diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -352,7 +352,8 @@
     for part in gen.iterparts():
         if parttypes and part.type not in parttypes:
             continue
-        ui.write('%s -- %s\n' % (part.type, _quasirepr(part.params)))
+        msg = '%s -- %s (mandatory: %r)\n'
+        ui.write((msg % (part.type, _quasirepr(part.params), part.mandatory)))
         if part.type == 'changegroup':
             version = part.params.get('version', '01')
             cg = changegroup.getunbundler(version, part, 'UN')
diff --git a/tests/test-bundle-phases.t b/tests/test-bundle-phases.t
--- a/tests/test-bundle-phases.t
+++ b/tests/test-bundle-phases.t
@@ -38,12 +38,12 @@
   3 changesets found
   $ hg debugbundle bundle
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 3, targetphase: 2, version: 02}
+  changegroup -- {nbchanges: 3, targetphase: 2, version: 02} (mandatory: True)
       26805aba1e600a82e93661149f2313866a221a7b
       f585351a92f85104bff7c284233c338b10eb1df7
       9bc730a19041f9ec7cb33c626e811aa233efb18c
-  cache:rev-branch-cache -- {}
-  phase-heads -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  phase-heads -- {} (mandatory: True)
       26805aba1e600a82e93661149f2313866a221a7b draft
   $ hg strip --no-backup C
   $ hg unbundle -q bundle
@@ -228,14 +228,14 @@
   5 changesets found
   $ hg debugbundle bundle
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 5, targetphase: 2, version: 02}
+  changegroup -- {nbchanges: 5, targetphase: 2, version: 02} (mandatory: True)
       426bada5c67598ca65036d57d9e4b64b0c1ce7a0
       112478962961147124edd43549aedd1a335e44bf
       dc0947a82db884575bb76ea10ac97b08536bfa03
       4e4f9194f9f181c57f62e823e8bdfa46ab9e4ff4
       03ca77807e919db8807c3749086dc36fb478cac0
-  cache:rev-branch-cache -- {}
-  phase-heads -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  phase-heads -- {} (mandatory: True)
       dc0947a82db884575bb76ea10ac97b08536bfa03 public
       03ca77807e919db8807c3749086dc36fb478cac0 draft
   $ hg strip --no-backup A
@@ -257,23 +257,23 @@
   2 changesets found
   $ hg debugbundle bundle
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 2, targetphase: 2, version: 02}
+  changegroup -- {nbchanges: 2, targetphase: 2, version: 02} (mandatory: True)
       112478962961147124edd43549aedd1a335e44bf
       4e4f9194f9f181c57f62e823e8bdfa46ab9e4ff4
-  cache:rev-branch-cache -- {}
-  phase-heads -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  phase-heads -- {} (mandatory: True)
   $ rm bundle
 
   $ hg bundle --base A -r D bundle
   3 changesets found
   $ hg debugbundle bundle
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 3, targetphase: 2, version: 02}
+  changegroup -- {nbchanges: 3, targetphase: 2, version: 02} (mandatory: True)
       112478962961147124edd43549aedd1a335e44bf
       dc0947a82db884575bb76ea10ac97b08536bfa03
       4e4f9194f9f181c57f62e823e8bdfa46ab9e4ff4
-  cache:rev-branch-cache -- {}
-  phase-heads -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  phase-heads -- {} (mandatory: True)
       dc0947a82db884575bb76ea10ac97b08536bfa03 public
   $ rm bundle
 
@@ -281,10 +281,10 @@
   2 changesets found
   $ hg debugbundle bundle
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 2, targetphase: 2, version: 02}
+  changegroup -- {nbchanges: 2, targetphase: 2, version: 02} (mandatory: True)
       4e4f9194f9f181c57f62e823e8bdfa46ab9e4ff4
       03ca77807e919db8807c3749086dc36fb478cac0
-  cache:rev-branch-cache -- {}
-  phase-heads -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  phase-heads -- {} (mandatory: True)
       03ca77807e919db8807c3749086dc36fb478cac0 draft
   $ rm bundle
diff --git a/tests/test-bundle-type.t b/tests/test-bundle-type.t
--- a/tests/test-bundle-type.t
+++ b/tests/test-bundle-type.t
@@ -66,9 +66,9 @@
   1 changesets found
   HG20\x00\x00 (esc)
   Stream params: {}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
   none-v2
   
   % test bundle type bzip2
@@ -76,9 +76,9 @@
   1 changesets found
   HG20\x00\x00 (esc)
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
   bzip2-v2
   
   % test bundle type gzip
@@ -86,9 +86,9 @@
   1 changesets found
   HG20\x00\x00 (esc)
   Stream params: {Compression: GZ}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
   gzip-v2
   
   % test bundle type none-v2
@@ -96,9 +96,9 @@
   1 changesets found
   HG20\x00\x00 (esc)
   Stream params: {}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
   none-v2
   
   % test bundle type v2
@@ -106,9 +106,9 @@
   1 changesets found
   HG20\x00\x00 (esc)
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
   bzip2-v2
   
