MDEV-20017 Implement TO_CHAR() Oracle compatible function

TO_CHAR(expr, fmt)
- expr: required parameter, data/time/timestamp type expression
- fmt: optional parameter, format string, supports
  YYYY/YYY/YY/RRRR/RR/MM/MON/MONTH/MI/DD/DY/HH/HH12/HH24/SS and special
  characters. The default value is "YYYY-MM-DD HH24:MI:SS"

In Oracle, TO_CHAR() can also be used to convert numbers to strings, but
this is not supported. This will gave an error in this patch.

Other things:
- If format strings is a constant, it's evaluated only once and if there
  is any errors in it, they are given at once and the statement will abort.

Original author: woqutech
Lots of optimizations and cleanups done as part of review

mysql-test/suite/compat/README.txt

+To run a test suite under this directory, you should use the format:
+
+mysql-test-run --suite=compat/oracle
+
+or to run one test:
+
+mysql-test-run compat/oracle.test_name

sql/item_create.cc

@@ -2132,6 +2132,19 @@ class Create_func_to_base64 : public Create_func_arg1
 };
 
 
+class Create_func_to_char : public Create_native_func
+{
+public:
+  virtual Item *create_native(THD *thd, LEX_CSTRING *name, List<Item> *item_list);
+
+  static Create_func_to_char s_singleton;
+
+protected:
+  Create_func_to_char() {}
+  virtual ~Create_func_to_char() {}
+};
+
+
 class Create_func_to_days : public Create_func_arg1
 {
 public:
@@ -5142,6 +5155,44 @@ Create_func_to_base64::create_1_arg(THD *thd, Item *arg1)
 }
 
 
+Create_func_to_char Create_func_to_char::s_singleton;
+
+Item*
+Create_func_to_char::create_native(THD *thd, LEX_CSTRING *name,
+				   List<Item> *item_list)
+{
+  Item *func= NULL;
+  int arg_count= 0;
+
+  if (item_list != NULL)
+    arg_count= item_list->elements;
+
+  switch (arg_count) {
+  case 1:
+  {
+    Item *param_1= item_list->pop();
+    Item *i0= new (thd->mem_root) Item_string_sys(thd, "YYYY-MM-DD HH24:MI:SS",  21);
+    func= new (thd->mem_root) Item_func_tochar(thd, param_1, i0);
+    break;
+  }
+  case 2:
+  {
+    Item *param_1= item_list->pop();
+    Item *param_2= item_list->pop();
+    func= new (thd->mem_root) Item_func_tochar(thd, param_1, param_2);
+    break;
+  }
+  default:
+  {
+    my_error(ER_WRONG_PARAMCOUNT_TO_NATIVE_FCT, MYF(0), name->str);
+    break;
+  }
+  }
+
+  return func;
+}
+
+
 Create_func_to_days Create_func_to_days::s_singleton;
 
 Item*
@@ -5601,6 +5652,7 @@ static Native_func_registry func_array[] =
   { { STRING_WITH_LEN("TIME_FORMAT") }, BUILDER(Create_func_time_format)},
   { { STRING_WITH_LEN("TIME_TO_SEC") }, BUILDER(Create_func_time_to_sec)},
   { { STRING_WITH_LEN("TO_BASE64") }, BUILDER(Create_func_to_base64)},
+  { { STRING_WITH_LEN("TO_CHAR") }, BUILDER(Create_func_to_char)},
   { { STRING_WITH_LEN("TO_DAYS") }, BUILDER(Create_func_to_days)},
   { { STRING_WITH_LEN("TO_SECONDS") }, BUILDER(Create_func_to_seconds)},
   { { STRING_WITH_LEN("UCASE") }, BUILDER(Create_func_ucase)},

sql/item_timefunc.h

@@ -978,6 +978,57 @@ class Item_func_time_format: public Item_func_date_format
 };
 
 
+/* the max length of datetime format models string in Oracle is 144 */
+#define MAX_DATETIME_FORMAT_MODEL_LEN 144
+
+class Item_func_tochar :public Item_str_func
+{
+  const MY_LOCALE *locale;
+  THD *thd;
+  String warning_message;
+  bool fixed_length;
+
+  /*
+    When datetime format models is parsed, use uint16 integers to
+    represent the format models and store in fmt_array.
+  */
+  uint16 fmt_array[MAX_DATETIME_FORMAT_MODEL_LEN+1];
+
+  bool check_arguments() const override
+  {
+    return check_argument_types_can_return_text(1, arg_count);
+  }
+
+public:
+  Item_func_tochar(THD *thd, Item *a, Item *b):
+    Item_str_func(thd, a, b), locale(0)
+  {
+    /* NOTE: max length of warning message is 64 */
+    warning_message.alloc(64);
+    warning_message.length(0);
+  }
+  ~Item_func_tochar() { warning_message.free(); }
+  String *val_str(String *str) override;
+  LEX_CSTRING func_name_cstring() const override
+  {
+    static LEX_CSTRING name= {STRING_WITH_LEN("to_char") };
+    return name;
+  }
+  bool fix_length_and_dec() override;
+  bool parse_format_string(const String *format, uint *fmt_len);
+
+  bool check_vcol_func_processor(void *arg) override
+  {
+    if (arg_count > 2)
+      return false;
+    return mark_unsupported_function(func_name(), "()", arg, VCOL_SESSION_FUNC);
+  }
+
+  Item *get_copy(THD *thd) override
+  { return get_item_copy<Item_func_tochar>(thd, this); }
+};
+
+
 class Item_func_from_unixtime :public Item_datetimefunc
 {
   bool check_arguments() const override

sql/share/errmsg-utf8.txt

@@ -7988,5 +7988,3 @@ ER_JSON_TABLE_MULTIPLE_MATCHES
         eng "Can't store multiple matches of the path in the column '%s' of JSON_TABLE '%s'."
 ER_WITH_TIES_NEEDS_ORDER
         eng "FETCH ... WITH TIES requires ORDER BY clause to be present"
-ER_FUNCTION_CANNOT_BE_USED_IN_CLAUSE
-        eng "Function '%s' cannot be used in the %s clause"

sql/sql_string.cc

@@ -502,16 +502,16 @@ bool String::set_ascii(const char *str, size_t arg_length)
 
 /* This is used by mysql.cc */
 
-bool Binary_string::fill(uint32 max_length,char fill_char)
+bool Binary_string::fill(size_t max_length,char fill_char)
 {
   if (str_length > max_length)
-    Ptr[str_length=max_length]=0;
+    Ptr[str_length= (uint32) max_length]=0;
   else
   {
     if (realloc(max_length))
       return TRUE;
     bfill(Ptr+str_length,max_length-str_length,fill_char);
-    str_length=max_length;
+    str_length= (uint32) max_length;
   }
   return FALSE;
 }

sql/sql_string.h

@@ -740,7 +740,7 @@ class Binary_string: public Static_binary_string
     thread_specific= s.thread_specific;
     s.alloced= 0;
   }
-  bool fill(uint32 max_length,char fill);
+  bool fill(size_t max_length,char fill);
   /*
     Replace substring with string
     If wrong parameter or not enough memory, do nothing