histedit: pick an appropriate base changeset by default (BC)

Previously, `hg histedit` required a revision argument specifying which
revision to use as the base for the current histedit operation. There
was an undocumented and experimental "histedit.defaultrev" option that
supported defining a single revision to be used if no argument is
passed.

Mercurial knows what changesets can be edited. And in most scenarios,
people want to edit this history of everything on the current head that
is rewritable. Making histedit do this by default and not require
an explicit argument or additional configuration is a major usability
win and will enable more people to use histedit.

This patch changes the behavior of the experimental and undocumented
"histedit.defaultrev" config option to select an appropriate base
revision by default. Comprehensive tests exercising the edge cases
in the new, somewhat complicated default revset have been added.
Surprisingly, no tests broke. I guess we were never testing the
behavior with no ANCESTOR argument (it used to fail with
"abort: histedit requires exactly one ancestor revision"). The new
behavior is much more user friendly.

The functionality for choosing the default base revision has been
moved to destutil.py, where it can easily be modified by extensions.

hgext/histedit.py

@@ -149,6 +149,13 b' configuration file::'
 
   [histedit]
   linelen = 120      # truncate rule lines at 120 characters
+
+``hg histedit`` attempts to automatically choose an appropriate base
+revision to use. To change which base revision is used, define a
+revset in your configuration file::
+
+  [histedit]
+  defaultrev = only(.) & draft()
 """
 
 try:
@@ -166,6 +173,7 b' from mercurial import discovery'
 from mercurial import error
 from mercurial import copies
 from mercurial import context
+from mercurial import destutil
 from mercurial import exchange
 from mercurial import extensions
 from mercurial import hg
@@ -786,13 +794,19 b' def findoutgoing(ui, repo, remote=None, '
      ('f', 'force', False,
       _('force outgoing even for unrelated repositories')),
      ('r', 'rev', [], _('first revision to be edited'), _('REV'))],
-     _("ANCESTOR | --outgoing [URL]"))
+     _("[ANCESTOR] | --outgoing [URL]"))
 def histedit(ui, repo, *freeargs, **opts):
     """interactively edit changeset history
 
-    This command edits changesets between ANCESTOR and the parent of
+    This command edits changesets between an ANCESTOR and the parent of
     the working directory.
 
+    The value from the "histedit.defaultrev" config option is used as a
+    revset to select the base revision when ANCESTOR is not specified.
+    The first revision returned by the revset is used. By default, this
+    selects the editable history that is unique to the ancestry of the
+    working directory.
+
     With --outgoing, this edits changesets not found in the
     destination repository. If URL of the destination is omitted, the
     'default-push' (or 'default') path will be used.
@@ -917,10 +931,10 b' def _histedit(ui, repo, state, *freeargs'
         else:
             revs.extend(freeargs)
             if len(revs) == 0:
-                # experimental config: histedit.defaultrev
-                histeditdefault = ui.config('histedit', 'defaultrev')
-                if histeditdefault:
-                    revs.append(histeditdefault)
+                defaultrev = destutil.desthistedit(ui, repo)
+                if defaultrev is not None:
+                    revs.append(defaultrev)
+
             if len(revs) != 1:
                 raise error.Abort(
                     _('histedit requires exactly one ancestor revision'))

mercurial/destutil.py

@@ -198,3 +198,18 b' def destmerge(repo):'
     else:
         node = _destmergebranch(repo)
     return repo[node].rev()
+
+histeditdefaultrevset = 'reverse(only(.) and not public() and not ::merge())'
+
+def desthistedit(ui, repo):
+    """Default base revision to edit for `hg histedit`."""
+    default = ui.config('histedit', 'defaultrev', histeditdefaultrevset)
+    if default:
+        revs = repo.revs(default)
+        if revs:
+            # The revset supplied by the user may not be in ascending order nor
+            # take the first revision. So do this manually.
+            revs.sort()
+            return revs.first()
+
+    return None

tests/test-histedit-arguments.t

@@ -347,3 +347,101 b' Histedit state has been exited'
   commit: 1 added, 1 unknown (new branch head)
   update: 4 new changesets (update)
 
+  $ cd ..
+
+Set up default base revision tests
+
+  $ hg init defaultbase
+  $ cd defaultbase
+  $ touch foo
+  $ hg -q commit -A -m root
+  $ echo 1 > foo
+  $ hg commit -m 'public 1'
+  $ hg phase --force --public -r .
+  $ echo 2 > foo
+  $ hg commit -m 'draft after public'
+  $ hg -q up -r 1
+  $ echo 3 > foo
+  $ hg commit -m 'head 1 public'
+  created new head
+  $ hg phase --force --public -r .
+  $ echo 4 > foo
+  $ hg commit -m 'head 1 draft 1'
+  $ echo 5 > foo
+  $ hg commit -m 'head 1 draft 2'
+  $ hg -q up -r 2
+  $ echo 6 > foo
+  $ hg commit -m 'head 2 commit 1'
+  $ echo 7 > foo
+  $ hg commit -m 'head 2 commit 2'
+  $ hg -q up -r 2
+  $ echo 8 > foo
+  $ hg commit -m 'head 3'
+  created new head
+  $ hg -q up -r 2
+  $ echo 9 > foo
+  $ hg commit -m 'head 4'
+  created new head
+  $ hg merge --tool :local -r 8
+  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg commit -m 'merge head 3 into head 4'
+  $ echo 11 > foo
+  $ hg commit -m 'commit 1 after merge'
+  $ echo 12 > foo
+  $ hg commit -m 'commit 2 after merge'
+
+  $ hg log -G -T '{rev}:{node|short} {phase} {desc}\n'
+  @  12:8cde254db839 draft commit 2 after merge
+  |
+  o  11:6f2f0241f119 draft commit 1 after merge
+  |
+  o    10:90506cc76b00 draft merge head 3 into head 4
+  |\
+  | o  9:f8607a373a97 draft head 4
+  | |
+  o |  8:0da92be05148 draft head 3
+  |/
+  | o  7:4c35cdf97d5e draft head 2 commit 2
+  | |
+  | o  6:931820154288 draft head 2 commit 1
+  |/
+  | o  5:8cdc02b9bc63 draft head 1 draft 2
+  | |
+  | o  4:463b8c0d2973 draft head 1 draft 1
+  | |
+  | o  3:23a0c4eefcbf public head 1 public
+  | |
+  o |  2:4117331c3abb draft draft after public
+  |/
+  o  1:4426d359ea59 public public 1
+  |
+  o  0:54136a8ddf32 public root
+  
+
+Default base revision should stop at public changesets
+
+  $ hg -q up 8cdc02b9bc63
+  $ hg histedit --commands - <<EOF
+  > pick 463b8c0d2973
+  > pick 8cdc02b9bc63
+  > EOF
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+Default base revision should stop at branchpoint
+
+  $ hg -q up 4c35cdf97d5e
+  $ hg histedit --commands - <<EOF
+  > pick 931820154288
+  > pick 4c35cdf97d5e
+  > EOF
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+Default base revision should stop at merge commit
+
+  $ hg -q up 8cde254db839
+  $ hg histedit --commands - <<EOF
+  > pick 6f2f0241f119
+  > pick 8cde254db839
+  > EOF
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved