[DAFFODIL-2295] priorAlignmentApprox incorrect if term is preceded by separator with text bit alignment

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 2.5.0
• Component/s: Middle "End"
• Assignee: Unassigned
• Reporter: Mike Beckerle
• Created: 19/Mar/20 16:55
• Updated: 30/Sep/24 13:54

Description

The AlignedMixin trait has a member priorAlignmentApprox which  for a term, computes an approximation of the alignment prior to it.

One of the things that could be before a term is a separator of a separated sequence (prefix or infix position), and in that case, the alignment will be the mandatory-text-alignment of that separator's encoding.

The code of priorAlignmentApprox takes a number of things into consideration, but does not take the possibility of a separator into account.

The design note https://daffodil.apache.org/dev/design-notes/term-sharing-in-schema-compiler/ shows numerous things in the "unique before" of a term including the separator text regions, but the code doesn't implement this fully.

This is a bug, because the schema compiler may not insert an alignment region when one is required to meet the term's alignment property requirement.