mu-init: automatic export labels with --reinit

When re-initializing the store, automatically write the labels to a file in mu's
cache, so user can later import them.

lib/mu-store-labels.cc

@@ -24,9 +24,9 @@
 using namespace Mu;
 
 namespace {
-constexpr std::string_view path_key = "path:";
+constexpr std::string_view	path_key       = "path:";
-constexpr std::string_view message_id_key = "message-id:";
+constexpr std::string_view	message_id_key = "message-id:";
-constexpr std::string_view labels_key = "labels:";
+constexpr std::string_view	labels_key     = "labels:";
 }
 
 using OutputPair = std::pair<std::ofstream, std::string>;
@@ -36,14 +36,26 @@ export_output(Option<std::string> path)
 {
 	const auto now_t{::time({})};
 	const auto now_tm{::localtime(&now_t)};
-
 	const auto now{mu_format("{:%F-%T}", *now_tm)};
-	auto fname = path.value_or(mu_format("mu-export-{}.txt", now));
+
+	// if path is not specified, use a generated file name (in pwd)
+	// if path is specified but ends in '/', use the generated file in that
+	// directory (must exist)
+	// otherwise, use the path.
+	auto fname = [&]() {
+		const auto default_fname{mu_format("mu-export-{}.txt", now)};
+		if (!path || path->empty())
+			return default_fname;
+		else if (path->at(path->length() - 1) == '/')
+			return *path + default_fname;
+		else
+			return *path;
+	}();
 
 	auto output{std::ofstream{fname, std::ios::out}};
 	if (!output.good())
 		return Err(Error{Error::Code::File,
-				"failed pen '{}' for writing", fname});
+				"failed to open '{}' for writing", fname});
 
 	mu_println(output, ";; version:0 @ {}\n", now);
 

lib/mu-store-labels.hh

@@ -129,11 +129,13 @@ public:
 		std::string       line;
 
 		while (std::getline(ss, line)) {
-			if (const auto parts = Mu::split(line, SepaChar2); parts.size() != 2)
+			if (const auto parts =
+			    Mu::split(line, SepaChar2); parts.size() != 2)
 				mu_warning("error: '{}'", line);
 			else
 				map.emplace(std::move(parts[0]),
-					    static_cast<std::size_t>(g_ascii_strtoll(parts[1].c_str(),{}, 10)));
+					    static_cast<std::size_t>(
+						    g_ascii_strtoll(parts[1].c_str(),{}, 10)));
 		}
 		return map;
 	}
@@ -148,14 +150,17 @@ class Store;
  * Export labels to a file
  *
  * If path is not specified, use a file in the current directory
+ * If path ends in '/', write file in the path-directory
  *
  * @param store a store object
- * @param query for the message whose labels to export
+ * @param query for the message whose labels to export (empty for "all")
  * @param path the path or nothing
  *
  * @return either the output filename or some error
  */
-Result<std::string> export_labels(const Store& store, const std::string& query="", Option<std::string> path);
+Result<std::string> export_labels(const Store& store,
+				  const std::string& query="",
+				  Option<std::string> path={});
 
 /**
  * Import labels from a file
@@ -170,7 +175,8 @@ Result<std::string> export_labels(const Store& store, const std::string& query="
  *
  * @return Ok or some error
  */
-Result<void> import_labels(Store&, const std::string& path, bool dry_run, bool quiet, bool verbose);
+Result<void> import_labels(Store&, const std::string& path, bool dry_run,
+			   bool quiet, bool verbose);
 
 } // namespace Mux
 #endif /*MU_LABELS_CACHE_HH*/

lib/mu-store.cc

@@ -127,7 +127,6 @@ struct Store::Private {
 	Result<Store::Id> update_message_unlocked(Message& msg, Store::Id docid);
 	Result<Store::Id> update_message_unlocked(Message& msg, const std::string& old_path);
 
-
 	using PathMessage = std::pair<std::string, Message>;
 	Result<PathMessage> move_message_unlocked(Message&& msg,
 						  Option<const std::string&> target_mdir,
@@ -211,9 +210,29 @@ Store::Private::find_duplicates_unlocked(const Store& store,
 	}
 }
 
+static void
+reinit_export_labels(const Store& store)
+{
+	// slightly hacky way to get the cache-path...
+	const auto cache_path{canonicalize_filename(
+		join_paths(store.path(), "..")) + "/"};
+
+	if (const auto res =
+	    Mu::export_labels(store, "", cache_path); !res)
+		throw Mu::Error(Error::Code::CannotReinit,
+				"cannot re-init; "
+				"failed to export labels: {}",
+				res.error().what())
+			.add_hint("see mu-init(1) for details");
+	else {
+		mu_info("exported labels to: {}", *res);
+		mu_println("exported labels to: {}", *res);
+	}
+}
 
