Upstreaming the Scalar command

index 7cff29e0fcd..0e627bb100e 100644
@@ -5,11 +5,266 @@
 #include "cache.h"
 #include "gettext.h"
 #include "parse-options.h"
+#include "config.h"
+#include "run-command.h"
+
+/*
+ * Remove the deepest subdirectory in the provided path string. Path must not
+ * include a trailing path separator. Returns 1 if parent directory found,
+ * otherwise 0.
+ */
+static int strbuf_parent_directory(struct strbuf *buf)
+{
+	size_t len = buf->len;
+	size_t offset = offset_1st_component(buf->buf);
+	char *path_sep = find_last_dir_sep(buf->buf + offset);
+	strbuf_setlen(buf, path_sep ? path_sep - buf->buf : offset);
+
+	return buf->len < len;
+}
+
+static void setup_enlistment_directory(int argc, const char **argv,
+				       const char * const *usagestr,
+				       const struct option *options,
+				       struct strbuf *enlistment_root)
+{
+	struct strbuf path = STRBUF_INIT;
+	char *root;
+	int enlistment_found = 0;
+
+	if (startup_info->have_repository)
+		BUG("gitdir already set up?!?");
+
+	if (argc > 1)
+		usage_with_options(usagestr, options);
+
+	/* find the worktree, determine its corresponding root */
+	if (argc == 1)
+		strbuf_add_absolute_path(&path, argv[0]);
+	else if (strbuf_getcwd(&path) < 0)
+		die(_("need a working directory"));
+
+	strbuf_trim_trailing_dir_sep(&path);
+	do {
+		const size_t len = path.len;
+
+		/* check if currently in enlistment root with src/ workdir */
+		strbuf_addstr(&path, "/src/.git");
+		if (is_git_directory(path.buf)) {
+			strbuf_strip_suffix(&path, "/.git");
+
+			if (enlistment_root)
+				strbuf_add(enlistment_root, path.buf, len);
+
+			enlistment_found = 1;
+			break;
+		}
+
+		/* reset to original path */
+		strbuf_setlen(&path, len);
+
+		/* check if currently in workdir */
+		strbuf_addstr(&path, "/.git");
+		if (is_git_directory(path.buf)) {
+			strbuf_setlen(&path, len);
+
+			if (enlistment_root) {
+				/*
+				 * If the worktree's directory's name is `src`, the enlistment is the
+				 * parent directory, otherwise it is identical to the worktree.
+				 */
+				root = strip_path_suffix(path.buf, "src");
+				strbuf_addstr(enlistment_root, root ? root : path.buf);
+				free(root);
+			}
+
+			enlistment_found = 1;
+			break;
+		}
+
+		strbuf_setlen(&path, len);
+	} while (strbuf_parent_directory(&path));
+
+	if (!enlistment_found)
+		die(_("could not find enlistment root"));
+
+	if (chdir(path.buf) < 0)
+		die_errno(_("could not switch to '%s'"), path.buf);
+
+	strbuf_release(&path);
+	setup_git_directory();
+}
+
+static int run_git(const char *arg, ...)
+{
+	struct strvec argv = STRVEC_INIT;
+	va_list args;
+	const char *p;
+	int res;
+
+	va_start(args, arg);
+	strvec_push(&argv, arg);
+	while ((p = va_arg(args, const char *)))
+		strvec_push(&argv, p);
+	va_end(args);
+
+	res = run_command_v_opt(argv.v, RUN_GIT_CMD);
+
+	strvec_clear(&argv);
+	return res;
+}
+
+static int set_recommended_config(void)
+{
+	struct {
+		const char *key;
+		const char *value;
+	} config[] = {
+		{ "am.keepCR", "true" },
+		{ "core.FSCache", "true" },
+		{ "core.multiPackIndex", "true" },
+		{ "core.preloadIndex", "true" },
+#ifndef WIN32
+		{ "core.untrackedCache", "true" },
+#else
+		/*
+		 * Unfortunately, Scalar's Functional Tests demonstrated
+		 * that the untracked cache feature is unreliable on Windows
+		 * (which is a bummer because that platform would benefit the
+		 * most from it). For some reason, freshly created files seem
+		 * not to update the directory's `lastModified` time
+		 * immediately, but the untracked cache would need to rely on
+		 * that.
+		 *
+		 * Therefore, with a sad heart, we disable this very useful
+		 * feature on Windows.
+		 */
+		{ "core.untrackedCache", "false" },
+#endif
+		{ "core.logAllRefUpdates", "true" },
+		{ "credential.https://dev.azure.com.useHttpPath", "true" },
+		{ "credential.validate", "false" }, /* GCM4W-only */
+		{ "gc.auto", "0" },
+		{ "gui.GCWarning", "false" },
+		{ "index.threads", "true" },
+		{ "index.version", "4" },
+		{ "merge.stat", "false" },
+		{ "merge.renames", "false" },
+		{ "pack.useBitmaps", "false" },
+		{ "pack.useSparse", "true" },
+		{ "receive.autoGC", "false" },
+		{ "reset.quiet", "true" },
+		{ "feature.manyFiles", "false" },
+		{ "feature.experimental", "false" },
+		{ "fetch.unpackLimit", "1" },
+		{ "fetch.writeCommitGraph", "false" },
+#ifdef WIN32
+		{ "http.sslBackend", "schannel" },
+#endif
+		{ "status.aheadBehind", "false" },
+		{ "commitGraph.generationVersion", "1" },
+		{ "core.autoCRLF", "false" },
+		{ "core.safeCRLF", "false" },
+		{ NULL, NULL },
+	};
+	int i;
+	char *value;
+
+	for (i = 0; config[i].key; i++) {
+		if (git_config_get_string(config[i].key, &value)) {
+			trace2_data_string("scalar", the_repository, config[i].key, "created");
+			if (git_config_set_gently(config[i].key,
+						  config[i].value) < 0)
+				return error(_("could not configure %s=%s"),
+					     config[i].key, config[i].value);
+		} else {
+			trace2_data_string("scalar", the_repository, config[i].key, "exists");
+			free(value);
+		}
+	}
+
+	/*
+	 * The `log.excludeDecoration` setting is special because it allows
+	 * for multiple values.
+	 */
+	if (git_config_get_string("log.excludeDecoration", &value)) {
+		trace2_data_string("scalar", the_repository,
+				   "log.excludeDecoration", "created");
+		if (git_config_set_multivar_gently("log.excludeDecoration",
+						   "refs/prefetch/*",
+						   CONFIG_REGEX_NONE, 0))
+			return error(_("could not configure "
+				       "log.excludeDecoration"));
+	} else {
+		trace2_data_string("scalar", the_repository,
+				   "log.excludeDecoration", "exists");
+		free(value);
+	}
+
+	return 0;
+}
+
+static int start_maintenance(void)
+{
+	return run_git("maintenance", "start", NULL);
+}
+
+static int add_enlistment(void)
+{
+	int res;
+
+	if (!the_repository->worktree)
+		die(_("Scalar enlistments require a worktree"));
+
+	res = run_git("config", "--global", "--get", "--fixed-value",
+		      "scalar.repo", the_repository->worktree, NULL);
+
+	/*
+	 * If the setting is already there, then do nothing.
+	 */
+	if (!res)
+		return 0;
+
+	return run_git("config", "--global", "--add",
+		       "scalar.repo", the_repository->worktree, NULL);
+}
+
+static int register_dir(void)
+{
+	int res = add_enlistment();
+
+	if (!res)
+		res = set_recommended_config();
+
+	if (!res)
+		res = start_maintenance();
+
+	return res;
+}
+
+static int cmd_register(int argc, const char **argv)
+{
+	struct option options[] = {
+		OPT_END(),
+	};
+	const char * const usage[] = {
+		N_("scalar register [<enlistment>]"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, NULL, options,
+			     usage, 0);
+
+	setup_enlistment_directory(argc, argv, usage, options, NULL);
+
+	return register_dir();
+}
 
 static struct {
 	const char *name;
 	int (*fn)(int, const char **);
 } builtins[] = {
+	{ "register", cmd_register },
 	{ NULL, NULL},
 };
 

index 0e627bb100e..2b5c52a25f5 100644
@@ -204,12 +204,12 @@ static int set_recommended_config(void)
 	return 0;
 }
 
