Treat simple spaces as equivalent in date-time format separators

The user might not be aware of, or able to see, the difference between
Unicode's assorted horizontal spacing characters, leading them to
expect their input to be accepted for a format despite differences in
spacing. So treat the various horizontal spacing (other than tab)
characters as equivalent when matching the separators in a date-time
format. Add a test-case that failed before this fix.

Fixes: QTBUG-114909
Pick-to: 6.6 6.5
Change-Id: I3e798d3e5b89adb8e86168ebd3954904b258d630
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Ievgenii Meshcheriakov <ievgenii.meshcheriakov@qt.io>

src/corelib/time/qdatetimeparser.cpp

@@ -728,11 +728,33 @@ int QDateTimeParser::sectionMaxSize(int index) const
 }
 
 // Separator matching
+//
+// QTBUG-114909: user may be oblivious to difference between visibly
+// indistinguishable spacing characters. For now we only treat horizontal
+// spacing characters, excluding tab, as equivalent.
+
 static int matchesSeparator(QStringView text, QStringView separator)
 {
+    const auto isSimpleSpace = [](char32_t ch) {
+        // Distinguish tab, CR and the vertical spaces from the rest:
+        return ch == u' ' || (ch > 127 && QChar::isSpace(ch));
+    };
     // -1 if not a match, else length of prefix of text that does match.
-    // For now, just check for exact match:
-    return text.startsWith(separator) ? separator.size() : -1;
+    // First check for exact match
+    if (!text.startsWith(separator)) {
+        // Failing that, check for space-identifying match:
+        QStringIterator given(text), sep(separator);
+        while (sep.hasNext()) {
+            if (!given.hasNext())
+                return -1;
+            char32_t s = sep.next(), g = given.next();
+            if (s != g && !(isSimpleSpace(s) && isSimpleSpace(g)))
+                return -1;
+        }
+        // One side may have used a surrogate pair space where the other didn't:
+        return given.index();
+    }
+    return separator.size();
 }
 
 /*!

tests/auto/corelib/text/qlocale/tst_qlocale.cpp

@@ -2431,6 +2431,10 @@ void tst_QLocale::toTime_data()
         << usa << QTime(16, 43, 32) << u"h:mm:ss AP "_s << u"4:43:32 PM "_s << true;
     QTest::newRow("shortFormat-PM")
         << usa << QTime(16, 43) << u"h:mm AP "_s << u"4:43 PM "_s << true;
+    // Some locales use a narrow non-breaking space as separator, but
+    // the user can't see the difference from a space (QTBUG-114909):
+    QTest::newRow("shortFormat-AM-mixspace")
+        << usa << QTime(4, 43) << u"h:mm\u202F" "AP "_s << u"4:43 AM "_s << true;
 
     // Parsing am/pm indicators case-insensitively:
     const QLocale czech{QLocale::Czech, QLocale::Czechia};