   {
     DBUG_PRINT("info",("Cursor asked for not SELECT stmt"));
-    my_error(ER_SP_BAD_CURSOR_QUERY, MYF(0));
     return TRUE;
   }
 

tests/mysql_client_test.c

@@ -15456,6 +15456,33 @@ static void test_bug21635()
   DBUG_VOID_RETURN;
 }
 
+/*
+  Bug#24179 "select b into $var" fails with --cursor_protocol"
+  The failure is correct, check that the returned message is meaningful.
+*/
+
+static void test_bug24179()
+{
+  int rc;
+  MYSQL_STMT *stmt;
+
+  DBUG_ENTER("test_bug24179");
+  myheader("test_bug24179");
+
+  stmt= open_cursor("select 1 into @a");
+  rc= mysql_stmt_execute(stmt);
+  DIE_UNLESS(rc);
+  if (!opt_silent)
+  {
+    printf("Got error (as expected): %d %s\n",
+           mysql_stmt_errno(stmt),
+           mysql_stmt_error(stmt));
+  }
+  DIE_UNLESS(mysql_stmt_errno(stmt) == 1323);
+
+  DBUG_VOID_RETURN;
+}
+
 
 /*
   Read and parse arguments and MySQL options from my.cnf
@@ -15735,6 +15762,7 @@ static struct my_tests_st my_tests[]= {
   { "test_bug21726", test_bug21726 },
   { "test_bug23383", test_bug23383 },
   { "test_bug21635", test_bug21635 },
+  { "test_bug24179", test_bug24179 },
   { 0, 0 }
 };