-static int start_maintenance(void)
+static int toggle_maintenance(int enable)
 {
-	return run_git("maintenance", "start", NULL);
+	return run_git("maintenance", enable ? "start" : "unregister", NULL);
 }
 
-static int add_enlistment(void)
+static int add_or_remove_enlistment(int add)
 {
 	int res;
 

@@ -220,24 +220,39 @@ static int add_enlistment(void)
 		      "scalar.repo", the_repository->worktree, NULL);
 
 	/*
-	 * If the setting is already there, then do nothing.
+	 * If we want to add and the setting is already there, then do nothing.
+	 * If we want to remove and the setting is not there, then do nothing.
 	 */
-	if (!res)
+	if ((add && !res) || (!add && res))
 		return 0;
 
-	return run_git("config", "--global", "--add",
+	return run_git("config", "--global", add ? "--add" : "--unset",
+		       add ? "--no-fixed-value" : "--fixed-value",
 		       "scalar.repo", the_repository->worktree, NULL);
 }
 
 static int register_dir(void)
 {
-	int res = add_enlistment();
+	int res = add_or_remove_enlistment(1);
 
 	if (!res)
 		res = set_recommended_config();
 
 	if (!res)
-		res = start_maintenance();
+		res = toggle_maintenance(1);
+
+	return res;
+}
+
+static int unregister_dir(void)
+{
+	int res = 0;
+
+	if (toggle_maintenance(0) < 0)
+		res = -1;
+
+	if (add_or_remove_enlistment(0) < 0)
+		res = -1;
 
 	return res;
 }

@@ -260,11 +275,30 @@ static int cmd_register(int argc, const char **argv)
 	return register_dir();
 }
 
+static int cmd_unregister(int argc, const char **argv)
+{
+	struct option options[] = {
+		OPT_END(),
+	};
+	const char * const usage[] = {
+		N_("scalar unregister [<enlistment>]"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, NULL, options,
+			     usage, 0);
+
+	setup_enlistment_directory(argc, argv, usage, options, NULL);
+
+	return unregister_dir();
+}
+
 static struct {
 	const char *name;
 	int (*fn)(int, const char **);
 } builtins[] = {
 	{ "register", cmd_register },
+	{ "unregister", cmd_unregister },
 	{ NULL, NULL},
 };
 

index 2b5c52a25f5..d114c038b64 100644
@@ -275,6 +275,24 @@ static int cmd_register(int argc, const char **argv)
 	return register_dir();
 }
 
+static int remove_deleted_enlistment(struct strbuf *path)
+{
+	int res = 0;
+	strbuf_realpath_forgiving(path, path->buf, 1);
+
+	if (run_git("config", "--global",
+		    "--unset", "--fixed-value",
+		    "scalar.repo", path->buf, NULL) < 0)
+		res = -1;
+
+	if (run_git("config", "--global",
+		    "--unset", "--fixed-value",
+		    "maintenance.repo", path->buf, NULL) < 0)
+		res = -1;
+
+	return res;
+}
+
 static int cmd_unregister(int argc, const char **argv)
 {
 	struct option options[] = {

@@ -288,6 +306,34 @@ static int cmd_unregister(int argc, const char **argv)
 	argc = parse_options(argc, argv, NULL, options,
 			     usage, 0);
 
+	/*
+	 * Be forgiving when the enlistment or worktree does not even exist any
+	 * longer; This can be the case if a user deleted the worktree by
+	 * mistake and _still_ wants to unregister the thing.
+	 */
+	if (argc == 1) {
+		struct strbuf src_path = STRBUF_INIT, workdir_path = STRBUF_INIT;
+
+		strbuf_addf(&src_path, "%s/src/.git", argv[0]);
+		strbuf_addf(&workdir_path, "%s/.git", argv[0]);
+		if (!is_directory(src_path.buf) && !is_directory(workdir_path.buf)) {
+			/* remove possible matching registrations */
+			int res = -1;
+
+			strbuf_strip_suffix(&src_path, "/.git");
+			res = remove_deleted_enlistment(&src_path) && res;
+
+			strbuf_strip_suffix(&workdir_path, "/.git");
+			res = remove_deleted_enlistment(&workdir_path) && res;
+
+			strbuf_release(&src_path);
+			strbuf_release(&workdir_path);
+			return res;
+		}
+		strbuf_release(&src_path);
+		strbuf_release(&workdir_path);
+	}
+
 	setup_enlistment_directory(argc, argv, usage, options, NULL);
 
 	return unregister_dir();

index d114c038b64..7f5436399da 100644
@@ -257,6 +257,16 @@ static int unregister_dir(void)
 	return res;
 }
 
+static int cmd_list(int argc, const char **argv)
+{
+	if (argc != 1)
+		die(_("`scalar list` does not take arguments"));
+
+	if (run_git("config", "--global", "--get-all", "scalar.repo", NULL) < 0)
+		return -1;
+	return 0;
+}
+
 static int cmd_register(int argc, const char **argv)
 {
 	struct option options[] = {

@@ -343,6 +353,7 @@ static struct {
 	const char *name;
 	int (*fn)(int, const char **);
 } builtins[] = {
+	{ "list", cmd_list },
 	{ "register", cmd_register },
 	{ "unregister", cmd_unregister },
 	{ NULL, NULL},

index 7f5436399da..bf18003b297 100644
@@ -7,6 +7,7 @@
 #include "parse-options.h"
 #include "config.h"
 #include "run-command.h"
+#include "refs.h"
 
 /*
  * Remove the deepest subdirectory in the provided path string. Path must not

