histedit: select the lowest rev when looking for a root in a revset (bc)

When we specify a revision or a revset we just get the last element from the
list. For revsets this can lead to unintended effects where you specify a
revset like only() but instead histedit selects the highest revision in the
set as root. Therefore we should always use the lowest revision number as
root.

hgext/histedit.py

@@ -158,7 +158,6 b' from mercurial import context'
 from mercurial import hg
 from mercurial import node
 from mercurial import repair
-from mercurial import scmutil
 from mercurial import util
 from mercurial import obsolete
 from mercurial import merge as mergemod
@@ -568,8 +567,11 b' def _histedit(ui, repo, *freeargs, **opt'
                 remote = None
             root = findoutgoing(ui, repo, remote, force, opts)
         else:
-            root = revs[0]
-            root = scmutil.revsingle(repo, root).node()
+            rootrevs = list(repo.set('roots(%lr)', revs))
+            if len(rootrevs) != 1:
+                raise util.Abort(_('The specified revisions must have ' +
+                    'exactly one common root'))
+            root = rootrevs[0].node()
 
         keep = opts.get('keep', False)
         revs = between(repo, root, topmost, keep)

tests/test-histedit-arguments.t

@@ -72,6 +72,26 b' Run on a revision not ancestors of the c'
   [255]
   $ hg up --quiet
 
+
+Test that we pick the minimum of a revrange
+---------------------------------------
+
+  $ HGEDITOR=cat hg histedit '2::' --commands - << EOF
+  > pick eb57da33312f 2 three
+  > pick c8e68270e35a 3 four
+  > pick 08d98a8350f3 4 five
+  > EOF
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg up --quiet
+
+  $ HGEDITOR=cat hg histedit 'tip:2' --commands - << EOF
+  > pick eb57da33312f 2 three
+  > pick c8e68270e35a 3 four
+  > pick 08d98a8350f3 4 five
+  > EOF
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg up --quiet
+
 Run on a revision not descendants of the initial parent
 --------------------------------------------------------------------
 
@@ -198,3 +218,12 b' short hash. This tests issue3893.'
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
   saved backup bundle to $TESTTMP/foo/.hg/strip-backup/*-backup.hg (glob)
+
+  $ hg update -q 2
+  $ echo x > x
+  $ hg add x
+  $ hg commit -m'x' x
+  created new head
+  $ hg histedit -r 'heads(all())'
+  abort: The specified revisions must have exactly one common root
+  [255]