use `confstr(_CS_DARWIN_USER_TEMP_DIR, ...)` as a `TMPDIR` fallback on darwin

1 files changed, 25 insertions, 0 deletions

diff --git a/library/std/src/sys/pal/unix/os/tests.rs b/library/std/src/sys/pal/unix/os/tests.rs
index efc29955b05..ab9742fc677 100644
--- a/library/std/src/sys/pal/unix/os/tests.rs
+++ b/library/std/src/sys/pal/unix/os/tests.rs
@@ -21,3 +21,28 @@ fn test_parse_glibc_version() {
         assert_eq!(parsed, super::parse_glibc_version(version_str));
     }
 }
+
+// Smoke check `confstr`, do it for several hint values, to ensure our resizing
+// logic is correct.
+#[test]
+#[cfg(target_os = "macos")]
+fn test_confstr() {
+    for key in [libc::_CS_DARWIN_USER_TEMP_DIR, libc::_CS_PATH] {
+        let value_nohint = super::confstr(key, None).unwrap_or_else(|e| {
+            panic!("confstr({key}, None) failed: {e:?}");
+        });
+        let end = (value_nohint.len() + 1) * 2;
+        for hint in 0..end {
+            assert_eq!(
+                super::confstr(key, Some(hint)).as_deref().ok(),
+                Some(&*value_nohint),
+                "confstr({key}, Some({hint})) failed",
+            );
+        }
+    }
+    // Smoke check that we don't loop forever or something if the input was not valid.
+    for hint in [None, Some(0), Some(1)] {
+        let hopefully_invalid = 123456789_i32;
+        assert!(super::confstr(hopefully_invalid, hint).is_err());
+    }
+}