[PATCH v4] commit: add a commit.allowEmpty config variable

[Tanushree Tumane <tanushreetumane@gmail.com>]

From: tanushree27 <tanushreetumane@gmail.com>

when we cherrypick an existing commit it doesn't change anything and
therefore it fails prompting to reset (skip commit) or commit using
--allow-empty attribute and then continue.

Add commit.allowEmpty configuration variable as a convenience to skip
this process.

Add tests to check the behavior introduced by this commit.

This closes https://github.com/git-for-windows/git/issues/1854

Signed-off-by: tanushree27 <tanushreetumane@gmail.com>
Signed-off-by: Tanushree Tumane <tanushreetumane@gmail.com>
---
 Documentation/config.txt     |  5 +++++
 Documentation/git-commit.txt |  3 ++-
 builtin/commit.c             |  8 ++++++++
 t/t3500-cherry.sh            | 10 ++++++++++
 4 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index c0727b7866..f3828518a5 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1467,6 +1467,11 @@ commit.verbose::
 	A boolean or int to specify the level of verbose with `git commit`.
 	See linkgit:git-commit[1].
 
+commit.allowEmpty::
+	A boolean to specify whether empty commits are allowed with `git
+	commit`. See linkgit:git-commit[1]. 
+	Defaults to false.
+
 credential.helper::
 	Specify an external helper to be called when a username or
 	password credential is needed; the helper may consult external
diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
index f970a43422..5d3bbf017a 100644
--- a/Documentation/git-commit.txt
+++ b/Documentation/git-commit.txt
@@ -176,7 +176,8 @@ The `-m` option is mutually exclusive with `-c`, `-C`, and `-F`.
 	Usually recording a commit that has the exact same tree as its
 	sole parent commit is a mistake, and the command prevents you
 	from making such a commit.  This option bypasses the safety, and
-	is primarily for use by foreign SCM interface scripts.
+	is primarily for use by foreign SCM interface scripts. See
+	`commit.allowEmpty` in linkgit:git-config[1].
 
 --allow-empty-message::
        Like --allow-empty this command is primarily for use by foreign
diff --git a/builtin/commit.c b/builtin/commit.c
index 67fa949204..4516309ac2 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -101,6 +101,7 @@ static int all, also, interactive, patch_interactive, only, amend, signoff;
 static int edit_flag = -1; /* unspecified */
 static int quiet, verbose, no_verify, allow_empty, dry_run, renew_authorship;
 static int config_commit_verbose = -1; /* unspecified */
+static int config_commit_allow_empty = -1; /* unspecified */
 static int no_post_rewrite, allow_empty_message;
 static char *untracked_files_arg, *force_date, *ignore_submodule_arg, *ignored_arg;
 static char *sign_commit;
@@ -1435,6 +1436,10 @@ static int git_commit_config(const char *k, const char *v, void *cb)
 		config_commit_verbose = git_config_bool_or_int(k, v, &is_bool);
 		return 0;
 	}
+	if (!strcmp(k, "commit.allowempty")) {
+		config_commit_allow_empty = git_config_bool(k, v);
+		return 0;
+	}
 
 	status = git_gpg_config(k, v, NULL);
 	if (status)
@@ -1556,6 +1561,9 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	if (verbose == -1)
 		verbose = (config_commit_verbose < 0) ? 0 : config_commit_verbose;
 
+	if (config_commit_allow_empty >= 0)  /* if allowEmpty is allowed in config*/
+		allow_empty = config_commit_allow_empty;
+	
 	if (dry_run)
 		return dry_run_commit(argc, argv, prefix, current_head, &s);
 	index_file = prepare_index(argc, argv, prefix, current_head, 0);
diff --git a/t/t3500-cherry.sh b/t/t3500-cherry.sh
index f038f34b7c..11504e2d9f 100755
--- a/t/t3500-cherry.sh
+++ b/t/t3500-cherry.sh
@@ -55,4 +55,14 @@ test_expect_success \
      expr "$(echo $(git cherry master my-topic-branch) )" : "+ [^ ]* - .*"
 '
 
+
+# Tests for commit.allowEmpty config
+
+test_expect_success 'cherry-pick existing commit with commit.allowEmpty' '
+    test_tick &&
+	test_commit "first" &&
+	test_commit "second" &&
+	git -c commit.allowEmpty=true cherry-pick HEAD~1
+'
+
 test_done
-- 
2.19.1.windows.1.495.g7e9d1c442b.dirty