core/command: add --tail to log subcommand

src/core/logging.cpp

@@ -28,6 +28,7 @@
 #include "logging_p.hpp"
 #include "logging_qtprivate.cpp" // NOLINT
 #include "paths.hpp"
+#include "ringbuf.hpp"
 
 Q_LOGGING_CATEGORY(logBare, "quickshell.bare");
 
@@ -65,6 +66,7 @@ void LogMessage::formatMessage(
 	}
 
 	if (msg.category == "quickshell.bare") {
+		if (!prefix.isEmpty()) stream << ' ';
 		stream << msg.body;
 	} else {
 		if (color) {
@@ -243,9 +245,9 @@ void LogManager::init(
 	thread->start();
 
 	QMetaObject::invokeMethod(
-			&instance->threadProxy,
-			&LoggingThreadProxy::initInThread,
-			Qt::BlockingQueuedConnection
+	    &instance->threadProxy,
+	    &LoggingThreadProxy::initInThread,
+	    Qt::BlockingQueuedConnection
 	);
 
 	qCDebug(logLogging) << "Logger initialized.";
@@ -735,7 +737,7 @@ bool EncodedLogReader::registerCategory() {
 	return true;
 }
 
-bool readEncodedLogs(QIODevice* device, bool timestamps, const QString& rulespec) {
+bool readEncodedLogs(QIODevice* device, bool timestamps, int tail, const QString& rulespec) {
 	QList<QLoggingRule> rules;
 
 	{
@@ -767,6 +769,8 @@ bool readEncodedLogs(QIODevice* device, bool timestamps, const QString& rulespec
 
 	auto filters = QHash<quint16, CategoryFilter>();
 
+	auto tailRing = RingBuffer<LogMessage>(tail);
+
 	LogMessage message;
 	auto stream = QTextStream(stdout);
 	while (reader.read(&message)) {
@@ -782,6 +786,18 @@ bool readEncodedLogs(QIODevice* device, bool timestamps, const QString& rulespec
 		}
 
 		if (filter.shouldDisplay(message.type)) {
+			if (tail == 0) {
+				LogMessage::formatMessage(stream, message, color, timestamps);
+				stream << '\n';
+			} else {
+				tailRing.emplace(message);
+			}
+		}
+	}
+
+	if (tail != 0) {
+		for (auto i = tailRing.size() - 1; i != -1; i--) {
+			auto& message = tailRing.at(i);
 			LogMessage::formatMessage(stream, message, color, timestamps);
 			stream << '\n';
 		}

src/core/logging.hpp

@@ -130,7 +130,7 @@ private:
 	LoggingThreadProxy threadProxy;
 };
 
-bool readEncodedLogs(QIODevice* device, bool timestamps, const QString& rulespec);
+bool readEncodedLogs(QIODevice* device, bool timestamps, int tail, const QString& rulespec);
 
 } // namespace qs::log
 

src/core/main.cpp

@@ -2,6 +2,7 @@
 #include <algorithm>
 #include <cstdio>
 #include <cstdlib>
+#include <limits>
 #include <string>
 
 #include <CLI/App.hpp>
@@ -94,6 +95,7 @@ struct CommandState {
 		bool noColor = !qEnvironmentVariableIsEmpty("NO_COLOR");
 		bool sparse = false;
 		size_t verbosity = 0;
+		int tail = 0;
 		QStringOption rules;
 		QStringOption readoutRules;
 		QStringOption file;
@@ -249,6 +251,10 @@ int runCommand(int argc, char** argv, QCoreApplication* coreApplication) {
 
 		auto* file = sub->add_option("--file", state.log.file, "Log file to read.");
 
+		sub->add_option("-t,--tail", state.log.tail)
+		    ->description("Maximum number of lines to print, starting from the bottom.")
+		    ->check(CLI::Range(1, std::numeric_limits<int>::max(), "INT > 0"));
+
 		sub->add_option("-r,--rules", state.log.readoutRules, "Log file to read.")
 		    ->description("Rules to apply to the log being read, in the format of QT_LOGGING_RULES.");
 
@@ -466,7 +472,9 @@ int readLogFile(CommandState& cmd) {
 		return -1;
 	}
 
-	return qs::log::readEncodedLogs(&file, cmd.log.timestamp, *cmd.log.readoutRules) ? 0 : -1;
+	return qs::log::readEncodedLogs(&file, cmd.log.timestamp, cmd.log.tail, *cmd.log.readoutRules)
+	         ? 0
+	         : -1;
 }
 
 int listInstances(CommandState& cmd) {