Improve error reporting when parsing JSON files

At least report the error string and the file offset where
the error happened.

Change-Id: Iaa1733593b8af2a7a52b67c0f495731f045d2c11
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
(cherry picked from qtbase/34c24ceb1ffce964c9f139d84b6b271bd2e45c33)
Reviewed-by: Jake Petroules <jake.petroules@qt.io>
Reviewed-by: Robert Loehning <robert.loehning@qt.io>

src/shared/proparser/qmakebuiltins.cpp

@@ -390,11 +390,16 @@ static void addJsonValue(const QJsonValue &value, const QString &keyPrefix, ProV
     }
 }
 
-static QMakeEvaluator::VisitReturn parseJsonInto(const QByteArray &json, const QString &into, ProValueMap *value)
+QMakeEvaluator::VisitReturn QMakeEvaluator::parseJsonInto(const QByteArray &json, const QString &into, ProValueMap *value)
 {
-    QJsonDocument document = QJsonDocument::fromJson(json);
-    if (document.isNull())
+    QJsonParseError error;
+    QJsonDocument document = QJsonDocument::fromJson(json, &error);
+    if (document.isNull()) {
+        if (error.error != QJsonParseError::NoError)
+            evalError(fL1S("Error parsing json at offset %1: %2")
+                      .arg(error.offset).arg(error.errorString()));
         return QMakeEvaluator::ReturnFalse;
+    }
 
     QString currentKey = into + QLatin1Char('.');
 

src/shared/proparser/qmakeevaluator.h

@@ -229,6 +229,7 @@ public:
 
     bool getMemberArgs(const ProKey &name, int srclen, const ProStringList &args,
                        int *start, int *end);
+    VisitReturn parseJsonInto(const QByteArray &json, const QString &into, ProValueMap *value);
 
     VisitReturn writeFile(const QString &ctx, const QString &fn, QIODevice::OpenMode mode,
                           bool exe, const QString &contents);