Hi, Raphael,

I've stumbled upon the same issue, and solved it this way: 

- clone the falkon repo, and,
- revert commit f792104be55fca03ad17cdc4244aafce47d0914e (or apply the patch below), which is essentially what you've asked for (the only lost is the ability to remove locally installed themes, which I'm sure you could live without),
- compile it without Python plugins support (see below);

There is a caveat, however, that you most likely would need to revert commit 479933e095168d07a54913f88642cfed4828c167 to compile it with PySide2 << 5.12, if you want Python plugins support under Qt 5.9.6. Be aware that last revert needs some extra "polishing" plus back-porting of the two special commits-fixes "from a future version" to alleviate a bug in PySide2

I'm myself a happy user of the latest Falkon and nearly latest the KDE Plasma, all are the manually compiled Ubuntu system packages under Qt 5.9.5 LTS ;-)

--- src/lib/preferences/thememanager.cpp
+++ src/lib/preferences/thememanager.cpp
@@ -26,17 +26,15 @@
 #include "mainapplication.h"

 #include <QDir>
-#include <QMessageBox>

 ThemeManager::ThemeManager(QWidget* parent, Preferences* preferences)
-    : QWidget(parent)
+    : QWidget()
     , ui(new Ui::ThemeManager)
     , m_preferences(preferences)
 {
     ui->setupUi(parent);
     ui->listWidget->setLayoutDirection(Qt::LeftToRight);
     ui->license->hide();
-    ui->remove->setIcon(QIcon::fromTheme(QSL("edit-delete")));

     Settings settings;
     settings.beginGroup("Themes");
@@ -69,7 +67,6 @@ ThemeManager::ThemeManager(QWidget* pare

     connect(ui->listWidget, &QListWidget::currentItemChanged, this, &ThemeManager::currentChanged);
     connect(ui->license, &ClickableLabel::clicked, this, &ThemeManager::showLicense);
-    connect(ui->remove, &QPushButton::clicked, this, &ThemeManager::removeTheme);

     currentChanged();
 }
@@ -88,25 +85,6 @@ void ThemeManager::showLicense()
     v->show();
 }

-void ThemeManager::removeTheme()
-{
-    QListWidgetItem* currentItem = ui->listWidget->currentItem();
-    if (!currentItem) {
-        return;
-    }
-    Theme currentTheme = m_themeHash[currentItem->data(Qt::UserRole).toString()];
-
-    const auto button = QMessageBox::warning(this, tr("Confirmation"),
-                                             tr("Are you sure you want to remove '%1'?").arg(currentTheme.name),
-                                             QMessageBox::Yes | QMessageBox::No);
-    if (button != QMessageBox::Yes) {
-        return;
-    }
-
-    QDir(currentTheme.themePath).removeRecursively();
-    delete currentItem;
-}
-
 void ThemeManager::currentChanged()
 {
     QListWidgetItem* currentItem = ui->listWidget->currentItem();
@@ -120,7 +98,6 @@ void ThemeManager::currentChanged()
     ui->author->setText(currentTheme.author);
     ui->description->setText(currentTheme.description);
     ui->license->setHidden(currentTheme.license.isEmpty());
-    ui->remove->setEnabled(QFileInfo(currentTheme.themePath).isWritable());
 }

 ThemeManager::Theme ThemeManager::parseTheme(const QString &path, const QString &name)
@@ -137,7 +114,6 @@ ThemeManager::Theme ThemeManager::parseT
     info.name = metadata.name();
     info.description = metadata.comment();
     info.author = metadata.value(QSL("X-Falkon-Author")).toString();
-    info.themePath = path.chopped(1);

     const QString iconName = metadata.icon();
     if (!iconName.isEmpty()) {
--- src/lib/preferences/thememanager.h
+++ src/lib/preferences/thememanager.h
@@ -45,7 +45,6 @@ public:
 private Q_SLOTS:
     void currentChanged();
     void showLicense();
-    void removeTheme();

 private:
     struct Theme {
@@ -55,7 +54,6 @@ private:
         QString author;
         QString description;
         QString license;
-        QString themePath;
     };

     Theme parseTheme(const QString &path, const QString &name);

Created attachment 122814 [details]
patch to allow compilation for qt<5.10

Hi Vialav,

thank you for your reply (sorry for the delay, I somehow missed it in my inbox). I went about it another way, and just changed the

     info.themePath = path.chopped(1);

to two lines:

    info.themePath = path;
    info.themePath.chop(1);

Which allowed me compile that part, but then I ran into another problem:

 undefined reference to `bool QTest::qCompare [...]

which took a few fixes (this happened in multiple locations and files). Not sure why I couldn't compile, did you have problems there too? In any case, I have attached the patch necessary to get it to compile for me.

Git commit 9eaffd1208f715785eac5b6d58e1bdb384629dbe by Juraj Oravec.
Committed on 02/02/2020 at 17:17.
Pushed by jurajo into branch 'master'.

Autotests Qml - fix compilation with Qt 5.9

Summary: BUG: 411197

Test Plan: Compile with Qt 5.9, e.g. on Ubuntu 18.04

Reviewers: #falkon, drosca

Reviewed By: #falkon, drosca

Subscribers: drosca, falkon

Tags: #falkon

Differential Revision: https://phabricator.kde.org/D27102

M  +1    -1    autotests/qml/qmlclipboardapitest.cpp
M  +5    -5    autotests/qml/qmlcookiesapitest.cpp
M  +1    -1    autotests/qml/qmlhistoryapitest.cpp
M  +3    -3    autotests/qml/qmltabsapitest.cpp
M  +2    -2    autotests/qml/qmltopsitesapitest.cpp

https://commits.kde.org/falkon/9eaffd1208f715785eac5b6d58e1bdb384629dbe