Bug 250985 – [GTK] mesa fails to create shader cache, xdg cache dir not mounted in flatpak-spawn subsandbox

• Component: WebKitGTK
• Status: RESOLVED MOVED

[Jeff Fortin]

Originally reported at https://gitlab.gnome.org/GNOME/epiphany/-/issues/1957 :

With the EpiphanyDevel flatpak from gnome nightly, this gets printed multiple times in the terminal on startup:

`Failed to create /home/user/.var/app/org.gnome.Epiphany.Devel/cache for shader cache (No such file or directory)---disabling.`

...even with the local storage/caching setting turned on in the Privacy tab in the Preferences dialog. And yet, the folder exists, and has subfolders:

```
$ ls ~/.var/app/org.gnome.Epiphany.Devel/cache
epiphany
fontconfig
mesa_shader_cache
tmp
webkitgtk-6.0
```

[Michael Catanzaro]

Looks like the shader cache is an ANGLE thing, so *probably* an ANGLE bug, although I'm failing to immediately find the code.

But wait, is your username literally "user"? Because the error message says "/home/user".

[Michael Catanzaro]

OK surprise, this is actually coming from mesa, not from ANGLE. It's in src/util/disk_cache_os.c.

[Michael Catanzaro]

Oh and I can reproduce:

Failed to create /home/mcatanzaro/.var/app/org.gnome.Epiphany.Devel/cache for shader cache (No such file or directory)---disabling.
Failed to create /home/mcatanzaro/.var/app/org.gnome.Epiphany.Devel/cache for shader cache (No such file or directory)---disabling.

I think it doesn't exist in the flatpak-spawn subsandbox. We don't want to provide access to the real host dirs because that defeats the point of subsandboxing, but I guess we could create empty ones.

[Michael Catanzaro]

This is https://gitlab.freedesktop.org/mesa/mesa/-/issues/8294