avoid overlapping stderr

src/bootstrap/render_tests.rs

@@ -7,7 +7,7 @@
 //! to reimplement all the rendering logic in this module because of that.
 
 use crate::builder::Builder;
-use std::io::{BufRead, BufReader, Write};
+use std::io::{BufRead, BufReader, Cursor, Write};
 use std::process::{ChildStdout, Command, Stdio};
 use std::time::Duration;
 use yansi_term::Color;
@@ -43,6 +43,7 @@ pub(crate) fn try_run_tests(builder: &Builder<'_>, cmd: &mut Command) -> bool {
 
 fn run_tests(builder: &Builder<'_>, cmd: &mut Command) -> bool {
     cmd.stdout(Stdio::piped());
+    cmd.stderr(Stdio::piped());
 
     builder.verbose(&format!("running: {cmd:?}"));
 
@@ -52,15 +53,20 @@ fn run_tests(builder: &Builder<'_>, cmd: &mut Command) -> bool {
     // run this on another thread since the builder is not Sync.
     Renderer::new(process.stdout.take().unwrap(), builder).render_all();
 
-    let result = process.wait().unwrap();
-    if !result.success() && builder.is_verbose() {
+    let result = process.wait_with_output().unwrap();
+    if !result.status.success() && builder.is_verbose() {
         println!(
             "\n\ncommand did not execute successfully: {cmd:?}\n\
-             expected success, got: {result}"
+             expected success, got: {}",
+            result.status
         );
     }
 
-    result.success()
+    // Show the stderr emitted by the test runner at the end. As of 2023-03-02 this is only the
+    // message at the end of a failed compiletest run.
+    std::io::copy(&mut Cursor::new(&result.stderr), &mut std::io::stderr().lock()).unwrap();
+
+    result.status.success()
 }
 
 struct Renderer<'a> {