thodg/libgit2

diff --git a/include/git2/repository.h b/include/git2/repository.h
index 18e515c..2687826 100644
--- a/include/git2/repository.h
+++ b/include/git2/repository.h
@@ -196,6 +196,8 @@ GIT_EXTERN(int) git_repository_init(
  *        looking the "template_path" from the options if set, or the
  *        `init.templatedir` global config if not, or falling back on
  *        "/usr/share/git-core/templates" if it exists.
+ * * GIT_REPOSITORY_INIT_RELATIVE_GITLINK - If an alternate workdir is
+ *        specified, use relative paths for the gitdir and core.worktree.
  */
 typedef enum {
 	GIT_REPOSITORY_INIT_BARE              = (1u << 0),
@@ -204,6 +206,7 @@ typedef enum {
 	GIT_REPOSITORY_INIT_MKDIR             = (1u << 3),
 	GIT_REPOSITORY_INIT_MKPATH            = (1u << 4),
 	GIT_REPOSITORY_INIT_EXTERNAL_TEMPLATE = (1u << 5),
+	GIT_REPOSITORY_INIT_RELATIVE_GITLINK  = (1u << 6),
 } git_repository_init_flag_t;
 
 /**
diff --git a/include/git2/submodule.h b/include/git2/submodule.h
index 864d1c5..616890d 100644
--- a/include/git2/submodule.h
+++ b/include/git2/submodule.h
@@ -471,6 +471,24 @@ GIT_EXTERN(git_submodule_recurse_t) git_submodule_set_fetch_recurse_submodules(
 GIT_EXTERN(int) git_submodule_init(git_submodule *submodule, int overwrite);
 
 /**
+ * Set up the subrepository for a submodule in preparation for clone.
+ *
+ * This function can be called to init and set up a submodule
+ * repository from a submodule in preparation to clone it from
+ * its remote.
+ *
+ * @param out Output pointer to the created git repository.
+ * @param sm The submodule to create a new subrepository from.
+ * @param use_gitlink Should the workdir contain a gitlink to
+ *        the repo in .git/modules vs. repo directly in workdir.
+ * @return 0 on success, <0 on failure.
+ */
+GIT_EXTERN(int) git_submodule_repo_init(
+	git_repository **out,
+	const git_submodule *sm,
+	int use_gitlink);
+
+/**
  * Copy submodule remote info into submodule repo.
  *
  * This copies the information about the submodules URL into the checked out
diff --git a/src/repository.c b/src/repository.c
index 4f7a5fe..d86d890 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -994,7 +994,7 @@ static int repo_init_config(
 	uint32_t mode)
 {
 	int error = 0;
-	git_buf cfg_path = GIT_BUF_INIT;
+	git_buf cfg_path = GIT_BUF_INIT, worktree_path = GIT_BUF_INIT;
 	git_config *config = NULL;
 	bool is_bare = ((flags & GIT_REPOSITORY_INIT_BARE) != 0);
 	bool is_reinit = ((flags & GIT_REPOSITORY_INIT__IS_REINIT) != 0);
@@ -1019,9 +1019,16 @@ static int repo_init_config(
 	if (!is_bare) {
 		SET_REPO_CONFIG(bool, "core.logallrefupdates", true);
 
-		if (!(flags & GIT_REPOSITORY_INIT__NATURAL_WD))
-			SET_REPO_CONFIG(string, "core.worktree", work_dir);
-		else if (is_reinit) {
+		if (!(flags & GIT_REPOSITORY_INIT__NATURAL_WD)) {
+			if ((error = git_buf_sets(&worktree_path, work_dir)) < 0)
+				goto cleanup;
+
+			if ((flags & GIT_REPOSITORY_INIT_RELATIVE_GITLINK))
+				if ((error = git_path_make_relative(&worktree_path, repo_dir)) < 0)
+					goto cleanup;
+
+			SET_REPO_CONFIG(string, "core.worktree", worktree_path.ptr);
+		} else if (is_reinit) {
 			if (git_config_delete_entry(config, "core.worktree") < 0)
 				giterr_clear();
 		}
@@ -1038,6 +1045,7 @@ static int repo_init_config(
 