@@ -257,6 +258,205 @@ static int unregister_dir(void)
 	return res;
 }
 
+/* printf-style interface, expects `<key>=<value>` argument */
+static int set_config(const char *fmt, ...)
+{
+	struct strbuf buf = STRBUF_INIT;
+	char *value;
+	int res;
+	va_list args;
+
+	va_start(args, fmt);
+	strbuf_vaddf(&buf, fmt, args);
+	va_end(args);
+
+	value = strchr(buf.buf, '=');
+	if (value)
+		*(value++) = '\0';
+	res = git_config_set_gently(buf.buf, value);
+	strbuf_release(&buf);
+
+	return res;
+}
+
+static char *remote_default_branch(const char *url)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf out = STRBUF_INIT;
+
+	cp.git_cmd = 1;
+	strvec_pushl(&cp.args, "ls-remote", "--symref", url, "HEAD", NULL);
+	if (!pipe_command(&cp, NULL, 0, &out, 0, NULL, 0)) {
+		const char *line = out.buf;
+
+		while (*line) {
+			const char *eol = strchrnul(line, '\n'), *p;
+			size_t len = eol - line;
+			char *branch;
+
+			if (!skip_prefix(line, "ref: ", &p) ||
+			    !strip_suffix_mem(line, &len, "\tHEAD")) {
+				line = eol + (*eol == '\n');
+				continue;
+			}
+
+			eol = line + len;
+			if (skip_prefix(p, "refs/heads/", &p)) {
+				branch = xstrndup(p, eol - p);
+				strbuf_release(&out);
+				return branch;
+			}
+
+			error(_("remote HEAD is not a branch: '%.*s'"),
+			      (int)(eol - p), p);
+			strbuf_release(&out);
+			return NULL;
+		}
+	}
+	warning(_("failed to get default branch name from remote; "
+		  "using local default"));
+	strbuf_reset(&out);
+
+	child_process_init(&cp);
+	cp.git_cmd = 1;
+	strvec_pushl(&cp.args, "symbolic-ref", "--short", "HEAD", NULL);
+	if (!pipe_command(&cp, NULL, 0, &out, 0, NULL, 0)) {
+		strbuf_trim(&out);
+		return strbuf_detach(&out, NULL);
+	}
+
+	strbuf_release(&out);
+	error(_("failed to get default branch name"));
+	return NULL;
+}
+
+static int cmd_clone(int argc, const char **argv)
+{
+	const char *branch = NULL;
+	int full_clone = 0;
+	struct option clone_options[] = {
+		OPT_STRING('b', "branch", &branch, N_("<branch>"),
+			   N_("branch to checkout after clone")),
+		OPT_BOOL(0, "full-clone", &full_clone,
+			 N_("when cloning, create full working directory")),
+		OPT_END(),
+	};
+	const char * const clone_usage[] = {
+		N_("scalar clone [<options>] [--] <repo> [<dir>]"),
+		NULL
+	};
+	const char *url;
+	char *enlistment = NULL, *dir = NULL;
+	struct strbuf buf = STRBUF_INIT;
+	int res;
+
+	argc = parse_options(argc, argv, NULL, clone_options, clone_usage, 0);
+
+	if (argc == 2) {
+		url = argv[0];
+		enlistment = xstrdup(argv[1]);
+	} else if (argc == 1) {
+		url = argv[0];
+
+		strbuf_addstr(&buf, url);
+		/* Strip trailing slashes, if any */
+		while (buf.len > 0 && is_dir_sep(buf.buf[buf.len - 1]))
+			strbuf_setlen(&buf, buf.len - 1);
+		/* Strip suffix `.git`, if any */
+		strbuf_strip_suffix(&buf, ".git");
+
+		enlistment = find_last_dir_sep(buf.buf);
+		if (!enlistment) {
+			die(_("cannot deduce worktree name from '%s'"), url);
+		}
+		enlistment = xstrdup(enlistment + 1);
+	} else {
+		usage_msg_opt(_("You must specify a repository to clone."),
+			      clone_usage, clone_options);
+	}
+
+	if (is_directory(enlistment))
+		die(_("directory '%s' exists already"), enlistment);
+
+	dir = xstrfmt("%s/src", enlistment);
+
+	strbuf_reset(&buf);
+	if (branch)
+		strbuf_addf(&buf, "init.defaultBranch=%s", branch);
+	else {
+		char *b = repo_default_branch_name(the_repository, 1);
+		strbuf_addf(&buf, "init.defaultBranch=%s", b);
+		free(b);
+	}
+
+	if ((res = run_git("-c", buf.buf, "init", "--", dir, NULL)))
+		goto cleanup;
+
+	if (chdir(dir) < 0) {
+		res = error_errno(_("could not switch to '%s'"), dir);
+		goto cleanup;
+	}
+
+	setup_git_directory();
+
+	/* common-main already logs `argv` */
+	trace2_def_repo(the_repository);
+
+	if (!branch && !(branch = remote_default_branch(url))) {
+		res = error(_("failed to get default branch for '%s'"), url);
+		goto cleanup;
+	}
+
+	if (set_config("remote.origin.url=%s", url) ||
+	    set_config("remote.origin.fetch="
+		       "+refs/heads/*:refs/remotes/origin/*") ||
+	    set_config("remote.origin.promisor=true") ||
+	    set_config("remote.origin.partialCloneFilter=blob:none")) {
+		res = error(_("could not configure remote in '%s'"), dir);
+		goto cleanup;
+	}
+
+	if (!full_clone &&
+	    (res = run_git("sparse-checkout", "init", "--cone", NULL)))
+		goto cleanup;
+
+	if (set_recommended_config())
+		return error(_("could not configure '%s'"), dir);
+
+	if ((res = run_git("fetch", "--quiet", "origin", NULL))) {
+		warning(_("partial clone failed; attempting full clone"));
+
+		if (set_config("remote.origin.promisor") ||
+		    set_config("remote.origin.partialCloneFilter")) {
+			res = error(_("could not configure for full clone"));
+			goto cleanup;
+		}
+
+		if ((res = run_git("fetch", "--quiet", "origin", NULL)))
+			goto cleanup;
+	}
+
+	if ((res = set_config("branch.%s.remote=origin", branch)))
+		goto cleanup;
+	if ((res = set_config("branch.%s.merge=refs/heads/%s",
+			      branch, branch)))
+		goto cleanup;
+
+	strbuf_reset(&buf);
+	strbuf_addf(&buf, "origin/%s", branch);
+	res = run_git("checkout", "-f", "-t", buf.buf, NULL);
+	if (res)
+		goto cleanup;
+
+	res = register_dir();
+
+cleanup:
+	free(enlistment);
+	free(dir);
+	strbuf_release(&buf);
+	return res;
+}
+
 static int cmd_list(int argc, const char **argv)
 {
 	if (argc != 1)

@@ -353,6 +553,7 @@ static struct {
 	const char *name;
 	int (*fn)(int, const char **);
 } builtins[] = {
+	{ "clone", cmd_clone },
 	{ "list", cmd_list },
 	{ "register", cmd_register },
 	{ "unregister", cmd_unregister },

index bf18003b297..7dd1f28948f 100644
@@ -333,12 +333,15 @@ static char *remote_default_branch(const char *url)
 static int cmd_clone(int argc, const char **argv)
 {
 	const char *branch = NULL;
-	int full_clone = 0;
+	int full_clone = 0, single_branch = 0;
 	struct option clone_options[] = {
 		OPT_STRING('b', "branch", &branch, N_("<branch>"),
 			   N_("branch to checkout after clone")),
 		OPT_BOOL(0, "full-clone", &full_clone,
 			 N_("when cloning, create full working directory")),
+		OPT_BOOL(0, "single-branch", &single_branch,
+			 N_("only download metadata for the branch that will "
+			    "be checked out")),
 		OPT_END(),
 	};
 	const char * const clone_usage[] = {

@@ -409,7 +412,9 @@ static int cmd_clone(int argc, const char **argv)
 
 	if (set_config("remote.origin.url=%s", url) ||
 	    set_config("remote.origin.fetch="
-		       "+refs/heads/*:refs/remotes/origin/*") ||
+		       "+refs/heads/%s:refs/remotes/origin/%s",
+		       single_branch ? branch : "*",
+		       single_branch ? branch : "*") ||
 	    set_config("remote.origin.promisor=true") ||
 	    set_config("remote.origin.partialCloneFilter=blob:none")) {
 		res = error(_("could not configure remote in '%s'"), dir);

index 7dd1f28948f..8a11f390251 100644
@@ -490,6 +490,69 @@ static int cmd_register(int argc, const char **argv)
 	return register_dir();
 }
 
