Auto merge of #81367 - andersk:join-test-threads, r=dtolnay

libtest: Wait for test threads to exit after they report completion

Otherwise we can miss bugs where a test reports that it succeeded but then panics within a TLS destructor.

Example:

```rust
use std::thread::sleep;
use std::time::Duration;

struct Foo;

impl Drop for Foo {
    fn drop(&mut self) {
        sleep(Duration::from_secs(1));
        panic!()
    }
}

thread_local!(static FOO: Foo = Foo);

#[test]
pub fn test() {
    FOO.with(|_| {});
}
```

Before this fix, `cargo test` incorrectly reports success.

```console
$ cargo test
    Finished test [unoptimized + debuginfo] target(s) in 0.01s
     Running target/debug/deps/panicking_test-85130fa46b54f758

running 1 test
test test ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

$ echo $?
0
```

After this fix, the failure is visible. (The entire process is aborted due to #24479.)

```console
$ cargo test
    Finished test [unoptimized + debuginfo] target(s) in 0.01s
     Running target/debug/deps/panicking_test-76180625bc2ee3c9

running 1 test
thread 'test' panicked at 'explicit panic', src/main.rs:9:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5
error: test failed, to rerun pass '--bin panicking-test'

Caused by:
  process didn't exit successfully: `/tmp/panicking-test/target/debug/deps/panicking_test-76180625bc2ee3c9 --nocapture` (signal: 6, SIGABRT: process abort signal)

$ echo $?
101
```

library/test/src/lib.rs

@@ -25,6 +25,7 @@
 #![feature(nll)]
 #![feature(available_concurrency)]
 #![feature(internal_output_capture)]
+#![feature(option_unwrap_none)]
 #![feature(panic_unwind)]
 #![feature(staged_api)]
 #![feature(termination_trait_lib)]
@@ -61,6 +62,7 @@ pub mod test {
 }
 
 use std::{
+    collections::VecDeque,
     env, io,
     io::prelude::Write,
     panic::{self, catch_unwind, AssertUnwindSafe, PanicInfo},
@@ -208,9 +210,19 @@ pub fn run_tests<F>(
     use std::collections::{self, HashMap};
     use std::hash::BuildHasherDefault;
     use std::sync::mpsc::RecvTimeoutError;
+
+    struct RunningTest {
+        join_handle: Option<thread::JoinHandle<()>>,
+    }
+
     // Use a deterministic hasher
     type TestMap =
-        HashMap<TestDesc, Instant, BuildHasherDefault<collections::hash_map::DefaultHasher>>;
+        HashMap<TestDesc, RunningTest, BuildHasherDefault<collections::hash_map::DefaultHasher>>;
+
+    struct TimeoutEntry {
+        desc: TestDesc,
+        timeout: Instant,
+    }
 
     let tests_len = tests.len();
 
@@ -255,23 +267,30 @@ pub fn run_tests<F>(
     };
 
     let mut running_tests: TestMap = HashMap::default();
+    let mut timeout_queue: VecDeque<TimeoutEntry> = VecDeque::new();
 
-    fn get_timed_out_tests(running_tests: &mut TestMap) -> Vec<TestDesc> {
+    fn get_timed_out_tests(
+        running_tests: &TestMap,
+        timeout_queue: &mut VecDeque<TimeoutEntry>,
+    ) -> Vec<TestDesc> {
         let now = Instant::now();
-        let timed_out = running_tests
-            .iter()
-            .filter_map(|(desc, timeout)| if &now >= timeout { Some(desc.clone()) } else { None })
-            .collect();
-        for test in &timed_out {
-            running_tests.remove(test);
+        let mut timed_out = Vec::new();
+        while let Some(timeout_entry) = timeout_queue.front() {
+            if now < timeout_entry.timeout {
+                break;
+            }
+            let timeout_entry = timeout_queue.pop_front().unwrap();
+            if running_tests.contains_key(&timeout_entry.desc) {
+                timed_out.push(timeout_entry.desc);
+            }
         }
         timed_out
     }
 
-    fn calc_timeout(running_tests: &TestMap) -> Option<Duration> {
-        running_tests.values().min().map(|next_timeout| {
+    fn calc_timeout(timeout_queue: &VecDeque<TimeoutEntry>) -> Option<Duration> {
+        timeout_queue.front().map(|&TimeoutEntry { timeout: next_timeout, .. }| {
             let now = Instant::now();
-            if *next_timeout >= now { *next_timeout - now } else { Duration::new(0, 0) }
+            if next_timeout >= now { next_timeout - now } else { Duration::new(0, 0) }
         })
     }
 
