Scripting: Fixed issues with absolute file paths on Windows

The strings were converted into URLs was broken on Windows, where an
absolute file path like "C:/..." was interpreted as a URL with the
scheme "C", which would then fail to load.

In addition to checking whether the resulting URL would be relative
(without scheme), we now also check whether the given string is a valid
absolute file path. In both cases, we produce a URL pointing to the
local file.

Closes mapeditor#2841

src/libtiled/imagelayer.cpp

@@ -74,9 +74,7 @@ bool ImageLayer::loadFromImage(const QPixmap &image, const QUrl &source)
  */
 bool ImageLayer::loadFromImage(const QImage &image, const QString &source)
 {
-    const QUrl url(source);
-    return loadFromImage(QPixmap::fromImage(image), url.isRelative() ? QUrl::fromLocalFile(source)
-                                                                     : url);
+    return loadFromImage(QPixmap::fromImage(image), Tiled::toUrl(source));
 }
 
 bool ImageLayer::loadFromImage(const QUrl &url)

src/libtiled/properties.cpp

@@ -43,10 +43,7 @@ QString FilePath::toString(const FilePath &path)
 
 FilePath FilePath::fromString(const QString &string)
 {
-    QUrl url(string);
-    if (url.isRelative())
-        url = QUrl::fromLocalFile(string);
-    return { url };
+    return { Tiled::toUrl(string) };
 }
 
 

src/libtiled/tiled.cpp

@@ -73,6 +73,18 @@ QUrl Tiled::toUrl(const QString &filePathOrUrl, const QDir &dir)
     return QUrl::fromLocalFile(absolutePath);
 }
 
+QUrl Tiled::toUrl(const QString &filePathOrUrl)
+{
+    QUrl url(filePathOrUrl);
+
+    if (filePathOrUrl.startsWith(QLatin1String(":/")))
+        url = QUrl(QLatin1String("qrc") + filePathOrUrl);
+    else if (QDir::isAbsolutePath(filePathOrUrl) || url.isRelative())
+        url = QUrl::fromLocalFile(filePathOrUrl);
+
+    return url;
+}
+
 /*
     If \a url is a local file returns a path suitable for passing to QFile.
     Otherwise returns an empty string.

src/libtiled/tiled.h

@@ -82,7 +82,8 @@ static const char PROPERTIES_MIMETYPE[] = "application/vnd.properties.list";
 TILEDSHARED_EXPORT QPointF alignmentOffset(const QRectF &r, Alignment alignment);
 
 TILEDSHARED_EXPORT QString toFileReference(const QUrl &url, const QDir &dir);
-TILEDSHARED_EXPORT QUrl toUrl(const QString &reference, const QDir &dir);
+TILEDSHARED_EXPORT QUrl toUrl(const QString &filePathOrUrl, const QDir &dir);
+TILEDSHARED_EXPORT QUrl toUrl(const QString &filePathOrUrl);
 TILEDSHARED_EXPORT QString urlToLocalFileOrQrc(const QUrl &url);
 
 inline QString colorToString(const QColor &color)

src/libtiled/tileset.cpp

@@ -262,8 +262,7 @@ bool Tileset::loadFromImage(const QImage &image, const QUrl &source)
  */
 bool Tileset::loadFromImage(const QImage &image, const QString &source)
 {
-    const QUrl url(source);
-    return loadFromImage(image, url.isRelative() ? QUrl::fromLocalFile(source) : url);
+    return loadFromImage(image, Tiled::toUrl(source));
 }
 
 /**
@@ -405,15 +404,14 @@ void Tileset::setImageSource(const QUrl &imageSource)
 
 /**
  * Exists only because the Python plugin interface does not handle QUrl (would
- * be nice to add this). Assumes \a source is a local file when it would
- * otherwise be a relative URL (without scheme).
+ * be nice to add this). Assumes \a source is a local file when it is either
+ * an absolute file path or would otherwise be a relative URL (without scheme).
  *
  * \sa loadFromImage
  */
 void Tileset::setImageSource(const QString &source)
 {
-    const QUrl url(source);
-    setImageSource(url.isRelative() ? QUrl::fromLocalFile(source) : url);
+    setImageSource(Tiled::toUrl(source));
 }
 
 /**

src/tiled/fileedit.cpp

@@ -21,6 +21,8 @@
 
 #include "fileedit.h"
 
+#include "tiled.h"
+
 #include <QFileDialog>
 #include <QFocusEvent>
 #include <QHBoxLayout>
@@ -71,10 +73,7 @@ void FileEdit::setFileUrl(const QUrl &url)
 QUrl FileEdit::fileUrl() const
 {
     const QString path = mLineEdit->text();
-    QUrl url(path);
-    if (url.isRelative())
-        url = QUrl::fromLocalFile(path);
-    return url;
+    return Tiled::toUrl(path);
 }
 
 void FileEdit::focusInEvent(QFocusEvent *e)