Bug#28875 Conversion between ASCII and LATIN1 charsets does not function

(Regression, caused by a patch for the bug 22646).
Problem: when result type of date_format() was changed from
binary string to character string, mixing date_format()
with a ascii column in CONCAT() stopped to work.
Fix:
- adding "repertoire" flag into DTCollation class,
to mark items which can return only pure ASCII strings.
- allow character set conversion from pure ASCII to other character sets.


include/m_ctype.h:
  Defining new flags.
  Adding new function prototypes.
mysql-test/r/ctype_ucs.result:
  Adding tests.
mysql-test/r/ctype_utf8.result:
  Adding tests.
mysql-test/r/func_time.result:
  Adding tests.
mysql-test/t/ctype_ucs.test:
  Adding tests.
mysql-test/t/ctype_utf8.test:
  Adding tests.
mysql-test/t/func_time.test:
  Adding test.
mysys/charset.c:
  Adding pure ASCII detection when loading a dynamic character set.
sql/item.cc:
  - Moving detection of a Unicode superset into function.
  - Adding detection of a ASCII subset.
  - Adding creation of to-ASCII character set convertor when
    safe_charset_converter() failed and when the argument.
    repertoire is know to be pure ASCII.
sql/item.h:
  - Adding "repertoire" member into DTCollation class.
  - Adding "repertoire" argument to constructors.
  - Adding new methods:
    set_repertoire_from_charset()
    set_repertoire_from_value()
sql/item_func.cc:
  Adding "repertoire" argument.
sql/item_strfunc.cc:
  Adding "repertoire" argument.
sql/item_timefunc.cc:
  Initializing the result repertoire taking into account the "is_ascii"
  flag of the current locale.
sql/sql_lex.cc:
  Detect 7bit strings, return in Lex->text_string_is_7bit.
sql/sql_lex.h:
  Adding new member into LEX structure.
  Adding new member into Lex_input_stream
sql/sql_string.cc:
  Allow simple copy from pure ASCII to a ASCII-based character set.
sql/sql_yacc.yy:
  Depening on Lex->text_string_is_7bit and character set features,
  create Item_string with MY_REPERTOIRE_ASCII when it is possible.
strings/conf_to_src.c:
  - Adding printing of the "MY_CS_PUREASCII" flag
  - Adding printing of copyright
strings/ctype-extra.c:
  Recreating ctype-extra.c: ascii_general_ci and ascii_bin
  are now marked with MY_CS_PUREASCII flag.
strings/ctype.c:
  Adding new functions.

strings/ctype.c

@@ -306,3 +306,89 @@ my_bool my_parse_charset_xml(const char *buf, uint len,
   my_xml_parser_free(&p);
   return rc;
 }
+
+
+/*
+  Check repertoire: detect pure ascii strings
+*/
+uint
+my_string_repertoire(CHARSET_INFO *cs, const char *str, ulong length)
+{
+  const char *strend= str + length;
+  if (cs->mbminlen == 1)
+  {
+    for ( ; str < strend; str++)
+    {
+      if (((uchar) *str) > 0x7F)
+        return MY_REPERTOIRE_UNICODE30;
+    }
+  }
+  else
+  {
+    my_wc_t wc;
+    int chlen;
+    for (; (chlen= cs->cset->mb_wc(cs, &wc, str, strend)) > 0; str+= chlen)
+    {
+      if (wc > 0x7F)
+        return MY_REPERTOIRE_UNICODE30;
+    }
+  }
+  return MY_REPERTOIRE_ASCII;
+}
+
+
+/*
+  Detect whether a character set is ASCII compatible.
+
+  Returns TRUE for:
+  
+  - all 8bit character sets whose Unicode mapping of 0x7B is '{'
+    (ignores swe7 which maps 0x7B to "LATIN LETTER A WITH DIAERESIS")
+  
+  - all multi-byte character sets having mbminlen == 1
+    (ignores ucs2 whose mbminlen is 2)
+  
+  TODO:
+  
+  When merging to 5.2, this function should be changed
+  to check a new flag MY_CS_NONASCII, 
+  
+     return (cs->flag & MY_CS_NONASCII) ? 0 : 1;
+  
+  This flag was previously added into 5.2 under terms
+  of WL#3759 "Optimize identifier conversion in client-server protocol"
+  especially to mark character sets not compatible with ASCII.
+  
+  We won't backport this flag to 5.0 or 5.1.
+  This function is Ok for 5.0 and 5.1, because we're not going
+  to introduce new tricky character sets between 5.0 and 5.2.
+*/
+my_bool
+my_charset_is_ascii_based(CHARSET_INFO *cs)
+{
+  return 
+    (cs->mbmaxlen == 1 && cs->tab_to_uni && cs->tab_to_uni['{'] == '{') ||
+    (cs->mbminlen == 1 && cs->mbmaxlen > 1);
+}
+
+
+/*
+  Detect if a character set is 8bit,
+  and it is pure ascii, i.e. doesn't have
+  characters outside U+0000..U+007F
+  This functions is shared between "conf_to_src"
+  and dynamic charsets loader in "mysqld".
+*/
+my_bool
+my_charset_is_8bit_pure_ascii(CHARSET_INFO *cs)
+{
+  size_t code;
+  if (!cs->tab_to_uni)
+    return 0;
+  for (code= 0; code < 256; code++)
+  {
+    if (cs->tab_to_uni[code] > 0x7F)
+      return 0;
+  }
+  return 1;
+}