qt5base-lts/util/unicode
Marc Mutz 19e7c0d2b5 QChar/QString: centralize case folding in qchar.cpp
There are (at least) two implementations of the low-level case-folding
algorithm, one of which (for QChar::toLower()) seems to be wrong (it
doesn't deal with special cases which expand to more than one code
point).

The algoithm hidden in QString and entangled with the QString
detaching code makes reusing the code much harder.

At the same time, the dependency of the algorithm on the unicode
tables makes exposing a non-allocating result type in the public API
hard. std::u16string would be an alternative if we can assure that all
implementations use SSO with at least four characters.

So, for the time being, leave this as internal API for use in an
upcoming QStringView::toLower() as well as case-insensitive hashing.

Change-Id: Iabb2611846f6176776aa20e634f44d8464f3305c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
2020-05-09 06:25:05 +00:00
..
codecs/big5
data
x11
.gitattributes
main.cpp QChar/QString: centralize case folding in qchar.cpp 2020-05-09 06:25:05 +00:00
README
unicode.pro
writingSystems.sh

Unicode is used to generate the unicode data in src/corelib/text/.

To update:
* Find the data (UAX #44, UCD; not the XML version) at
  ftp://www.unicode.org/Public/zipped/$Version/
* Unpack the zip file; for each file in data/, replace with the new
  version; find the *BreakProperty.txt in auxiliary/. (These last are
  only in the zip, not in the web-space's unpacked versions.)
* In tst_QTextBoundaryFinder's data/ sub-directory, update its files
  from the auxiliary/ sub-directory of the UCD data.
* If needed, add an entry to enum QChar::UnicodeVersion for the new
  Unicode version
* In that case, also update main.cpp's initAgeMap and DATA_VERSION_S*
  to match
* Build this project. Its binary, unicode, ignores command-line
  options and assumes it is being run from this directory. When run,
  it produces lots of output. If it gets as far as updating
  qunicodetables.cpp the output hopefully doesn't matter.
* It'll end prematurely with a qFatal() message if it needs updates,
  either in main.cpp or in QChar:
  * "unassigned or unhandled age value:" initAgeMap() and
    QChar::UnicodeVersion;
  * "Unhandled script property value:" initScriptMap(), QChar::Script,
    qharfbuzzng.cpp's _qtscript_to_hbscript[] array and
    qfontconfigdatabase.cpp's specialLanguages.
  * "unassigned word break class:" enum WordBreakClass,
    word_break_class_string and initWordBreak();
* Assertions or other qFatal()s may trigger: if so, study code and
  understand what's more complicated about this update; talk to folk
  named in the git logs, maybe push a WIP to gerrit to solicit
  advice. Some bit-field may need to be expanded, for example. In some
  cases QChar may need additions to some of its enums.
* Build with the modified code, fix any compilation issues, make check
  in suitable directories, including tst_QTextBoundaryFinder.
* That may have updated qtbase/src/corelib/text/qunicodetables.cpp; if
  so the update matters; be sure to commit the changes to data/ at the
  same time and update text/qt_attribution.json to match; use the UCD
  Revision number, rather than the Unicode standard number, as the
  Version, for all that qunicodetables.cpp uses the latter (see the
  'UAX #44, UCD' page linked from https://www.unicode.org/ucd/ for the
  table with this).
* If there are enum additions in qchar.h (public API), be sure to also
  update the documentation in qchar.cpp for each affected enum,
  respecting the existing ordering.
* If you don't normally build in the source tree, remember to delete
  qtbase/.qmake.stash while you're cleaning up.

The script writingSystems.sh generates a list of writing systems,
ostensibly as a the basis for updating QFontDatabase::WritingSystem
enum; however, the Release 20 output of it contains many more writing
systems than are present in that enum, suggesting it has not been run
in a very long time. Further research needed.