Erratum — draft-fossil-repo-state-01 §6.2

Document	draft-fossil-repo-state-01
Section	6.2 — Branch creation (the cancel cards)
Type	Technical (the normative sentence names the wrong check-in)
Status	Applied in draft-fossil-repo-state-01 (2026-10-12)
Reported	2026-10-12
Submitter	Dan Mestas
Found via	A reader implementing §6.2 from the text alone

1. Summary

The normative paragraph says branch creation "MUST also cancel every pre-existing active sym-* tag on the branch-root check-in". The branch-root check-in is the one being written, so it has no pre-existing tags; the tags to cancel are the ones it would inherit from its parent. The informative paragraph added in -01 says Fossil computes the cards from the parent, but the normative sentence still points at the root, and a reader cannot tell whether the new branch's own sym-* tag is among the tags to cancel.

2. Location

§6.2, second paragraph.

3. The reference behavior

Verified against Fossil 2.28. commit --branch (src/checkin.c:2100-2112) emits T -sym-NAME * for each propagating sym-* tag of the parent check-in other than the new branch's own. branch new (src/branch.c: 170-183) emits one for every active sym-* tag of the parent, singletons included. In both, the source is the parent, never the root.

4. Impact

Observable in corner cases only: an implementation that reads "on the branch-root check-in" literally emits no cancel cards, and the root then inherits the parent's symbolic names, which §6.2 says it must not.

5. Correction

-   Branch creation MUST also cancel every pre-existing active sym-* tag
-   on the branch-root check-in by emitting corresponding - (cancel)
-   cards, because symbolic tags are otherwise inherited from a check-
-   in's parent.  This ensures a newly created branch does not carry
-   forward the parent branch's symbolic names alongside its own.
+   Branch creation MUST also cancel every sym-* tag the branch-root
+   check-in would otherwise inherit from its parent, that is, every
+   propagating sym-* tag active on the parent other than the new
+   branch's own, by emitting a corresponding - (cancel) card on the
+   root.  This ensures a newly created branch does not carry forward
+   the parent branch's symbolic names alongside its own.  Cancel cards
+   for tags the root would not inherit are permitted and have no
+   effect.

Also, in the informative paragraph after "the extra cards cancel nothing on the root.":

   If the parent itself carries a propagating sym-* tag of the new
   branch's own name, branch new emits both the propagating card and a
   cancel card for that name; this document does not define their
   combined effect.

6. Rationale

Names the check-in whose tags are read, excludes the new branch's own tag (cancelling it would undo the creation), and keeps branch new's extra cards conformant, as the informative paragraph already describes them.

7. Verification

• Source: Fossil 2.28 src/checkin.c:2100-2112, src/branch.c:170-183.