core: hash scanned files and don't trigger a reload if matching

Nix builds often trip QFileSystemWatcher, causing random reloads.

changelog/next.md

@@ -33,6 +33,7 @@ set shell id.
 - IPC operations filter available instances to the current display connection by default.
 - PwNodeLinkTracker ignores sound level monitoring programs.
 - Replaced breakpad with cpptrace.
+- Reloads are prevented if no file content has changed.
 
 ## Bug Fixes
 

src/core/generation.cpp

@@ -209,6 +209,8 @@ bool EngineGeneration::setExtraWatchedFiles(const QVector<QString>& files) {
 	for (const auto& file: files) {
 		if (!this->scanner.scannedFiles.contains(file)) {
 			this->extraWatchedFiles.append(file);
+			QByteArray data;
+			this->scanner.readAndHashFile(file, data);
 		}
 	}
 
@@ -229,6 +231,11 @@ void EngineGeneration::onFileChanged(const QString& name) {
 		auto fileInfo = QFileInfo(name);
 		if (fileInfo.isFile() && fileInfo.size() == 0) return;
 
+		if (!this->scanner.hasFileContentChanged(name)) {
+			qCDebug(logQmlScanner) << "Ignoring file change with unchanged content:" << name;
+			return;
+		}
+
 		emit this->filesChanged();
 	}
 }
@@ -237,6 +244,11 @@ void EngineGeneration::onDirectoryChanged() {
 	// try to find any files that were just deleted from a replace operation
 	for (auto& file: this->deletedWatchedFiles) {
 		if (QFileInfo(file).exists()) {
+			if (!this->scanner.hasFileContentChanged(file)) {
+				qCDebug(logQmlScanner) << "Ignoring restored file with unchanged content:" << file;
+				continue;
+			}
+
 			emit this->filesChanged();
 			break;
 		}

src/core/scan.cpp

@@ -3,6 +3,7 @@
 #include <utility>
 
 #include <qcontainerfwd.h>
+#include <qcryptographichash.h>
 #include <qdir.h>
 #include <qfileinfo.h>
 #include <qjsengine.h>
@@ -21,6 +22,25 @@
 
 QS_LOGGING_CATEGORY(logQmlScanner, "quickshell.qmlscanner", QtWarningMsg);
 
+bool QmlScanner::readAndHashFile(const QString& path, QByteArray& data) {
+	auto file = QFile(path);
+	if (!file.open(QFile::ReadOnly)) return false;
+	data = file.readAll();
+	this->fileHashes.insert(path, QCryptographicHash::hash(data, QCryptographicHash::Md5));
+	return true;
+}
+
+bool QmlScanner::hasFileContentChanged(const QString& path) const {
+	auto it = this->fileHashes.constFind(path);
+	if (it == this->fileHashes.constEnd()) return true;
+
+	auto file = QFile(path);
+	if (!file.open(QFile::ReadOnly)) return true;
+
+	auto newHash = QCryptographicHash::hash(file.readAll(), QCryptographicHash::Md5);
+	return newHash != it.value();
+}
+
 void QmlScanner::scanDir(const QDir& dir) {
 	if (this->scannedDirs.contains(dir)) return;
 	this->scannedDirs.push_back(dir);
@@ -109,13 +129,13 @@ bool QmlScanner::scanQmlFile(const QString& path, bool& singleton, bool& interna
 
 	qCDebug(logQmlScanner) << "Scanning qml file" << path;
 
-	auto file = QFile(path);
+	QByteArray fileData;
-	if (!file.open(QFile::ReadOnly | QFile::Text)) {
+	if (!this->readAndHashFile(path, fileData)) {
 		qCWarning(logQmlScanner) << "Failed to open file" << path;
 		return false;
 	}
 
-	auto stream = QTextStream(&file);
+	auto stream = QTextStream(&fileData);
 	auto imports = QVector<QString>();
 
 	bool inHeader = true;
@@ -219,8 +239,6 @@ bool QmlScanner::scanQmlFile(const QString& path, bool& singleton, bool& interna
 		postError("unclosed preprocessor if block");
 	}
 
-	file.close();
-
 	if (isOverridden) {
 		this->fileIntercepts.insert(path, overrideText);
 	}
@@ -257,8 +275,11 @@ bool QmlScanner::scanQmlFile(const QString& path, bool& singleton, bool& interna
 			continue;
 		}
 
-		if (import.endsWith(".js")) this->scannedFiles.push_back(cpath);
+		if (import.endsWith(".js")) {
-		else this->scanDir(cpath);
+			this->scannedFiles.push_back(cpath);
+			QByteArray jsData;
+			this->readAndHashFile(cpath, jsData);
+		} else this->scanDir(cpath);
 	}
 
 	return true;
@@ -273,14 +294,12 @@ void QmlScanner::scanQmlRoot(const QString& path) {
 bool QmlScanner::scanQmlJson(const QString& path) {
 	qCDebug(logQmlScanner) << "Scanning qml.json file" << path;
 
-	auto file = QFile(path);
+	QByteArray data;
-	if (!file.open(QFile::ReadOnly | QFile::Text)) {
+	if (!this->readAndHashFile(path, data)) {
 		qCWarning(logQmlScanner) << "Failed to open file" << path;
 		return false;
 	}
 
-	auto data = file.readAll();
-
 	// Importing this makes CI builds fail for some reason.
 	QJsonParseError error; // NOLINT (misc-include-cleaner)
 	auto json = QJsonDocument::fromJson(data, &error);

src/core/scan.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <qbytearray.h>
 #include <qcontainerfwd.h>
 #include <qdir.h>
 #include <qhash.h>
@@ -21,6 +22,7 @@ public:
 
 	QVector<QDir> scannedDirs;
 	QVector<QString> scannedFiles;
+	QHash<QString, QByteArray> fileHashes;
 	QHash<QString, QString> fileIntercepts;
 
 	struct ScanError {
@@ -31,6 +33,9 @@ public:
 
 	QVector<ScanError> scanErrors;
 
+	bool readAndHashFile(const QString& path, QByteArray& data);
+	[[nodiscard]] bool hasFileContentChanged(const QString& path) const;
+
 private:
 	QDir rootPath;