Disallow running Zed with root privileges (#31331)

This will fix a lot of weird problems that are based on file access
issues.

As discussed in
https://github.com/zed-industries/zed/pull/31219#issuecomment-2905371710,
for now it's better to just prevent running Zed with root privileges.

Release Notes:

- Explicitly disallow running Zed with root privileges

---------

Co-authored-by: Peter Tripp <peter@zed.dev>

crates/zed/Cargo.toml

@@ -85,7 +85,7 @@ markdown_preview.workspace = true
 menu.workspace = true
 migrator.workspace = true
 mimalloc = { version = "0.1", optional = true }
-nix = { workspace = true, features = ["pthread", "signal"] }
+nix = { workspace = true, features = ["pthread", "signal", "user"] }
 node_runtime.workspace = true
 notifications.workspace = true
 outline.workspace = true

crates/zed/src/main.rs

@@ -164,6 +164,24 @@ fn fail_to_open_window(e: anyhow::Error, _cx: &mut App) {
 }
 
 fn main() {
+    #[cfg(unix)]
+    {
+        let is_root = nix::unistd::geteuid().is_root();
+        let allow_root = env::var("ZED_ALLOW_ROOT").is_ok_and(|val| val == "true");
+
+        // Prevent running Zed with root privileges on Unix systems unless explicitly allowed
+        if is_root && !allow_root {
+            eprintln!(
+                "\
+Error: Running Zed as root or via sudo is unsupported.
+       Doing so (even once) may subtly break things for all subsequent non-root usage of Zed.
+       It is untested and not recommended, don't complain when things break.
+       If you wish to proceed anyways, set `ZED_ALLOW_ROOT=true` in your environment."
+            );
+            process::exit(1);
+        }
+    }
+
     // Check if there is a pending installer
     // If there is, run the installer and exit
     // And we don't want to run the installer if we are not the first instance