rewrite libtest-thread-limit to rmake

Author: Oneirical

Cargo.lock

@@ -3148,6 +3148,7 @@ 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

@@ -13,7 +13,6 @@ 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/long-linker-command-lines-cmd-exe/Makefile
 run-make/long-linker-command-lines/Makefile
 run-make/min-global-align/Makefile

tests/run-make/libtest-thread-limit/Makefile

@@ -0,0 +1,26 @@
+// 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 run_make_support::{libc, run, rustc};
+
+fn main() {
+    rustc().input("test.rs").arg("--test").run();
+    let rlimit = libc::rlimit {
+        rlim_cur: 1, // or 1, needs testing
+        rlim_max: 1, // or 1, needs testing
+    };
+    let ptr = &rlimit as *const libc::rlimit;
+    unsafe {
+        libc::setrlimit(0, ptr);
+    }
+    run("test");
+}

tests/run-make/libtest-thread-limit/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};