store: improve label handling

In particular, clear_labels

And some cosmetics

lib/message/mu-labels.cc

@@ -89,7 +89,6 @@ Mu::Labels::parse_delta_label(const std::string &expr)
 	return Ok(DeltaLabel{std::move(delta), std::move(label)});
 }
 
-
 Result<DeltaLabelVec>
 Mu::Labels::parse_delta_labels(const std::string& exprs,
 			       const std::string sepa)
@@ -106,10 +105,6 @@ Mu::Labels::parse_delta_labels(const std::string& exprs,
 	return Ok(std::move(deltas));
 }
 
-
-
-
-
 struct cmp_delta_label { // can not yet be a λ in C++17
 	bool operator()(const DeltaLabel& dl1, const DeltaLabel& dl2) const {
 		return dl1.second < dl2.second;

lib/mu-store-labels.hh

@@ -52,20 +52,22 @@ public:
 	/**
 	 * Add a label occurrence to the cache
 	 *
-	 * @param label
+	 * @param label some label
 	 */
-	void add(const std::string& label) {
+	void increase(const std::string& label) {
 		if (auto it = label_map_.find(label); it == label_map_.end())
 			label_map_.insert({label, 1});
 		else
 			++it->second;
 	}
 	/**
-	 * Remove label occurrence from the cache
+	 * Remove a label occurrence from the cache
 	 *
-	 * @param label
+	 * Removes the label completely if this was the _last_ occurence.
+	 *
+	 * @param label some label
 	 */
-	void remove(const std::string& label) {
+	void decrease(const std::string& label) {
 		if (auto it = label_map_.find(label); it != label_map_.end()) {
 			if (it->second == 1)
 				label_map_.erase(it);
@@ -83,10 +85,10 @@ public:
 		for(const auto& [delta, label]: updates) {
 			switch(delta) {
 			case Labels::Delta::Add:
-				add(label);
+				increase(label);
 				break;
 			case Labels::Delta::Remove:
-				remove(label);
+				decrease(label);
 				break;
 			}
 		}
@@ -99,7 +101,6 @@ public:
 	 */
 	Map label_map() const { return label_map_; }
 
-
 	// serialization/deserialization could be optimized, but is not super
 	// time-critical
 
@@ -116,7 +117,6 @@ public:
 		return s;
 	}
 
-
 	/**
 	 * Deserialize the cache into a Map
 	 *

lib/mu-store.cc

@@ -632,7 +632,6 @@ Store::update_labels(Message& message, const Labels::DeltaLabelVec& labels_delta
 	if (updates.second.empty())
 		return Ok(std::move(updates.second)); // nothing to do
 
-
 	message.set_labels(updates.first);
 	auto res{priv_->update_message_unlocked(message, message.docid())};
 	if (!res)
@@ -643,24 +642,30 @@ Store::update_labels(Message& message, const Labels::DeltaLabelVec& labels_delta
 	return Ok(std::move(updates.second));
 }
 
-Result<void>
+Result<Labels::DeltaLabelVec>
 Store::clear_labels(Message& message)
 {
+	using namespace Labels;
+
 	std::unique_lock lock{priv_->lock_};
 
+	DeltaLabelVec updates;
+
 	const auto labels{message.labels()};
 	if (labels.empty())
-		return Ok(); // nothing to do
+		return Ok(std::move(updates)); // nothing to do
 
 	message.set_labels({}); // clear all
 	auto res{priv_->update_message_unlocked(message, message.docid())};
 	if (!res)
 		return Err(res.error());
 
-	for (auto label: labels)
-		priv_->labels_cache_.remove(label);
+	for (auto label: labels) {
+		updates.emplace_back(DeltaLabel{Delta::Remove, label});
+		priv_->labels_cache_.decrease(label);
+	}
 
-	return Ok();
+	return Ok(std::move(updates));
 }
 
 LabelsCache::Map

lib/mu-store.hh

@@ -347,18 +347,20 @@ public:
 	 * @param message some message
 	 * @param labels_delta the set of changes
 	 *
-	 * @return the effective changes for this message
+	 * @return the effective changes for this message or an error
 	 */
-	Result<Labels::DeltaLabelVec> update_labels(Message& message, const Labels::DeltaLabelVec& labels_delta);
-
+	Result<Labels::DeltaLabelVec> update_labels(Message& message,
+						    const Labels::DeltaLabelVec& labels_delta);
 	/**
-	 * Clear all labels from message
+	 * Clear all labels from a message
+	 *
+	 * Update the message in the store, and update the labels-cache
 	 *
 	 * @param message some message
 	 *
-	 * @return Ok or some error
+	 * @return the effective changes for this message or an error
 	 */
-	Result<void> clear_labels(Message& message);
+	Result<Labels::DeltaLabelVec> clear_labels(Message& message);
 
 	/**
 	 * Get a copy of the map of labels in use.