 cleanup:
 	git_buf_free(&cfg_path);
+	git_buf_free(&worktree_path);
 	git_config_free(config);
 
 	return error;
@@ -1126,10 +1134,11 @@ static int repo_write_template(
 }
 
 static int repo_write_gitlink(
-	const char *in_dir, const char *to_repo)
+	const char *in_dir, const char *to_repo, bool use_relative_path)
 {
 	int error;
 	git_buf buf = GIT_BUF_INIT;
+	git_buf path_to_repo = GIT_BUF_INIT;
 	struct stat st;
 
 	git_path_dirname_r(&buf, to_repo);
@@ -1157,13 +1166,20 @@ static int repo_write_gitlink(
 
 	git_buf_clear(&buf);
 
-	error = git_buf_printf(&buf, "%s %s", GIT_FILE_CONTENT_PREFIX, to_repo);
+	error = git_buf_sets(&path_to_repo, to_repo);
+
+	if (!error && use_relative_path)
+		error = git_path_make_relative(&path_to_repo, in_dir);
+
+	if (!error)
+		error = git_buf_join(&buf, ' ', GIT_FILE_CONTENT_PREFIX, path_to_repo.ptr);
 
 	if (!error)
 		error = repo_write_template(in_dir, true, DOT_GIT, 0666, true, buf.ptr);
 
 cleanup:
 	git_buf_free(&buf);
+	git_buf_free(&path_to_repo);
 	return error;
 }
 
@@ -1207,7 +1223,7 @@ static int repo_init_structure(
 	if ((opts->flags & GIT_REPOSITORY_INIT_BARE) == 0 &&
 		(opts->flags & GIT_REPOSITORY_INIT__NATURAL_WD) == 0)
 	{
-		if (repo_write_gitlink(work_dir, repo_dir) < 0)
+		if (repo_write_gitlink(work_dir, repo_dir, opts->flags & GIT_REPOSITORY_INIT_RELATIVE_GITLINK) < 0)
 			return -1;
 	}
 
@@ -1635,7 +1651,7 @@ int git_repository_set_workdir(
 		if (git_repository_config__weakptr(&config, repo) < 0)
 			return -1;
 
-		error = repo_write_gitlink(path.ptr, git_repository_path(repo));
+		error = repo_write_gitlink(path.ptr, git_repository_path(repo), false);
 
 		/* passthrough error means gitlink is unnecessary */
 		if (error == GIT_PASSTHROUGH)
diff --git a/src/submodule.c b/src/submodule.c
index b1291df..ccc8ad1 100644
--- a/src/submodule.c
+++ b/src/submodule.c
@@ -306,6 +306,56 @@ void git_submodule_cache_free(git_repository *repo)
 		submodule_cache_free(cache);
 }
 
+static int submodule_repo_init(
+	git_repository **out,
+	git_repository *parent_repo,
+	const char *path,
+	const char *url,
+	bool use_gitlink)
+{
+	int error = 0;
+	git_buf workdir = GIT_BUF_INIT, repodir = GIT_BUF_INIT;
+	git_repository_init_options initopt = GIT_REPOSITORY_INIT_OPTIONS_INIT;
+	git_repository *subrepo = NULL;
+
+	error = git_buf_joinpath(&workdir, git_repository_workdir(parent_repo), path);
+	if (error < 0)
+		goto cleanup;
+
+	initopt.flags = GIT_REPOSITORY_INIT_MKPATH | GIT_REPOSITORY_INIT_NO_REINIT;
+	initopt.origin_url = url;
+
+	/* init submodule repository and add origin remote as needed */
+
+	/* New style: sub-repo goes in <repo-dir>/modules/<name>/ with a
+	 * gitlink in the sub-repo workdir directory to that repository
+	 *
+	 * Old style: sub-repo goes directly into repo/<name>/.git/
+	 */
+	 if (use_gitlink) {
+		error = git_buf_join3(
+			&repodir, '/', git_repository_path(parent_repo), "modules", path);
+		if (error < 0)
+			goto cleanup;
+
+		initopt.workdir_path = workdir.ptr;
+		initopt.flags |=
+			GIT_REPOSITORY_INIT_NO_DOTGIT_DIR |
+			GIT_REPOSITORY_INIT_RELATIVE_GITLINK;
+
+		error = git_repository_init_ext(&subrepo, repodir.ptr, &initopt);
+	} else
+		error = git_repository_init_ext(&subrepo, workdir.ptr, &initopt);
+
+cleanup:
+	git_buf_free(&workdir);
+	git_buf_free(&repodir);
+
+	*out = subrepo;
+
+	return error;
+}
+
 int git_submodule_add_setup(
 	git_submodule **out,
 	git_repository *repo,
@@ -317,7 +367,6 @@ int git_submodule_add_setup(
 	git_config_backend *mods = NULL;
 	git_submodule *sm = NULL;
 	git_buf name = GIT_BUF_INIT, real_url = GIT_BUF_INIT;
-	git_repository_init_options initopt = GIT_REPOSITORY_INIT_OPTIONS_INIT;
 	git_repository *subrepo = NULL;
 
