LibCore: Create ConfigFiles with an already-open File

This moves the fallible action of opening the file, from the
constructor, into the factory methods which can propagate any errors.

The wrinkle here is that failure to open a ConfigFile in read-only mode
is allowed (and expected, since the file may not exist), and treated as
if an empty file was successfully opened.

Userland/Libraries/LibCore/ConfigFile.cpp

@@ -18,48 +18,44 @@ ErrorOr<NonnullRefPtr<ConfigFile>> ConfigFile::open_for_lib(String const& lib_na
 {
     String directory = StandardPaths::config_directory();
     auto path = String::formatted("{}/lib/{}.ini", directory, lib_name);
-
-    return adopt_nonnull_ref_or_enomem(new (nothrow) ConfigFile(path, allow_altering));
+    return ConfigFile::open(path, allow_altering);
 }
 
 ErrorOr<NonnullRefPtr<ConfigFile>> ConfigFile::open_for_app(String const& app_name, AllowWriting allow_altering)
 {
     String directory = StandardPaths::config_directory();
     auto path = String::formatted("{}/{}.ini", directory, app_name);
-    return adopt_nonnull_ref_or_enomem(new (nothrow) ConfigFile(path, allow_altering));
+    return ConfigFile::open(path, allow_altering);
 }
 
 ErrorOr<NonnullRefPtr<ConfigFile>> ConfigFile::open_for_system(String const& app_name, AllowWriting allow_altering)
 {
     auto path = String::formatted("/etc/{}.ini", app_name);
-    return adopt_nonnull_ref_or_enomem(new (nothrow) ConfigFile(path, allow_altering));
+    return ConfigFile::open(path, allow_altering);
 }
 
 ErrorOr<NonnullRefPtr<ConfigFile>> ConfigFile::open(String const& filename, AllowWriting allow_altering)
 {
-    return adopt_nonnull_ref_or_enomem(new (nothrow) ConfigFile(filename, allow_altering));
+    auto file = File::construct(filename);
+    if (!file->open(allow_altering == AllowWriting::Yes ? OpenMode::ReadWrite : OpenMode::ReadOnly)) {
+        // Failure to open a read-only file is OK, and behaves as if the file was empty.
+        if (allow_altering == AllowWriting::Yes)
+            return Error::from_string_literal("Unable to open config file");
+    }
+    return adopt_nonnull_ref_or_enomem(new (nothrow) ConfigFile(filename, move(file)));
 }
 
 ErrorOr<NonnullRefPtr<ConfigFile>> ConfigFile::open(String const& filename, int fd)
 {
-    return adopt_nonnull_ref_or_enomem(new (nothrow) ConfigFile(filename, fd));
-}
-
-ConfigFile::ConfigFile(String const& filename, AllowWriting allow_altering)
-    : m_file(File::construct(filename))
-{
-    if (!m_file->open(allow_altering == AllowWriting::Yes ? OpenMode::ReadWrite : OpenMode::ReadOnly))
-        return;
-
-    reparse();
+    auto file = File::construct(filename);
+    if (!file->open(fd, OpenMode::ReadWrite, File::ShouldCloseFileDescriptor::Yes))
+        return Error::from_string_literal("Unable to open config file");
+    return adopt_nonnull_ref_or_enomem(new (nothrow) ConfigFile(filename, move(file)));
 }
 
-ConfigFile::ConfigFile(String const& filename, int fd)
-    : m_file(File::construct(filename))
+ConfigFile::ConfigFile(String const&, NonnullRefPtr<File> open_file)
+    : m_file(move(open_file))
 {
-    if (!m_file->open(fd, OpenMode::ReadWrite, File::ShouldCloseFileDescriptor::Yes))
-        return;
-
     reparse();
 }
 

Userland/Libraries/LibCore/ConfigFile.h

@@ -60,8 +60,7 @@ public:
     String filename() const { return m_file->filename(); }
 
 private:
-    explicit ConfigFile(String const& filename, AllowWriting);
-    explicit ConfigFile(String const& filename, int fd);
+    ConfigFile(String const& filename, NonnullRefPtr<File> open_file);
 
     void reparse();