worktree: add write_worktree_linking_files() function

A new helper function, `write_worktree_linking_files()`, centralizes
the logic for computing and writing either relative or absolute
paths, based on the provided configuration. This function accepts
`strbuf` pointers to both the worktree’s `.git` link and the
repository’s `gitdir`, and then writes the appropriate path to each.
The `relativeWorktrees` extension is automatically set when a worktree
is linked with relative paths.

Signed-off-by: Caleb White <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: calebdw

worktree.c

@@ -1032,3 +1032,38 @@ int init_worktree_config(struct repository *r)
 	free(main_worktree_file);
 	return res;
 }
+
+void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
+				  int use_relative_paths)
+{
+	struct strbuf path = STRBUF_INIT;
+	struct strbuf repo = STRBUF_INIT;
+	struct strbuf tmp = STRBUF_INIT;
+
+	strbuf_addbuf(&path, &dotgit);
+	strbuf_strip_suffix(&path, "/.git");
+	strbuf_realpath(&path, path.buf, 1);
+	strbuf_addbuf(&repo, &gitdir);
+	strbuf_strip_suffix(&repo, "/gitdir");
+	strbuf_realpath(&repo, repo.buf, 1);
+
+	if (use_relative_paths && !the_repository->repository_format_relative_worktrees) {
+		if (upgrade_repository_format(1) < 0)
+			die(_("unable to upgrade repository format to support relative worktrees"));
+		if (git_config_set_gently("extensions.relativeWorktrees", "true"))
+			die(_("unable to set extensions.relativeWorktrees setting"));
+		the_repository->repository_format_relative_worktrees = 1;
+	}
+
+	if (use_relative_paths) {
+		write_file(gitdir.buf, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
+		write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
+	} else {
+		write_file(gitdir.buf, "%s/.git", path.buf);
+		write_file(dotgit.buf, "gitdir: %s", repo.buf);
+	}
+
+	strbuf_release(&path);
+	strbuf_release(&repo);
+	strbuf_release(&tmp);
+}

worktree.h

@@ -215,4 +215,17 @@ void strbuf_worktree_ref(const struct worktree *wt,
  */
 int init_worktree_config(struct repository *r);
 
+/**
+ * Write the .git file and gitdir file that links the worktree to the repository.
+ *
+ * The `dotgit` parameter is the path to the worktree's .git file, and `gitdir`
+ * is the path to the repository's `gitdir` file.
+ *
+ * Example
+ *  dotgit: "/path/to/foo/.git"
+ *  gitdir: "/path/to/repo/worktrees/foo/gitdir"
+ */
+void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
+				  int use_relative_paths);
+
 #endif