+static int cmd_run(int argc, const char **argv)
+{
+	struct option options[] = {
+		OPT_END(),
+	};
+	struct {
+		const char *arg, *task;
+	} tasks[] = {
+		{ "config", NULL },
+		{ "commit-graph", "commit-graph" },
+		{ "fetch", "prefetch" },
+		{ "loose-objects", "loose-objects" },
+		{ "pack-files", "incremental-repack" },
+		{ NULL, NULL }
+	};
+	struct strbuf buf = STRBUF_INIT;
+	const char *usagestr[] = { NULL, NULL };
+	int i;
+
+	strbuf_addstr(&buf, N_("scalar run <task> [<enlistment>]\nTasks:\n"));
+	for (i = 0; tasks[i].arg; i++)
+		strbuf_addf(&buf, "\t%s\n", tasks[i].arg);
+	usagestr[0] = buf.buf;
+
+	argc = parse_options(argc, argv, NULL, options,
+			     usagestr, 0);
+
+	if (!argc)
+		usage_with_options(usagestr, options);
+
+	if (!strcmp("all", argv[0])) {
+		i = -1;
+	} else {
+		for (i = 0; tasks[i].arg && strcmp(tasks[i].arg, argv[0]); i++)
+			; /* keep looking for the task */
+
+		if (i > 0 && !tasks[i].arg) {
+			error(_("no such task: '%s'"), argv[0]);
+			usage_with_options(usagestr, options);
+		}
+	}
+
+	argc--;
+	argv++;
+	setup_enlistment_directory(argc, argv, usagestr, options, NULL);
+	strbuf_release(&buf);
+
+	if (i == 0)
+		return register_dir();
+
+	if (i > 0)
+		return run_git("maintenance", "run",
+			       "--task", tasks[i].task, NULL);
+
+	if (register_dir())
+		return -1;
+	for (i = 1; tasks[i].arg; i++)
+		if (run_git("maintenance", "run",
+			    "--task", tasks[i].task, NULL))
+			return -1;
+	return 0;
+}
+
 static int remove_deleted_enlistment(struct strbuf *path)
 {
 	int res = 0;

@@ -562,6 +625,7 @@ static struct {
 	{ "list", cmd_list },
 	{ "register", cmd_register },
 	{ "unregister", cmd_unregister },
+	{ "run", cmd_run },
 	{ NULL, NULL},
 };
 

index 8a11f390251..1fff7eb7c12 100644
@@ -115,18 +115,20 @@ static int run_git(const char *arg, ...)
 	return res;
 }
 
-static int set_recommended_config(void)
+static int set_recommended_config(int reconfigure)
 {
 	struct {
 		const char *key;
 		const char *value;
+		int overwrite_on_reconfigure;
 	} config[] = {
-		{ "am.keepCR", "true" },
-		{ "core.FSCache", "true" },
-		{ "core.multiPackIndex", "true" },
-		{ "core.preloadIndex", "true" },
+		/* Required */
+		{ "am.keepCR", "true", 1 },
+		{ "core.FSCache", "true", 1 },
+		{ "core.multiPackIndex", "true", 1 },
+		{ "core.preloadIndex", "true", 1 },
 #ifndef WIN32
-		{ "core.untrackedCache", "true" },
+		{ "core.untrackedCache", "true", 1 },
 #else
 		/*
 		 * Unfortunately, Scalar's Functional Tests demonstrated

@@ -140,28 +142,29 @@ static int set_recommended_config(void)
 		 * Therefore, with a sad heart, we disable this very useful
 		 * feature on Windows.
 		 */
-		{ "core.untrackedCache", "false" },
+		{ "core.untrackedCache", "false", 1 },
 #endif
-		{ "core.logAllRefUpdates", "true" },
-		{ "credential.https://dev.azure.com.useHttpPath", "true" },
-		{ "credential.validate", "false" }, /* GCM4W-only */
-		{ "gc.auto", "0" },
-		{ "gui.GCWarning", "false" },
-		{ "index.threads", "true" },
-		{ "index.version", "4" },
-		{ "merge.stat", "false" },
-		{ "merge.renames", "false" },
-		{ "pack.useBitmaps", "false" },
-		{ "pack.useSparse", "true" },
-		{ "receive.autoGC", "false" },
-		{ "reset.quiet", "true" },
-		{ "feature.manyFiles", "false" },
-		{ "feature.experimental", "false" },
-		{ "fetch.unpackLimit", "1" },
-		{ "fetch.writeCommitGraph", "false" },
+		{ "core.logAllRefUpdates", "true", 1 },
+		{ "credential.https://dev.azure.com.useHttpPath", "true", 1 },
+		{ "credential.validate", "false", 1 }, /* GCM4W-only */
+		{ "gc.auto", "0", 1 },
+		{ "gui.GCWarning", "false", 1 },
+		{ "index.threads", "true", 1 },
+		{ "index.version", "4", 1 },
+		{ "merge.stat", "false", 1 },
+		{ "merge.renames", "false", 1 },
+		{ "pack.useBitmaps", "false", 1 },
+		{ "pack.useSparse", "true", 1 },
+		{ "receive.autoGC", "false", 1 },
+		{ "reset.quiet", "true", 1 },
+		{ "feature.manyFiles", "false", 1 },
+		{ "feature.experimental", "false", 1 },
+		{ "fetch.unpackLimit", "1", 1 },
+		{ "fetch.writeCommitGraph", "false", 1 },
 #ifdef WIN32
-		{ "http.sslBackend", "schannel" },
+		{ "http.sslBackend", "schannel", 1 },
 #endif
+		/* Optional */
 		{ "status.aheadBehind", "false" },
 		{ "commitGraph.generationVersion", "1" },
 		{ "core.autoCRLF", "false" },

@@ -172,7 +175,8 @@ static int set_recommended_config(void)
 	char *value;
 
 	for (i = 0; config[i].key; i++) {
-		if (git_config_get_string(config[i].key, &value)) {
+		if ((reconfigure && config[i].overwrite_on_reconfigure) ||
+		    git_config_get_string(config[i].key, &value)) {
 			trace2_data_string("scalar", the_repository, config[i].key, "created");
 			if (git_config_set_gently(config[i].key,
 						  config[i].value) < 0)

@@ -237,7 +241,7 @@ static int register_dir(void)
 	int res = add_or_remove_enlistment(1);
 
 	if (!res)
-		res = set_recommended_config();
+		res = set_recommended_config(0);
 
 	if (!res)
 		res = toggle_maintenance(1);

@@ -425,7 +429,7 @@ static int cmd_clone(int argc, const char **argv)
 	    (res = run_git("sparse-checkout", "init", "--cone", NULL)))
 		goto cleanup;
 
-	if (set_recommended_config())
+	if (set_recommended_config(0))
 		return error(_("could not configure '%s'"), dir);
 
 	if ((res = run_git("fetch", "--quiet", "origin", NULL))) {

@@ -490,6 +494,24 @@ static int cmd_register(int argc, const char **argv)
 	return register_dir();
 }
 
+static int cmd_reconfigure(int argc, const char **argv)
+{
+	struct option options[] = {
+		OPT_END(),
+	};
+	const char * const usage[] = {
+		N_("scalar reconfigure [<enlistment>]"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, NULL, options,
+			     usage, 0);
+
+	setup_enlistment_directory(argc, argv, usage, options, NULL);
+
+	return set_recommended_config(1);
+}
+
 static int cmd_run(int argc, const char **argv)
 {
 	struct option options[] = {

@@ -626,6 +648,7 @@ static struct {
 	{ "register", cmd_register },
 	{ "unregister", cmd_unregister },
 	{ "run", cmd_run },
+	{ "reconfigure", cmd_reconfigure },
 	{ NULL, NULL},
 };
 

index 1fff7eb7c12..67fa5305225 100644
@@ -494,22 +494,77 @@ static int cmd_register(int argc, const char **argv)
 	return register_dir();
 }
 
