Handle QCollator with locale C by delegating to QString

Previously, the C locale was treated as English because each back-end
takes the locale's bcp47Name(), which maps C to en. However, the C
locale has its own rules; which QString helpfully implements; so we
can delegate to it in this case. Extended this to sort keys, where
possible. Clean up existing implementations in the process.

Extended tst_QCollator::compare() with some cases to check this. That
required wrapping the test's calls to collator.compare() in a sign
canonicalizer, since it can return any -ve for < or +ve for >, not
just -1 and +1 for these cases (and it'd be rash to hard-code specific
negative and positive values, as they may vary between backends).

[ChangeLog][QtCore][QCollator] Added support for collation in the C
locale, albeit this is only well-defined for ASCII. Collation sort
keys remain unsupported on Darwin.

Fixes: QTBUG-58621
Change-Id: I327010d90f09bd1b1816f5590cb124e3d423e61d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/corelib/tools/qcollator_win.cpp b/src/corelib/tools/qcollator_win.cpp
index 5a838c1b50..35142bb8b8 100644
--- a/src/corelib/tools/qcollator_win.cpp
+++ b/src/corelib/tools/qcollator_win.cpp
@@ -60,6 +60,8 @@ extern LCID qt_inIsoNametoLCID(const char *name);
 void QCollatorPrivate::init()
 {
     collator = 0;
+    if (isC())
+        return;
 
 #ifndef USE_COMPARESTRINGEX
     localeID = qt_inIsoNametoLCID(QLocalePrivate::get(locale)->bcp47Name().constData());
@@ -86,6 +88,9 @@ void QCollatorPrivate::cleanup()
 
 int QCollator::compare(const QChar *s1, int len1, const QChar *s2, int len2) const
 {
+    if (d->isC())
+        return QString::compare_helper(s1, len1, s2, len2, d->caseSensitivity);
+
     if (d->dirty)
         d->init();
 
@@ -119,6 +124,8 @@ QCollatorSortKey QCollator::sortKey(const QString &string) const
 {
     if (d->dirty)
         d->init();
+    if (d->isC())
+        return QCollatorSortKey(new QCollatorSortKeyPrivate(string));
 
 #ifndef USE_COMPARESTRINGEX
     int size = LCMapStringW(d->localeID, LCMAP_SORTKEY | d->collator,