Rename my_snprintf’s %uE to %iE

… and delete `%uU` (just use `%d` for that)

The follow-up #3360 discovered `%M` usages that suggest that it was
designed for `errno` and similar **signed** `int` (“errno_t”) variables.
Besides convenience, if the old `%M` read a `signed int`,
so should the new version to maintain compatibility.

I only added `%iE` (no `%dE`) to keep the new suffix mechanics
away from the popular `%d`. Beïng synonyms (originally),
this decision on preserving `%d` also saves the need for `%iI`/`%dD`.

include/mysql/service_my_snprintf.h

@@ -67,21 +67,22 @@
       <precision> bytes without terminating on any '\0's in the sequence.
       The default <precision> when it's unspecified is not defined.
 
-    Format 'uE'
-      treats the argument as an errno number. It prints this number, a space,
-      then its corresponding error message in double quotes. In other words:
-        printf("%uE", n) === printf("%d \"%sT\"", n, strerror(n))
-
     Format 'sT'
       replaces the end of the printed string with "..." if it was truncated.
 
-    Format 'sS' and 'uU'
-      are synonyms of 's' and 'u' respectively. They are escapes that avoid
+    Format 'sS'
+      is a synonym for 's'. It's an escape that avoid
       consuming the following plain char as one of the above extension suffixes.
-      Example: "Data size: %uUEiB"
+      Example: "Data Class: %sSType"
+
+    Format 'iE'
+      treats the argument as an errno number. It prints this number, a space,
+      then its corresponding error message in double quotes. In other words:
+        printf("%iE", n) === printf("%i \"%sT\"", n, strerror(n))
+      Format 'dE' has no effect. Therefore, to escape '%iE', use '%dE' instead.
 
     Unrecognized and multiple suffixes are not parsed;
-      for example, both "%sTQ" and "%uQ" will print a literal 'Q'.
+      for example, both "%sTQ" and "%iQ" will suffix with a literal 'Q'.
 */
 
 #ifdef __cplusplus

strings/my_vsnprintf.c

@@ -586,16 +586,12 @@ start:
         /* Integer parameter */
         longlong larg= args_arr[print_arr[i].arg_idx].longlong_arg;
         my_bool suffix_e= arg_type == 'M';
-        if (arg_type == 'u')
-          switch (*print_arr[idx].begin) // look at the start of the next chunk
-          {
-          case 'E':
-            suffix_e= TRUE;
-            // fall-through
-          case 'U': // escape
-            ++print_arr[idx].begin; // roll forward to consume the char
-            break;
-          }
+        // look at the start of the next chunk
+        if (arg_type == 'i' && *print_arr[i].begin == 'E')
+        {
+          suffix_e= TRUE;
+          ++print_arr[i].begin; // roll forward to consume the char
+        }
         if (suffix_e)
         {
           const char *real_end;
@@ -807,16 +803,11 @@ size_t my_vsnprintf_ex(CHARSET_INFO *cs, char *to, size_t n,
         larg= va_arg(ap, int);
       else
         larg= va_arg(ap, uint);
-      if (arg_type == 'u')
-        switch (fmt[1]) // look-ahead
-        {
-        case 'E':
-          suffix_e= TRUE;
-          // fall-through
-        case 'U': // escape
-          ++fmt;
-          break;
-        }
+      if (arg_type == 'i' && fmt[1] == 'E') // look-ahead
+      {
+        suffix_e= TRUE;
+        ++fmt;
+      }
       if (suffix_e)
       {
         const char *real_end= MY_MIN(to + width, end);

unittest/mysys/my_vsnprintf-t.c

@@ -113,9 +113,6 @@ int main(void)
 
   test1("MariaDB extension escape sS works",
         "MariaDB extension escape sS %sS", "works");
-  test1("MariaDB extension escape uU 2",
-        "MariaDB extension escape uU %uU", 2);
-
   test1("MariaDB extension sQ works: `abcd` `op``q`",
         "MariaDB extension sQ works: %sQ %.4sQ", "abcd", "op`qrst");
 
@@ -131,21 +128,24 @@ int main(void)
   }
 
   {
-    // Test that %uE works
+    // Test that %iE works
     const char *results[]=
     {
-      "MariaDB extension uE works: 1 \"Operation not permitted\"", // Linux
-      "MariaDB extension uE works: 1 \"Not owner\"",               // Solaris
+      "MariaDB extension iE works: 1 \"Operation not permitted\"", // Linux
+      "MariaDB extension iE works: 1 \"Not owner\"",               // Solaris
       NullS
     };
-    test_many(results, "MariaDB extension uE works: %uE", 1);
+    test_many(results, "MariaDB extension iE works: %iE", 1);
   }
-  test1("uE with 0 errno: 0 \"Internal error/check (Not system error)\"",
-        "uE with 0 errno: %uE", 0);
-  test1("uE with width: <0 \"Internal error...>",
-        "uE with width: <%.20uE>", 0);
-  test_w_len("uE with small buf: 0 \"..",
-         25, "uE with small buf: %uE", 0);
+  test1("iE with 0 errno: 0 \"Internal error/check (Not system error)\"",
+        "iE with 0 errno: %iE", 0);
+  test1("iE with width: <0 \"Internal error...>",
+        "iE with width: <%.20iE>", 0);
+  test_w_len("iE with small buf: 0 \"..",
+         25, "iE with small buf: %iE", 0);
+
+  test1("MariaDB extension dE DOESN'T work: 0E",
+        "MariaDB extension dE DOESN'T work: %dE", 0);
 
   test1("MariaDB extension sT works: <abcd> <op...>",
         "MariaDB extension sT %sT: <%.5sT> <%.5sT>", "works", "abcd", "opqrst");