add err output when server failed to start

src/server.rs

@@ -16,6 +16,9 @@ pub enum Error {
     #[error("Server exit with `{status}`")]
     ServerExitWithStatus { status: ExitStatus },
 
+    #[error("Server exit with `{status}` :\n{msg}")]
+    ServerExitWithError { status: ExitStatus, msg: String },
+
     #[error("Error append during check grammalecte-server status")]
     ServerCheckStatus(#[source] io::Error),
 
@@ -91,7 +94,7 @@ impl EmbeddedServer {
             .arg("-p")
             .arg(port.to_string())
             .stdout(Stdio::null())
-            .stderr(Stdio::null())
+            .stderr(Stdio::piped())
             .spawn()
             .map_err(Error::StartServerProcess)?;
 
@@ -118,6 +121,8 @@ impl Drop for EmbeddedServer {
 
 mod utils {
     use super::Error;
+    use std::fmt::Write;
+    use std::io::{BufRead, BufReader};
     use std::process::Child;
     use std::time::Duration;
 
@@ -151,7 +156,24 @@ mod utils {
     fn check_server(child: &mut Child) -> Result<(), Error> {
         match child.try_wait().map_err(Error::ServerCheckStatus)? {
             None => Ok(()), // Continue
-            Some(status) => Err(Error::ServerExitWithStatus { status }),
+            Some(status) => {
+                if let Some(err) = child.stderr.take() {
+                    let mut msg = format!("grammalecte-server exit with `{status}`");
+                    writeln!(&mut msg, " :").unwrap();
+                    let err = BufReader::new(err);
+                    err.lines().for_each(|line| match line {
+                        Ok(line) => {
+                            writeln!(&mut msg, "\t{}", line).unwrap();
+                        }
+                        Err(err) => {
+                            writeln!(&mut msg, "__{err:?}").unwrap();
+                        }
+                    });
+                    Err(Error::ServerExitWithError { status, msg })
+                } else {
+                    Err(Error::ServerExitWithStatus { status })
+                }
+            }
         }
     }
 }