 Store::Store(const std::string& path, Store::Options opts)
-    : priv_{std::make_unique<Private>(path, none_of(opts & Store::Options::Writable))}
+    : priv_{std::make_unique<Private>(
+		path, none_of(opts & Store::Options::Writable))}
 {
 	if (none_of(opts & Store::Options::Writable) &&
 	    any_of(opts & Store::Options::ReInit))
@@ -222,12 +241,19 @@ Store::Store(const std::string& path, Store::Options opts)
 
 	const auto s_version{config().get<Config::Id::SchemaVersion>()};
 	if (any_of(opts & Store::Options::ReInit)) {
-		/* don't try to recover from version with an incompatible scheme */
+
+		/* export labels, if necessary (throws if there's an error) */
+		if (!label_map().empty())
+			reinit_export_labels(*this);
+
+		/* don't try to recover from version with an incompatible
+		 * scheme */
 		if (s_version < 500)
-			throw Mu::Error(Error::Code::CannotReinit,
+			throw Mu::Error(
-					"old schema ({}) is too old to re-initialize from",
+				Error::Code::CannotReinit,
-					s_version).add_hint("Invoke 'mu init' without '--reinit'; "
+				"old schema ({}) is too old to re-initialize from",
-							    "see mu-init(1) for details");
+				s_version).add_hint("Invoke 'mu init' without '--reinit'; "
+						    "see mu-init(1) for details");
 		const auto old_root_maildir{root_maildir()};
 
 		MemDb mem_db;

lib/utils/mu-utils-file.cc

@@ -131,9 +131,6 @@ Mu::remove_directory(const std::string& path)
 		return Ok();
 }
 
-
-
-
 std::string
 Mu::runtime_path(Mu::RuntimePath path, const std::string& muhome)
 {

man/mu-init.1.org

@@ -13,26 +13,26 @@ mu-init - initialize the *mu* message database
 * DESCRIPTION
 
 *mu init* is the subcommand for setting up the *mu* message database. After *mu init*
-has completed, you can run *mu index*
+has completed, you can run *mu index*.
 
 * INIT OPTIONS
 
 ** -m, --maildir _maildir_
 Use _maildir_ as the root-maildir.
 
-By default, *mu* uses the *MAILDIR* environment; if it is not set, it uses _~/Maildir_
+By default, *mu* uses the *MAILDIR* environment to find the root-maildir. If it is
-if it is an existing directory. If neither of those can be used, the *--maildir*
+not set, it uses _~/Maildir_ if it is an existing directory. If neither of those
-option is required; it must be an absolute path (but ~~/~ expansion is
+can be used, the *--maildir* option is required; it must be an absolute path (but
-performed).
+~~/~ expansion is performed).
 
 ** --personal-address _email-address-or-regex_
 ** --my-address _email-address-or-regex_  (alias)
-Specifies that some e-mail address is a personal address. The option can be used
+Specifies that some e-mail address is a /personal/ address. The option can be used
 multiple times, to specify all your addresses.
 
-Any message in which at least one of the contact fields contains such an address
+Any message in which at least one of the contact fields matches a personal
-is considered a `personal' message; this can then be used for filtering in
+address, is considered a `personal' message; this can then be used for filtering
-{{{man-link(mu-find,1)}}}, {{{man-link(mu-cfind,1)}}} and *mu4e*, e.g. to
+in {{{man-link(mu-find,1)}}}, {{{man-link(mu-cfind,1)}}} and *mu4e*, e.g. to
 filter-out mailing list messages.
 
 _email-address-or-regex_ can be either a plain e-mail address (such as
@@ -78,6 +78,8 @@ Reinitialize the database from an earlier version; that is, create a new empty
 database with the existing settings. This cannot be combined with the other *init*
 options.
 
+When you have _labels_ defined for messages in your database, *mu* automatically exports those to file for importing later. See *RESTORING LABELS* below.
+
 #+include: "muhome.inc" :minlevel 2
 
 * NGRAM SUPPORT
@@ -93,6 +95,22 @@ variables such as *XAPIAN_CJK_NGRAM* are ignored.
 
 #+include: "exit-code.inc" :minlevel 1
 
+* RESTORING LABELS
+
+When you have any _labels_ defined for your database, *mu* automatically exports
+those to a file in the *mu* cache directory; you see this in the ~--init~ output.
+
+#+begin_example
+$ mu init --reinit
+exported labels to: /home/user/.cache/mu/mu-export-2025-08-16-13:43:27.txt
+#+end_example
+
+You can restore those labels _after_ re-indexing, e.g.,
+#+begin_example
+$ mu label import /home/user/.cache/mu/mu-export-2025-08-16-13:43:27.txt
+#+end_example
+
+Please see {{{man-link(mu-label,1)}}} for further details.
 
 * EXAMPLE
 #+begin_example
@@ -105,5 +123,6 @@ $ mu init --maildir=~/Maildir --my-address=alice@example.com --my-address=bob@ex
 
 {{{man-link(mu-index,1)}}},
 {{{man-link(mu-find,1)}}},
+{{{man-link(mu-label,1)}}},
 {{{man-link(mu-cfind,1)}}},
 {{{man-link(pcre,3)}}}

man/mu-label.1.org

@@ -71,12 +71,17 @@ The *list* command lists all the labels that are currently in use in the store.
 * EXPORT OPTIONS
 
 The *export* command outputs /all/ labels in the store to a file, so you can *import*
-it later. The command takes a path to a file as its argument.
+it later. The command takes a path to a file or a directory (ending in '/') as
+its argument.
+
+If a file is specified, *mu* writes the export to it.
+
+If a directory is specified, *mu* writes to a file in that directory. The directory must already exist.
+
+When neither is specified, *mu* writes to a file in the current directory.
 
 See *EXPORT FORMAT* below for details about the format.
 
-If no file is specified, *mu* creates one for you, in the current directory.
-
 * IMPORT OPTIONS
 
 The *import* command is for restoring the labels from a file created through