[PATCH] git.c: add --index-file command-line option.

[Manlio Perillo <manlio.perillo@gmail.com>]

Unlike other environment variables (e.g. GIT_WORK_TREE,
GIT_NAMESPACE), it was not possible to set the GIT_INDEX_FILE
environment variable using the command line.

Add a new --index-file command-line option.

Update the t7500-commit test to include --index-file option coverage.
The tests have been adapted from the existing
'using alternate GIT_INDEX_FILE (1)' and
'using alternate GIT_INDEX_FILE (2)' tests.

Signed-off-by: Manlio Perillo <manlio.perillo@gmail.com>
---
 Documentation/git.txt | 10 +++++++++-
 git.c                 | 17 ++++++++++++++++-
 t/t7500-commit.sh     | 29 +++++++++++++++++++++++++++++
 3 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index e643683..5a582dd 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -12,7 +12,8 @@ SYNOPSIS
 'git' [--version] [--help] [-c <name>=<value>]
     [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
     [-p|--paginate|--no-pager] [--no-replace-objects] [--bare]
-    [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
+    [--git-dir=<path>] [--work-tree=<path>] [--index-file=<path>]
+    [--namespace=<name>]
     <command> [<args>]
 
 DESCRIPTION
@@ -408,6 +409,12 @@ help ...`.
 	variable (see core.worktree in linkgit:git-config[1] for a
 	more detailed discussion).
 
+--index-file=<path>::
+	Set the path to the index file. It can be an absolute path
+	or a path relative to the current working directory.
+	This can also be controlled by setting the GIT_INDEX_FILE
+	environment variable.
+
 --namespace=<path>::
 	Set the git namespace.  See linkgit:gitnamespaces[7] for more
 	details.  Equivalent to setting the `GIT_NAMESPACE` environment
@@ -632,6 +639,7 @@ git so take care if using Cogito etc.
 	This environment allows the specification of an alternate
 	index file. If not specified, the default of `$GIT_DIR/index`
 	is used.
+	The '--index-file command-line option also sets this value.
 
 'GIT_OBJECT_DIRECTORY'::
 	If the object storage directory is specified via this
diff --git a/git.c b/git.c
index d33f9b3..b0f473d 100644
--- a/git.c
+++ b/git.c
@@ -8,7 +8,8 @@
 const char git_usage_string[] =
 	"git [--version] [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]\n"
 	"           [-p|--paginate|--no-pager] [--no-replace-objects] [--bare]\n"
-	"           [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]\n"
+	"           [--git-dir=<path>] [--work-tree=<path>] [--index-file=<path>]\n"
+	"           [--namespace=<name>]\n"
 	"           [-c name=value] [--help]\n"
 	"           <command> [<args>]";
 
@@ -121,6 +122,20 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			setenv(GIT_WORK_TREE_ENVIRONMENT, cmd + 12, 1);
 			if (envchanged)
 				*envchanged = 1;
+		} else if (!strcmp(cmd, "--index-file")) {
+			if (*argc < 2) {
+				fprintf(stderr, "No path given for --index-file.\n" );
+				usage(git_usage_string);
+			}
+			setenv(INDEX_ENVIRONMENT, (*argv)[1], 1);
+			if (envchanged)
+				*envchanged = 1;
+			(*argv)++;
+			(*argc)--;
+		} else if (!prefixcmp(cmd, "--index-file=")) {
+			setenv(INDEX_ENVIRONMENT, cmd + 13, 1);
+			if (envchanged)
+				*envchanged = 1;
 		} else if (!strcmp(cmd, "--bare")) {
 			static char git_dir[PATH_MAX+1];
 			is_bare_repository_cfg = 1;
diff --git a/t/t7500-commit.sh b/t/t7500-commit.sh
index 1c908f4..c405a78 100755
--- a/t/t7500-commit.sh
+++ b/t/t7500-commit.sh
@@ -168,6 +168,35 @@ test_expect_success 'using alternate GIT_INDEX_FILE (2)' '
 	cmp .git/index saved-index >/dev/null
 '
 
+test_expect_success 'using alternate --index-file (1)' '
+
+	cp .git/index saved-index &&
+	(
+		echo some new content >file &&
+		index_file=.git/another_index &&
+		git --index-file=$index_file add file &&
+		git --index-file=$index_file commit -m "commit using another index" &&
+		git --index-file=$index_file diff-index --exit-code HEAD &&
+		git --index-file=$index_file diff-files --exit-code
+	) &&
+	cmp .git/index saved-index >/dev/null
+
+'
+
+test_expect_success 'using alternate --index-file (2)' '
+
+	cp .git/index saved-index &&
+	(
+		rm -f .git/no-such-index &&
+		index_file=.git/no-such-index &&
+		git --index-file=$index_file commit -m "commit using nonexistent index" &&
+		test -z "$(git --index-file=$index_file ls-files)" &&
+		test -z "$(git --index-file=$index_file ls-tree HEAD)"
+
+	) &&
+	cmp .git/index saved-index >/dev/null
+'
+
 cat > expect << EOF
 zort
 
-- 
1.8.1.rc1.17.g75ed918.dirty