Autostart doesn't work on NixOS

[YizhePKU]

Flameshot version
Tested on both master and v0.11.1

Describe the bug

Autostart doesn't work.

On NixOS, if the directory ~/.config/autostart doesn't exist, Flameshot will try to write the desktop file to somewhere in /nix/store. However, /nix/store is read-only, so that fails.

To Reproduce

Install Flameshot on NixOS. Launch it with strace flameshot 2>&1 | grep open so that we can observe where it tries to write files. When flipping Launch at startup in configuations, strace will print some like this:

openat(AT_FDCWD, "/nix/store/nkgiwqxc5i6fhkzm4lj8p11gjpclm5cj-plasma-workspace-5.21.5/etc/xdg/autostart/Flameshot.desktop", O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, 0666) = -1 EROFS (Read-only file system)

Expected behavior

The desktop file should be written to ~/.config/autostart, creating the directory if necessary.

System Information

NixOS 21.05

[YizhePKU]

The buggy code is in src/utils/confighandler.cpp, function ConfigHandler::setStartupLaunch.

    QString path = QStandardPaths::locate(QStandardPaths::GenericConfigLocation,
                                          "autostart/",
                                          QStandardPaths::LocateDirectory);
    QDir autostartDir(path);
    if (!autostartDir.exists()) {
        autostartDir.mkpath(".");
    }

    QFile file(path + "Flameshot.desktop");

I think QStandardPaths::locate prefers existent path to writable path. My suggested fix is:

    QString path = QStandardPaths::writableLocation(QStandardPaths::GenericConfigLocation) + "/autostart/";
    QDir autostartDir(path);
    if (!autostartDir.exists()) {
        autostartDir.mkpath(".");
    }

    QFile file(path + "Flameshot.desktop");

[veracioux]

@YizhePKU I suspect your solution is correct. If you have a development environment set up and you are up for it, feel free to submit a pull request. If not, I can do that.

[YizhePKU]

I tested my solution locally and it works nicely. Didn't run the test suite though, this should be fine?