 	assert(repo && url && path);
@@ -371,41 +420,14 @@ int git_submodule_add_setup(
 	if (error < 0)
 		goto cleanup;
 
-	/* New style: sub-repo goes in <repo-dir>/modules/<name>/ with a
-	 * gitlink in the sub-repo workdir directory to that repository
-	 *
-	 * Old style: sub-repo goes directly into repo/<name>/.git/
+	/* if the repo does not already exist, then init a new repo and add it.
+	 * Otherwise, just add the existing repo.
 	 */
-
-	initopt.flags = GIT_REPOSITORY_INIT_MKPATH |
-		GIT_REPOSITORY_INIT_NO_REINIT;
-	initopt.origin_url = real_url.ptr;
-
-	if (git_path_exists(name.ptr) &&
-		git_path_contains(&name, DOT_GIT))
-	{
-		/* repo appears to already exist - reinit? */
-	}
-	else if (use_gitlink) {
-		git_buf repodir = GIT_BUF_INIT;
-
-		error = git_buf_join3(
-			&repodir, '/', git_repository_path(repo), "modules", path);
-		if (error < 0)
+	if (!(git_path_exists(name.ptr) &&
+		git_path_contains(&name, DOT_GIT))) {
+		if ((error = submodule_repo_init(&subrepo, repo, path, real_url.ptr, use_gitlink)) < 0)
 			goto cleanup;
-
-		initopt.workdir_path = name.ptr;
-		initopt.flags |= GIT_REPOSITORY_INIT_NO_DOTGIT_DIR;
-
-		error = git_repository_init_ext(&subrepo, repodir.ptr, &initopt);
-
-		git_buf_free(&repodir);
 	}
-	else {
-		error = git_repository_init_ext(&subrepo, name.ptr, &initopt);
-	}
-	if (error < 0)
-		goto cleanup;
 
 	/* add submodule to hash and "reload" it */
 
@@ -437,6 +459,23 @@ cleanup:
 	return error;
 }
 
+int git_submodule_repo_init(
+	git_repository **out,
+	const git_submodule *sm,
+	int use_gitlink)
+{
+	int error;
+	git_repository *sub_repo = NULL;
+
+	assert(out && sm);
+
+	error = submodule_repo_init(&sub_repo, sm->repo, sm->path, sm->url, use_gitlink);
+
+	*out = sub_repo;
+
+	return error;
+}
+
 int git_submodule_add_finalize(git_submodule *sm)
 {
 	int error;
@@ -1897,6 +1936,7 @@ static void submodule_get_index_status(unsigned int *status, git_submodule *sm)
 		*status |= GIT_SUBMODULE_STATUS_INDEX_MODIFIED;
 }
 
+
 static void submodule_get_wd_status(
 	unsigned int *status,
 	git_submodule *sm,
diff --git a/tests/repo/init.c b/tests/repo/init.c
index aea383c..999afd6 100644
--- a/tests/repo/init.c
+++ b/tests/repo/init.c
@@ -367,6 +367,84 @@ void test_repo_init__extended_1(void)
 	cl_fixture_cleanup("root");
 }
 
