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, 1 insertions, 0 deletions

diff --git a/src/corelib/tools/qcollator_p.h b/src/corelib/tools/qcollator_p.h
index e89c08447c..361c3fb987 100644
--- a/src/corelib/tools/qcollator_p.h
+++ b/src/corelib/tools/qcollator_p.h
@@ -110,6 +110,7 @@ public:
 
     QCollatorPrivate(const QLocale &locale) : locale(locale) {}
     ~QCollatorPrivate() { cleanup(); }
+    bool isC() { return locale.language() == QLocale::C; }
 
     void clear() {
         cleanup();