worktree: implement locking mechanisms

Working trees support locking by creating a file `locked` inside
the tree's gitdir with an optional reason inside. Support this
feature by adding functions to get and set the locking status.

include/git2/worktree.h

@@ -8,6 +8,7 @@
 #define INCLUDE_git_worktree_h__
 
 #include "common.h"
+#include "buffer.h"
 #include "types.h"
 #include "strarray.h"
 
@@ -76,6 +77,41 @@ GIT_EXTERN(int) git_worktree_validate(const git_worktree *wt);
  */
 GIT_EXTERN(int) git_worktree_add(git_worktree **out, git_repository *repo, const char *name, const char *path);
 
+/*
+ * Lock worktree if not already locked
+ *
+ * Lock a worktree, optionally specifying a reason why the linked
+ * working tree is being locked.
+ *
+ * @param wt Worktree to lock
+ * @param reason Reason why the working tree is being locked
+ * @return 0 on success, non-zero otherwise
+ */
+GIT_EXTERN(int) git_worktree_lock(git_worktree *wt, char *reason);
+
+/**
+ * Unlock a locked worktree
+ *
+ * @param wt Worktree to unlock
+ * @return 0 on success, 1 if worktree was not locked, error-code
+ *  otherwise
+ */
+GIT_EXTERN(int) git_worktree_unlock(git_worktree *wt);
+
+/**
+ * Check if worktree is locked
+ *
+ * A worktree may be locked if the linked working tree is stored
+ * on a portable device which is not available.
+ *
+ * @param reason Buffer to store reason in. If NULL no reason is stored.
+ * @param wt Worktree to check
+ * @return 0 when the working tree not locked, a value greater
+ *  than zero if it is locked, less than zero if there was an
+ *  error
+ */
+GIT_EXTERN(int) git_worktree_is_locked(git_buf *reason, const git_worktree *wt);
+
 /** @} */
 GIT_END_DECL
 #endif

src/worktree.c

@@ -143,6 +143,7 @@ int git_worktree_lookup(git_worktree **out, git_repository *repo, const char *na
 		goto out;
 	}
 	wt->gitdir_path = git_buf_detach(&path);
+	wt->locked = !!git_worktree_is_locked(NULL, wt);
 
 	(*out) = wt;
 
@@ -283,3 +284,75 @@ out:
 
 	return err;
 }
+
+int git_worktree_lock(git_worktree *wt, char *creason)
+{
+	git_buf buf = GIT_BUF_INIT, path = GIT_BUF_INIT;
+	int err;
+
+	assert(wt);
+
+	if ((err = git_worktree_is_locked(NULL, wt)) < 0)
+		goto out;
+
+	if ((err = git_buf_joinpath(&path, wt->gitdir_path, "locked")) < 0)
+		goto out;
+
+	if (creason)
+		git_buf_attach_notowned(&buf, creason, strlen(creason));
+
+	if ((err = git_futils_writebuffer(&buf, path.ptr, O_CREAT|O_EXCL|O_WRONLY, 0644)) < 0)
+		goto out;
+
+	wt->locked = 1;
+
+out:
+	git_buf_free(&path);
+
+	return err;
+}
+
+int git_worktree_unlock(git_worktree *wt)
+{
+	git_buf path = GIT_BUF_INIT;
+
+	assert(wt);
+
+	if (!git_worktree_is_locked(NULL, wt))
+		return 0;
+
+	if (git_buf_joinpath(&path, wt->gitdir_path, "locked") < 0)
+		return -1;
+
+	if (p_unlink(path.ptr) != 0) {
+		git_buf_free(&path);
+		return -1;
+	}
+
+	wt->locked = 0;
+
+	git_buf_free(&path);
+
+	return 0;
+}
+
+int git_worktree_is_locked(git_buf *reason, const git_worktree *wt)
+{
+	git_buf path = GIT_BUF_INIT;
+	int ret;
+
+	assert(wt);
+
+	if (reason)
+		git_buf_clear(reason);
+
+	if ((ret = git_buf_joinpath(&path, wt->gitdir_path, "locked")) < 0)
+		goto out;
+	if ((ret = git_path_exists(path.ptr)) && reason)
+		git_futils_readbuffer(reason, path.ptr);
+
+out:
+	git_buf_free(&path);
+
+	return ret;
+}

src/worktree.h

@@ -26,6 +26,8 @@ struct git_worktree {
 	char *commondir_path;
 	/* Path to the parent's .git directory */
 	char *parent_path;
+
+	int locked:1;
 };
 
 #endif

tests/worktree/worktree.c

@@ -336,3 +336,62 @@ void test_worktree_worktree__validate_invalid_parent(void)
 	wt->parent_path = NULL;
 	git_worktree_free(wt);
 }
+
+void test_worktree_worktree__lock_with_reason(void)
+{
+	git_worktree *wt;
+	git_buf reason = GIT_BUF_INIT;
+
+	cl_git_pass(git_worktree_lookup(&wt, fixture.repo, "testrepo-worktree"));
+
+	cl_assert(!git_worktree_is_locked(NULL, wt));
+	cl_git_pass(git_worktree_lock(wt, "because"));
+	cl_assert(git_worktree_is_locked(&reason, wt) > 0);
+	cl_assert_equal_s(reason.ptr, "because");
+	cl_assert(wt->locked);
+
+	git_buf_free(&reason);
+	git_worktree_free(wt);
+}
+
+void test_worktree_worktree__lock_without_reason(void)
+{
+	git_worktree *wt;
+	git_buf reason = GIT_BUF_INIT;
+
+	cl_git_pass(git_worktree_lookup(&wt, fixture.repo, "testrepo-worktree"));
+
+	cl_assert(!git_worktree_is_locked(NULL, wt));
+	cl_git_pass(git_worktree_lock(wt, NULL));
+	cl_assert(git_worktree_is_locked(&reason, wt) > 0);
+	cl_assert_equal_i(reason.size, 0);
+	cl_assert(wt->locked);
+
+	git_buf_free(&reason);
+	git_worktree_free(wt);
+}
+
+void test_worktree_worktree__unlock_unlocked_worktree(void)
+{
+	git_worktree *wt;
+
+	cl_git_pass(git_worktree_lookup(&wt, fixture.repo, "testrepo-worktree"));
+	cl_assert(!git_worktree_is_locked(NULL, wt));
+	cl_assert(git_worktree_unlock(wt) == 0);
+	cl_assert(!wt->locked);
+
+	git_worktree_free(wt);
+}
+
+void test_worktree_worktree__unlock_locked_worktree(void)
+{
+	git_worktree *wt;
+
+	cl_git_pass(git_worktree_lookup(&wt, fixture.repo, "testrepo-worktree"));
+	cl_git_pass(git_worktree_lock(wt, NULL));
+	cl_assert(git_worktree_is_locked(NULL, wt));
+	cl_git_pass(git_worktree_unlock(wt));
+	cl_assert(!wt->locked);
+
+	git_worktree_free(wt);
+}