QChar: add fromUcs{2,4}()

The fromUcs2() named ctor is designed to replace all the non-char
integral-type constructors of QChar which make it very hard to control
the implicit QChar conversions, which have caused a few bugs in Qt
itself. As a classical named contructor, it simply returns QChar.

The fromUcs4() named "ctor", however, needs to expand surrogate pairs,
and thus can't just return QChar. Instead, it returns a small struct
that contains one or two char16_t's, can be iterated over and be
implicitly converted to QStringView.  To avoid bikeshedding the name
(FromUcs4Result, of course :), it's defined inline and thus can't be
named outside the function. This function replaces most uses of
QChar::requiresSurrogates() in QtBase.

[ChangeLog][QtCore][QChar] Added fromUcs2(), fromUcs4().

Change-Id: I803708c14001040f75cb599e33c24a3fb8d2579c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 31 insertions, 7 deletions

diff --git a/tests/auto/corelib/text/qchar/tst_qchar.cpp b/tests/auto/corelib/text/qchar/tst_qchar.cpp
index cf4f6d21e2..83a6765f2e 100644
--- a/tests/auto/corelib/text/qchar/tst_qchar.cpp
+++ b/tests/auto/corelib/text/qchar/tst_qchar.cpp
@@ -37,6 +37,8 @@ class tst_QChar : public QObject
     Q_OBJECT
 private slots:
     void fromChar16_t();
+    void fromUcs4_data();
+    void fromUcs4();
     void fromWchar_t();
     void operator_eqeq_null();
     void operators_data();
@@ -89,6 +91,34 @@ void tst_QChar::fromChar16_t()
 #endif
 }
 
+void tst_QChar::fromUcs4_data()
+{
+    QTest::addColumn<uint>("ucs4");
+    auto row = [](uint ucs4) {
+        QTest::addRow("0x%08X", ucs4) << ucs4;
+    };
+
+    row(0x2f868);
+    row(0x1D157);
+    row(0x1D157);
+}
+
+void tst_QChar::fromUcs4()
+{
+    QFETCH(const uint, ucs4);
+
+    const auto result = QChar::fromUcs4(ucs4);
+    if (QChar::requiresSurrogates(ucs4)) {
+        QCOMPARE(result.chars[0], QChar::highSurrogate(ucs4));
+        QCOMPARE(result.chars[1], QChar::lowSurrogate(ucs4));
+        QCOMPARE(QStringView{result}.size(), 2);
+    } else {
+        QCOMPARE(result.chars[0], ucs4);
+        QCOMPARE(result.chars[1], 0u);
+        QCOMPARE(QStringView{result}.size(), 1);
+    }
+}
+
 void tst_QChar::fromWchar_t()
 {
 #if defined(Q_OS_WIN)
@@ -835,13 +865,7 @@ void tst_QChar::normalization_data()
             for (int j = 0; j < c.size(); ++j) {
                 bool ok;
                 uint uc = c.at(j).toInt(&ok, 16);
-                if (!QChar::requiresSurrogates(uc)) {
-                    columns[i].append(QChar(uc));
-                } else {
-                    // convert to utf16
-                    columns[i].append(QChar(QChar::highSurrogate(uc)));
-                    columns[i].append(QChar(QChar::lowSurrogate(uc)));
-                }
+                columns[i].append(QChar::fromUcs4(uc));
             }
         }