LibCore: Use ErrorOr<T> for Core::File::open()

Userland/Applications/FontEditor/GlyphEditorWidget.cpp

@@ -11,6 +11,7 @@
 #include <LibGUI/Painter.h>
 #include <LibGfx/BitmapFont.h>
 #include <LibGfx/Palette.h>
+#include <string.h>
 
 static int x_offset;
 static int y_offset;

Userland/Applications/HexEditor/HexEditor.cpp

@@ -23,6 +23,7 @@
 #include <ctype.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <string.h>
 #include <unistd.h>
 
 HexEditor::HexEditor()

Userland/Applications/PixelPaint/Image.cpp

@@ -159,7 +159,7 @@ Result<void, String> Image::write_to_file(const String& file_path) const
 
     auto file_or_error = Core::File::open(file_path, (Core::OpenMode)(Core::OpenMode::WriteOnly | Core::OpenMode::Truncate));
     if (file_or_error.is_error())
-        return String { file_or_error.error().string() };
+        return String { strerror(file_or_error.error().code()) };
 
     if (!file_or_error.value()->write(builder.string_view()))
         return String { file_or_error.value()->error_string() };

Userland/Applications/PixelPaint/PaletteWidget.cpp

@@ -15,6 +15,7 @@
 #include <LibGUI/ColorPicker.h>
 #include <LibGUI/MessageBox.h>
 #include <LibGfx/Palette.h>
+#include <string.h>
 
 REGISTER_WIDGET(PixelPaint, PaletteWidget);
 
@@ -263,7 +264,7 @@ Result<Vector<Color>, String> PaletteWidget::load_palette_path(String const& fil
 {
     auto file_or_error = Core::File::open(file_path, Core::OpenMode::ReadOnly);
     if (file_or_error.is_error())
-        return String { file_or_error.error().string() };
+        return String { strerror(file_or_error.error().code()) };
 
     auto& file = *file_or_error.value();
     return load_palette_file(file);

Userland/Applications/Run/RunWindow.cpp

@@ -20,6 +20,7 @@
 #include <LibGUI/Widget.h>
 #include <spawn.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/wait.h>
 #include <unistd.h>
 

Userland/Applications/Spreadsheet/ExportDialog.cpp

@@ -22,6 +22,7 @@
 #include <LibGUI/TextBox.h>
 #include <LibGUI/Wizards/WizardDialog.h>
 #include <LibGUI/Wizards/WizardPage.h>
+#include <string.h>
 #include <unistd.h>
 
 // This is defined in ImportDialog.cpp, we can't include it twice, since the generated symbol is exported.

Userland/Applications/Spreadsheet/Readers/Test/TestXSV.cpp

@@ -10,6 +10,7 @@
 #include "../XSV.h"
 #include <AK/ByteBuffer.h>
 #include <LibCore/File.h>
+#include <string.h>
 
 TEST_CASE(should_parse_valid_data)
 {

Userland/Applications/Spreadsheet/Workbook.cpp

@@ -51,7 +51,7 @@ Result<bool, String> Workbook::load(const StringView& filename)
         sb.append("Failed to open ");
         sb.append(filename);
         sb.append(" for reading. Error: ");
-        sb.append(file_or_error.error().string());
+        sb.appendff("{}", file_or_error.error());
 
         return sb.to_string();
     }