+void test_repo_init__relative_gitdir(void)
+{
+	git_repository_init_options opts = GIT_REPOSITORY_INIT_OPTIONS_INIT;
+	git_config *cfg;
+	const char *worktree_path;
+	git_buf dot_git_content = GIT_BUF_INIT;
+
+	opts.workdir_path = "../c_wd";
+	opts.flags =
+		GIT_REPOSITORY_INIT_MKPATH |
+		GIT_REPOSITORY_INIT_RELATIVE_GITLINK |
+		GIT_REPOSITORY_INIT_NO_DOTGIT_DIR;
+
+	/* make the directory first, then it should succeed */
+	cl_git_pass(git_repository_init_ext(&_repo, "root/b/my_repository", &opts));
+
+	cl_assert(!git__suffixcmp(git_repository_workdir(_repo), "root/b/c_wd/"));
+	cl_assert(!git__suffixcmp(git_repository_path(_repo), "root/b/my_repository/"));
+	cl_assert(!git_repository_is_bare(_repo));
+	cl_assert(git_repository_is_empty(_repo));
+
+	/* Verify that the gitlink and worktree entries are relative */
+
+	/* Verify worktree */
+	cl_git_pass(git_repository_config(&cfg, _repo));
+	cl_git_pass(git_config_get_string(&worktree_path, cfg, "core.worktree"));
+	cl_assert_equal_s("../c_wd/", worktree_path);
+
+	/* Verify gitlink */
+	cl_git_pass(git_futils_readbuffer(&dot_git_content, "root/b/c_wd/.git"));
+	cl_assert_equal_s("gitdir: ../my_repository/", dot_git_content.ptr);
+
+	git_buf_free(&dot_git_content);
+	git_config_free(cfg);
+	cleanup_repository("root");
+}
+
+void test_repo_init__relative_gitdir_2(void)
+{
+	git_repository_init_options opts = GIT_REPOSITORY_INIT_OPTIONS_INIT;
+	git_config *cfg;
+	const char *worktree_path;
+	git_buf dot_git_content = GIT_BUF_INIT;
+	git_buf full_path = GIT_BUF_INIT;
+
+	cl_git_pass(git_path_prettify(&full_path, ".", NULL));
+	cl_git_pass(git_buf_joinpath(&full_path, full_path.ptr, "root/b/c_wd"));
+
+	opts.workdir_path = full_path.ptr;
+	opts.flags =
+		GIT_REPOSITORY_INIT_MKPATH |
+		GIT_REPOSITORY_INIT_RELATIVE_GITLINK |
+		GIT_REPOSITORY_INIT_NO_DOTGIT_DIR;
+
+	/* make the directory first, then it should succeed */
+	cl_git_pass(git_repository_init_ext(&_repo, "root/b/my_repository", &opts));
+
+	cl_assert(!git__suffixcmp(git_repository_workdir(_repo), "root/b/c_wd/"));
+	cl_assert(!git__suffixcmp(git_repository_path(_repo), "root/b/my_repository/"));
+	cl_assert(!git_repository_is_bare(_repo));
+	cl_assert(git_repository_is_empty(_repo));
+
+	/* Verify that the gitlink and worktree entries are relative */
+
+	/* Verify worktree */
+	cl_git_pass(git_repository_config(&cfg, _repo));
+	cl_git_pass(git_config_get_string(&worktree_path, cfg, "core.worktree"));
+	cl_assert_equal_s("../c_wd/", worktree_path);
+
+	/* Verify gitlink */
+	cl_git_pass(git_futils_readbuffer(&dot_git_content, "root/b/c_wd/.git"));
+	cl_assert_equal_s("gitdir: ../my_repository/", dot_git_content.ptr);
+
+	git_buf_free(&dot_git_content);
+	git_config_free(cfg);
+	cleanup_repository("root");
+}
+
 #define CLEAR_FOR_CORE_FILEMODE(M) ((M) &= ~0177)
 
 static void assert_hooks_match(
diff --git a/tests/submodule/add.c b/tests/submodule/add.c
index 9fdc7cc..1071780 100644
--- a/tests/submodule/add.c
+++ b/tests/submodule/add.c
@@ -2,6 +2,7 @@
 #include "posix.h"
 #include "path.h"
 #include "submodule_helpers.h"
+#include "fileops.h"
 
 static git_repository *g_repo = NULL;
 
