fix: use drawn cursor by default in wsl

refs #930

6 files changed, 51 insertions, 4 deletions

diff --git a/src/client/mod.rs b/src/client/mod.rs
index bdc67880..90a73ec8 100644
--- a/src/client/mod.rs
+++ b/src/client/mod.rs
@@ -453,7 +453,9 @@ fn write_terminal_restore_postlude(
 
 fn should_draw_host_cursor(mode: crate::config::HostCursorModeConfig) -> bool {
     match mode {
-        crate::config::HostCursorModeConfig::Auto => cfg!(windows),
+        crate::config::HostCursorModeConfig::Auto => {
+            crate::platform::should_draw_host_cursor_by_default()
+        }
         crate::config::HostCursorModeConfig::Native => false,
         crate::config::HostCursorModeConfig::Drawn => true,
     }
@@ -2198,10 +2200,10 @@ mod tests {
     }
 
     #[test]
-    fn host_cursor_policy_auto_uses_drawn_cursor_on_windows() {
+    fn host_cursor_policy_auto_uses_platform_default() {
         assert_eq!(
             should_draw_host_cursor(crate::config::HostCursorModeConfig::Auto),
-            cfg!(windows)
+            crate::platform::should_draw_host_cursor_by_default()
         );
     }
 
diff --git a/src/main.rs b/src/main.rs
index deb332b9..575e23f8 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -259,7 +259,7 @@ const DEFAULT_CONFIG: &str = r##"# herdr configuration
 # mouse_capture = true
 
 # Host cursor policy: "auto", "native", or "drawn".
-# "auto" draws Herdr's own cursor on Windows to avoid ConPTY cursor flicker, and uses the native terminal cursor elsewhere.
+# "auto" draws Herdr's own cursor on native Windows builds and WSL to avoid ConPTY cursor flicker, and uses the native terminal cursor elsewhere.
 # "native" always uses the outer terminal cursor. "drawn" always draws Herdr's cursor as terminal cell content.
 # host_cursor = "auto"
 
diff --git a/src/platform/fallback.rs b/src/platform/fallback.rs
index 382ccf5e..6b5700cc 100644
--- a/src/platform/fallback.rs
+++ b/src/platform/fallback.rs
@@ -6,6 +6,10 @@ use super::{ClipboardImage, ForegroundJob, Signal};
 /// Unsupported platform stub.
 pub fn raise_server_nofile_limit() {}
 
+pub(crate) fn should_draw_host_cursor_by_default() -> bool {
+    false
+}
+
 fn raw_command_argv(command: &str, flag: &str) -> Vec<std::ffi::OsString> {
     vec!["/bin/sh".into(), flag.into(), command.into()]
 }
diff --git a/src/platform/linux.rs b/src/platform/linux.rs
index be0c97b9..2013873f 100644
--- a/src/platform/linux.rs
+++ b/src/platform/linux.rs
@@ -14,6 +14,7 @@ use super::{
 };
 
 const FOREGROUND_MEMBERS_CACHE_TTL: Duration = Duration::from_millis(250);
+const WSL_MARKER_ENV_VARS: &[&str] = &["WSL_DISTRO_NAME", "WSL_INTEROP"];
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct ProcGroupMember {
@@ -39,6 +40,30 @@ static FOREGROUND_MEMBERS_CACHE: Mutex<ForegroundMembersCache> =
 
 pub fn raise_server_nofile_limit() {}
 
+pub(crate) fn should_draw_host_cursor_by_default() -> bool {
+    running_inside_wsl()
+}
+
+fn running_inside_wsl() -> bool {
+    proc_file_indicates_wsl("/proc/sys/kernel/osrelease")
+        || proc_file_indicates_wsl("/proc/version")
+        || WSL_MARKER_ENV_VARS
+            .iter()
+            .any(|key| std::env::var_os(key).is_some())
+        || std::path::Path::new("/run/WSL").exists()
+}
+
+fn proc_file_indicates_wsl(path: &str) -> bool {
+    std::fs::read_to_string(path)
+        .map(|text| text_indicates_wsl(&text))
+        .unwrap_or(false)
+}
+
+fn text_indicates_wsl(text: &str) -> bool {
+    let text = text.to_ascii_lowercase();
+    text.contains("microsoft") || text.contains("wsl")
+}
+
 fn raw_command_argv(command: &str, flag: &str) -> Vec<std::ffi::OsString> {
     vec!["/bin/sh".into(), flag.into(), command.into()]
 }
@@ -713,6 +738,14 @@ mod tests {
     }
 
     #[test]
+    fn wsl_marker_detection_matches_kernel_release_text() {
+        assert!(text_indicates_wsl("5.15.167.4-microsoft-standard-WSL2"));
+        assert!(text_indicates_wsl("4.4.0-19041-Microsoft"));
+        assert!(!text_indicates_wsl("6.8.0-64-generic"));
+        assert!(!text_indicates_wsl(""));
+    }
+
+    #[test]
     fn foreground_members_indexes_by_process_group() {
         let by_group = foreground_members(&[
             (10, "shell", 10),
diff --git a/src/platform/macos.rs b/src/platform/macos.rs
index f2441f06..70eea7ec 100644
--- a/src/platform/macos.rs
+++ b/src/platform/macos.rs
@@ -16,6 +16,10 @@ const PROC_PGRP_ONLY: u32 = 2;
 const SERVER_NOFILE_LIMIT_TARGET: libc::rlim_t = 8192;
 const CF_STRING_ENCODING_UTF8: u32 = 0x0800_0100;
 
+pub(crate) fn should_draw_host_cursor_by_default() -> bool {
+    false
+}
+
 fn raw_command_argv(command: &str, flag: &str) -> Vec<std::ffi::OsString> {
     vec!["/bin/sh".into(), flag.into(), command.into()]
 }
diff --git a/src/platform/windows.rs b/src/platform/windows.rs
index 49a68111..a44ebafd 100644
--- a/src/platform/windows.rs
+++ b/src/platform/windows.rs
@@ -38,6 +38,10 @@ use super::{ClipboardImage, ForegroundJob, Signal};
 
 const STILL_ACTIVE: u32 = 259;
 
+pub(crate) fn should_draw_host_cursor_by_default() -> bool {
+    true
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct WindowsProcessEntry {
     pid: u32,