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, 20 insertions, 0 deletions

diff --git a/src/corelib/tools/qcollator_macx.cpp b/src/corelib/tools/qcollator_macx.cpp
index 9aa59a81dc..42e67e0c12 100644
--- a/src/corelib/tools/qcollator_macx.cpp
+++ b/src/corelib/tools/qcollator_macx.cpp
@@ -55,6 +55,15 @@ QT_BEGIN_NAMESPACE
 void QCollatorPrivate::init()
 {
     cleanup();
+    /*
+      LocaleRefFromLocaleString() will accept "POSIX" as the locale name, but
+      the locale it produces (named "pos") doesn't implement the [A-Z] < [a-z]
+      behavior we expect of the C locale.  We can use QStringView to get round
+      that for collation, but this leaves no way to do a sort key.
+    */
+    if (isC())
+        return;
+
     LocaleRef localeRef;
     int rc = LocaleRefFromLocaleString(QLocalePrivate::get(locale)->bcp47Name().constData(), &localeRef);
     if (rc != 0)
@@ -92,6 +101,8 @@ int QCollator::compare(const QChar *s1, int len1, const QChar *s2, int len2) con
 {
     if (d->dirty)
         d->init();
+    if (!d->collator)
+        return QStringView(s1, len1).compare(QStringView(s2, len2), caseSensitivity());
 
     SInt32 result;
     Boolean equivalent;
@@ -104,6 +115,7 @@ int QCollator::compare(const QChar *s1, int len1, const QChar *s2, int len2) con
         return 0;
     return result < 0 ? -1 : 1;
 }
+
 int QCollator::compare(const QString &str1, const QString &str2) const
 {
     return compare(str1.constData(), str1.size(), str2.constData(), str2.size());
@@ -118,6 +130,11 @@ QCollatorSortKey QCollator::sortKey(const QString &string) const
 {
     if (d->dirty)
         d->init();
+    if (!d->collator) {
+        // What should (or even *can*) we do here ? (See init()'s comment.)
+        qWarning("QCollator doesn't support sort keys for the C locale on Darwin");
+        return QCollatorSortKey(nullptr);
+    }
 
     //Documentation recommends having it 5 times as big as the input
     QVector<UCCollationValue> ret(string.size() * 5);
@@ -136,6 +153,9 @@ QCollatorSortKey QCollator::sortKey(const QString &string) const
 
 int QCollatorSortKey::compare(const QCollatorSortKey &key) const
 {
+    if (!d.data())
+        return 0;
+
     SInt32 order;
     UCCompareCollationKeys(d->m_key.data(), d->m_key.size(),
                            key.d->m_key.data(), key.d->m_key.size(),