| Document | draft-fossil-repo-state-00 |
| Section | 5.4 — Tag propagation, step 3 (qualification) |
| Type | Technical (the text diverges from Fossil's implemented behavior) |
| Status | Reported |
| Reported | 2026-08-13 |
| Submitter | Dan Mestas |
| Found via | Editorial cross-check of two divergent draft copies against Fossil C (tag.c) |
1. Summary
§5.4 step 3 says a child with no same-tag entry "always qualifies" for propagation. That is true only for PROPAGATING tags. For a cancel-type propagation, Fossil's walk halts at a child with no same-tag row: there is nothing to cancel there, and the walk does not continue past it.
2. The text in error
Page 15 (§5.4 step 3):
A child that currently has no same-tag entry always qualifies.
3. What Fossil implements
tag.c (the propagation query and its queue gate):
tag.c:55-61 doit = coalesce(srcid=0 AND tagxref.mtime<:mtime, tagType==2)
tag.c:88-93 pqueuex_insert(...) runs only if( doit )
The qualification is computed over a LEFT JOIN. When the child has no
tagxref row, the first coalesce argument is NULL and doit falls back
to tagType==2 — true for a propagating tag (tagtype 2), FALSE for a
cancel (tagtype 0). Because pqueuex_insert is gated on doit, a
cancel-type walk genuinely stops at a childless-of-that-tag node.
4. Corrected text
A child that currently has no same-tag entry qualifies only when the propagating tag is of propagate type; a cancel-type propagation does not qualify at such a child — it has no entry to cancel — and the walk does not continue past it.
5. Observable consequence of the uncorrected text
On a chain carrying a gap — a descendant that never had the tag — an implementation of the literal text walks a cancel through the gap and can cancel same-tag entries further down than Fossil would, so the derived tagxref-equivalent state diverges from what Fossil computes for the same artifact sequence.
6. Provenance note
The wording traces to one of two divergent working copies of the draft; the other copy did not generalize "always qualifies" beyond propagating tags. The zit reference implementation had followed the wrong copy (fixed, with the halt pinned by a step-count test).