   % test bundle type v1
@@ -171,9 +171,9 @@
   1 changesets found
   HG20\x00\x00 (esc)
   Stream params: {Compression: ZS}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
   zstd-v2
   
   % test bundle type zstd-v2
@@ -181,9 +181,9 @@
   1 changesets found
   HG20\x00\x00 (esc)
   Stream params: {Compression: ZS}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
   zstd-v2
   
 
diff --git a/tests/test-bundle2-format.t b/tests/test-bundle2-format.t
--- a/tests/test-bundle2-format.t
+++ b/tests/test-bundle2-format.t
@@ -993,7 +993,7 @@
 
   $ hg debugbundle ../rev.hg2
   Stream params: {}
-  changegroup -- {}
+  changegroup -- {} (mandatory: False)
       32af7686d403cf45b5d95f2d70cebea587ac806a
       9520eea781bcca16c1e15acc0ba14335a0e8e5ba
       eea13746799a9e0bfd88f29d3c2e9dc9389f524f
@@ -1122,7 +1122,7 @@
   0370: 3b 19 fd af c5 3f f1 60 c3 17                   |;....?.`..|
   $ hg debugbundle ../rev.hg2.bz
   Stream params: {Compression: GZ}
-  changegroup -- {}
+  changegroup -- {} (mandatory: False)
       32af7686d403cf45b5d95f2d70cebea587ac806a
       9520eea781bcca16c1e15acc0ba14335a0e8e5ba
       eea13746799a9e0bfd88f29d3c2e9dc9389f524f
@@ -1209,7 +1209,7 @@
   0430: 2e e4 8a 70 a1 21 46 96 30 7a                   |...p.!F.0z|
   $ hg debugbundle ../rev.hg2.bz
   Stream params: {Compression: BZ}
-  changegroup -- {}
+  changegroup -- {} (mandatory: False)
       32af7686d403cf45b5d95f2d70cebea587ac806a
       9520eea781bcca16c1e15acc0ba14335a0e8e5ba
       eea13746799a9e0bfd88f29d3c2e9dc9389f524f
diff --git a/tests/test-debugbundle.t b/tests/test-debugbundle.t
--- a/tests/test-debugbundle.t
+++ b/tests/test-debugbundle.t
@@ -31,17 +31,17 @@
 
   $ hg debugbundle bundle2.hg
   Stream params: {}
-  changegroup -- {nbchanges: 2, version: 02}
+  changegroup -- {nbchanges: 2, version: 02} (mandatory: True)
       0e067c57feba1a5694ca4844f05588bb1bf82342
       991a3460af53952d10ec8a295d3d2cc2e5fa9690
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
 
 Quiet output
 
   $ hg debugbundle --quiet bundle2.hg
   Stream params: {}
-  changegroup -- {nbchanges: 2, version: 02}
-  cache:rev-branch-cache -- {}
+  changegroup -- {nbchanges: 2, version: 02} (mandatory: True)
+  cache:rev-branch-cache -- {} (mandatory: True)
 
 Verbose output:
 
@@ -64,7 +64,7 @@
 
   $ hg debugbundle --all bundle2.hg
   Stream params: {}
-  changegroup -- {nbchanges: 2, version: 02}
+  changegroup -- {nbchanges: 2, version: 02} (mandatory: True)
       format: id, p1, p2, cset, delta base, len(delta)
   
       changelog
@@ -80,6 +80,6 @@
   
       c
       b80de5d138758541c5f05265ad144ab9fa86d1db 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 0000000000000000000000000000000000000000 0
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
 
   $ cd ..
diff --git a/tests/test-generaldelta.t b/tests/test-generaldelta.t
--- a/tests/test-generaldelta.t
+++ b/tests/test-generaldelta.t
@@ -159,10 +159,10 @@
   saved backup bundle to $TESTTMP/aggressive/.hg/strip-backup/1c5d4dc9a8b8-6c68e60c-backup.hg
   $ hg debugbundle .hg/strip-backup/*
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       1c5d4dc9a8b8d6e1750966d343e94db665e7a1e9
-  cache:rev-branch-cache -- {}
-  phase-heads -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  phase-heads -- {} (mandatory: True)
       1c5d4dc9a8b8d6e1750966d343e94db665e7a1e9 draft
 
   $ cd ..
diff --git a/tests/test-getbundle.t b/tests/test-getbundle.t
--- a/tests/test-getbundle.t
+++ b/tests/test-getbundle.t
@@ -170,7 +170,7 @@
   $ hg debuggetbundle repo bundle -t bundle2
   $ hg debugbundle bundle
   Stream params: {}
-  changegroup -- {version: 01}
+  changegroup -- {version: 01} (mandatory: True)
       7704483d56b2a7b5db54dcee7c62378ac629b348
       29a4d1f17bd3f0779ca0525bebb1cfb51067c738
       713346a995c363120712aed1aee7e04afd867638
diff --git a/tests/test-obsolete-changeset-exchange.t b/tests/test-obsolete-changeset-exchange.t
--- a/tests/test-obsolete-changeset-exchange.t
+++ b/tests/test-obsolete-changeset-exchange.t
@@ -93,15 +93,15 @@
   1 changesets found
   $ hg debugbundle ../f89bcc95eba5.hg
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
-  cache:rev-branch-cache -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
   $ hg debugbundle ../f89bcc95eba5-obs.hg
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
-  cache:rev-branch-cache -- {}
-  obsmarkers -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  obsmarkers -- {} (mandatory: True)
       version: 1 (70 bytes)
       9d73aac1b2ed7d53835eaeec212ed41ea47da53a f89bcc95eba5174b1ccc3e33a82e84c96e8338ee 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
 
diff --git a/tests/test-obsolete.t b/tests/test-obsolete.t
--- a/tests/test-obsolete.t
+++ b/tests/test-obsolete.t
@@ -1452,10 +1452,10 @@
   