@@ -29,6 +30,10 @@ static void assert_submodule_url(const char* name, const char *url)
 void test_submodule_add__url_absolute(void)
 {
 	git_submodule *sm;
+	git_config *cfg;
+	git_repository *repo;
+	const char *worktree_path;
+	git_buf dot_git_content = GIT_BUF_INIT;
 
 	g_repo = setup_fixture_submod2();
 
@@ -51,6 +56,21 @@ void test_submodule_add__url_absolute(void)
 	cl_assert(git_path_isfile("submod2/.git/modules/" "sm_libgit2" "/HEAD"));
 	assert_submodule_url("sm_libgit2", "https://github.com/libgit2/libgit2.git");
 
+	cl_git_pass(git_repository_open(&repo, "submod2/" "sm_libgit2"));
+
+	/* Verify worktree path is relative */
+	cl_git_pass(git_repository_config(&cfg, repo));
+	cl_git_pass(git_config_get_string(&worktree_path, cfg, "core.worktree"));
+	cl_assert_equal_s("../../../sm_libgit2/", worktree_path);
+
+	/* Verify gitdir path is relative */
+	cl_git_pass(git_futils_readbuffer(&dot_git_content, "submod2/" "sm_libgit2" "/.git"));
+	cl_assert_equal_s("gitdir: ../.git/modules/sm_libgit2/", dot_git_content.ptr);
+
+	git_config_free(cfg);
+	git_repository_free(repo);
+	git_buf_free(&dot_git_content);
+
 	/* add a submodule not using a gitlink */
 
 	cl_git_pass(
diff --git a/tests/submodule/repository_init.c b/tests/submodule/repository_init.c
new file mode 100644
index 0000000..24b47af
--- /dev/null
+++ b/tests/submodule/repository_init.c
@@ -0,0 +1,40 @@
+#include "clar_libgit2.h"
+#include "posix.h"
+#include "path.h"
+#include "submodule_helpers.h"
+#include "fileops.h"
+
+static git_repository *g_repo = NULL;
+
+void test_submodule_repository_init__basic(void)
+{
+	git_submodule *sm;
+	git_repository *repo;
+	git_config *cfg;
+	const char *worktree_path;
+	git_buf dot_git_content = GIT_BUF_INIT;
+
+	g_repo = setup_fixture_submod2();
+
+	cl_git_pass(git_submodule_lookup(&sm, g_repo, "sm_gitmodules_only"));
+	cl_git_pass(git_submodule_repo_init(&repo, sm, 1));
+
+	/* Verify worktree */
+	cl_git_pass(git_repository_config(&cfg, repo));
+	cl_git_pass(git_config_get_string(&worktree_path, cfg, "core.worktree"));
+	cl_assert_equal_s("../../../sm_gitmodules_only/", worktree_path);
+
+	/* Verify gitlink */
+	cl_git_pass(git_futils_readbuffer(&dot_git_content, "submod2/" "sm_gitmodules_only" "/.git"));
+	cl_assert_equal_s("gitdir: ../.git/modules/sm_gitmodules_only/", dot_git_content.ptr);
+
+	cl_assert(git_path_isfile("submod2/" "sm_gitmodules_only" "/.git"));
+
+	cl_assert(git_path_isdir("submod2/.git/modules"));
+	cl_assert(git_path_isdir("submod2/.git/modules/" "sm_gitmodules_only"));
+	cl_assert(git_path_isfile("submod2/.git/modules/" "sm_gitmodules_only" "/HEAD"));
+
+	git_config_free(cfg);
+	git_repository_free(repo);
+	git_buf_free(&dot_git_content);
+}