subrepo: avoids empty commit when .hgsubstate is dirty (issue2403)

This patch avoids empty commit when .hgsubstate is dirty. Empty commit
was caused by .hgsubstate being updated back to the state of the
working copy parent when committing, if a user had changed it manually
and not made any changes in subrepositories.

The subrepository state from the working copies parent is compared
with the state calculated as a result of trying to commit the
subrepositories. If the two states are the same, then return None
otherwise the commit is just done.

The line: "committing subrepository x" will be written if there is
nothing committed, but .hgsubstate is dirty for x subrepository.

tests/test-subrepo-empty-commit.t

@@ -0,0 +1,64 b''
+  $ hg init
+  $ hg init sub
+  $ echo 'sub = sub' > .hgsub
+  $ hg add .hgsub
+  $ echo c1 > f1
+  $ echo c2 > sub/f2
+  $ hg add -S
+  adding f1
+  adding sub/f2
+  $ hg commit -m0
+  committing subrepository sub
+
+Make .hgsubstate dirty:
+
+  $ echo '0000000000000000000000000000000000000000 sub' > .hgsubstate
+  $ hg diff --nodates
+  diff -r 853ea21970bb .hgsubstate
+  --- a/.hgsubstate
+  +++ b/.hgsubstate
+  @@ -1,1 +1,1 @@
+  -5bbc614a5b06ad7f3bf7c2463d74b005324f34c1 sub
+  +0000000000000000000000000000000000000000 sub
+
+trying to do an empty commit:
+
+  $ hg commit -m1
+  committing subrepository sub
+  nothing changed
+  [1]
+
+an okay update of .hgsubstate
+  $ cd sub
+  $ echo c3 > f2
+  $ hg commit -m "Sub commit"
+  $ cd ..
+  $ hg commit -m "Updated sub"
+  committing subrepository sub
+
+deleting again:
+  $ echo '' > .hgsub
+  $ hg commit -m2
+  $ cat .hgsub
+  
+  $ cat .hgsubstate
+
+an okay commit, but with a dirty .hgsubstate
+  $ echo 'sub = sub' > .hgsub
+  $ hg commit -m3
+  committing subrepository sub
+  $ echo '0000000000000000000000000000000000000000 sub' > .hgsubstate
+  $ hg diff --nodates
+  diff -r 41e1dee3d5d9 .hgsubstate
+  --- a/.hgsubstate
+  +++ b/.hgsubstate
+  @@ -1,1 +1,1 @@
+  -fe0229ee9a0a38b43163c756bb51b94228b118e7 sub
+  +0000000000000000000000000000000000000000 sub
+  $ echo c4 > f3
+  $ hg add f3
+  $ hg status 
+  M .hgsubstate
+  A f3
+  $ hg commit -m4
+  committing subrepository sub

mercurial/localrepo.py

@@ -949,6 +949,7 b' class localrepository(repo.repository):'
 
             # commit subs
             if subs or removedsubs:
+                pstate = subrepo.substate(self['.'])
                 state = wctx.substate.copy()
                 for s in sorted(subs):
                     sub = wctx.sub(s)
@@ -956,7 +957,19 b' class localrepository(repo.repository):'
                         subrepo.subrelpath(sub))
                     sr = sub.commit(cctx._text, user, date)
                     state[s] = (state[s][0], sr)
-                subrepo.writestate(self, state)
+
+                changed = False
+                if len(pstate) != len(state):
+                    changed = True
+                if not changed:
+                    for newstate in state:
+                        if state[newstate][1] != pstate[newstate]:
+                            changed = True
+                if changed:
+                    subrepo.writestate(self, state)
+                elif (changes[0] == ['.hgsubstate'] and changes[1] == [] and
+                     changes[2] == []):
+                    return None
 
             # Save commit message in case this transaction gets rolled back
             # (e.g. by a pretxncommit hook).  Leave the content alone on

mercurial/subrepo.py

@@ -13,6 +13,19 b' hg = None'
 
 nullstate = ('', '', 'empty')
 
+
+def substate(ctx):
+    rev = {}
+    if '.hgsubstate' in ctx:
+        try:
+            for l in ctx['.hgsubstate'].data().splitlines():
+                revision, path = l.split(" ", 1)
+                rev[path] = revision
+        except IOError as err:
+            if err.errno != errno.ENOENT:
+                raise
+    return rev
+
 def state(ctx, ui):
     """return a state dict, mapping subrepo paths configured in .hgsub
     to tuple: (source from .hgsub, revision from .hgsubstate, kind
@@ -39,15 +52,7 b' def state(ctx, ui):'
     for path, src in ui.configitems('subpaths'):
         p.set('subpaths', path, src, ui.configsource('subpaths', path))
 
-    rev = {}
-    if '.hgsubstate' in ctx:
-        try:
-            for l in ctx['.hgsubstate'].data().splitlines():
-                revision, path = l.split(" ", 1)
-                rev[path] = revision
-        except IOError, err:
-            if err.errno != errno.ENOENT:
-                raise
+    rev = substate(ctx)
 
     state = {}
     for path, src in p[''].items():