[Interest] Size of libQt5Core in 5.3

[Daniel Bowen]

Thanks again for the info.

Here's where I've gotten to so far.

Starting from the last ./configure command line I mentioned, plus
-no-feature- for every qfeature.txt item (minus LIBRARY, SETTINGS and
REGULAREXPRESSION, since it doesn't build without those), I was at 4.3 MB
stripped.

Added to the size:
1. From the "-no-feature- for every feature" list, I pulled out a few more
of the -no-feature- things for features we need directly or indirectly.  So,
these things are not specified to ./configure anymore (and so the feature is
included).
	(removed -no-feature-LIBRARY -no-feature-SETTINGS
-no-feature-REGULAREXPRESSION earlier)
	-no-feature-XMLSTREAM -no-feature-XMLSTREAMREADER
-no-feature-XMLSTREAMWRITER -no-feature-TEMPORARYFILE -no-feature-TEXTDATE
-no-feature-DATESTRING -no-feature-PROPERTIES -no-feature-TEXTCODEC
-no-feature-CODECS -no-feature-SYSTEMSEMAPHORE, -no-feature-SHAREDMEMORY,
-no-feature-TRANSLATION -no-feature-HTTP -no-feature-UDPSOCKET
-no-feature-NETWORKPROXY -no-feature-SOCKS5 -no-feature-NETWORKINTERFACE
-no-feature-NETWORKDISKCACHE -no-feature-BEARERMANAGEMENT
-no-feature-LOCALSERVER
(I still want to switch over to the -qconfig way, but qconfig is not
automatically built in the Linux desktop build, and has errors for me when
compiling).

I realize not all those affect libQt5Core. At that point,
libQt5Core.so.5.3.0 was about 4.8 MB after stripping (up from 4.3 MB).

Reduced the size:
1. In qtbase/mkspecs/common/gcc-base.conf, I had previously updated
QMAKE_CFLAGS_OPTIMIZE to use -Os but had left QMAKE_CLAGS_OPTIMIZE_FULL to
-O3. I then updated QMAKE_CFLAGS_OPTIMIZE_FULL to use -Os. (Save ~0.8 MB)
2. Edit corelib.pro to comment out "CONFIG += exceptions" (Save ~380 KB)
3. Use the steps that John Layt gave for updating the
qtbase/util/local_database stuff for locale data, to generate a qlocale.xml,
remove <locale> items for everything except "C" and US English, then run
qlocalexml2cpp.py. Noted the effect on
qtbase/src/corelib/tools/qlocale_data_p.h
(Save ~0.7 MB)
4. Have version of
qtbase/src/corelib/mimetypes/mime/packages/freedesktop.org.xml without
<comment xml:lang items
	 sed '/\<comment xml:lang/d' freedesktop.org.xml >
no-lang.freedesktop.org.xml
 Update qtbase/src/corelib/mimetypes/mimetypes.qrc to reference
no-lang.freedesktop.org.xml
(Save ~220 KB)

After these changes, libQt5Core.so.5.3.0 was 3.0 MB stripped!  (3048028
bytes). If I trimmed the mime types down to a single item and took out the
DOCTYPE, it went down a little bit more (25KB less).  So, that's "within
striking distance" now.

Other things I might still try:
- Updating the TLD stuff to slim it down.
- See if I can safely remove some other things from the locale information.
John? ("likely subtags", language name list, etc.)
- If there's an update that makes -no-feature-REGULAREXPRESSION work, use
that.


A few other comments:

>Peter Kümmel wrote:
> Maybe it is worth to think about a Qt library which really only
> provides essential stuff. What would such a library contain,
> when all the "but the GUI needs it" was removed?

QtCore generally has just essential stuff for either UI or non-UI. Of course
there's other libraries too that have nice things for both UI and non-UI
like QtNetwork, etc. QtCore does have some things typically used for UI that
might not be needed for non-UI use, like animations, etc., but there are
-no-feature items for those (or most those).  We've been using Qt for many
things for a few years now.  It's a great C++ library in general.  We have
embedded software without any UI, middleware that runs on desktops or (some)
mobile without any direct UI, and then UI pieces as well. The middleware
piece has been used in apps that run .NET on Windows or Objective-C on Mac
(exposing exported C functions or COM interop/PInvoke, and keeping C++ class
use internal to the library).

There's other libraries too that are interesting for non-UI use that Qt
provides.

>Thiago Macieira
> Note that it's configuring something outside of Qt and
> possibly affecting other applications in your system.

It seems like the locale reference by qtbase/util/local_database and the
locale classes are self contained.  It does use data from the outside, but
I'm not sure how it would affect other applications in the system (unless
they're using the Qt version we make).

>Thiago Macieira
> Why are you even trying to build qttools for your target environment? Just
> skip the module altogether.

That's a good idea. I had run it mainly for qtpaths and lrelease.

>Peter Kümmel
> So maybe the question should be, what does an essential 1M Qt lib need
> to be of any use?

I don't know what a target size would be per-se, but the specific list might
depend on who you ask.  There are some things that might sound like UI
related at first, like say QSize QPoint and QRect, but those are actually
nice to have for non-UI stuff.  I think QtCore largely has essential non-UI
common things, but a few things that I don't see us using from QtCore for
non-UI things would be things like the animation related things and the item
models (though, I could imagine there might be non-UI uses for others to use
those).

Thanks,
-Daniel