labels: allow restoring cache-map

E.g. with unexpected termination for mu it is possible that the
labels-cache (i.e., the one that is used for auto-completion) gets disconnected
from reality.

Add a --restore option to `mu label list` to restore the actual labels from the
labels seen in the store.

lib/mu-store-labels.cc

@@ -23,6 +23,25 @@
 
 using namespace Mu;
 
+Result<void>
+Mu::LabelsCache::restore(const Store& store)
+{
+	const auto res{store.run_query("")};
+	if (!res)
+		return Err(Error{Error::Code::Query,
+				"failed to run query: {}",
+				 *res.error().what()});
+	label_map_.clear();
+
+	for (auto&& item: *res) {
+		if (auto &&msg{item.message()}; msg) {
+			for (const auto& label: msg->labels())
+				increase(label);
+		}
+	}
+	return Ok();
+}
+
 namespace {
 constexpr std::string_view	path_key       = "path:";
 constexpr std::string_view	message_id_key = "message-id:";

lib/mu-store-labels.hh

@@ -30,6 +30,8 @@
 
 namespace Mu {
 
+class Store;
+
 /**
  * The cache keeps track of what labels are being used. This can be used
  * for completion etc. and `mu label list`
@@ -143,6 +145,17 @@ public:
 		return map;
 	}
 
+
+	/**
+	 * Restore the labels-cache from the labels seen in the store.
+	 *
+	 * @param store a store
+	 *
+	 * @return Ok() or some error
+	 */
+	Result<void> restore(const Store& store);
+
+
 	/**
 	 * Is the cache "dirty"?
 	 *
@@ -159,8 +172,6 @@ private:
 	mutable bool dirty_{};
 };
 
-class Store;
-
 /**
  * Export labels to a file
  *

lib/mu-store.cc

@@ -694,6 +694,14 @@ Store::clear_labels(Message& message)
 	return Ok(std::move(updates));
 }
 
+Result<void>
+Store::restore_label_map()
+{
+	std::unique_lock lock{priv_->lock_};
+
+	return priv_->labels_cache_.restore(*this);
+}
+
 LabelsCache::Map
 Store::label_map() const
 {

lib/mu-store.hh

@@ -373,6 +373,16 @@ public:
 	 */
 	Result<Labels::DeltaLabelVec> clear_labels(Message& message);
 
+	/**
+	 * Restore label-map from store
+	 *
+	 * Restore the labels list in the store, i.e., restore the cached list of labels which is
+	 * used for e.g. auto-completion in mu4e from the labels in the store.
+	 *
+	 * @return Ok or some error.
+	 */
+	Result<void> restore_label_map();
+
 	/**
 	 * Get a copy of the map of labels in use.
 	 *
@@ -382,6 +392,8 @@ public:
 	 */
 	LabelsCache::Map label_map() const;
 
+
+
 	/**
 	 * Prototype for the ForEachMessageFunc
 	 *

man/mu-label.1.org

@@ -71,6 +71,15 @@ when using a shell.
 * LIST OPTIONS
 
 The *list* command lists all the labels that are currently in use in the store.
+This is the same information used for auto-completion in *mu4e*.
+
+With the (global, directly after *mu) *--verbose* option, this also includes the
+counts.
+
+** --restore
+
+  attempt to restore the list from the labels in the store.
+  It is possible that the list to get outdated, *--restore* fixes this.
 
 * EXPORT OPTIONS
 

mu/mu-cmd-label.cc

@@ -113,11 +113,16 @@ label_clear(Mu::Store& store, const Options& opts)
 }
 
 static Result<void>
-label_list(const Mu::Store& store, const Options& opts)
+label_list(Mu::Store& store, const Options& opts)
 {
-	const auto label_map{store.label_map()};
+	if (opts.label.restore) {
+		if (!opts.quiet)
+			mu_println("labels: restoring list from store...");
+		if (const auto res = store.restore_label_map(); !res)
+			return res;
+	}
 
-	for (const auto& [label, n]: label_map)
+	for (const auto& [label, n]: store.label_map())
 		if (opts.verbose)
 			mu_println("{}: {}", label, n);
 		else

mu/mu-options.cc

@@ -528,6 +528,8 @@ sub_label(CLI::App& sub, Options& opts)
 
 	// list
 	[[maybe_unused]] auto list = sub.add_subcommand("list", "list labels in the store");
+	list->add_flag("--restore", opts.label.restore,
+			 "Restore the label-list from the labels in store");
 	add_muhome_option(*list, opts);
 
 	// export

mu/mu-options.hh

@@ -209,7 +209,9 @@ struct Options {
 		bool dry_run{};				 /**< Merely print the messages that would be
 							  * labeled without doing so */
 		StringVec delta_labels;                  /**< labels to add (+) or remove (-) */
-		bool read_only{};                        /** do not require writable store */
+		bool read_only{};                        /**< do not require writable store */
+
+		bool restore{};                         /**< restore the labels list */
 
 		OptString file;                           /** file for import/export */
 

mu4e/mu4e.texi

@@ -2524,8 +2524,8 @@ field. To see them in your headers / message views, you need to add the field to
 the @code{mu4e-headers-fields} and @code{mu4e-view-fields}, respectively.
 
 To change the labels for some message, you specify a @emph{label expression},
-which consists of a space-separated sequence of labels, each prefixed either
-with a @t{+} to add the label or @t{-} to remove it.
+which consists of a space-separated sequence of labels, each prefixed with
+either a @t{+} to add the label, or @t{-} to remove it.
 
 For instance, to remove the @t{boring} label and add @t{urgent} from the message
 at point or the messages in region, press @kbd{l} and enter:
@@ -2533,16 +2533,16 @@ at point or the messages in region, press @kbd{l} and enter:
 +urgent -boring
 @end example
 
-For @emph{clearing all labels}, you mark with @kbd{L} ('unlabel').
+For clearing @emph{all} labels, you can mark with @kbd{L} ('unlabel').
 
 You can search for labels using the @t{label:} field. For instance,
 @t{label:urgent} retrieves all messages labeled @t{urgent}.
 
-It is important to note that the labels are only stored in the database (the
-message files are not changed). This means that you loose this information when
-you remove the database and recrate it; it is however possible to @emph{export}
-the labels and re-@emph{import} them later; see the @t{mu-label} man-page for
-further details.
+@emph{Important}: the labels are only stored in the database (the message files
+are not changed). This means that you would @emph{loose} this information when
+you remove the database and recreate it, @emph{unless} you @emph{export} the
+labels before removin the database and re-@emph{import} them after re-creating
+and re-indexing it; see the @t{mu-label} man-page for further details.
 
 @subsection Doing @emph{something}
 
@@ -3185,9 +3185,7 @@ It is easy to add such actions to your configuration; for instance, to enable
 @emph{tagging}@footnote{@t{mu4e} does not offer tagging by default since it
 mutates the message files, something that @t{mu}/@t{mu4e} generally try to
 avoid. An alternative to tagging is @emph{labeling}, @xref{Applying and clearing
-labels}
-
-} both in the message view and headers view, you could add:
+labels}}, you could add:
 @lisp
 (add-to-list 'mu4e-headers-actions
              '("Tag message" . mu4e-action-retag-message))