   $ hg debugbundle .hg/strip-backup/e008cf283490-*-backup.hg
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       e008cf2834908e5d6b0f792a9d4b0e2272260fb8
-  cache:rev-branch-cache -- {}
-  phase-heads -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  phase-heads -- {} (mandatory: True)
       e008cf2834908e5d6b0f792a9d4b0e2272260fb8 draft
 
 #if repobundlerepo
@@ -1495,14 +1495,14 @@
   
   $ hg debugbundle .hg/strip-backup/e016b03fd86f-*-backup.hg
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 2, version: 02}
+  changegroup -- {nbchanges: 2, version: 02} (mandatory: True)
       e016b03fd86fcccc54817d120b90b751aaf367d6
       b0551702f918510f01ae838ab03a463054c67b46
-  cache:rev-branch-cache -- {}
-  obsmarkers -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  obsmarkers -- {} (mandatory: True)
       version: 1 (92 bytes)
       e008cf2834908e5d6b0f792a9d4b0e2272260fb8 b0551702f918510f01ae838ab03a463054c67b46 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '8', 'operation': 'amend', 'user': 'test'}
-  phase-heads -- {}
+  phase-heads -- {} (mandatory: True)
       b0551702f918510f01ae838ab03a463054c67b46 draft
 
   $ hg unbundle .hg/strip-backup/e016b03fd86f-*-backup.hg
diff --git a/tests/test-shelve.t b/tests/test-shelve.t
--- a/tests/test-shelve.t
+++ b/tests/test-shelve.t
@@ -1122,7 +1122,7 @@
   0 files updated, 0 files merged, 1 files removed, 0 files unresolved
   $ hg debugbundle .hg/shelved/*.hg
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       45993d65fe9dc3c6d8764b9c3b07fa831ee7d92d
   $ cd ..
 
diff --git a/tests/test-stream-bundle-v2.t b/tests/test-stream-bundle-v2.t
--- a/tests/test-stream-bundle-v2.t
+++ b/tests/test-stream-bundle-v2.t
@@ -46,7 +46,7 @@
   $ hg bundle -a --type="none-v2;stream=v2" bundle.hg
   $ hg debugbundle bundle.hg
   Stream params: {}
-  stream2 -- {bytecount: 1693, filecount: 11, requirements: dotencode%2Cfncache%2Cgeneraldelta%2Crevlogv1%2Cstore}
+  stream2 -- {bytecount: 1693, filecount: 11, requirements: dotencode%2Cfncache%2Cgeneraldelta%2Crevlogv1%2Cstore} (mandatory: True)
   $ hg debugbundle --spec bundle.hg
   none-v2;stream=v2;requirements%3Ddotencode%2Cfncache%2Cgeneraldelta%2Crevlogv1%2Cstore
 
diff --git a/tests/test-strip.t b/tests/test-strip.t
--- a/tests/test-strip.t
+++ b/tests/test-strip.t
@@ -210,10 +210,10 @@
   
   $ hg debugbundle .hg/strip-backup/*
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 1, version: 02}
+  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
       264128213d290d868c54642d13aeaa3675551a78
-  cache:rev-branch-cache -- {}
-  phase-heads -- {}
+  cache:rev-branch-cache -- {} (mandatory: True)
+  phase-heads -- {} (mandatory: True)
       264128213d290d868c54642d13aeaa3675551a78 draft
   $ hg unbundle .hg/strip-backup/*
   adding changesets
diff --git a/tests/test-tags.t b/tests/test-tags.t
--- a/tests/test-tags.t
+++ b/tests/test-tags.t
@@ -727,13 +727,13 @@
   4 changesets found
   $ hg debugbundle ./test-cache-in-bundle-all-rev.hg
   Stream params: {Compression: BZ}
-  changegroup -- {nbchanges: 4, version: 02}
+  changegroup -- {nbchanges: 4, version: 02} (mandatory: True)
       96ee1d7354c4ad7372047672c36a1f561e3a6a4c
       c4dab0c2fd337eb9191f80c3024830a4889a8f34
       f63cc8fe54e4d326f8d692805d70e092f851ddb1
       40f0358cb314c824a5929ee527308d90e023bc10
-  hgtagsfnodes -- {}
-  cache:rev-branch-cache -- {}
+  hgtagsfnodes -- {} (mandatory: True)
+  cache:rev-branch-cache -- {} (mandatory: True)
 
 Check that local clone includes cache data