MDEV-30746 Regression in ucs2_general_mysql500_ci

1. Adding a separate MY_COLLATION_HANDLER
   my_collation_ucs2_general_mysql500_ci_handler
   implementing a proper order for ucs2_general_mysql500_ci
   The problem happened because ucs2_general_mysql500_ci
   erroneously used my_collation_ucs2_general_ci_handler.

2. Cosmetic changes: Renaming:
   - plane00_mysql500 to my_unicase_mysql500_page00
   - my_unicase_pages_mysql500 to my_unicase_mysql500_pages
   to use the same naming style with:
   - my_unicase_default_page00
   - my_unicase_defaul_pages

3. Moving code fragments from
   - handler::check_collation_compatibility() in handler.cc
   - upgrade_collation() in table.cc
   into new methods in class Charset, to reuse the code easier.

3 files changed, 50 insertions, 10 deletions

diff --git a/strings/ctype-ucs2.c b/strings/ctype-ucs2.c
index 2e6b1239c0a..80a267dbf1d 100644
--- a/strings/ctype-ucs2.c
+++ b/strings/ctype-ucs2.c
@@ -2987,6 +2987,14 @@ static inline int my_weight_mb2_ucs2_general_ci(uchar b0, uchar b1)
 }
 
 
+static inline int my_weight_mb2_ucs2_general_mysql500_ci(uchar b0, uchar b1)
+{
+  my_wc_t wc= UCS2_CODE(b0, b1);
+  MY_UNICASE_CHARACTER *page= my_unicase_mysql500_pages[wc >> 8];
+  return (int) (page ? page[wc & 0xFF].sort : wc);
+}
+
+
 #define MY_FUNCTION_NAME(x)      my_ ## x ## _ucs2_general_ci
 #define DEFINE_STRNXFRM_UNICODE
 #define DEFINE_STRNXFRM_UNICODE_NOPAD
@@ -3000,6 +3008,18 @@ static inline int my_weight_mb2_ucs2_general_ci(uchar b0, uchar b1)
 #include "strcoll.inl"
 
 
+#define MY_FUNCTION_NAME(x)      my_ ## x ## _ucs2_general_mysql500_ci
+#define DEFINE_STRNXFRM_UNICODE
+#define MY_MB_WC(cs, pwc, s, e)  my_mb_wc_ucs2_quick(pwc, s, e)
+#define OPTIMIZE_ASCII           0
+#define UNICASE_MAXCHAR          MY_UNICASE_INFO_DEFAULT_MAXCHAR
+#define UNICASE_PAGE0            my_unicase_mysql500_page00
+#define UNICASE_PAGES            my_unicase_mysql500_pages
+#define WEIGHT_ILSEQ(x)          (0xFF0000 + (uchar) (x))
+#define WEIGHT_MB2(b0,b1)        my_weight_mb2_ucs2_general_mysql500_ci(b0,b1)
+#include "strcoll.inl"
+
+
 #define MY_FUNCTION_NAME(x)      my_ ## x ## _ucs2_bin
 #define DEFINE_STRNXFRM_UNICODE_BIN2
 #define MY_MB_WC(cs, pwc, s, e)  my_mb_wc_ucs2_quick(pwc, s, e)
@@ -3285,6 +3305,23 @@ static MY_COLLATION_HANDLER my_collation_ucs2_general_ci_handler =
 };
 
 
+static MY_COLLATION_HANDLER my_collation_ucs2_general_mysql500_ci_handler =
+{
+    NULL,		/* init */
+    my_strnncoll_ucs2_general_mysql500_ci,
+    my_strnncollsp_ucs2_general_mysql500_ci,
+    my_strnncollsp_nchars_ucs2_general_mysql500_ci,
+    my_strnxfrm_ucs2_general_mysql500_ci,
+    my_strnxfrmlen_unicode,
+    my_like_range_generic,
+    my_wildcmp_ucs2_ci,
+    my_strcasecmp_mb2_or_mb4,
+    my_instr_mb,
+    my_hash_sort_ucs2,
+    my_propagate_simple
+};
+
+
 static MY_COLLATION_HANDLER my_collation_ucs2_bin_handler =
 {
     NULL,		/* init */
@@ -3431,7 +3468,7 @@ struct charset_info_st my_charset_ucs2_general_mysql500_ci=
   0,                          /* escape_with_backslash_is_dangerous    */
   1,                                               /* levels_for_order   */
   &my_charset_ucs2_handler,
-  &my_collation_ucs2_general_ci_handler
+  &my_collation_ucs2_general_mysql500_ci_handler
 };
 
 
diff --git a/strings/ctype-unidata.h b/strings/ctype-unidata.h
index 6712f5e1d79..9900fd0cedd 100644
--- a/strings/ctype-unidata.h
+++ b/strings/ctype-unidata.h
@@ -21,6 +21,9 @@
 extern MY_UNICASE_CHARACTER my_unicase_default_page00[256];
 extern MY_UNICASE_CHARACTER *my_unicase_default_pages[256];
 
