patchhg-to-git: handle an empty dir in hg by combining git commits

diff --git a/contrib/hg-to-git/hg-to-git.py b/contrib/hg-to-git/hg-to-git.py
index 6bff49b..06e1b41 100755
--- a/contrib/hg-to-git/hg-to-git.py
+++ b/contrib/hg-to-git/hg-to-git.py
@@ -139,6 +139,7 @@ if not hgvers.has_key("0"):
     os.system('git-init-db')
 
 # loop through every hg changeset
+previous_comment = None
 for cset in range(int(tip) + 1):
 
     # incremental, already seen
@@ -159,6 +160,8 @@ for cset in range(int(tip) + 1):
 
     (fdcomment, filecomment) = tempfile.mkstemp()
     csetcomment = os.popen('hg log -r %d -v | grep -v ^changeset: | grep -v ^parent: | grep -v ^user: | grep -v ^date | grep -v ^files: | grep -v ^description: | grep -v ^tag: | grep -v ^branch:' % cset).read().strip()
+    if (previous_comment):
+	csetcomment += previous_comment
     os.write(fdcomment, csetcomment)
     os.close(fdcomment)
 
@@ -181,8 +184,8 @@ for cset in range(int(tip) + 1):
         print 'tag:', tag
     print '-----------------------------------------'
 
-    # checkout the parent if necessary
-    if cset != 0:
+    # checkout the parent if there is a repo to checkout from
+    if hgvers.has_key("0"):
         if hgbranch[str(cset)] == "branch-" + str(cset):
             print 'creating new branch', hgbranch[str(cset)]
             os.system('git-checkout -b %s %s' % (hgbranch[str(cset)], hgvers[parent]))
@@ -210,6 +213,14 @@ for cset in range(int(tip) + 1):
     # delete removed files
     os.system('git-ls-files -x .hg --deleted | git-update-index --remove --stdin')
 
+    # is there something that git will commit (maybe just empty dir was added)
+    stat = os.system('git-status -a')
+    if (stat != 0):
+	print "No changes git notices, will combine log with next commit (maybe empty dir?)"
+	previous_comment = "\n\n--- hg-to-git merged commit ---\n\n" + csetcomment
+	continue
+    previous_comment = None
+
     # commit
     os.system(getgitenv(user, date) + 'git-commit -a -F %s' % filecomment)
     os.unlink(filecomment)

Documentation/git-commit.txt, builtin-commit.c

diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
index d4bfd49..a7ef71f 100644
--- a/Documentation/git-commit.txt
+++ b/Documentation/git-commit.txt
@@ -10,7 +10,7 @@ SYNOPSIS
 [verse]
 'git-commit' [-a | --interactive] [-s] [-v] [-u]
 	   [(-c | -C) <commit> | -F <file> | -m <msg> | --amend]
-	   [--no-verify] [-e] [--author <author>]
+	   [--allow-empty] [--no-verify] [-e] [--author <author>]
 	   [--] [[-i | -o ]<file>...]
 
 DESCRIPTION
@@ -89,6 +89,12 @@ OPTIONS
 	This option bypasses the pre-commit hook.
 	See also link:hooks.html[hooks].
 
+--allow-empty::
+	Usually recording a commit that has the exact same tree as its
+	sole parent commit and the command prevents you from making such
+	a mistake.  This option bypasses the safety, and is primarily
+	for use by foreign scm interface scripts.
+
 -e|--edit::
 	The message taken from file with `-F`, command line with
 	`-m`, and from file with `-C` are usually used as the
diff --git a/builtin-commit.c b/builtin-commit.c
index 6c2dc39..e635d99 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -46,7 +46,7 @@ static enum {
 static char *logfile, *force_author, *template_file;
 static char *edit_message, *use_message;
 static int all, edit_flag, also, interactive, only, amend, signoff;
-static int quiet, verbose, untracked_files, no_verify;
+static int quiet, verbose, untracked_files, no_verify, allow_empty;
 
 static int no_edit, initial_commit, in_merge;
 const char *only_include_assumed;
@@ -87,6 +87,7 @@ static struct option builtin_commit_options[] = {
 	OPT_BOOLEAN('n', "no-verify", &no_verify, "bypass pre-commit hook"),
 	OPT_BOOLEAN(0, "amend", &amend, "amend previous commit"),
 	OPT_BOOLEAN(0, "untracked-files", &untracked_files, "show all untracked files"),
+	OPT_BOOLEAN(0, "allow-empty", &allow_empty, "ok to record an empty change"),
 
