Unify /opt and /usr install paths for QT

[DJ Lucas]

This should occur at next update of QT if possible (unless we are very close to 9.0 release). Original comments:

As an aside, and mostly for Bruce (but others are absolutely welcome to comment), what would you say to unifying the install of QT5, making it match a system install? This breakage in the book brings to the forefront why it might be nice. This would basically mean supplying the following to configure (for both camps):

./configure -prefix $QT5PREFIX-sysconfdir /etc/xdg            \
            -confirm-license -opensource -dbus-linked      \
            -openssl-linked -system-harfbuzz -system-sqlite   \
            -nomake examples -no-rpath -skip qtwebengine       \
            -archdatadir $QT5PREFIX/lib/qt5                 \
            -bindir $QT5PREFIX/bin                     \
            -plugindir $QT5PREFIX/lib/qt5/plugins         \
            -importdir $QT5PREFIX/lib/qt5/imports         \
            -headerdir $QT5PREFIX/include/qt5             \
            -datadir $QT5PREFIX/share/qt5               \
            -docdir /usr/share/doc/qt5-&qt5-version;         \
            -translationdir $QT5PREFIX/share/qt5/translations  \
            -examplesdir /usr/share/doc/qt5-&qt5-version;/examples &&

Obviously, the above needs to be tested yet, and I wouldn't want to do it until at least the next QT update, but I understand the reluctance to do so WRT how pretty the install looks in /opt.There may be some room to go the other way as well - really, we could drop all of the qt5 suffixes, only headerdir is really invasive in the /usr hierarchy (funny that is the variance that caused the breakage in the book). That would result in, I believe, only headerdir, docdir, and examplesdir being passed in.

[Bruce Dubbs]

Reformatting:

./configure -prefix         $QT5PREFIX                        \
            -archdatadir    $QT5PREFIX/lib/qt5                \
            -bindir         $QT5PREFIX/bin                    \
            -plugindir      $QT5PREFIX/lib/qt5/plugins        \
            -importdir      $QT5PREFIX/lib/qt5/imports        \
            -headerdir      $QT5PREFIX/include/qt5            \
            -datadir        $QT5PREFIX/share/qt5              \
            -translationdir $QT5PREFIX/share/qt5/translations \
            -confirm-license  \
            -opensource       \
            -dbus-linked      \
            -openssl-linked   \ 
            -system-harfbuzz  \ 
            -system-sqlite    \
            -nomake examples  \
            -no-rpath         \
            -skip qtwebengine \
            -sysconfdir  /etc/xdg                         \
            -docdir      /usr/share/doc/qt5-&qt5-version; \
            -examplesdir /usr/share/doc/qt5-&qt5-version;/examples 

I still prefer what we have now as I think it is more clear, but I can be persuaded depending on what others think.

The placement in /opt makes a lot more sense in an LFS environment. An update becomes easy. What I use is:

VERSION=5.12.2
QT5PREFIX=/opt/qt5

sudo rm -rf /opt/qt-$VERSION $QT5PREFIX
sudo mkdir -p $QT5PREFIX
...  qt5 build instructions
sudo mv $QT5PREFIX /opt/qt-$VERSION 
sudo ln -svfn qt-$VERSION /opt/qt5

That retains older versions and reverting is as simple as changing the /opt/qt5 symlink.

[Douglas R. Reno]

I think unifying the installation paths is the best here, especially for consistency purposes. What we have right now is rather inconsistent and misleading if you are installing in /usr, but that's just my opinion from a simple glanceover, I've never built in /usr (although I'm not opposed to the idea on another system of mine). The problems described in #12201 are a good example of this. The problems with systemsettings5 not being able to find KCM modules described at ​http://lists.linuxfromscratch.org/pipermail/blfs-dev/2019-June/036230.html (Although as Bruce notes, this may be a Plasma-specific problem).

[DJ Lucas]

For users of PM's, /opt installation makes little sense. I'm thinking we can go the other way, however (make the /usr installation match the cleanliness of the /opt install, we only need change the path of the headers in the /opt case to $QT5PREFIX/include/qt5. I recognize the otherwise empty include directory, but this simple change fixes AFAICT and doesn't introduce a mess in /usr. QT's build machinery is really clean compared to other toolkits, IOW, very little chance of breakage. I'm going to revisit this on my next KF5/Plasma pass and report back. I'll post a DESTDIR tree of both.

[Bruce Dubbs]

Closing as wontfix as we have a note in the book about how to install in /usr. When we install qt6, it may be a good thing to do.