+static int get_scalar_repos(const char *key, const char *value, void *data)
+{
+	struct string_list *list = data;
+
+	if (!strcmp(key, "scalar.repo"))
+		string_list_append(list, value);
+
+	return 0;
+}
+
 static int cmd_reconfigure(int argc, const char **argv)
 {
+	int all = 0;
 	struct option options[] = {
+		OPT_BOOL('a', "all", &all,
+			 N_("reconfigure all registered enlistments")),
 		OPT_END(),
 	};
 	const char * const usage[] = {
-		N_("scalar reconfigure [<enlistment>]"),
+		N_("scalar reconfigure [--all | <enlistment>]"),
 		NULL
 	};
+	struct string_list scalar_repos = STRING_LIST_INIT_DUP;
+	int i, res = 0;
+	struct repository r = { NULL };
+	struct strbuf commondir = STRBUF_INIT, gitdir = STRBUF_INIT;
 
 	argc = parse_options(argc, argv, NULL, options,
 			     usage, 0);
 
-	setup_enlistment_directory(argc, argv, usage, options, NULL);
+	if (!all) {
+		setup_enlistment_directory(argc, argv, usage, options, NULL);
+
+		return set_recommended_config(1);
+	}
+
+	if (argc > 0)
+		usage_msg_opt(_("--all or <enlistment>, but not both"),
+			      usage, options);
+
+	git_config(get_scalar_repos, &scalar_repos);
 
-	return set_recommended_config(1);
+	for (i = 0; i < scalar_repos.nr; i++) {
+		const char *dir = scalar_repos.items[i].string;
+
+		strbuf_reset(&commondir);
+		strbuf_reset(&gitdir);
+
+		if (chdir(dir) < 0) {
+			warning_errno(_("could not switch to '%s'"), dir);
+			res = -1;
+		} else if (discover_git_directory(&commondir, &gitdir) < 0) {
+			warning_errno(_("git repository gone in '%s'"), dir);
+			res = -1;
+		} else {
+			git_config_clear();
+
+			the_repository = &r;
+			r.commondir = commondir.buf;
+			r.gitdir = gitdir.buf;
+
+			if (set_recommended_config(1) < 0)
+				res = -1;
+		}
+	}
+
+	string_list_clear(&scalar_repos, 1);
+	strbuf_release(&commondir);
+	strbuf_release(&gitdir);
+
+	return res;
 }
 
 static int cmd_run(int argc, const char **argv)

index 67fa5305225..00bedb0bf66 100644
@@ -8,6 +8,7 @@
 #include "config.h"
 #include "run-command.h"
 #include "refs.h"
+#include "dir.h"
 
 /*
  * Remove the deepest subdirectory in the provided path string. Path must not

@@ -334,6 +335,33 @@ static char *remote_default_branch(const char *url)
 	return NULL;
 }
 
+static int delete_enlistment(struct strbuf *enlistment)
+{
+#ifdef WIN32
+	struct strbuf parent = STRBUF_INIT;
+#endif
+
+	if (unregister_dir())
+		die(_("failed to unregister repository"));
+
+#ifdef WIN32
+	/*
+	 * Change the current directory to one outside of the enlistment so
+	 * that we may delete everything underneath it.
+	 */
+	strbuf_addbuf(&parent, enlistment);
+	strbuf_parent_directory(&parent);
+	if (chdir(parent.buf) < 0)
+		die_errno(_("could not switch to '%s'"), parent.buf);
+	strbuf_release(&parent);
+#endif
+
+	if (remove_dir_recursively(enlistment, 0))
+		die(_("failed to delete enlistment directory"));
+
+	return 0;
+}
+
 static int cmd_clone(int argc, const char **argv)
 {
 	const char *branch = NULL;

@@ -694,6 +722,32 @@ static int cmd_unregister(int argc, const char **argv)
 	return unregister_dir();
 }
 
+static int cmd_delete(int argc, const char **argv)
+{
+	struct option options[] = {
+		OPT_END(),
+	};
+	const char * const usage[] = {
+		N_("scalar delete <enlistment>"),
+		NULL
+	};
+	struct strbuf enlistment = STRBUF_INIT;
+	int res = 0;
+
+	argc = parse_options(argc, argv, NULL, options,
+			     usage, 0);
+
+	if (argc != 1)
+		usage_with_options(usage, options);
+
+	setup_enlistment_directory(argc, argv, usage, options, &enlistment);
+
+	res = delete_enlistment(&enlistment);
+	strbuf_release(&enlistment);
+
+	return res;
+}
+
 static struct {
 	const char *name;
 	int (*fn)(int, const char **);

@@ -704,6 +758,7 @@ static struct {
 	{ "unregister", cmd_unregister },
 	{ "run", cmd_run },
 	{ "reconfigure", cmd_reconfigure },
+	{ "delete", cmd_delete },
 	{ NULL, NULL},
 };
 

index 00bedb0bf66..728166aa97a 100644
@@ -9,6 +9,7 @@
 #include "run-command.h"
 #include "refs.h"
 #include "dir.h"
+#include "help.h"
 
 /*
  * Remove the deepest subdirectory in the provided path string. Path must not

@@ -362,6 +363,15 @@ static int delete_enlistment(struct strbuf *enlistment)
 	return 0;
 }
 
+/*
+ * Dummy implementation; Using `get_version_info()` would cause a link error
+ * without this.
+ */
+void load_builtin_commands(const char *prefix, struct cmdnames *cmds)
+{
+	die("not implemented");
+}
+
 static int cmd_clone(int argc, const char **argv)
 {
 	const char *branch = NULL;

@@ -748,6 +758,34 @@ static int cmd_delete(int argc, const char **argv)
 	return res;
 }
 
+static int cmd_version(int argc, const char **argv)
+{
+	int verbose = 0, build_options = 0;
+	struct option options[] = {
+		OPT__VERBOSE(&verbose, N_("include Git version")),
+		OPT_BOOL(0, "build-options", &build_options,
+			 N_("include Git's build options")),
+		OPT_END(),
+	};
+	const char * const usage[] = {
+		N_("scalar verbose [-v | --verbose] [--build-options]"),
+		NULL
+	};
+	struct strbuf buf = STRBUF_INIT;
+
+	argc = parse_options(argc, argv, NULL, options,
+			     usage, 0);
+
+	if (argc != 0)
+		usage_with_options(usage, options);
+
+	get_version_info(&buf, build_options);
+	fprintf(stderr, "%s\n", buf.buf);
+	strbuf_release(&buf);
+
+	return 0;
+}
+
 static struct {
 	const char *name;
 	int (*fn)(int, const char **);

@@ -759,6 +797,7 @@ static struct {
 	{ "run", cmd_run },
 	{ "reconfigure", cmd_reconfigure },
 	{ "delete", cmd_delete },
+	{ "version", cmd_version },
 	{ NULL, NULL},
 };
 

index 728166aa97a..76a77ca1ed0 100644
@@ -806,6 +806,25 @@ int cmd_main(int argc, const char **argv)
 	struct strbuf scalar_usage = STRBUF_INIT;
 	int i;
 