 	OPT_END()
 };
@@ -710,7 +711,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	}
 
 	if (!prepare_log_message(index_file, prefix) && !in_merge &&
-	    !(amend && is_a_merge(head_sha1))) {
+	    !allow_empty && !(amend && is_a_merge(head_sha1))) {
 		run_status(stdout, index_file, prefix);
 		rollback_index_files();
 		unlink(commit_editmsg);

Documentation/git-commit.txt, git-commit.sh, t/t7501-commit.sh

diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
index d4bfd49..a7ef71f 100644
--- a/Documentation/git-commit.txt
+++ b/Documentation/git-commit.txt
@@ -10,7 +10,7 @@ SYNOPSIS
 [verse]
 'git-commit' [-a | --interactive] [-s] [-v] [-u]
 	   [(-c | -C) <commit> | -F <file> | -m <msg> | --amend]
-	   [--no-verify] [-e] [--author <author>]
+	   [--allow-empty] [--no-verify] [-e] [--author <author>]
 	   [--] [[-i | -o ]<file>...]
 
 DESCRIPTION
@@ -89,6 +89,12 @@ OPTIONS
 	This option bypasses the pre-commit hook.
 	See also link:hooks.html[hooks].
 
+--allow-empty::
+	Usually recording a commit that has the exact same tree as its
+	sole parent commit and the command prevents you from making such
+	a mistake.  This option bypasses the safety, and is primarily
+	for use by foreign scm interface scripts.
+
 -e|--edit::
 	The message taken from file with `-F`, command line with
 	`-m`, and from file with `-C` are usually used as the
diff --git a/git-commit.sh b/git-commit.sh
index cef76a7..2c4a406 100755
--- a/git-commit.sh
+++ b/git-commit.sh
@@ -74,6 +74,7 @@ trap '
 
 all=
 also=
+allow_empty=f
 interactive=
 only=
 logfile=
@@ -114,6 +115,10 @@ do
 	-a|--a|--al|--all)
 		all=t
 		;;
+	--allo|--allow|--allow-|--allow-e|--allow-em|--allow-emp|\
+	--allow-empt|--allow-empty)
+		allow_empty=t
+		;;
 	--au=*|--aut=*|--auth=*|--autho=*|--author=*)
 		force_author="${1#*=}"
 		;;
@@ -515,9 +520,11 @@ else
 	# we need to check if there is anything to commit
 	run_status >/dev/null
 fi
-case "$?,$PARENTS" in
-0,* | *,-p' '?*-p' '?*)
-	# a merge commit can record the same tree as its parent.
+case "$allow_empty,$?,$PARENTS" in
+t,* | ?,0,* | ?,*,-p' '?*-p' '?*)
+	# an explicit --allow-empty, or a merge commit can record the
+	# same tree as its parent.  Otherwise having commitable paths
+	# is required.
 	;;
 *)
 	rm -f "$GIT_DIR/COMMIT_EDITMSG" "$GIT_DIR/SQUASH_MSG"
diff --git a/t/t7501-commit.sh b/t/t7501-commit.sh
index 2e7bcb0..0316ecf 100755
--- a/t/t7501-commit.sh
+++ b/t/t7501-commit.sh
@@ -256,6 +256,13 @@ test_expect_success 'same tree (single parent)' '
 
 '
 
+test_expect_success 'same tree (single parent) --allow-empty' '
+
+	git commit --allow-empty -m "forced empty" &&
+	git cat-file commit HEAD | grep forced
+
+'
+
 test_expect_success 'same tree (merge and amend merge)' '
 
 	git checkout -b side HEAD^ &&

diff --git a/contrib/hg-to-git/hg-to-git.py b/contrib/hg-to-git/hg-to-git.py
index 7a1c3e4..9befb92 100755
--- a/contrib/hg-to-git/hg-to-git.py
+++ b/contrib/hg-to-git/hg-to-git.py
@@ -211,7 +211,7 @@ for cset in range(int(tip) + 1):
     os.system('git-ls-files -x .hg --deleted | git-update-index --remove --stdin')
 
     # commit
-    os.system(getgitenv(user, date) + 'git-commit -a -F %s' % filecomment)
+    os.system(getgitenv(user, date) + 'git commit --allow-empty -a -F %s' % filecomment)
     os.unlink(filecomment)
 
     # tag