Rollup merge of #90431 - jkugelman:must-use-std-o-through-z, r=joshtriplett

Add #[must_use] to remaining std functions (O-Z)

I've run out of compelling reasons to group functions together across crates so I'm just going to go module-by-module. This is half of the remaining items from the `std` crate, from O-Z.

`panicking::take_hook` has a side effect: it unregisters the current panic hook, returning it. I almost ignored it, but the documentation example shows `let _ = panic::take_hook();`, so following suit I went ahead and added a `#[must_use]`.

```rust
std::panicking   fn take_hook() -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>;
```

I added these functions that clippy did not flag:

```rust
std::path::Path   fn starts_with<P: AsRef<Path>>(&self, base: P) -> bool;
std::path::Path   fn ends_with<P: AsRef<Path>>(&self, child: P) -> bool;
std::path::Path   fn with_file_name<S: AsRef<OsStr>>(&self, file_name: S) -> PathBuf;
std::path::Path   fn with_extension<S: AsRef<OsStr>>(&self, extension: S) -> PathBuf;
```

Parent issue: #89692

r? `@joshtriplett`

3 files changed, 8 insertions, 0 deletions

diff --git a/library/std/src/os/unix/net/ancillary.rs b/library/std/src/os/unix/net/ancillary.rs
index 353bf2f1166..6e6f5212b46 100644
--- a/library/std/src/os/unix/net/ancillary.rs
+++ b/library/std/src/os/unix/net/ancillary.rs
@@ -201,6 +201,7 @@ impl SocketCred {
     }
 
     /// Get the current PID.
+    #[must_use]
     #[unstable(feature = "unix_socket_ancillary_data", issue = "76915")]
     pub fn get_pid(&self) -> libc::pid_t {
         self.0.pid
@@ -213,6 +214,7 @@ impl SocketCred {
     }
 
     /// Get the current UID.
+    #[must_use]
     #[unstable(feature = "unix_socket_ancillary_data", issue = "76915")]
     pub fn get_uid(&self) -> libc::uid_t {
         self.0.uid
@@ -225,6 +227,7 @@ impl SocketCred {
     }
 
     /// Get the current GID.
+    #[must_use]
     #[unstable(feature = "unix_socket_ancillary_data", issue = "76915")]
     pub fn get_gid(&self) -> libc::gid_t {
         self.0.gid
@@ -330,6 +333,7 @@ impl<'a> AncillaryData<'a> {
 }
 
 /// This struct is used to iterate through the control messages.
+#[must_use = "iterators are lazy and do nothing unless consumed"]
 #[unstable(feature = "unix_socket_ancillary_data", issue = "76915")]
 pub struct Messages<'a> {
     buffer: &'a [u8],
@@ -425,6 +429,7 @@ impl<'a> SocketAncillary<'a> {
     }
 
     /// Returns the capacity of the buffer.
+    #[must_use]
     #[unstable(feature = "unix_socket_ancillary_data", issue = "76915")]
     pub fn capacity(&self) -> usize {
         self.buffer.len()
@@ -473,6 +478,7 @@ impl<'a> SocketAncillary<'a> {
     ///     Ok(())
     /// }
     /// ```
+    #[must_use]
     #[unstable(feature = "unix_socket_ancillary_data", issue = "76915")]
     pub fn truncated(&self) -> bool {
         self.truncated
diff --git a/library/std/src/os/unix/net/listener.rs b/library/std/src/os/unix/net/listener.rs
index 97348afe7de..b23dd6062f6 100644
--- a/library/std/src/os/unix/net/listener.rs
+++ b/library/std/src/os/unix/net/listener.rs
@@ -365,6 +365,7 @@ impl<'a> IntoIterator for &'a UnixListener {
 /// }
 /// ```
 #[derive(Debug)]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
 #[stable(feature = "unix_socket", since = "1.10.0")]
 pub struct Incoming<'a> {
     listener: &'a UnixListener,
diff --git a/library/std/src/os/unix/process.rs b/library/std/src/os/unix/process.rs
index 9b94615d247..286a7c3b386 100644
--- a/library/std/src/os/unix/process.rs
+++ b/library/std/src/os/unix/process.rs
@@ -436,6 +436,7 @@ impl From<crate::process::ChildStderr> for OwnedFd {
 }
 
 /// Returns the OS-assigned process identifier associated with this process's parent.
+#[must_use]
 #[stable(feature = "unix_ppid", since = "1.27.0")]
 pub fn parent_id() -> u32 {
     crate::sys::os::getppid()