Re: ancient convert rules

[Joram Noeck]

Hi Jonas,

some comments to that:

1. I (hopefully) fixed all the escaping issues like #6024 in my merge
request: https://gitlab.com/lilypond/lilypond/-/merge_requests/363
The python re syntax is clear, it just requires the right amout of
backslashes or r-prefixes;

  re.sub(r'\\command', r'\command', s)  or
  re.sub('\\\\command', '\\command', s)

2. pylint spots the clearly wrong ones (e.g. \m) but not the valid ones
(e.g. \n in \numbers or \t in \times). I would gladly compare your fixes
to mine.

3. We might want to cleanup convertrules.py. And I doubt that all
conversions work flawlessly for ancient versions all the way to 2.21.
But IMHO this issue is not the right excuse to drop possibly working
functionality.

4. Mutopia uses very old versions. There was an effort in 2014 - 2015 to
update all Mutopia scores to a version > 2.0.0. So version 0 or 1 should
not be used any more (one exception). But 2.2.0 is also very old.



Details for Mutopia:

Update Mutopia pieces with LilyPond versions < 2.0
https://github.com/MutopiaProject/MutopiaProject/milestone/5

Apparently, one work (KV487) is missing from that effort.
2.16 and 2.18 are the most frequent versions in Mutopia:

    766 \version "2.16.0"
    736 \version "2.18.0"
    553 \version "2.18.2"
    519 \version "2.16.1"
    300 \version "2.14.2"
    186 \version "2.10.33"
    184 \version "2.12.2"
    176 \version "2.10.3"
    156 \version "2.6.0"    !!!

Besides KV487 with version 1.9.8, the oldest versions are (with number
of occurances):

      1 \version "2.2.0"
     41 \version "2.4.0"
      1 \version "2.4.1"
      7 \version "2.4.2"
      1 \version "2.4.6"
      4 \version "2.5.21"
    156 \version "2.6.0"
     12 \version "2.6.2"
      9 \version "2.6.3"
     51 \version "2.6.4"
      4 \version "2.6.4.3"
      5 \version "2.6.5"
      1 \version "2.7.13"
      1 \version "2.7.24"
     37 \version "2.7.29"
      1 \version "2.7.30"
      3 \version "2.7.38"
      1 \version "2.7.39"
     58 \version "2.7.40"
     46 \version "2.8.0"
     23 \version "2.8.1"
      5 \version "2.8.2"
      1 \version "2.8.3"
     11 \version "2.8.4"
     58 \version "2.8.5"
      2 \version "2.8.6"
      2 \version "2.8.7"
      4 \version "2.8.8"
      1 \version "2.9.16"
      1 \version "2.9.18"
      4 \version "2.9.2"
      9 \version "2.9.9"


tl;dr: I would not drop conversion rules unless we know that they fail.

Cheers,
Joram