Add Latin1 to the set of supported encodings in QStringConverter

Latin1 is the only non Unicode encoding that is still being used
to some extent. Current web site statistics show that it is
being used in ~2% of all web sites. An additional 1% of web sites
use Windows1251 (which is almost the same as latin1).

As it's trivial to support this encoding, we keep it supported
in QStringConverter.

Change-Id: I0eff53a490b6c43d3e474107e7823be245d1715a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/text/qstringconverter.cpp

@@ -1296,6 +1296,33 @@ static char *toUtf32LE(char *out, QStringView in, QStringConverter::State *state
     return out + s.length();
 }
 
+void qt_from_latin1(char16_t *dst, const char *str, size_t size) noexcept;
+
+static QChar *fromLatin1(QChar *out, const char *chars, qsizetype len, QStringConverter::State *)
+{
+    qt_from_latin1(reinterpret_cast<char16_t *>(out), chars, size_t(len));
+    return out + len;
+}
+
+
+static char *toLatin1(char *out, QStringView in, QStringConverter::State *state)
+{
+    const char replacement = (state && state->flags & QStringConverter::ConvertInvalidToNull) ? 0 : '?';
+    int invalid = 0;
+    for (qsizetype i = 0; i < in.length(); ++i) {
+        if (in[i] > QChar(0xff)) {
+            *out = replacement;
+            ++invalid;
+        } else {
+            *out = (char)in[i].cell();
+        }
+        ++out;
+    }
+    if (state)
+        state->invalidChars += invalid;
+    return out;
+}
+
 static QChar *fromLocal8Bit(QChar *out, const char *in, qsizetype length, QStringConverter::State *state)
 {
     QString s = QLocal8Bit::convertToUnicode(in, length, state);
@@ -1320,6 +1347,9 @@ static qsizetype toUtf16Len(qsizetype l) { return 2*(l + 1); }
 static qsizetype fromUtf32Len(qsizetype l) { return l + 1; }
 static qsizetype toUtf32Len(qsizetype l) { return 4*(l + 1); }
 
+static qsizetype fromLatin1Len(qsizetype l) { return l + 1; }
+static qsizetype toLatin1Len(qsizetype l) { return l + 1; }
+
 const QStringConverter::Interface QStringConverter::encodingInterfaces[QStringConverter::LastEncoding + 1] =
 {
     { fromUtf8, fromUtf8Len, toUtf8, toUtf8Len },
@@ -1329,6 +1359,7 @@ const QStringConverter::Interface QStringConverter::encodingInterfaces[QStringCo
     { fromUtf32, fromUtf32Len, toUtf32, toUtf32Len },
     { fromUtf32LE, fromUtf32Len, toUtf32LE, toUtf32Len },
     { fromUtf32BE, fromUtf32Len, toUtf32BE, toUtf32Len },
+    { fromLatin1, fromLatin1Len, toLatin1, toLatin1Len },
     { fromLocal8Bit, fromUtf8Len, toLocal8Bit, toUtf8Len }
 };
 

src/corelib/text/qstringconverter.h

@@ -96,6 +96,7 @@ public:
         Utf32,
         Utf32LE,
         Utf32BE,
+        Latin1,
         Locale,
         LastEncoding = Locale
     };