worktree: introduce `struct git_worktree`

Introduce a new `struct git_worktree`, which holds information
about a possible working tree connected to a repository.
Introduce functions to allow opening working trees for a
repository.

include/git2/types.h

@@ -104,6 +104,9 @@ typedef struct git_refdb_backend git_refdb_backend;
  */
 typedef struct git_repository git_repository;
 
+/** Representation of a working tree */
+typedef struct git_worktree git_worktree;
+
 /** Representation of a generic object in a repository */
 typedef struct git_object git_object;
 

include/git2/worktree.h

@@ -32,6 +32,23 @@ GIT_BEGIN_DECL
  */
 GIT_EXTERN(int) git_worktree_list(git_strarray *out, git_repository *repo);
 
+/**
+ * Lookup a working tree by its name for a given repository
+ *
+ * @param out Output pointer to looked up worktree or `NULL`
+ * @param repo The repository containing worktrees
+ * @param name Name of the working tree to look up
+ * @return 0 or an error code
+ */
+GIT_EXTERN(int) git_worktree_lookup(git_worktree **out, git_repository *repo, const char *name);
+
+/**
+ * Free a previously allocated worktree
+ *
+ * @param wt worktree handle to close. If NULL nothing occurs.
+ */
+GIT_EXTERN(void) git_worktree_free(git_worktree *wt);
+
 /** @} */
 GIT_END_DECL
 #endif

src/worktree.c

@@ -9,6 +9,7 @@
 
 #include "common.h"
 #include "repository.h"
+#include "worktree.h"
 
 static bool is_worktree_dir(git_buf *dir)
 {
@@ -56,3 +57,91 @@ exit:
 
 	return error;
 }
+
+static char *read_link(const char *base, const char *file)
+{
+	git_buf path = GIT_BUF_INIT, buf = GIT_BUF_INIT;
+
+	assert(base && file);
+
+	if (git_buf_joinpath(&path, base, file) < 0)
+		goto err;
+	if (git_futils_readbuffer(&buf, path.ptr) < 0)
+		goto err;
+	git_buf_free(&path);
+
+	git_buf_rtrim(&buf);
+
+	if (!git_path_is_relative(buf.ptr))
+		return git_buf_detach(&buf);
+
+	if (git_buf_sets(&path, base) < 0)
+		goto err;
+	if (git_path_apply_relative(&path, buf.ptr) < 0)
+		goto err;
+	git_buf_free(&buf);
+
+	return git_buf_detach(&path);
+
+err:
+	git_buf_free(&buf);
+	git_buf_free(&path);
+
+	return NULL;
+}
+
+int git_worktree_lookup(git_worktree **out, git_repository *repo, const char *name)
+{
+	git_buf path = GIT_BUF_INIT;
+	git_worktree *wt = NULL;
+	int error;
+
+	assert(repo && name);
+
+	*out = NULL;
+
+	if ((error = git_buf_printf(&path, "%s/worktrees/%s", repo->commondir, name)) < 0)
+		goto out;
+
+	if (!is_worktree_dir(&path)) {
+		error = -1;
+		goto out;
+	}
+
+	if ((wt = git__malloc(sizeof(struct git_repository))) == NULL) {
+		error = -1;
+		goto out;
+	}
+
+	if ((wt->name = git__strdup(name)) == NULL
+	    || (wt->commondir_path = read_link(path.ptr, "commondir")) == NULL
+	    || (wt->gitlink_path = read_link(path.ptr, "gitdir")) == NULL
+	    || (wt->parent_path = git__strdup(git_repository_path(repo))) == NULL) {
+		error = -1;
+		goto out;
+	}
+	wt->gitdir_path = git_buf_detach(&path);
+
+	(*out) = wt;
+
+out:
+	git_buf_free(&path);
+
+	if (error)
+		git_worktree_free(wt);
+
+	return error;
+}
+
+void git_worktree_free(git_worktree *wt)
+{
+	if (!wt)
+		return;
+
+	git__free(wt->commondir_path);
+	git__free(wt->gitlink_path);
+	git__free(wt->gitdir_path);
+	git__free(wt->parent_path);
+	git__free(wt->name);
+	git__free(wt);
+}

src/worktree.h

+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_worktree_h__
+#define INCLUDE_worktree_h__
+
+#include "git2/common.h"
+#include "git2/worktree.h"
+
+struct git_worktree {
+	/* Name of the working tree. This is the name of the
+	 * containing directory in the `$PARENT/.git/worktrees/`
+	 * directory. */
+	char *name;
+
+	/* Path to the .git file in the working tree's repository */
+	char *gitlink_path;
+	/* Path to the .git directory inside the parent's
+	 * worktrees directory */
+	char *gitdir_path;
+	/* Path to the common directory contained in the parent
+	 * repository */
+	char *commondir_path;
+	/* Path to the parent's .git directory */
+	char *parent_path;
+};
+
+#endif

tests/worktree/worktree.c

 #include "clar_libgit2.h"
 #include "worktree_helpers.h"
 
-#include "git2/worktree.h"
 #include "repository.h"
+#include "worktree.h"
 
 #define COMMON_REPO "testrepo"
 #define WORKTREE_REPO "testrepo-worktree"
@@ -105,3 +105,29 @@ void test_worktree_worktree__list_without_worktrees(void)
 
 	git_repository_free(repo);
 }
+
+void test_worktree_worktree__lookup(void)
+{
+	git_worktree *wt;
+	git_buf gitdir_path = GIT_BUF_INIT;
+
+	cl_git_pass(git_worktree_lookup(&wt, fixture.repo, "testrepo-worktree"));
+
+	git_buf_printf(&gitdir_path, "%s/worktrees/%s", fixture.repo->commondir, "testrepo-worktree");
+
+	cl_assert_equal_s(wt->gitdir_path, gitdir_path.ptr);
+	cl_assert_equal_s(wt->parent_path, fixture.repo->path_repository);
+	cl_assert_equal_s(wt->gitlink_path, fixture.worktree->path_gitlink);
+	cl_assert_equal_s(wt->commondir_path, fixture.repo->commondir);
+
+	git_buf_free(&gitdir_path);
+	git_worktree_free(wt);
+}
+
+void test_worktree_worktree__lookup_nonexistent_worktree(void)
+{
+	git_worktree *wt;
+
+	cl_git_fail(git_worktree_lookup(&wt, fixture.repo, "nonexistent"));
+	cl_assert_equal_p(wt, NULL);
+}