Comment 0 for bug 1654840

# Test Case
$ python3
>>> from PyQt5.QtGui import QTextDocument
>>> d = QTextDocument()
>>> d.setPlainText('÷ Σ')
>>> d.toPlainText()
'÷ £'

This should not happen. d.toPlainText() should return '÷ Σ'.

# Impact
The bug was initially reported upstream: https://www.riverbankcomputing.com/pipermail/pyqt/2015-March/035627.html.

Some time ago I got the same issue in ReText CI, which uses Ubuntu Trusty. The test failure was observed at https://travis-ci.org/retext-project/retext/builds/186945524. With the proposed upload, the failure disappears.

This can also affect other editors which allow to input unicode, like eric.

# Proposed Fix
The fix which I am uploading to -proposed is taken from this upstream changeset:

2014-04-15 Phil Thompson <email address hidden>

    * qpy/QtCore/qpycore_qstring.cpp:
    Fixed a bug in the conversion of QStrings with surrogate pairs.
    [16a9c19d08cf] <5.2-maint>

It is present in all releases since v5.3.

# Regression Potential
The patch is small, should not introduce any regressions.