CBOR: fix the UTF8-and-UTF16 detection

This isn't a bug, it just removes dead code. The code to compare
US-ASCII to UTF-16 was never engaged because this conditional was wrong
and effectively catching everything. Fortunately, because that
comparison code is now wrong with the unit tests added to tst_QCborValue
in the past few commits.

Pick-to: 6.7
Change-Id: If1bf59ecbe014b569ba1fffd17c4ce184948e646
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

1 files changed, 17 insertions, 41 deletions

diff --git a/src/corelib/serialization/qcborvalue.cpp b/src/corelib/serialization/qcborvalue.cpp
index 3414cff5fc..70a9539a8a 100644
--- a/src/corelib/serialization/qcborvalue.cpp
+++ b/src/corelib/serialization/qcborvalue.cpp
@@ -1221,12 +1221,6 @@ static int compareElementRecursive(const QCborContainerPrivate *c1, const Elemen
     const ByteData *b1 = c1 ? c1->byteData(e1) : nullptr;
     const ByteData *b2 = c2 ? c2->byteData(e2) : nullptr;
     if (b1 || b2) {
-        auto compareStrings = [mode](auto s1, auto s2) {
-            if (mode == Comparison::ForEquality)
-                return QtPrivate::equalStrings(s1, s2) ? 0 : 1;
-            return QtPrivate::compareStrings(s1, s2);
-        };
-
         auto len1 = b1 ? b1->len : 0;
         auto len2 = b2 ? b2->len : 0;
 
@@ -1242,22 +1236,14 @@ static int compareElementRecursive(const QCborContainerPrivate *c1, const Elemen
         Q_ASSERT(b2);
 
         // Officially with CBOR, we sort first the string with the shortest
-        // UTF-8 length. The length of an ASCII string is the same as its UTF-8
-        // and UTF-16 ones, but the UTF-8 length of a string is bigger than the
-        // UTF-16 equivalent. Combinations are:
-        //  1) UTF-16 and UTF-16
-        //  2) UTF-16 and UTF-8  <=== this is the problem case
-        //  3) UTF-16 and US-ASCII
-        //  4) UTF-8 and UTF-8
-        //  5) UTF-8 and US-ASCII
-        //  6) US-ASCII and US-ASCII
-        if ((e1.flags & Element::StringIsUtf16) && (e2.flags & Element::StringIsUtf16)) {
-            // Case 1: both UTF-16
+        // UTF-8 length. Since US-ASCII is just a subset of UTF-8, its length
+        // is the UTF-8 length. But the UTF-16 length may not be directly
+        // comparable.
+        if ((e1.flags & Element::StringIsUtf16) && (e2.flags & Element::StringIsUtf16))
             return compareStringsInUtf8(b1->asStringView(), b2->asStringView(), mode);
-        }
 
         if (!(e1.flags & Element::StringIsUtf16) && !(e2.flags & Element::StringIsUtf16)) {
-            // Cases 4, 5 and 6: neither is UTF-16, so lengths are comparable too
+            // Neither is UTF-16, so lengths are comparable too
             // (this case includes byte arrays too)
             if (len1 == len2) {
                 if (mode == Comparison::ForEquality) {
@@ -1269,29 +1255,19 @@ static int compareElementRecursive(const QCborContainerPrivate *c1, const Elemen
             return len1 < len2 ? -1 : 1;
         }
 
-        if (!(e1.flags & Element::StringIsAscii) || !(e2.flags & Element::StringIsAscii)) {
-            // Case 2: one of them is UTF-8 and the other is UTF-16, so lengths
-            // are NOT comparable. We need to convert to UTF-8 first...
-            // (we can't use QUtf8::compareUtf8 because we need to compare lengths)
-            auto string = [](const Element &e, const ByteData *b) -> QByteArray {
-                if (e.flags & Element::StringIsUtf16)
-                    return b->asStringView().toUtf8();
-                return b->asByteArrayView();    // actually a QByteArray::fromRaw
-            };
-
-            QByteArray s1 = string(e1, b1);
-            QByteArray s2 = string(e2, b2);
-            if (s1.size() == s2.size())
-                return memcmp(s1.constData(), s2.constData(), s1.size());
-            return s1.size() < s2.size() ? -1 : 1;
-        }
+        // Only one is UTF-16
+        // (we can't use QUtf8::compareUtf8 because we need to compare lengths)
+        auto string = [](const Element &e, const ByteData *b) -> QByteArray {
+            if (e.flags & Element::StringIsUtf16)
+                return b->asStringView().toUtf8();
+            return b->asByteArrayView();    // actually a QByteArray::fromRaw
+        };
 
-        // Case 3 (UTF-16 and US-ASCII) remains, so lengths are comparable again
-        if (len1 != len2)
-            return len1 < len2 ? -1 : 1;
-        if (e1.flags & Element::StringIsUtf16)
-            return compareStrings(b1->asStringView(), b2->asLatin1());
-        return compareStrings(b1->asLatin1(), b2->asStringView());
+        QByteArray s1 = string(e1, b1);
+        QByteArray s2 = string(e2, b2);
+        if (s1.size() == s2.size())
+            return memcmp(s1.constData(), s2.constData(), s1.size());
+        return s1.size() < s2.size() ? -1 : 1;
     }
 
     return compareElementNoData(e1, e2);