Regex replacement for biblatex/biber to eliminate the warning "month not integer..."

Question

I am using biblatex with biber from TL2018 for my PhD thesis. Due to various reasons, I am forced to use Mendeley for citation managements and cannot switch to another tool now. Mendeley is capable of generating a bib file - but it is compatible with only the classic natbib/bibtex combo (although it correctly escapes special characters).

I understand that with biblatex/biber combo, the month field is not a string, but rather must be an integer. So, as expected and discussed here, I get the warning

 [784] Utils.pm:193> WARN - month field 'Apr' in entry 'coolauthor2012' is not an integer - this will probably not sort properly.

Taking inspiration from a tangentially related question here, I used the following month -> integer hand-conversion in the preamble.

\DeclareSourcemap{
    \maps[datatype=bibtex]{
        \map[overwrite]{
            \step[fieldsource=month, match={jan}, replace=${1}]
            \step[fieldsource=month, match={feb}, replace=${2}]
            \step[fieldsource=month, match={mar}, replace=${3}]
            \step[fieldsource=month, match={apr}, replace=${4}]
            \step[fieldsource=month, match={may}, replace=${5}]
            \step[fieldsource=month, match={jun}, replace=${6}]
            \step[fieldsource=month, match={jul}, replace=${7}]
            \step[fieldsource=month, match={aug}, replace=${8}]
            \step[fieldsource=month, match={sep}, replace=${9}]
            \step[fieldsource=month, match={oct}, replace=${10}]
            \step[fieldsource=month, match={nov}, replace=${11}]
            \step[fieldsource=month, match={dec}, replace=${12}]
        }
    }
}

I have two nagging questions now.

1. Will this work? I don't see any more of the aforementioned warnings, but I wonder if the citations are correctly sorted, and the month replacement was indeed accounted for and handled correctly.
2. Is there a better way to handle this problem? Clearly, hand-mapping each month to an integer is not efficient.

This will help all folks who want to use mendeley especially for re-using their existing mendeley library for manuscript submissions to publishers who are mostly stuck behind in natbib/bibtex era.

Answer 1

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map[overwrite]{
      \step[fieldsource=month, match=\regexp{\A(j|J)an(uary)?\Z}, replace=1]
      \step[fieldsource=month, match=\regexp{\A(f|F)eb(ruary)?\Z}, replace=2]
      \step[fieldsource=month, match=\regexp{\A(m|M)ar(ch)?\Z}, replace=3]
      \step[fieldsource=month, match=\regexp{\A(a|A)pr(il)?\Z}, replace=4]
      \step[fieldsource=month, match=\regexp{\A(m|M)ay\Z}, replace=5]
      \step[fieldsource=month, match=\regexp{\A(j|J)un(e)?\Z}, replace=6]
      \step[fieldsource=month, match=\regexp{\A(j|J)ul(y)?\Z}, replace=7]
      \step[fieldsource=month, match=\regexp{\A(a|A)ug(ust)?\Z}, replace=8]
      \step[fieldsource=month, match=\regexp{\A(s|S)ep(tember)?\Z}, replace=9]
      \step[fieldsource=month, match=\regexp{\A(o|O)ct(ober)?\Z}, replace=10]
      \step[fieldsource=month, match=\regexp{\A(n|N)ov(ember)?\Z}, replace=11]
      \step[fieldsource=month, match=\regexp{\A(d|D)ec(ember)?\Z}, replace=12]
    }
  }
}

This replaces either three-letter name abbreviations or full month names with the correct month number. Since Biber's RegExp is case sensitive this matches the lower-case month abbreviation and the version where the first letter is capitalised (i.e. jan and Jan). (biber 2.12 and higher support matchi for case-insensitive matches; see this issue.)

This is only needed to suppress the warnings that Biber throws when it is presented with

month = {mar},

even without this code the month will be correctly recognised.

---

Note that for most BibTeX styles month = {mar}, is also not the best (correct) form of input. The brace-less month = mar, is usually better because it is then converted to the desired output via BibTeX strings. Q13 of BibTeX Tips and FAQ

Q13: Should I use words or numerals for the month, edition, etc., fields, and why?

You should always use the three letter month macros (undelimited) for the name of the month (jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec) as this lets each .bst file format the month names as is required for that bibliography style.

BTXdoc states on p. 10

month The month in which the work was published or, for an unpublished work, in which it was written. You should use the standard three-letter abbreviation, as described in Appendix B.1.3 of the LaTeX book

See also https://www.ece.ucdavis.edu/~jowens/biberrors.html