qt5base-lts/util/unicode
Edward Welbourne 78cf89c07d Use checked string iteration in case conversions
The Unicode table code can only be safely called on valid code-points.
So code that calls it must only pass it valid Unicode data. The string
iterator's Unchecked Unchecked methods only provide this guarantee
when the string being iterated is guaranteed to be valid UTF-16; while
client code should only use QString, QStringView and friends on valid
UTF-16 data, we have no way to be sure they have respected that.

So take the few extra cycles to actually check validity in the course
of iterating strings, when the resulting code-points are to be passed
to the Unicode table look-ups. Add tests that case mapping doesn't
access Unicode tables out of range (it'll trigger the new assertion).
Added some comments to qchar.h that helped me understand surrogates.

Change-Id: Iec2c3106bf1a875bdaa1d622f6cf94d7007e281e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
2020-08-29 18:15:27 +02:00
..
data Update UCD to Revision 26 2020-03-14 11:26:59 +01:00
x11
.gitattributes
main.cpp Use checked string iteration in case conversions 2020-08-29 18:15:27 +02:00
README Update UCD to Revision 26 2020-03-14 11:26:59 +01:00
unicode.pro
writingSystems.sh Updated license headers 2016-01-21 18:55:18 +00:00

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.