+	while (argc > 1 && *argv[1] == '-') {
+		if (!strcmp(argv[1], "-C")) {
+			if (argc < 3)
+				die(_("-C requires a <directory>"));
+			if (chdir(argv[2]) < 0)
+				die_errno(_("could not change to '%s'"),
+					  argv[2]);
+			argc -= 2;
+			argv += 2;
+		} else if (!strcmp(argv[1], "-c")) {
+			if (argc < 3)
+				die(_("-c requires a <key>=<value> argument"));
+			git_config_push_parameter(argv[2]);
+			argc -= 2;
+			argv += 2;
+		} else
+			break;
+	}
+
 	if (argc > 1) {
 		argv++;
 		argc--;

@@ -816,7 +835,8 @@ int cmd_main(int argc, const char **argv)
 	}
 
 	strbuf_addstr(&scalar_usage,
-		      N_("scalar <command> [<options>]\n\nCommands:\n"));
+		      N_("scalar [-C <directory>] [-c <key>=<value>] "
+			 "<command> [<options>]\n\nCommands:\n"));
 	for (i = 0; builtins[i].name; i++)
 		strbuf_addf(&scalar_usage, "\t%s\n", builtins[i].name);
 

new file mode 100644
index 00000000000..7cff29e0fcd
@@ -0,0 +1,36 @@
+/*
+ * The Scalar command-line interface.
+ */
+
+#include "cache.h"
+#include "gettext.h"
+#include "parse-options.h"
+
+static struct {
+	const char *name;
+	int (*fn)(int, const char **);
+} builtins[] = {
+	{ NULL, NULL},
+};
+
+int cmd_main(int argc, const char **argv)
+{
+	struct strbuf scalar_usage = STRBUF_INIT;
+	int i;
+
+	if (argc > 1) {
+		argv++;
+		argc--;
+
+		for (i = 0; builtins[i].name; i++)
+			if (!strcmp(builtins[i].name, argv[0]))
+				return !!builtins[i].fn(argc, argv);
+	}
+
+	strbuf_addstr(&scalar_usage,
+		      N_("scalar <command> [<options>]\n\nCommands:\n"));
+	for (i = 0; builtins[i].name; i++)
+		strbuf_addf(&scalar_usage, "\t%s\n", builtins[i].name);
+
+	usage(scalar_usage.buf);
+}

index 7cff29e0fcd..38721d671ba 100644
@@ -5,11 +5,259 @@
 #include "cache.h"
 #include "gettext.h"
 #include "parse-options.h"
+#include "config.h"
+#include "run-command.h"
+
+/*
+ * Remove the deepest subdirectory in the provided path string. Path must not
+ * include a trailing path separator. Returns 1 if parent directory found,
+ * otherwise 0.
+ */
+static int strbuf_parent_directory(struct strbuf *buf)
+{
+	size_t len = buf->len;
+	size_t offset = offset_1st_component(buf->buf);
+	char *path_sep = find_last_dir_sep(buf->buf + offset);
+	strbuf_setlen(buf, path_sep ? path_sep - buf->buf : offset);
+
+	return buf->len < len;
+}
+
+static void setup_enlistment_directory(int argc, const char **argv,
+				       const char * const *usagestr,
+				       const struct option *options,
+				       struct strbuf *enlistment_root)
+{
+	struct strbuf path = STRBUF_INIT;
+	char *root;
+	int enlistment_found = 0;
+
+	if (startup_info->have_repository)
+		BUG("gitdir already set up?!?");
+
+	if (argc > 1)
+		usage_with_options(usagestr, options);
+
+	/* find the worktree, determine its corresponding root */
+	if (argc == 1)
+		strbuf_add_absolute_path(&path, argv[0]);
+	else if (strbuf_getcwd(&path) < 0)
+		die(_("need a working directory"));
+
+	strbuf_trim_trailing_dir_sep(&path);
+	do {
+		const size_t len = path.len;
+
+		/* check if currently in enlistment root with src/ workdir */
+		strbuf_addstr(&path, "/src");
+		if (is_nonbare_repository_dir(&path)) {
+			if (enlistment_root)
+				strbuf_add(enlistment_root, path.buf, len);
+
+			enlistment_found = 1;
+			break;
+		}
+
+		/* reset to original path */
+		strbuf_setlen(&path, len);
+
+		/* check if currently in workdir */
+		if (is_nonbare_repository_dir(&path)) {
+			if (enlistment_root) {
+				/*
+				 * If the worktree's directory's name is `src`, the enlistment is the
+				 * parent directory, otherwise it is identical to the worktree.
+				 */
+				root = strip_path_suffix(path.buf, "src");
+				strbuf_addstr(enlistment_root, root ? root : path.buf);
+				free(root);
+			}
+
+			enlistment_found = 1;
+			break;
+		}
+	} while (strbuf_parent_directory(&path));
+
+	if (!enlistment_found)
+		die(_("could not find enlistment root"));
+
+	if (chdir(path.buf) < 0)
+		die_errno(_("could not switch to '%s'"), path.buf);
+
+	strbuf_release(&path);
+	setup_git_directory();
+}
+
+static int run_git(const char *arg, ...)
+{
+	struct strvec argv = STRVEC_INIT;
+	va_list args;
+	const char *p;
+	int res;
+
+	va_start(args, arg);
+	strvec_push(&argv, arg);
+	while ((p = va_arg(args, const char *)))
+		strvec_push(&argv, p);
+	va_end(args);
+
+	res = run_command_v_opt(argv.v, RUN_GIT_CMD);
+
+	strvec_clear(&argv);
+	return res;
+}
+
+static int set_recommended_config(void)
+{
+	struct {
+		const char *key;
+		const char *value;
+	} config[] = {
+		{ "am.keepCR", "true" },
+		{ "core.FSCache", "true" },
+		{ "core.multiPackIndex", "true" },
+		{ "core.preloadIndex", "true" },
+#ifndef WIN32
+		{ "core.untrackedCache", "true" },
+#else
+		/*
+		 * Unfortunately, Scalar's Functional Tests demonstrated
+		 * that the untracked cache feature is unreliable on Windows
+		 * (which is a bummer because that platform would benefit the
+		 * most from it). For some reason, freshly created files seem
+		 * not to update the directory's `lastModified` time
+		 * immediately, but the untracked cache would need to rely on
+		 * that.
+		 *
+		 * Therefore, with a sad heart, we disable this very useful
+		 * feature on Windows.
+		 */
+		{ "core.untrackedCache", "false" },
+#endif
+		{ "core.logAllRefUpdates", "true" },
+		{ "credential.https://dev.azure.com.useHttpPath", "true" },
+		{ "credential.validate", "false" }, /* GCM4W-only */
+		{ "gc.auto", "0" },
+		{ "gui.GCWarning", "false" },
+		{ "index.threads", "true" },
+		{ "index.version", "4" },
+		{ "merge.stat", "false" },
+		{ "merge.renames", "false" },
+		{ "pack.useBitmaps", "false" },
+		{ "pack.useSparse", "true" },
+		{ "receive.autoGC", "false" },
+		{ "reset.quiet", "true" },
+		{ "feature.manyFiles", "false" },
+		{ "feature.experimental", "false" },
+		{ "fetch.unpackLimit", "1" },
+		{ "fetch.writeCommitGraph", "false" },
+#ifdef WIN32
+		{ "http.sslBackend", "schannel" },
+#endif
+		{ "status.aheadBehind", "false" },
+		{ "commitGraph.generationVersion", "1" },
+		{ "core.autoCRLF", "false" },
+		{ "core.safeCRLF", "false" },
+		{ NULL, NULL },
+	};
+	int i;
+	char *value;
+
+	for (i = 0; config[i].key; i++) {
+		if (git_config_get_string(config[i].key, &value)) {
+			trace2_data_string("scalar", the_repository, config[i].key, "created");
+			if (git_config_set_gently(config[i].key,
+						  config[i].value) < 0)
+				return error(_("could not configure %s=%s"),
+					     config[i].key, config[i].value);
+		} else {
+			trace2_data_string("scalar", the_repository, config[i].key, "exists");
+			free(value);
+		}
+	}
+
+	/*
+	 * The `log.excludeDecoration` setting is special because it allows
+	 * for multiple values.
+	 */
+	if (git_config_get_string("log.excludeDecoration", &value)) {
+		trace2_data_string("scalar", the_repository,
+				   "log.excludeDecoration", "created");
+		if (git_config_set_multivar_gently("log.excludeDecoration",
+						   "refs/prefetch/*",
+						   CONFIG_REGEX_NONE, 0))
+			return error(_("could not configure "
+				       "log.excludeDecoration"));
+	} else {
+		trace2_data_string("scalar", the_repository,
+				   "log.excludeDecoration", "exists");
+		free(value);
+	}
+
+	return 0;
+}
+
+static int start_maintenance(void)
+{
+	return run_git("maintenance", "start", NULL);
+}
+
+static int add_enlistment(void)
+{
+	int res;
+
+	if (!the_repository->worktree)
+		die(_("Scalar enlistments require a worktree"));
+
+	res = run_git("config", "--global", "--get", "--fixed-value",
+		      "scalar.repo", the_repository->worktree, NULL);
+
+	/*
+	 * If the setting is already there, then do nothing.
+	 */
+	if (!res)
+		return 0;
+
+	return run_git("config", "--global", "--add",
+		       "scalar.repo", the_repository->worktree, NULL);
+}
+
+static int register_dir(void)
+{
+	int res = add_enlistment();
+
+	if (!res)
+		res = set_recommended_config();
+
+	if (!res)
+		res = start_maintenance();
+
+	return res;
+}
+
+static int cmd_register(int argc, const char **argv)
+{
+	struct option options[] = {
+		OPT_END(),
+	};
+	const char * const usage[] = {
+		N_("scalar register [<enlistment>]"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, NULL, options,
+			     usage, 0);
+
+	setup_enlistment_directory(argc, argv, usage, options, NULL);
+
+	return register_dir();
+}
 
