ssh: Treat "connection refused" on Windows

Slightly relax the conditions under which an error is considered to
indicate that the SSH agent is not running, to accommodate differences
in the API of named pipes on Windows vs. Unix domain sockets.

crates/radicle-ssh/src/agent/client.rs

@@ -52,7 +52,20 @@ pub enum Error {
 
 impl Error {
     pub fn is_not_running(&self) -> bool {
-        matches!(self, Self::EnvVar { .. } | Self::BadAuthSock { .. })
+        match self {
+            Self::EnvVar { .. } | Self::BadAuthSock { .. } => true,
+            #[cfg(windows)]
+            Self::Connect { source, .. }
+                if source.kind() == std::io::ErrorKind::ConnectionRefused =>
+            {
+                // On Windows, a named pipe might be used, and if no
+                // agent is running, we might get a "connection refused"
+                // error, even though the `SSH_AUTH_SOCK` environment
+                // variable is set and the named pipe exists.
+                true
+            }
+            _ => false,
+        }
     }
 }
 
@@ -104,24 +117,20 @@ impl AgentClient<Stream> {
     pub fn connect_env() -> Result<Self, Error> {
         const SSH_AUTH_SOCK: &str = "SSH_AUTH_SOCK";
 
-        let path = match std::env::var(SSH_AUTH_SOCK) {
-            Ok(var) => var,
-            Err(err) => {
-                if cfg!(windows) {
-                    // Windows uses a named pipe for the SSH agent, which
-                    // we fall back to in case reading the environment
-                    // variable fails.
-                    "\\\\.\\pipe\\openssh-ssh-agent".to_string()
-                } else {
-                    return Err(Error::EnvVar {
-                        var: SSH_AUTH_SOCK.to_string(),
-                        source: err,
-                    });
-                }
-            }
-        };
+        let var = std::env::var(SSH_AUTH_SOCK);
 
-        Self::connect(path)
+        #[cfg(windows)]
+        let var = var.or({
+            // Windows uses a named pipe for the SSH agent, which
+            // we fall back to in case reading the environment
+            // variable fails.
+            Ok(r"\\.\pipe\openssh-ssh-agent".to_string())
+        });
+
+        Self::connect(var.map_err(|err| Error::EnvVar {
+            var: SSH_AUTH_SOCK.to_string(),
+            source: err,
+        })?)
     }
 }