clone: allow for linking in local clone

If requested, git_clone_local_into() will try to link the object files
instead of copying them.

This only works on non-Windows (since it doesn't have this) when both
are on the same filesystem (which are unix semantics).

include/git2/clone.h

@@ -144,6 +144,9 @@ GIT_EXTERN(int) git_clone_into(
  * @param co_opts options to use during checkout
  * @param branch the branch to checkout after the clone, pass NULL for the
  *        remote's default branch
+ * @param link wether to use hardlinks instead of copying
+ * objects. This is only possible if both repositories are on the same
+ * filesystem.
  * @param signature the identity used when updating the reflog
  * @return 0 on success, any non-zero return value from a callback
  *         function, or a negative value to indicate an error (use
@@ -154,6 +157,7 @@ GIT_EXTERN(int) git_clone_local_into(
 	git_remote *remote,
 	const git_checkout_options *co_opts,
 	const char *branch,
+	int link,
 	const git_signature *signature);
 
 /** @} */

src/clone.c

@@ -405,9 +405,10 @@ int git_clone(
 
 	if (!(error = create_and_configure_origin(&origin, repo, url, &options))) {
 		if (git_clone__should_clone_local(url, options.local)) {
+			int link = options.local != GIT_CLONE_LOCAL_NO_LINKS;
 			error = git_clone_local_into(
 				repo, origin, &options.checkout_opts,
-				options.checkout_branch, options.signature);
+				options.checkout_branch, link, options.signature);
 		} else {
 			error = git_clone_into(
 				repo, origin, &options.checkout_opts,
@@ -448,15 +449,36 @@ static const char *repository_base(git_repository *repo)
 	return git_repository_workdir(repo);
 }
 
-int git_clone_local_into(git_repository *repo, git_remote *remote, const git_checkout_options *co_opts, const char *branch, const git_signature *signature)
+static bool can_link(const char *src, const char *dst, int link)
 {
-	int error, root;
+#ifdef GIT_WIN32
+	return false;
+#else
+
+	struct stat st_src, st_dst;
+
+	if (!link)
+		return false;
+
+	if (p_stat(src, &st_src) < 0)
+		return false;
+
+	if (p_stat(dst, &st_dst) < 0)
+		return false;
+
+	return st_src.st_dev == st_dst.st_dev;
+#endif
+}
+
+int git_clone_local_into(git_repository *repo, git_remote *remote, const git_checkout_options *co_opts, const char *branch, int link, const git_signature *signature)
+{
+	int error, root, flags;
 	git_repository *src;
 	git_buf src_odb = GIT_BUF_INIT, dst_odb = GIT_BUF_INIT, src_path = GIT_BUF_INIT;
 	git_buf reflog_message = GIT_BUF_INIT;
 	const char *url;
 
-	assert(repo && remote && co_opts);
+	assert(repo && remote);
 
 	if (!git_repository_is_empty(repo)) {
 		giterr_set(GITERR_INVALID, "the repository is not empty");
@@ -495,8 +517,12 @@ int git_clone_local_into(git_repository *repo, git_remote *remote, const git_che
 		goto cleanup;
 	}
 
+	flags = 0;
+	if (can_link(git_repository_path(src), git_repository_path(repo), link))
+		flags |= GIT_CPDIR_LINK_FILES;
+
 	if ((error = git_futils_cp_r(git_buf_cstr(&src_odb), git_buf_cstr(&dst_odb),
-				     0, GIT_OBJECT_DIR_MODE)) < 0)
+				     flags, GIT_OBJECT_DIR_MODE)) < 0)
 		goto cleanup;
 
 	git_buf_printf(&reflog_message, "clone: from %s", git_remote_url(remote));

tests/clone/local.c

@@ -3,6 +3,8 @@
 #include "git2/clone.h"
 #include "clone.h"
 #include "buffer.h"
+#include "path.h"
+#include "posix.h"
 
 void assert_clone(const char *path, git_clone_local_t opt, int val)
 {
@@ -29,3 +31,60 @@ void test_clone_local__should_clone_local(void)
 	cl_assert_equal_i(true,  git_clone__should_clone_local(path, GIT_CLONE_LOCAL_NO_LINKS));
 	cl_assert_equal_i(false, git_clone__should_clone_local(path, GIT_CLONE_NO_LOCAL));
 }
+
+void test_clone_local__hardlinks(void)
+{
+	git_repository *repo;
+	git_remote *remote;
+	git_signature *sig;
+	git_buf buf = GIT_BUF_INIT;
+	struct stat st;
+
+	cl_git_pass(git_repository_init(&repo, "./clone.git", true));
+	cl_git_pass(git_remote_create(&remote, repo, "origin", cl_fixture("testrepo.git")));
+	cl_git_pass(git_signature_now(&sig, "foo", "bar"));
+	cl_git_pass(git_clone_local_into(repo, remote, NULL, NULL, true, sig));
+
+	git_remote_free(remote);
+	git_repository_free(repo);
+
+	/*
+	 * We can't rely on the link option taking effect in the first
+	 * clone, since the temp dir and fixtures dir may reside on
+	 * different filesystems. We perform the second clone
+	 * side-by-side to make sure this is the case.
+	 */
+
+	cl_git_pass(git_repository_init(&repo, "./clone2.git", true));
+	cl_git_pass(git_buf_puts(&buf, cl_git_path_url("clone.git")));
+	cl_git_pass(git_remote_create(&remote, repo, "origin", buf.ptr));
+	cl_git_pass(git_clone_local_into(repo, remote, NULL, NULL, true, sig));
+
+#ifndef GIT_WIN32
+	git_buf_clear(&buf);
+	cl_git_pass(git_buf_join_n(&buf, '/', 4, git_repository_path(repo), "objects", "08", "b041783f40edfe12bb406c9c9a8a040177c125"));
+
+	cl_git_pass(p_stat(buf.ptr, &st));
+	cl_assert(st.st_nlink > 1);
+#endif
+
+	git_remote_free(remote);
+	git_repository_free(repo);
+	git_buf_clear(&buf);
+
+	cl_git_pass(git_repository_init(&repo, "./clone3.git", true));
+	cl_git_pass(git_buf_puts(&buf, cl_git_path_url("clone.git")));
+	cl_git_pass(git_remote_create(&remote, repo, "origin", buf.ptr));
+	cl_git_pass(git_clone_local_into(repo, remote, NULL, NULL, false, sig));
+
+	git_buf_clear(&buf);
+	cl_git_pass(git_buf_join_n(&buf, '/', 4, git_repository_path(repo), "objects", "08", "b041783f40edfe12bb406c9c9a8a040177c125"));
+
+	cl_git_pass(p_stat(buf.ptr, &st));
+	cl_assert_equal_i(1, st.st_nlink);
+
+	git_buf_free(&buf);
+	git_signature_free(sig);
+	git_remote_free(remote);
+	git_repository_free(repo);
+}