commit: warn the user when a commit already exists

Sometimes, a commit will result in an exact match of a preexisting
commit, and if that commit isn't a branch head, hg will incorrectly
note that it created a new head. Instead, we should warn the user that
commit already existed in the repository.

In practice, this bug is rather uncommon, and will only occur when the
usr explicitly sets the date.

Please note that this commit contains an API change to
cmdutil.commitstatus()

Differential Revision: https://phab.mercurial-scm.org/D9257

mercurial/cmdutil.py

@@ -3089,13 +3089,18 b' def buildcommittext(repo, ctx, subs, ext'
     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

mercurial/commands.py

@@ -850,11 +850,14 b' def _dobackout(ui, repo, node=None, rev='
             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))
@@ -2022,6 +2025,7 b' def _docommit(ui, repo, *pats, **opts):'
 
     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'):
@@ -2111,7 +2115,7 b' def _docommit(ui, repo, *pats, **opts):'
                 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(

tests/test-backout.t

@@ -819,5 +819,5 b' Ensure that backout out the same changes'
   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

tests/test-merge-tools.t

@@ -1868,6 +1868,7 b' Verify naming of temporary files and tha'
   $ 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' \

tests/test-phases.t

@@ -1010,7 +1010,7 b' draft:'
   $ 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 b' Same, but for secret:'
   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 b' But what about obsoleted changesets?'
   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

tests/test-remotefilelog-local.t

@@ -204,5 +204,6 b''
   $ 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

tests/test-unamend.t

@@ -405,8 +405,10 b' Rename a->b, then amend b->c, and workin'
   $ 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 .