rewrite libtest-thread-limit to rmake

Cargo.lock

@@ -3147,6 +3147,7 @@ dependencies = [
  "bstr",
  "build_helper",
  "gimli 0.31.0",
+ "libc",
  "object 0.36.2",
  "regex",
  "similar",

src/tools/run-make-support/Cargo.toml

@@ -11,3 +11,4 @@ wasmparser = { version = "0.214", default-features = false, features = ["std"] }
 regex = "1.8" # 1.8 to avoid memchr 2.6.0, as 2.5.0 is pinned in the workspace
 gimli = "0.31.0"
 build_helper = { path = "../build_helper" }
+libc = "0.2"

src/tools/run-make-support/src/lib.rs

@@ -36,6 +36,7 @@ pub mod rfs {
 // Re-exports of third-party library crates.
 pub use bstr;
 pub use gimli;
+pub use libc;
 pub use object;
 pub use regex;
 pub use wasmparser;

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -11,7 +11,6 @@ run-make/jobserver-error/Makefile
 run-make/libs-through-symlinks/Makefile
 run-make/libtest-json/Makefile
 run-make/libtest-junit/Makefile
-run-make/libtest-thread-limit/Makefile
 run-make/min-global-align/Makefile
 run-make/native-link-modifier-bundle/Makefile
 run-make/no-alloc-shim/Makefile

tests/run-make/libtest-thread-limit/rmake.rs

@@ -0,0 +1,42 @@
+// libtest used to panic if it hit the thread limit. This often resulted in spurious test failures
+// (thread 'main' panicked at 'called Result::unwrap() on an Err value: Os
+// { code: 11, kind: WouldBlock, message: "Resource temporarily unavailable" }' ...
+// error: test failed, to rerun pass '--lib').
+// Since the fix in #81546, the test should continue to run synchronously
+// if it runs out of threads. Therefore, this test's final execution step
+// should succeed without an error.
+// See https://github.com/rust-lang/rust/pull/81546
+
+//@ only-linux
+// Reason: thread limit modification
+
+use std::ffi::{self, CStr, CString};
+use std::path::PathBuf;
+
+use run_make_support::{libc, run, rustc};
+
+fn main() {
+    rustc().input("test.rs").arg("--test").run();
+
+    let pid = unsafe { libc::fork() };
+    assert!(pid >= 0);
+
+    if pid == 0 {
+        let test = CString::new("test").unwrap();
+        // The argv array should be terminated with a NULL pointer.
+        let argv = [test.as_ptr(), std::ptr::null()];
+        let rlimit = libc::rlimit { rlim_cur: 1, rlim_max: 1 };
+        let ret = unsafe { libc::setrlimit(libc::RLIMIT_NPROC, &rlimit as *const libc::rlimit) };
+        assert!(ret == 0);
+
+        let ret = unsafe { libc::execv(test.as_ptr(), argv.as_ptr()) };
+        assert!(ret == 0);
+    } else {
+        // parent
+
+        let mut child_exit_status: libc::c_int = 0;
+        let ret = unsafe { libc::waitpid(pid, &mut child_exit_status as *mut libc::c_int, 0) };
+        assert!(ret == pid);
+        assert!(child_exit_status == 0);
+    }
+}

tests/run-make/libtest-thread-limit/test.rs

@@ -10,7 +10,11 @@ fn spawn_thread_would_block() {
     THREAD_ID.set(thread::current().id()).unwrap();
 }
 
+// HACK(Oneirical): Tests are run in alphabetical order, and the second test is dependent on the
+// first to set THREAD_ID. Do not rename the tests in such a way that `test_run_in_same_thread`
+// would run before `spawn_thread_would_block`.
+
 #[test]
-fn run_in_same_thread() {
+fn test_run_in_same_thread() {
     assert_eq!(*THREAD_ID.get().unwrap(), thread::current().id());
 }

tests/run-make/macos-deployment-target/rmake.rs

@@ -4,6 +4,7 @@
 // See https://github.com/rust-lang/rust/pull/105123
 
 //@ only-macos
+// Reason: this test exercises an OSX-specific issue
 
 use run_make_support::{cmd, rustc};
 
@@ -18,7 +19,7 @@ fn main() {
     } else {
         "version 10.13"
     };
-    // XXX: The check is for either the x86_64 minimum OR the aarch64 minimum
+    // NOTE: The check is for either the x86_64 minimum OR the aarch64 minimum
     // (M1 starts at macOS 11). They also use different load commands, so we let that change with
     // each too. The aarch64 check isn't as robust as the x86 one, but testing both seems unneeded.
     cmd("vtool")