TO_NUMBER() with format element PR rejects positive values without surrounding blanks, unlike Oracle

TO_NUMBER() with the PR format element (added in MDEV-20022) does not handle positive values the way Oracle does. MariaDB requires the value to be surrounded by blanks, while Oracle accepts it without them and rejects the blank-surrounded form.

Negative values in angle brackets work the same in both: TO_NUMBER('<1234.50>', '9999.99PR') returns -1234.5.

Cause

get_PR() in sql/item_numconvfunc.cc accepts a subject only if its first and last characters are both blanks or are '<' and '>':

if (!(leading == ' ' && trailing == ' ') &&

    !(leading == '<' && trailing == '>'))

  return true; // Unknown

Expected

Positive values are accepted as in Oracle: without surrounding blanks, and with a leading blank.

Notes

• MI was also checked: TO_NUMBER('1234.50', '9999.99MI') is rejected by both Oracle (ORA-01722) and MariaDB (NULL), so MI is not part of this report.
• Oracle results were provided by bar (sqlfiddle.com). MariaDB results are from 13.0.2; the code is unchanged in 12.2 and 13.1.
• Found while documenting TO_NUMBER format strings (DOCS-6982). Until this is fixed, the documentation shows only negative PR values.