@@ -280,7 +299,8 @@ fn calc_timeout(running_tests: &TestMap) -> Option<Duration> {
             let test = remaining.pop().unwrap();
             let event = TestEvent::TeWait(test.desc.clone());
             notify_about_test_event(event)?;
-            run_test(opts, !opts.run_tests, test, run_strategy, tx.clone(), Concurrent::No);
+            run_test(opts, !opts.run_tests, test, run_strategy, tx.clone(), Concurrent::No)
+                .unwrap_none();
             let completed_test = rx.recv().unwrap();
 
             let event = TestEvent::TeResult(completed_test);
@@ -291,19 +311,28 @@ fn calc_timeout(running_tests: &TestMap) -> Option<Duration> {
             while pending < concurrency && !remaining.is_empty() {
                 let test = remaining.pop().unwrap();
                 let timeout = time::get_default_test_timeout();
-                running_tests.insert(test.desc.clone(), timeout);
+                let desc = test.desc.clone();
 
-                let event = TestEvent::TeWait(test.desc.clone());
+                let event = TestEvent::TeWait(desc.clone());
                 notify_about_test_event(event)?; //here no pad
-                run_test(opts, !opts.run_tests, test, run_strategy, tx.clone(), Concurrent::Yes);
+                let join_handle = run_test(
+                    opts,
+                    !opts.run_tests,
+                    test,
+                    run_strategy,
+                    tx.clone(),
+                    Concurrent::Yes,
+                );
+                running_tests.insert(desc.clone(), RunningTest { join_handle });
+                timeout_queue.push_back(TimeoutEntry { desc, timeout });
                 pending += 1;
             }
 
             let mut res;
             loop {
-                if let Some(timeout) = calc_timeout(&running_tests) {
+                if let Some(timeout) = calc_timeout(&timeout_queue) {
                     res = rx.recv_timeout(timeout);
-                    for test in get_timed_out_tests(&mut running_tests) {
+                    for test in get_timed_out_tests(&running_tests, &mut timeout_queue) {
                         let event = TestEvent::TeTimeout(test);
                         notify_about_test_event(event)?;
                     }
@@ -323,8 +352,16 @@ fn calc_timeout(running_tests: &TestMap) -> Option<Duration> {
                 }
             }
 
-            let completed_test = res.unwrap();
-            running_tests.remove(&completed_test.desc);
+            let mut completed_test = res.unwrap();
+            let running_test = running_tests.remove(&completed_test.desc).unwrap();
+            if let Some(join_handle) = running_test.join_handle {
+                if let Err(_) = join_handle.join() {
+                    if let TrOk = completed_test.result {
+                        completed_test.result =
+                            TrFailedMsg("panicked after reporting success".to_string());
+                    }
+                }
+            }
 
             let event = TestEvent::TeResult(completed_test);
             notify_about_test_event(event)?;
@@ -415,7 +452,7 @@ pub fn run_test(
     strategy: RunStrategy,
     monitor_ch: Sender<CompletedTest>,
     concurrency: Concurrent,
-) {
+) -> Option<thread::JoinHandle<()>> {
     let TestDescAndFn { desc, testfn } = test;
 
     // Emscripten can catch panics but other wasm targets cannot
@@ -426,7 +463,7 @@ pub fn run_test(
     if force_ignore || desc.ignore || ignore_because_no_process_support {
         let message = CompletedTest::new(desc, TrIgnored, None, Vec::new());
         monitor_ch.send(message).unwrap();
-        return;
+        return None;
     }
 
     struct TestRunOpts {
@@ -441,7 +478,7 @@ fn run_test_inner(
         monitor_ch: Sender<CompletedTest>,
         testfn: Box<dyn FnOnce() + Send>,
         opts: TestRunOpts,
-    ) {
+    ) -> Option<thread::JoinHandle<()>> {
         let concurrency = opts.concurrency;
         let name = desc.name.clone();
 
@@ -469,9 +506,10 @@ fn run_test_inner(
         let supports_threads = !cfg!(target_os = "emscripten") && !cfg!(target_arch = "wasm32");
         if concurrency == Concurrent::Yes && supports_threads {
             let cfg = thread::Builder::new().name(name.as_slice().to_owned());
-            cfg.spawn(runtest).unwrap();
+            Some(cfg.spawn(runtest).unwrap())
         } else {
             runtest();
+            None
         }
     }
 
@@ -484,10 +522,12 @@ fn run_test_inner(
             crate::bench::benchmark(desc, monitor_ch, opts.nocapture, |harness| {
                 bencher.run(harness)
             });
+            None
         }
         StaticBenchFn(benchfn) => {
             // Benchmarks aren't expected to panic, so we run them all in-process.
             crate::bench::benchmark(desc, monitor_ch, opts.nocapture, benchfn);
+            None
         }
         DynTestFn(f) => {
             match strategy {
@@ -499,7 +539,7 @@ fn run_test_inner(
                 monitor_ch,
                 Box::new(move || __rust_begin_short_backtrace(f)),
                 test_run_opts,
-            );
+            )
         }
         StaticTestFn(f) => run_test_inner(
             desc,