ruff server: Support the usage of tildes and environment variables in logFile (#11945)

## Summary

Fixes #11911.

`shellexpand` is now used on `logFile` to expand the file path, allowing
the usage of `~` and environment variables.

## Test Plan

1. Set `logFile` in either Neovim or Helix to a file path that needs
expansion, like `~/.config/helix/ruff_logs.txt`.
2. Ensure that `RUFF_TRACE` is set to `messages` or `verbose`
3. Open a Python file in Neovim/Helix
4. Confirm that a file at the path specified was created, with the
expected logs.

crates/ruff_server/src/session/settings.rs

@@ -83,6 +83,7 @@ pub(crate) struct ClientSettings {
 #[serde(rename_all = "camelCase")]
 pub(crate) struct TracingSettings {
     pub(crate) log_level: Option<crate::trace::LogLevel>,
+    /// Path to the log file - tildes and environment variables are supported.
     pub(crate) log_file: Option<PathBuf>,
 }
 

crates/ruff_server/src/trace.rs

@@ -16,7 +16,11 @@
 //! A `logFile` path can also be specified in the settings, and output will be directed there instead.
 use lsp_types::TraceValue;
 use serde::Deserialize;
-use std::sync::{Arc, Mutex, OnceLock};
+use std::{
+    path::PathBuf,
+    str::FromStr,
+    sync::{Arc, Mutex, OnceLock},
+};
 use tracing::level_filters::LevelFilter;
 use tracing_subscriber::{
     fmt::{time::Uptime, writer::BoxMakeWriter},
@@ -48,13 +52,35 @@ pub(crate) fn init_tracing(
         .set(sender)
         .expect("logging sender should only be initialized once");
 
-    let log_file = log_file.and_then(|path| {
-        std::fs::OpenOptions::new()
-            .create(true)
-            .append(true)
-            .open(path)
-            .ok()
-    });
+    let log_file = log_file
+        .map(|path| {
+            // this expands `logFile` so that tildes and environment variables
+            // are replaced with their values, if possible.
+            if let Some(expanded) = shellexpand::full(&path.to_string_lossy())
+                .ok()
+                .and_then(|path| PathBuf::from_str(&path).ok())
+            {
+                expanded
+            } else {
+                path.to_path_buf()
+            }
+        })
+        .and_then(|path| {
+            std::fs::OpenOptions::new()
+                .create(true)
+                .append(true)
+                .open(&path)
+                .map_err(|err| {
+                    #[allow(clippy::print_stderr)]
+                    {
+                        eprintln!(
+                            "Failed to open file at {} for logging: {err}",
+                            path.display()
+                        );
+                    }
+                })
+                .ok()
+        });
 
     let subscriber = tracing_subscriber::Registry::default().with(
         tracing_subscriber::fmt::layer()