Fix 2024 edition doctest panic output

src/librustdoc/doctest/runner.rs

@@ -113,6 +113,7 @@ impl DocTestRunner {
 mod __doctest_mod {{
     use std::sync::OnceLock;
     use std::path::PathBuf;
+    use std::process::ExitCode;
 
     pub static BINARY_PATH: OnceLock<PathBuf> = OnceLock::new();
     pub const RUN_OPTION: &str = \"RUSTDOC_DOCTEST_RUN_NB_TEST\";
@@ -123,16 +124,17 @@ mod __doctest_mod {{
     }}
 
     #[allow(unused)]
-    pub fn doctest_runner(bin: &std::path::Path, test_nb: usize) -> Result<(), String> {{
+    pub fn doctest_runner(bin: &std::path::Path, test_nb: usize) -> ExitCode {{
         let out = std::process::Command::new(bin)
             .env(self::RUN_OPTION, test_nb.to_string())
             .args(std::env::args().skip(1).collect::<Vec<_>>())
             .output()
             .expect(\"failed to run command\");
         if !out.status.success() {{
-            Err(String::from_utf8_lossy(&out.stderr).to_string())
+            eprintln!(\"{{}}\", String::from_utf8_lossy(&out.stderr));
+            ExitCode::FAILURE
         }} else {{
-            Ok(())
+            ExitCode::SUCCESS
         }}
     }}
 }}

tests/rustdoc-ui/edition-2024-doctest-error-output.rs

@@ -0,0 +1,12 @@
+// This is a regression test for <https://github.com/rust-lang/rust/issues/137970>.
+// The output must look nice and not like a `Debug` display of a `String`.
+
+//@ edition: 2024
+//@ compile-flags: --test
+//@ normalize-stdout: "tests/rustdoc-ui/doctest" -> "$$DIR"
+//@ normalize-stdout: "finished in \d+\.\d+s" -> "finished in $$TIME"
+//@ failure-status: 101
+
+//! ```rust
+//! assert_eq!(2 + 2, 5);
+//! ```

tests/rustdoc-ui/edition-2024-doctest-error-output.stdout

@@ -0,0 +1,32 @@
+
+running 1 test
+test tests/rustdoc-ui/edition-2024-doctest-error-output.rs - (line 10) ... FAILED
+
+failures:
+
+---- tests/rustdoc-ui/edition-2024-doctest-error-output.rs - (line 10) stdout ----
+
+thread 'main' panicked at /tmp/rustdoctestSZq9aS/doctest_bundle_2024.rs:6:1:
+assertion `left == right` failed
+  left: 4
+ right: 5
+stack backtrace:
+   0: __rustc::rust_begin_unwind
+   1: core::panicking::panic_fmt
+   2: core::panicking::assert_failed_inner
+   3: core::panicking::assert_failed
+   4: doctest_bundle_2024::__doctest_0::main
+   5: doctest_bundle_2024::__doctest_0::__main_fn
+   6: doctest_runner_2024::__doctest_0::TEST::{{closure}}
+   7: core::ops::function::FnOnce::call_once
+   8: doctest_runner_2024::main
+   9: core::ops::function::FnOnce::call_once
+note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
+
+
+
+failures:
+    tests/rustdoc-ui/edition-2024-doctest-error-output.rs - (line 10)
+
+test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+