AutoMapping: Ignore rules with empty input or output regions

Rules with an empty input region were causing issues, because they don't
have a valid bounding rectangle. They are also commonly created by
accident. If intended as a rule that always matches, such a rule can be
made by placing the special "Ignore" tile in the rule's input.

Rules with empty output region are no longer matched because they would
not produce any output anyway.

As a drive-by, AutoMapper no longer derives from QObject, which appears
to have only been done to access the tr() function. This is now made
available using Q_DECLARE_TR_FUNCTIONS instead.

Closes mapeditor#3834

src/tiled/automapper.cpp

@@ -639,9 +639,16 @@ void AutoMapper::setupRules()
     mRules.reserve(combinedRegions.size());
 
     for (const QRegion &combinedRegion : combinedRegions) {
+        QRegion inputRegion = combinedRegion & regionInput;
+        QRegion outputRegion = combinedRegion & regionOutput;
+
+        // Skip rules where either input or output region is empty
+        if (inputRegion.isEmpty() || outputRegion.isEmpty())
+            continue;
+
         Rule &rule = mRules.emplace_back();
-        rule.inputRegion = combinedRegion & regionInput;
-        rule.outputRegion = combinedRegion & regionOutput;
+        rule.inputRegion = std::move(inputRegion);
+        rule.outputRegion = std::move(outputRegion);
         rule.options = mRuleOptions;
 
         for (const auto &optionsArea : setup.mRuleOptionsAreas)
@@ -1474,5 +1481,3 @@ void AutoMapper::addWarning(const QString &message, std::function<void ()> callb
 }
 
 } // namespace Tiled
-
-#include "moc_automapper.cpp"

src/tiled/automapper.h

@@ -27,6 +27,7 @@
 #include "tilelayer.h"
 #include "tileset.h"
 
+#include <QCoreApplication>
 #include <QList>
 #include <QMap>
 #include <QRegion>
@@ -275,9 +276,9 @@ struct TILED_EDITOR_EXPORT AutoMappingContext
  * - copy regions of Maps (multiple Layers, the layerlist is a
  *                         lookup-table for matching the Layers)
  */
-class TILED_EDITOR_EXPORT AutoMapper : public QObject
+class TILED_EDITOR_EXPORT AutoMapper
 {
-    Q_OBJECT
+    Q_DECLARE_TR_FUNCTIONS(Tiled::AutoMapper)
 
 public:
     struct Options
@@ -333,7 +334,7 @@ class TILED_EDITOR_EXPORT AutoMapper : public QObject
      *                 AutoMapper takes ownership of this map.
      */
     AutoMapper(std::unique_ptr<Map> rulesMap, const QRegularExpression &mapNameFilter = {});
-    ~AutoMapper() override;
+    ~AutoMapper();
 
     QString rulesMapFileName() const;
     const QRegularExpression &mapNameFilter() const;