+extern MY_UNICASE_CHARACTER my_unicase_mysql500_page00[256];
+extern MY_UNICASE_CHARACTER *my_unicase_mysql500_pages[256];
+
 size_t my_strxfrm_pad_nweights_unicode(uchar *str, uchar *strend, size_t nweights);
 size_t my_strxfrm_pad_unicode(uchar *str, uchar *strend);
 
diff --git a/strings/ctype-utf8.c b/strings/ctype-utf8.c
index 69ebb6b523e..cdac17be3c6 100644
--- a/strings/ctype-utf8.c
+++ b/strings/ctype-utf8.c
@@ -248,7 +248,7 @@ MY_UNICASE_CHARACTER my_unicase_default_page00[]={
   Almost similar to my_unicase_default_page00, but maps sorting order
   for U+00DF to 0x00DF instead of 0x0053.
 */
-static MY_UNICASE_CHARACTER plane00_mysql500[]={
+MY_UNICASE_CHARACTER my_unicase_mysql500_page00[]={
   {0x0000,0x0000,0x0000},  {0x0001,0x0001,0x0001},
   {0x0002,0x0002,0x0002},  {0x0003,0x0003,0x0003},
   {0x0004,0x0004,0x0004},  {0x0005,0x0005,0x0005},
@@ -1739,8 +1739,8 @@ MY_UNICASE_INFO my_unicase_default=
 /*
   Reproduce old utf8_general_ci behaviour before we fixed Bug#27877.
 */
-MY_UNICASE_CHARACTER *my_unicase_pages_mysql500[256]={
- plane00_mysql500,
+MY_UNICASE_CHARACTER *my_unicase_mysql500_pages[256]={
+ my_unicase_mysql500_page00,
           plane01, plane02, plane03, plane04, plane05,    NULL,    NULL,
     NULL,    NULL,    NULL,    NULL,    NULL,    NULL,    NULL,    NULL,
     NULL,    NULL,    NULL,    NULL,    NULL,    NULL,    NULL,    NULL,
@@ -1780,7 +1780,7 @@ MY_UNICASE_CHARACTER *my_unicase_pages_mysql500[256]={
 MY_UNICASE_INFO my_unicase_mysql500=
 {
   0xFFFF,
-  my_unicase_pages_mysql500
+  my_unicase_mysql500_pages
 };
 
 
@@ -5266,14 +5266,14 @@ static inline int my_weight_mb3_utf8_general_ci(uchar b0, uchar b1, uchar b2)
 
 static inline int my_weight_mb1_utf8_general_mysql500_ci(uchar b)
 {
-  return (int) plane00_mysql500[b & 0xFF].sort;
+  return (int) my_unicase_mysql500_page00[b & 0xFF].sort;
 }
 
 
 static inline int my_weight_mb2_utf8_general_mysql500_ci(uchar b0, uchar b1)
 {
   my_wc_t wc= UTF8MB2_CODE(b0, b1);
-  MY_UNICASE_CHARACTER *page= my_unicase_pages_mysql500[wc >> 8];
+  MY_UNICASE_CHARACTER *page= my_unicase_mysql500_pages[wc >> 8];
   return (int) (page ? page[wc & 0xFF].sort : wc);
 }
 
@@ -5282,7 +5282,7 @@ static inline int
 my_weight_mb3_utf8_general_mysql500_ci(uchar b0, uchar b1, uchar b2)
 {
   my_wc_t wc= UTF8MB3_CODE(b0, b1, b2);
-  MY_UNICASE_CHARACTER *page= my_unicase_pages_mysql500[wc >> 8];
+  MY_UNICASE_CHARACTER *page= my_unicase_mysql500_pages[wc >> 8];
   return (int) (page ? page[wc & 0xFF].sort : wc);
 }
 
@@ -5292,8 +5292,8 @@ my_weight_mb3_utf8_general_mysql500_ci(uchar b0, uchar b1, uchar b2)
 #define MY_MB_WC(cs, pwc, s, e)  my_mb_wc_utf8mb3_quick(pwc, s, e)
 #define OPTIMIZE_ASCII           1
 #define UNICASE_MAXCHAR          MY_UNICASE_INFO_DEFAULT_MAXCHAR
-#define UNICASE_PAGE0            plane00_mysql500
-#define UNICASE_PAGES            my_unicase_pages_mysql500
+#define UNICASE_PAGE0            my_unicase_mysql500_page00
+#define UNICASE_PAGES            my_unicase_mysql500_pages
 #define WEIGHT_ILSEQ(x)          (0xFF0000 + (uchar) (x))
 #define WEIGHT_MB1(x)            my_weight_mb1_utf8_general_mysql500_ci(x)
 #define WEIGHT_MB2(x,y)          my_weight_mb2_utf8_general_mysql500_ci(x,y)