Auto-beaming issues

[Mats Bengtsson]

   Hi,

   I know that there are several old bug reports on auto-beaming, but I've
   come across a couple of problems that are not necessarily covered by
   the existing reports.

   Problem 1: Automatic beaming doesn't always work if a voice context
   ends in the wrong place. This might be closely related to #4690, but
   I'm not sure. Example:

   \version "2.24.0"
     \score{
       \new Voice \fixed c' {
         << { e8 f } \\ c4 >> g2. | % Autobeaming fails!
         << { e8 f g f } \\ c2 >> g2 | % Autobeaming successful!
         << { e8 f g f e f } \\ c2. >> g4 | % Autobeaming fails!
         << { e8 f g f e f g f } \\ c1 >> |  % Autobeaming successful!
     }
   }

   Another example of the same problem is
   \version "2.24.0"
   \score{
     \fixed c' { \partial 4 e8 | f e f g f e f \fine }
   }

   Problem 2: The current logic which only provides rules on when a beam
   should be ended, obviously provides limited possibilities to express
   the beaming patterns. I was recently typesetting some 18th century
   music where I wanted to imitate the original beaming patterns, where in
   4/4, 16th triplets and 32nd notes were beamed in half beats, but where
   patterns like 8. 32 32 were beamed together. Unfortunately that cannot
   be handled by the current logic, but the following example is extra
   ugly since also the two eighth notes in the first beat don't get any
   beam:

   \version "2.24.0"
   \score{
     \fixed c' {
       a8 g f8.-\trill ( e32 f ) e32 f g f e f g f e4 |
     }
     \layout{
       \context {
          \Score{
             \overrideTimeSignatureSettings
             4/4        % timeSignatureFraction
             1/4        % baseMomentFraction
             1,1,1,1        % beatStructure
             #'((end . ((1/8 . (4 4))  ; 1/8 notes half measure
                (1/12 . (3 3 3 3))  ; triplets and shorter by beat
                        (1/24 . (3 3 3 3 3 3 3 3 )) ; 16th triplets and
   shorter by half beats
                )))
         }
       }
     }
   }

   Fortunately, in this specific example, it's actually enough to manually
   beam the second beat, in order to get an automatic beam on the first
   beat:
   a8 g f8.-\trill [ ( e32 f ) ] e32 f g f e f g f e4 |

   Feature request: It would of course be desirable to have more rich
   possibilities to express beaming patterns, where I for example would be
   able to express beaming patterns so that the previous example
   automatically gives the same as

   \score{
     \fixed c' {
       a8 [ g ] f8.-\trill [ ( e32 f ) ] e32 [ f g f ] e [ f g f ] e4 |
     }
   }

      /Mats