fs: Expect a test failure if file locks aren't supported

Rather than skipping the tests, make sure that they fail. This ensures
that if file locking support is added for more platforms in the future,
the tests don't wind up quietly skipped.

Author: tgross35

library/std/src/fs/tests.rs

@@ -1,24 +1,7 @@
 use rand::RngCore;
 
-#[cfg(any(
-    windows,
-    target_os = "freebsd",
-    target_os = "linux",
-    target_os = "netbsd",
-    target_os = "illumos",
-    target_vendor = "apple",
-))]
 use crate::assert_matches::assert_matches;
-#[cfg(any(
-    windows,
-    target_os = "freebsd",
-    target_os = "linux",
-    target_os = "netbsd",
-    target_os = "illumos",
-    target_vendor = "apple",
-))]
-use crate::fs::TryLockError;
-use crate::fs::{self, File, FileTimes, OpenOptions};
+use crate::fs::{self, File, FileTimes, OpenOptions, TryLockError};
 use crate::io::prelude::*;
 use crate::io::{BorrowedBuf, ErrorKind, SeekFrom};
 use crate::mem::MaybeUninit;
@@ -222,19 +205,22 @@ fn file_test_io_seek_and_write() {
 }
 
 #[test]
-#[cfg(any(
-    windows,
-    target_os = "aix",
-    target_os = "cygwin",
-    target_os = "freebsd",
-    target_os = "fuchsia",
-    target_os = "illumos",
-    target_os = "linux",
-    target_os = "netbsd",
-    target_os = "openbsd",
-    target_os = "solaris",
-    target_vendor = "apple",
-))]
+#[cfg_attr(
+    not(any(
+        windows,
+        target_os = "aix",
+        target_os = "cygwin",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "solaris",
+        target_vendor = "apple",
+    )),
+    should_panic
+)]
 fn file_lock_multiple_shared() {
     let tmpdir = tmpdir();
     let filename = &tmpdir.join("file_lock_multiple_shared_test.txt");
@@ -251,19 +237,22 @@ fn file_lock_multiple_shared() {
 }
 
 #[test]
-#[cfg(any(
-    windows,
-    target_os = "aix",
-    target_os = "cygwin",
-    target_os = "freebsd",
-    target_os = "fuchsia",
-    target_os = "illumos",
-    target_os = "linux",
-    target_os = "netbsd",
-    target_os = "openbsd",
-    target_os = "solaris",
-    target_vendor = "apple",
-))]
+#[cfg_attr(
+    not(any(
+        windows,
+        target_os = "aix",
+        target_os = "cygwin",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "solaris",
+        target_vendor = "apple",
+    )),
+    should_panic
+)]
 fn file_lock_blocking() {
     let tmpdir = tmpdir();
     let filename = &tmpdir.join("file_lock_blocking_test.txt");
@@ -281,19 +270,22 @@ fn file_lock_blocking() {
 }
 
 #[test]
-#[cfg(any(
-    windows,
-    target_os = "aix",
-    target_os = "cygwin",
-    target_os = "freebsd",
-    target_os = "fuchsia",
-    target_os = "illumos",
-    target_os = "linux",
-    target_os = "netbsd",
-    target_os = "openbsd",
-    target_os = "solaris",
-    target_vendor = "apple",
-))]
+#[cfg_attr(
+    not(any(
+        windows,
+        target_os = "aix",
+        target_os = "cygwin",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "solaris",
+        target_vendor = "apple",
+    )),
+    should_panic
+)]
 fn file_lock_drop() {
     let tmpdir = tmpdir();
     let filename = &tmpdir.join("file_lock_dup_test.txt");
@@ -308,19 +300,22 @@ fn file_lock_drop() {
 }
 
 #[test]
-#[cfg(any(
-    windows,
-    target_os = "aix",
-    target_os = "cygwin",
-    target_os = "freebsd",
-    target_os = "fuchsia",
-    target_os = "illumos",
-    target_os = "linux",
-    target_os = "netbsd",
-    target_os = "openbsd",
-    target_os = "solaris",
-    target_vendor = "apple",
-))]
+#[cfg_attr(
+    not(any(
+        windows,
+        target_os = "aix",
+        target_os = "cygwin",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "solaris",
+        target_vendor = "apple",
+    )),
+    should_panic
+)]
 fn file_lock_dup() {
     let tmpdir = tmpdir();
     let filename = &tmpdir.join("file_lock_dup_test.txt");