Auto merge of rust-lang#126223 - jieyouxu:rmake-run-in-tmpdir-self-test, r=<try>

run-make: add `run_in_tmpdir` self-test

Add a basic sanity test for `run_in_tmpdir` to make sure that files (including read-only files) and directories created inside the "scratch" tmpdir are removed after the closure returns.

r? ghost (while i run a try job)

try-job: x86_64-msvc

Author: bors

tests/run-make/run-in-tmpdir-self-test/rmake.rs

@@ -0,0 +1,37 @@
+//! This is a self-test for the `run_in_tmpdir` helper in the support library. This test tries to
+//! check that files and directories created within the temporary directory gets properly cleared
+//! when returning from the closure.
+
+use std::fs;
+use std::path::{Path, PathBuf};
+
+use run_make_support::{cwd, run_in_tmpdir};
+
+fn main() {
+    let mut file_path = PathBuf::new();
+    let mut dir_path = PathBuf::new();
+    let mut readonly_file_path = PathBuf::new();
+    let test_cwd = cwd();
+    run_in_tmpdir(|| {
+        assert_ne!(test_cwd, cwd(), "test cwd should not be the same as tmpdir cwd");
+
+        file_path = cwd().join("foo.txt");
+        fs::write(&file_path, "hi").unwrap();
+
+        dir_path = cwd().join("bar");
+        fs::create_dir_all(&dir_path).unwrap();
+
+        readonly_file_path = cwd().join("readonly-file.txt");
+        fs::write(&readonly_file_path, "owo").unwrap();
+        let mut perms = fs::metadata(&readonly_file_path).unwrap().permissions();
+        perms.set_readonly(true);
+        fs::set_permissions(&mut readonly_file_path, perms).unwrap();
+
+        assert!(file_path.exists());
+        assert!(dir_path.exists());
+        assert!(readonly_file_path.exists());
+    });
+    assert!(!file_path.exists());
+    assert!(!dir_path.exists());
+    assert!(!readonly_file_path.exists());
+}