`jj absorb` makes a hidden revision visible

[dzaima]

Description

When jj absorb modifies a revision which has a hidden descendant that's referred to by immutable_heads(), it makes the hidden revision visible and rebases it.

Steps to Reproduce the Problem

# setup
jj config set --repo 'revset-aliases."immutable_heads()"' 'builtin_immutable_heads() ~ tags(glob:backup/*)'

# commit to absorb into
echo foo > file
jj new

# add a hidden revision
jj new -o@- --no-edit -m 'hidden revision'
jj tag set -r '@-+~@' backup/whatever
jj abandon backup/whatever

# absorb
echo bar > file
jj log -r:: # there are only 2 visible commits
jj absorb
jj log -r:: # now there are 3 commits!

Expected Behavior

jj absorb should act like jj squash -f@ -t@- in this example, and not make hidden revisions visible

Actual Behavior

$ jj log -r::
@  rpsmomsr 2026-08-09 00:36:11 dzaima ee6e395d
│  (no description set)
○  vsuwznzt 2026-08-09 00:36:04 dzaima 136e9406
│  (no description set)
◆  zzzzzzzz root() 00000000
$ jj absorb
Absorbed changes into 1 revisions:
  vsuwznzt 74b133b8 (no description set)
Rebased 1 descendant commits.
Working copy  (@) now at: otpolmmv 1fdb4a73 (empty) (no description set)
Parent commit (@-)      : vsuwznzt 74b133b8 (no description set)
$ jj log -r::
@  otpolmmv 2026-08-09 00:45:24 dzaima 1fdb4a73
│  (no description set) (empty)
│ ○  nlrqqrty 2026-08-09 00:36:07 dzaima a1036b70
├─╯  hidden revision (empty)
○  vsuwznzt 2026-08-09 00:36:04 dzaima 74b133b8
│  (no description set)
◆  zzzzzzzz root() 00000000

Specifications

• Platform: Linux
• Version: Happens on 0.43.0 and 0.44.0, but not 0.42.0

[yuja]

I'm not sure why jj absorb and jj squash behave differently, but adding hidden revisions to the immutable_heads() set would cause various problems. Any revisions explicitly referenced in a revset become reachable within that revset evaluation.

You can probably rewrite the immutable expression as follows:

trunk() | tags(~'backup/*') | untracked_remote_bookmarks()