--- a/mercurial/cmdutil.py	Tue Oct 06 13:34:51 2020 +0200
+++ b/mercurial/cmdutil.py	Thu Oct 29 13:54:25 2020 +0100
@@ -3113,13 +3113,18 @@
     return b"\n".join(edittext)
 
 
-def commitstatus(repo, node, branch, bheads=None, opts=None):
+def commitstatus(repo, node, branch, bheads=None, tip=None, opts=None):
     if opts is None:
         opts = {}
     ctx = repo[node]
     parents = ctx.parents()
 
-    if (
+    if tip is not None and repo.changelog.tip() == tip:
+        # avoid reporting something like "committed new head" when
+        # recommitting old changesets, and issue a helpful warning
+        # for most instances
+        repo.ui.warn(_("warning: commit already existed in the repository!\n"))
+    elif (
         not opts.get(b'amend')
         and bheads
         and node not in bheads

--- a/mercurial/commands.py	Tue Oct 06 13:34:51 2020 +0200
+++ b/mercurial/commands.py	Thu Oct 29 13:54:25 2020 +0100
@@ -851,11 +851,14 @@
             message, opts.get(b'user'), opts.get(b'date'), match, editor=e
         )
 
+    # save to detect changes
+    tip = repo.changelog.tip()
+
     newnode = cmdutil.commit(ui, repo, commitfunc, [], opts)
     if not newnode:
         ui.status(_(b"nothing changed\n"))
         return 1
-    cmdutil.commitstatus(repo, newnode, branch, bheads)
+    cmdutil.commitstatus(repo, newnode, branch, bheads, tip)
 
     def nice(node):
         return b'%d:%s' % (repo.changelog.rev(node), short(node))
@@ -2024,6 +2027,7 @@
 
     branch = repo[None].branch()
     bheads = repo.branchheads(branch)
+    tip = repo.changelog.tip()
 
     extra = {}
     if opts.get(b'close_branch') or opts.get(b'force_close_branch'):
@@ -2113,7 +2117,7 @@
                 ui.status(_(b"nothing changed\n"))
             return 1
 
-    cmdutil.commitstatus(repo, node, branch, bheads, opts)
+    cmdutil.commitstatus(repo, node, branch, bheads, tip, opts)
 
     if not ui.quiet and ui.configbool(b'commands', b'commit.post-status'):
         status(

--- a/tests/test-backout.t	Tue Oct 06 13:34:51 2020 +0200
+++ b/tests/test-backout.t	Thu Oct 29 13:54:25 2020 +0100
@@ -819,5 +819,5 @@
   1 files updated, 0 files merged, 1 files removed, 0 files unresolved
   $ hg backout 2
   removing 3
-  created new head
+  warning: commit already existed in the repository!
   changeset 3:8f188de730d9 backs out changeset 2:cccc23d9d68f

--- a/tests/test-merge-tools.t	Tue Oct 06 13:34:51 2020 +0200
+++ b/tests/test-merge-tools.t	Thu Oct 29 13:54:25 2020 +0100
@@ -1868,6 +1868,7 @@
   $ hg update -q -C 1
   $ hg mv f f.txt
   $ hg ci -qm "f.txt"
+  warning: commit already existed in the repository!
   $ hg update -q -C 2
   $ hg merge -y -r tip --tool echo \
   >    --config merge-tools.echo.args='$base $local $other $output' \

--- a/tests/test-phases.t	Tue Oct 06 13:34:51 2020 +0200
+++ b/tests/test-phases.t	Thu Oct 29 13:54:25 2020 +0100
@@ -1010,7 +1010,7 @@
   $ hg up -C 1
   0 files updated, 0 files merged, 4 files removed, 0 files unresolved
   $ mkcommit C
-  created new head
+  warning: commit already existed in the repository!
   $ hg phase -r 2
   2: public
 
@@ -1027,6 +1027,7 @@
   7: draft
   $ mkcommit F
   test-debug-phase: new rev 8:  x -> 2
+  warning: commit already existed in the repository!
   test-hook-close-phase: de414268ec5ce2330c590b942fbb5ff0b0ca1a0a:   -> secret
   $ hg phase -r tip
   8: secret
@@ -1037,7 +1038,7 @@
   0 files updated, 0 files merged, 2 files removed, 0 files unresolved
   $ mkcommit H
   test-debug-phase: new rev 5:  x -> 2
-  created new head
+  warning: commit already existed in the repository!
   test-hook-close-phase: a030c6be5127abc010fcbff1851536552e6951a8:   -> secret
   $ hg phase -r 5
   5: secret

--- a/tests/test-remotefilelog-local.t	Tue Oct 06 13:34:51 2020 +0200
+++ b/tests/test-remotefilelog-local.t	Thu Oct 29 13:54:25 2020 +0100
@@ -204,5 +204,6 @@
   $ hg update -r '.^' -q
   $ echo 1 > A
   $ hg commit -m foo -A A
+  warning: commit already existed in the repository!
   $ hg log -r . -T '{node}\n'
   383ce605500277f879b7460a16ba620eb6930b7f

--- a/tests/test-unamend.t	Tue Oct 06 13:34:51 2020 +0200
+++ b/tests/test-unamend.t	Thu Oct 29 13:54:25 2020 +0100
@@ -405,8 +405,10 @@
   $ hg co -q 0
   $ hg mv a b
   $ hg ci -qm 'move to a b'
+  warning: commit already existed in the repository!
   $ hg mv b c
   $ hg amend
+  warning: commit already existed in the repository!
   $ hg mv c d
   $ hg unamend
   $ hg st --copies --change .