Add --user-data-dir CLI flag and propose renaming support_dir to data_dir (#26886)

This PR introduces support for a `--user-data-dir` CLI flag to override
Zed's data directory and proposes renaming `support_dir` to `data_dir`
for better cross-platform clarity. It builds on the discussion in #25349
about custom data directories, aiming to provide a flexible
cross-platform solution.

### Changes

The PR is split into two commits:
1. **[feat(cli): add --user-data-dir to override data
directory](https://github.com/zed-industries/zed/pull/26886/commits/28e8889105847401e783d1739722d0998459fe5a)**
2. **[refactor(paths): rename support_dir to data_dir for cross-platform
clarity](https://github.com/zed-industries/zed/pull/26886/commits/affd2fc606b39af1b25432a688a9006229a8fc3a)**


### Context
Inspired by the need for custom data directories discussed in #25349,
this PR provides an immediate implementation in the first commit, while
the second commit suggests a naming improvement for broader appeal.
@mikayla-maki, I’d appreciate your feedback, especially on the rename
proposal, given your involvement in the original discussion!

### Testing
- `cargo build `
- `./target/debug/zed --user-data-dir ~/custom-data-dir`

Release Notes:
- Added --user-data-dir CLI flag

---------

Signed-off-by: Marko Kungla <marko.kungla@gmail.com>

crates/cli/src/main.rs

@@ -26,7 +26,11 @@ struct Detect;
 trait InstalledApp {
     fn zed_version_string(&self) -> String;
     fn launch(&self, ipc_url: String) -> anyhow::Result<()>;
-    fn run_foreground(&self, ipc_url: String) -> io::Result<ExitStatus>;
+    fn run_foreground(
+        &self,
+        ipc_url: String,
+        user_data_dir: Option<&str>,
+    ) -> io::Result<ExitStatus>;
     fn path(&self) -> PathBuf;
 }
 
@@ -58,6 +62,13 @@ struct Args {
     /// Create a new workspace
     #[arg(short, long, overrides_with = "add")]
     new: bool,
+    /// Sets a custom directory for all user data (e.g., database, extensions, logs).
+    /// This overrides the default platform-specific data directory location.
+    /// On macOS, the default is `~/Library/Application Support/Zed`.
+    /// On Linux/FreeBSD, the default is `$XDG_DATA_HOME/zed`.
+    /// On Windows, the default is `%LOCALAPPDATA%\Zed`.
+    #[arg(long, value_name = "DIR")]
+    user_data_dir: Option<String>,
     /// The paths to open in Zed (space-separated).
     ///
     /// Use `path:line:column` syntax to open a file at the given line and column.
@@ -135,6 +146,12 @@ fn main() -> Result<()> {
     }
     let args = Args::parse();
 
+    // Set custom data directory before any path operations
+    let user_data_dir = args.user_data_dir.clone();
+    if let Some(dir) = &user_data_dir {
+        paths::set_custom_data_dir(dir);
+    }
+
     #[cfg(any(target_os = "linux", target_os = "freebsd"))]
     let args = flatpak::set_bin_if_no_escape(args);
 
@@ -246,6 +263,7 @@ fn main() -> Result<()> {
 
     let sender: JoinHandle<anyhow::Result<()>> = thread::spawn({
         let exit_status = exit_status.clone();
+        let user_data_dir_for_thread = user_data_dir.clone();
         move || {
             let (_, handshake) = server.accept().context("Handshake after Zed spawn")?;
             let (tx, rx) = (handshake.requests, handshake.responses);
@@ -256,6 +274,7 @@ fn main() -> Result<()> {
                 wait: args.wait,
                 open_new_workspace,
                 env,
+                user_data_dir: user_data_dir_for_thread,
             })?;
 
             while let Ok(response) = rx.recv() {
@@ -291,7 +310,7 @@ fn main() -> Result<()> {
         .collect();
 
     if args.foreground {
-        app.run_foreground(url)?;
+        app.run_foreground(url, user_data_dir.as_deref())?;
     } else {
         app.launch(url)?;
         sender.join().unwrap()?;
@@ -437,7 +456,7 @@ mod linux {
         }
 
         fn launch(&self, ipc_url: String) -> anyhow::Result<()> {
-            let sock_path = paths::support_dir().join(format!("zed-{}.sock", *RELEASE_CHANNEL));
+            let sock_path = paths::data_dir().join(format!("zed-{}.sock", *RELEASE_CHANNEL));
             let sock = UnixDatagram::unbound()?;
             if sock.connect(&sock_path).is_err() {
                 self.boot_background(ipc_url)?;
@@ -447,10 +466,17 @@ mod linux {
             Ok(())
         }
 
-        fn run_foreground(&self, ipc_url: String) -> io::Result<ExitStatus> {
-            std::process::Command::new(self.0.clone())
-                .arg(ipc_url)
-                .status()
+        fn run_foreground(
+            &self,
+            ipc_url: String,
+            user_data_dir: Option<&str>,
+        ) -> io::Result<ExitStatus> {
+            let mut cmd = std::process::Command::new(self.0.clone());
+            cmd.arg(ipc_url);
+            if let Some(dir) = user_data_dir {
+                cmd.arg("--user-data-dir").arg(dir);
+            }
+            cmd.status()
         }
 
         fn path(&self) -> PathBuf {
@@ -688,12 +714,17 @@ mod windows {
             Ok(())
         }
 
-        fn run_foreground(&self, ipc_url: String) -> io::Result<ExitStatus> {
-            std::process::Command::new(self.0.clone())
-                .arg(ipc_url)
-                .arg("--foreground")
-                .spawn()?
-                .wait()
+        fn run_foreground(
+            &self,
+            ipc_url: String,
+            user_data_dir: Option<&str>,
+        ) -> io::Result<ExitStatus> {
+            let mut cmd = std::process::Command::new(self.0.clone());
+            cmd.arg(ipc_url).arg("--foreground");
+            if let Some(dir) = user_data_dir {
+                cmd.arg("--user-data-dir").arg(dir);
+            }
+            cmd.spawn()?.wait()
         }
 
         fn path(&self) -> PathBuf {
@@ -875,13 +906,22 @@ mod mac_os {
             Ok(())
         }
 
-        fn run_foreground(&self, ipc_url: String) -> io::Result<ExitStatus> {
+        fn run_foreground(
+            &self,
+            ipc_url: String,
+            user_data_dir: Option<&str>,
+        ) -> io::Result<ExitStatus> {
             let path = match self {
                 Bundle::App { app_bundle, .. } => app_bundle.join("Contents/MacOS/zed"),
                 Bundle::LocalPath { executable, .. } => executable.clone(),
             };
 
-            std::process::Command::new(path).arg(ipc_url).status()
+            let mut cmd = std::process::Command::new(path);
+            cmd.arg(ipc_url);
+            if let Some(dir) = user_data_dir {
+                cmd.arg("--user-data-dir").arg(dir);
+            }
+            cmd.status()
         }
 
         fn path(&self) -> PathBuf {