 static struct {
 	const char *name;
 	int (*fn)(int, const char **);
 } builtins[] = {
+	{ "register", cmd_register },
 	{ NULL, NULL},
 };
 

index 38721d671ba..fc55404230d 100644
@@ -197,12 +197,12 @@ static int set_recommended_config(void)
 	return 0;
 }
 
-static int start_maintenance(void)
+static int toggle_maintenance(int enable)
 {
-	return run_git("maintenance", "start", NULL);
+	return run_git("maintenance", enable ? "start" : "unregister", NULL);
 }
 
-static int add_enlistment(void)
+static int add_or_remove_enlistment(int add)
 {
 	int res;
 

@@ -213,24 +213,39 @@ static int add_enlistment(void)
 		      "scalar.repo", the_repository->worktree, NULL);
 
 	/*
-	 * If the setting is already there, then do nothing.
+	 * If we want to add and the setting is already there, then do nothing.
+	 * If we want to remove and the setting is not there, then do nothing.
 	 */
-	if (!res)
+	if ((add && !res) || (!add && res))
 		return 0;
 
-	return run_git("config", "--global", "--add",
+	return run_git("config", "--global", add ? "--add" : "--unset",
+		       add ? "--no-fixed-value" : "--fixed-value",
 		       "scalar.repo", the_repository->worktree, NULL);
 }
 
 static int register_dir(void)
 {
-	int res = add_enlistment();
+	int res = add_or_remove_enlistment(1);
 
 	if (!res)
 		res = set_recommended_config();
 
 	if (!res)
-		res = start_maintenance();
+		res = toggle_maintenance(1);
+
+	return res;
+}
+
+static int unregister_dir(void)
+{
+	int res = 0;
+
+	if (toggle_maintenance(0) < 0)
+		res = -1;
+
+	if (add_or_remove_enlistment(0) < 0)
+		res = -1;
 
 	return res;
 }

@@ -253,11 +268,30 @@ static int cmd_register(int argc, const char **argv)
 	return register_dir();
 }
 
+static int cmd_unregister(int argc, const char **argv)
+{
+	struct option options[] = {
+		OPT_END(),
+	};
+	const char * const usage[] = {
+		N_("scalar unregister [<enlistment>]"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, NULL, options,
+			     usage, 0);
+
+	setup_enlistment_directory(argc, argv, usage, options, NULL);
+
+	return unregister_dir();
+}
+
 static struct {
 	const char *name;
 	int (*fn)(int, const char **);
 } builtins[] = {
 	{ "register", cmd_register },
+	{ "unregister", cmd_unregister },
 	{ NULL, NULL},
 };
 

index fc55404230d..dc84ce0d5b2 100644
@@ -268,6 +268,24 @@ static int cmd_register(int argc, const char **argv)
 	return register_dir();
 }
 
+static int remove_deleted_enlistment(struct strbuf *path)
+{
+	int res = 0;
+	strbuf_realpath_forgiving(path, path->buf, 1);
+
+	if (run_git("config", "--global",
+		    "--unset", "--fixed-value",
+		    "scalar.repo", path->buf, NULL) < 0)
+		res = -1;
+
+	if (run_git("config", "--global",
+		    "--unset", "--fixed-value",
+		    "maintenance.repo", path->buf, NULL) < 0)
+		res = -1;
+
+	return res;
+}
+
 static int cmd_unregister(int argc, const char **argv)
 {
 	struct option options[] = {

@@ -281,6 +299,34 @@ static int cmd_unregister(int argc, const char **argv)
 	argc = parse_options(argc, argv, NULL, options,
 			     usage, 0);
 
+	/*
+	 * Be forgiving when the enlistment or worktree does not even exist any
+	 * longer; This can be the case if a user deleted the worktree by
+	 * mistake and _still_ wants to unregister the thing.
+	 */
+	if (argc == 1) {
+		struct strbuf src_path = STRBUF_INIT, workdir_path = STRBUF_INIT;
+
+		strbuf_addf(&src_path, "%s/src/.git", argv[0]);
+		strbuf_addf(&workdir_path, "%s/.git", argv[0]);
+		if (!is_directory(src_path.buf) && !is_directory(workdir_path.buf)) {
+			/* remove possible matching registrations */
+			int res = -1;
+
+			strbuf_strip_suffix(&src_path, "/.git");
+			res = remove_deleted_enlistment(&src_path) && res;
+
+			strbuf_strip_suffix(&workdir_path, "/.git");
+			res = remove_deleted_enlistment(&workdir_path) && res;
+
+			strbuf_release(&src_path);
+			strbuf_release(&workdir_path);
+			return res;
+		}
+		strbuf_release(&src_path);
+		strbuf_release(&workdir_path);
+	}
+
 	setup_enlistment_directory(argc, argv, usage, options, NULL);
 
 	return unregister_dir();

index dc84ce0d5b2..d13eb951c3d 100644
@@ -250,6 +250,16 @@ static int unregister_dir(void)
 	return res;
 }
 
+static int cmd_list(int argc, const char **argv)
+{
+	if (argc != 1)
+		die(_("`scalar list` does not take arguments"));
+
+	if (run_git("config", "--global", "--get-all", "scalar.repo", NULL) < 0)
+		return -1;
+	return 0;
+}
+
 static int cmd_register(int argc, const char **argv)
 {
 	struct option options[] = {

