Disallow conversion of const {Image,Trade::ImageData}&& to ImageReference.

The conversion is done implicitly, thus this seemingly innocent code
would be allowed:

    ImageReference2D reference = Image2D(...);
    foo(reference.data()); // crash on access, data already deleted

src/Image.h

@@ -80,12 +80,18 @@ template<UnsignedInt dimensions> class Image: public AbstractImage {
         /** @brief Destructor */
         ~Image() { delete[] _data; }
 
-        /**
-         * @brief Conversion to reference
-         *
-         * @todo GCC 4.8: don't allow this on rvalue-ref
-         */
-        /*implicit*/ operator ImageReference<dimensions>() const;
+        /** @brief Conversion to reference */
+        /*implicit*/ operator ImageReference<dimensions>()
+        #ifndef CORRADE_GCC47_COMPATIBILITY
+        const &;
+        #else
+        const;
+        #endif
+
+        #ifndef CORRADE_GCC47_COMPATIBILITY
+        /** @overload */
+        /*implicit*/ operator ImageReference<dimensions>() const && = delete;
+        #endif
 
         /** @brief %Image size */
         typename DimensionTraits<Dimensions, Int>::VectorType size() const { return _size; }
@@ -132,7 +138,13 @@ template<UnsignedInt dimensions> inline Image<dimensions>& Image<dimensions>::op
     return *this;
 }
 
-template<UnsignedInt dimensions> inline Image<dimensions>::operator ImageReference<dimensions>() const {
+template<UnsignedInt dimensions> inline Image<dimensions>::operator ImageReference<dimensions>()
+#ifndef CORRADE_GCC47_COMPATIBILITY
+const &
+#else
+const
+#endif
+{
     return ImageReference<dimensions>(AbstractImage::format(), AbstractImage::type(), _size, _data);
 }
 

src/Test/ImageTest.cpp

@@ -71,13 +71,22 @@ void ImageTest::moveAssignment() {
 
 void ImageTest::toReference() {
     unsigned char* data = new unsigned char[3];
-    Image2D a(ColorFormat::Red, ColorType::UnsignedByte, {1, 3}, data);
+    const Image2D a(ColorFormat::Red, ColorType::UnsignedByte, {1, 3}, data);
 
     ImageReference2D b = a;
     CORRADE_COMPARE(b.format(), ColorFormat::Red);
     CORRADE_COMPARE(b.type(), ColorType::UnsignedByte);
     CORRADE_COMPARE(b.size(), Vector2i(1, 3));
     CORRADE_VERIFY(b.data() == data);
+
+    CORRADE_VERIFY((std::is_convertible<const Image2D&, ImageReference2D>::value));
+    {
+        #ifdef CORRADE_GCC47_COMPATIBILITY
+        CORRADE_EXPECT_FAIL("Rvalue references for *this are not supported in GCC < 4.8.1.");
+        #endif
+        CORRADE_VERIFY(!(std::is_convertible<const Image2D, ImageReference2D>::value));
+        CORRADE_VERIFY(!(std::is_convertible<const Image2D&&, ImageReference2D>::value));
+    }
 }
 
 }}

src/Trade/ImageData.h

@@ -70,12 +70,18 @@ template<UnsignedInt dimensions> class ImageData: public AbstractImage {
         /** @brief Destructor */
         ~ImageData() { delete[] _data; }
 
-        /**
-         * @brief Conversion to reference
-         *
-         * @todo GCC 4.8: don't allow this on rvalue-ref
-         */
-        /*implicit*/ operator ImageReference<dimensions>() const;
+        /** @brief Conversion to reference */
+        /*implicit*/ operator ImageReference<dimensions>()
+        #ifndef CORRADE_GCC47_COMPATIBILITY
+        const &;
+        #else
+        const;
+        #endif
+
+        #ifndef CORRADE_GCC47_COMPATIBILITY
+        /** @overload */
+        /*implicit*/ operator ImageReference<dimensions>() const && = delete;
+        #endif
 
         /** @brief %Image size */
         typename DimensionTraits<Dimensions, Int>::VectorType size() const { return _size; }
@@ -110,7 +116,13 @@ template<UnsignedInt dimensions> inline ImageData<dimensions>& ImageData<dimensi
     return *this;
 }
 
-template<UnsignedInt dimensions> inline ImageData<dimensions>::operator ImageReference<dimensions>() const {
+template<UnsignedInt dimensions> inline ImageData<dimensions>::operator ImageReference<dimensions>()
+#ifndef CORRADE_GCC47_COMPATIBILITY
+const &
+#else
+const
+#endif
+{
     return ImageReference<dimensions>(AbstractImage::format(), AbstractImage::type(), _size, _data);
 }
 

src/Trade/Test/ImageDataTest.cpp

@@ -71,13 +71,22 @@ void ImageDataTest::moveAssignment() {
 
 void ImageDataTest::toReference() {
     unsigned char* data = new unsigned char[3];
-    Trade::ImageData2D a(ColorFormat::Red, ColorType::UnsignedByte, {1, 3}, data);
+    const Trade::ImageData2D a(ColorFormat::Red, ColorType::UnsignedByte, {1, 3}, data);
 
     ImageReference2D b = a;
     CORRADE_COMPARE(b.format(), ColorFormat::Red);
     CORRADE_COMPARE(b.type(), ColorType::UnsignedByte);
     CORRADE_COMPARE(b.size(), Vector2i(1, 3));
     CORRADE_COMPARE(b.data(), data);
+
+    CORRADE_VERIFY((std::is_convertible<const Trade::ImageData2D&, ImageReference2D>::value));
+    {
+        #ifdef CORRADE_GCC47_COMPATIBILITY
+        CORRADE_EXPECT_FAIL("Rvalue references for *this are not supported in GCC < 4.8.1.");
+        #endif
+        CORRADE_VERIFY(!(std::is_convertible<const Trade::ImageData2D, ImageReference2D>::value));
+        CORRADE_VERIFY(!(std::is_convertible<const Trade::ImageData2D&&, ImageReference2D>::value));
+    }
 }
 
 }}}