QRestReply: optionally return the QJsonParseError from json()

... and remove the debug output of the internal QJsonParseError.

This allows users of the function to get the details in
machine-readable form, and to distinguish between !finished and an
actual Json parsing error.

Found in API-review.

Change-Id: Ia237b192a894d692b965f6bedb4c94d3b6537535
Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>
(cherry picked from commit 3a61de282c4740efe4a6fa1672e66efaf7c2b408)
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

src/network/access/qrestreply.cpp

@@ -157,31 +157,34 @@ void QRestReply::abort()
 
     The returned value is wrapped in \c std::optional. If the conversion
     from the received data fails (empty data or JSON parsing error),
-    \c std::nullopt is returned.
+    \c std::nullopt is returned, and \a error is filled with details.
 
     Calling this function consumes the received data, and any further calls
     to get response data will return empty.
 
     This function returns \c {std::nullopt} and will not consume
-    any data if the reply is not finished.
+    any data if the reply is not finished. If \a error is passed, it will be
+    set to QJsonParseError::NoError to distinguish this case from an actual
+    error.
 
     \sa body(), text(), finished(), isFinished()
 */
-std::optional<QJsonDocument> QRestReply::json()
+std::optional<QJsonDocument> QRestReply::json(QJsonParseError *error)
 {
     Q_D(QRestReply);
     if (!isFinished()) {
         qCWarning(lcQrest, "Attempt to read json() of an unfinished reply, ignoring.");
+        if (error)
+            *error = {0, QJsonParseError::ParseError::NoError};
         return std::nullopt;
     }
     QJsonParseError parseError;
     const QByteArray data = d->networkReply->readAll();
     const QJsonDocument doc = QJsonDocument::fromJson(data, &parseError);
-    if (parseError.error != QJsonParseError::NoError) {
-        qCDebug(lcQrest) << "Response data not JSON:" << parseError.errorString()
-                         << "at" << parseError.offset << data;
+    if (error)
+        *error = parseError;
+    if (parseError.error)
         return std::nullopt;
-    }
     return doc;
 }
 

src/network/access/qrestreply.h

@@ -12,6 +12,7 @@ QT_BEGIN_NAMESPACE
 
 class QByteArray;
 class QDebug;
+struct QJsonParseError;
 class QJsonDocument;
 class QString;
 
@@ -25,7 +26,7 @@ public:
 
     QNetworkReply *networkReply() const;
 
-    std::optional<QJsonDocument> json();
+    std::optional<QJsonDocument> json(QJsonParseError *error = nullptr);
     QByteArray body();
     QString text();