sccache: error: path must be shorter than SUN_LEN

[nagisa]

This morning I encountered a relatively baffling error message:

# sccache $HOME/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustc -vV
sccache: error: path must be shorter than SUN_LEN

From the looks of it, what's happening is that I was 5 nix-shells deep and my $TMPDIR got quite long:

/tmp/nix-shell-1869814-3862691756/nix-shell-1870212-64442319/nix-shell-1870771-4262528264/nix-shell-1879125-3109976699/nix-shell.xlRp88

Initially I thought this was affecting specifically the client-server socket, overriding that path would fail the same way:

# env SCCACHE_SERVER_UDS=$HOME/.cache/sccache/sock sccache $HOME/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustc -vV
sccache: error: path must be shorter than SUN_LEN

My current theory is that its the following part:

sccache/src/commands.rs

Lines 94 to 110 in de9895c

	let socket_path = tempdir.path().join("sock");
	let runtime = Runtime::new()?;
	let exe_path = env::current_exe()?;
	let workdir = exe_path.parent().expect("executable path has no parent?!");
	// Spawn a blocking task to bind the Unix socket. Note that the socket
	// must be bound before spawning `_child` below to avoid a race between
	// the parent binding the socket and the child connecting to it.
	let listener = {
	let _guard = runtime.enter();
	tokio::net::UnixListener::bind(&socket_path)?
	};
	let _child = process::Command::new(&exe_path)
	.current_dir(workdir)
	.env("SCCACHE_START_SERVER", "1")
	.env("SCCACHE_STARTUP_NOTIFY", &socket_path)

which probably could be made more resilient by inheriting a pipe file descriptor.

---

Recovering from this was not as straightforward as exiting the nix shells and fixing up TMPDIR – there seems to have been some sort of a leftover in target/ that kept sccache try the long path until I deleted target/. Only then I was able to successfully invoke cargo/rustc with the RUSTC_WRAPPER=sccache set.