@@ -336,6 +346,7 @@ static struct {
 	const char *name;
 	int (*fn)(int, const char **);
 } builtins[] = {
+	{ "list", cmd_list },
 	{ "register", cmd_register },
 	{ "unregister", cmd_unregister },
 	{ NULL, NULL},

index d13eb951c3d..0401462b9b3 100644
@@ -7,6 +7,7 @@
 #include "parse-options.h"
 #include "config.h"
 #include "run-command.h"
+#include "refs.h"
 
 /*
  * Remove the deepest subdirectory in the provided path string. Path must not

@@ -250,6 +251,205 @@ static int unregister_dir(void)
 	return res;
 }
 
+/* printf-style interface, expects `<key>=<value>` argument */
+static int set_config(const char *fmt, ...)
+{
+	struct strbuf buf = STRBUF_INIT;
+	char *value;
+	int res;
+	va_list args;
+
+	va_start(args, fmt);
+	strbuf_vaddf(&buf, fmt, args);
+	va_end(args);
+
+	value = strchr(buf.buf, '=');
+	if (value)
+		*(value++) = '\0';
+	res = git_config_set_gently(buf.buf, value);
+	strbuf_release(&buf);
+
+	return res;
+}
+
+static char *remote_default_branch(const char *url)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf out = STRBUF_INIT;
+
+	cp.git_cmd = 1;
+	strvec_pushl(&cp.args, "ls-remote", "--symref", url, "HEAD", NULL);
+	if (!pipe_command(&cp, NULL, 0, &out, 0, NULL, 0)) {
+		const char *line = out.buf;
+
+		while (*line) {
+			const char *eol = strchrnul(line, '\n'), *p;
+			size_t len = eol - line;
+			char *branch;
+
+			if (!skip_prefix(line, "ref: ", &p) ||
+			    !strip_suffix_mem(line, &len, "\tHEAD")) {
+				line = eol + (*eol == '\n');
+				continue;
+			}
+
+			eol = line + len;
+			if (skip_prefix(p, "refs/heads/", &p)) {
+				branch = xstrndup(p, eol - p);
+				strbuf_release(&out);
+				return branch;
+			}
+
+			error(_("remote HEAD is not a branch: '%.*s'"),
+			      (int)(eol - p), p);
+			strbuf_release(&out);
+			return NULL;
+		}
+	}
+	warning(_("failed to get default branch name from remote; "
+		  "using local default"));
+	strbuf_reset(&out);
+
+	child_process_init(&cp);
+	cp.git_cmd = 1;
+	strvec_pushl(&cp.args, "symbolic-ref", "--short", "HEAD", NULL);
+	if (!pipe_command(&cp, NULL, 0, &out, 0, NULL, 0)) {
+		strbuf_trim(&out);
+		return strbuf_detach(&out, NULL);
+	}
+
+	strbuf_release(&out);
+	error(_("failed to get default branch name"));
+	return NULL;
+}
+
+static int cmd_clone(int argc, const char **argv)
+{
+	const char *branch = NULL;
+	int full_clone = 0;
+	struct option clone_options[] = {
+		OPT_STRING('b', "branch", &branch, N_("<branch>"),
+			   N_("branch to checkout after clone")),
+		OPT_BOOL(0, "full-clone", &full_clone,
+			 N_("when cloning, create full working directory")),
+		OPT_END(),
+	};
+	const char * const clone_usage[] = {
+		N_("scalar clone [<options>] [--] <repo> [<dir>]"),
+		NULL
+	};
+	const char *url;
+	char *enlistment = NULL, *dir = NULL;
+	struct strbuf buf = STRBUF_INIT;
+	int res;
+
+	argc = parse_options(argc, argv, NULL, clone_options, clone_usage, 0);
+
+	if (argc == 2) {
+		url = argv[0];
+		enlistment = xstrdup(argv[1]);
+	} else if (argc == 1) {
+		url = argv[0];
+
+		strbuf_addstr(&buf, url);
+		/* Strip trailing slashes, if any */
+		while (buf.len > 0 && is_dir_sep(buf.buf[buf.len - 1]))
+			strbuf_setlen(&buf, buf.len - 1);
+		/* Strip suffix `.git`, if any */
+		strbuf_strip_suffix(&buf, ".git");
+
+		enlistment = find_last_dir_sep(buf.buf);
+		if (!enlistment) {
+			die(_("cannot deduce worktree name from '%s'"), url);
+		}
+		enlistment = xstrdup(enlistment + 1);
+	} else {
+		usage_msg_opt(_("You must specify a repository to clone."),
+			      clone_usage, clone_options);
+	}
+
+	if (is_directory(enlistment))
+		die(_("directory '%s' exists already"), enlistment);
+
+	dir = xstrfmt("%s/src", enlistment);
+
+	strbuf_reset(&buf);
+	if (branch)
+		strbuf_addf(&buf, "init.defaultBranch=%s", branch);
+	else {
+		char *b = repo_default_branch_name(the_repository, 1);
+		strbuf_addf(&buf, "init.defaultBranch=%s", b);
+		free(b);
+	}
+
+	if ((res = run_git("-c", buf.buf, "init", "--", dir, NULL)))
+		goto cleanup;
+
+	if (chdir(dir) < 0) {
+		res = error_errno(_("could not switch to '%s'"), dir);
+		goto cleanup;
+	}
+
+	setup_git_directory();
+
+	/* common-main already logs `argv` */
+	trace2_def_repo(the_repository);
+
+	if (!branch && !(branch = remote_default_branch(url))) {
+		res = error(_("failed to get default branch for '%s'"), url);
+		goto cleanup;
+	}
+
+	if (set_config("remote.origin.url=%s", url) ||
+	    set_config("remote.origin.fetch="
+		       "+refs/heads/*:refs/remotes/origin/*") ||
+	    set_config("remote.origin.promisor=true") ||
+	    set_config("remote.origin.partialCloneFilter=blob:none")) {
+		res = error(_("could not configure remote in '%s'"), dir);
+		goto cleanup;
+	}
+
+	if (!full_clone &&
+	    (res = run_git("sparse-checkout", "init", "--cone", NULL)))
+		goto cleanup;
+
+	if (set_recommended_config())
+		return error(_("could not configure '%s'"), dir);
+
+	if ((res = run_git("fetch", "--quiet", "origin", NULL))) {
+		warning(_("partial clone failed; attempting full clone"));
+
+		if (set_config("remote.origin.promisor") ||
+		    set_config("remote.origin.partialCloneFilter")) {
+			res = error(_("could not configure for full clone"));
+			goto cleanup;
+		}
+
+		if ((res = run_git("fetch", "--quiet", "origin", NULL)))
+			goto cleanup;
+	}
+
+	if ((res = set_config("branch.%s.remote=origin", branch)))
+		goto cleanup;
+	if ((res = set_config("branch.%s.merge=refs/heads/%s",
+			      branch, branch)))
+		goto cleanup;
+
+	strbuf_reset(&buf);
+	strbuf_addf(&buf, "origin/%s", branch);
+	res = run_git("checkout", "-f", "-t", buf.buf, NULL);
+	if (res)
+		goto cleanup;
+
+	res = register_dir();
+
+cleanup:
+	free(enlistment);
+	free(dir);
+	strbuf_release(&buf);
+	return res;
+}
+
 static int cmd_list(int argc, const char **argv)
 {
 	if (argc != 1)

@@ -346,6 +546,7 @@ static struct {
 	const char *name;
 	int (*fn)(int, const char **);
 } builtins[] = {
+	{ "clone", cmd_clone },
 	{ "list", cmd_list },
 	{ "register", cmd_register },
 	{ "unregister", cmd_unregister },