GL: port to Utility::Path.

Shader::addSource() won't silently ignore file read errors anymore, like
in the other cases mentioned with plugins etc. before.

src/Magnum/GL/Shader.cpp

@@ -30,10 +30,11 @@
 #ifndef MAGNUM_TARGET_WEBGL
 #include <Corrade/Containers/String.h>
 #endif
+#include <Corrade/Containers/StringStl.h> /** @todo remove once Shader is <string>-free */
 #include <Corrade/Utility/Assert.h>
 #include <Corrade/Utility/Debug.h>
 #include <Corrade/Utility/DebugStl.h>
-#include <Corrade/Utility/Directory.h>
+#include <Corrade/Utility/Path.h>
 
 #include "Magnum/GL/Context.h"
 #include "Magnum/GL/Extensions.h"
@@ -740,10 +741,9 @@ void Shader::addSourceImplementationEmscriptenPthread(std::string source) {
 #endif
 
 Shader& Shader::addFile(const std::string& filename) {
-    CORRADE_ASSERT(Utility::Directory::exists(filename),
-        "GL::Shader file " << '\'' + filename + '\'' << " cannot be read.", *this);
-
-    addSource(Utility::Directory::readString(filename));
+    const Containers::Optional<Containers::String> string = Utility::Path::readString(filename);
+    CORRADE_ASSERT(string, "GL::Shader::addFile(): can't read" << filename, *this);
+    addSource(*string);
     return *this;
 }
 

src/Magnum/GL/Test/RendererGLTest.cpp

@@ -24,9 +24,14 @@
 */
 
 #include <Corrade/Containers/StridedArrayView.h>
+#include <Corrade/Containers/String.h>
 #include <Corrade/Containers/Reference.h>
 #include <Corrade/PluginManager/Manager.h>
-#include <Corrade/Utility/Directory.h>
+#include <Corrade/Utility/Path.h>
+
+#ifdef CORRADE_TARGET_APPLE
+#include <Corrade/Utility/System.h> /* isSandboxed() */
+#endif
 
 #include "Magnum/Image.h"
 #include "Magnum/DebugTools/CompareImage.h"
@@ -65,7 +70,7 @@ struct RendererGLTest: OpenGLTester {
 
     private:
         PluginManager::Manager<Trade::AbstractImporter> _manager{"nonexistent"};
-        std::string _testDir;
+        Containers::String _testDir;
 
         GL::Renderbuffer _color{NoCreate};
         GL::Framebuffer _framebuffer{NoCreate};
@@ -95,13 +100,13 @@ RendererGLTest::RendererGLTest() {
     #endif
 
     #ifdef CORRADE_TARGET_APPLE
-    if(Utility::Directory::isSandboxed()
+    if(Utility::System::isSandboxed()
         #if defined(CORRADE_TARGET_IOS) && defined(CORRADE_TESTSUITE_TARGET_XCTEST)
         /** @todo Fix this once I persuade CMake to run XCTest tests properly */
         && std::getenv("SIMULATOR_UDID")
         #endif
     ) {
-        _testDir = Utility::Directory::join(Utility::Directory::path(Utility::Directory::executableLocation()), "RendererGLTestFiles");
+        _testDir = Utility::Path::join(Utility::Path::split(*Utility::Path::executableLocation()).first(), "RendererGLTestFiles");
     } else
     #endif
     {
@@ -232,7 +237,7 @@ void RendererGLTest::pointCoord() {
     CORRADE_COMPARE_WITH(
         /* Dropping the alpha channel, as it's always 1.0 */
         Containers::arrayCast<Color3ub>(_framebuffer.read(_framebuffer.viewport(), {Magnum::PixelFormat::RGBA8Unorm}).pixels<Color4ub>()),
-        Utility::Directory::join(_testDir, "pointcoord.tga"),
+        Utility::Path::join(_testDir, "pointcoord.tga"),
         (DebugTools::CompareImageToFile{_manager, maxThreshold, meanThreshold}));
 }
 

src/Magnum/GL/Test/ShaderGLTest.cpp

@@ -23,8 +23,9 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <Corrade/Containers/StringStl.h> /** @todo remove once Shader is <string>-free */
 #include <Corrade/Utility/DebugStl.h>
-#include <Corrade/Utility/Directory.h>
+#include <Corrade/Utility/Path.h>
 
 #include "Magnum/GL/Context.h"
 #include "Magnum/GL/Extensions.h"
@@ -243,7 +244,7 @@ void ShaderGLTest::addFile() {
     Shader shader(Version::GLES200, Shader::Type::Fragment);
     #endif
 
-    shader.addFile(Utility::Directory::join(SHADERGLTEST_FILES_DIR, "shader.glsl"));
+    shader.addFile(Utility::Path::join(SHADERGLTEST_FILES_DIR, "shader.glsl"));
 
     #ifndef MAGNUM_TARGET_GLES
     CORRADE_COMPARE(shader.sources(), (std::vector<std::string>{