Rollup merge of #123867 - eduardosm:unsafe-fns, r=ChrisDenton

Add `unsafe` to two functions with safety invariants

library/std/src/sys/pal/windows/thread.rs

@@ -45,13 +45,11 @@ pub unsafe fn new(stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
             Err(io::Error::last_os_error())
         };
 
-        extern "system" fn thread_start(main: *mut c_void) -> c::DWORD {
-            unsafe {
-                // Next, reserve some stack space for if we otherwise run out of stack.
-                stack_overflow::reserve_stack();
-                // Finally, let's run some code.
-                Box::from_raw(main as *mut Box<dyn FnOnce()>)();
-            }
+        unsafe extern "system" fn thread_start(main: *mut c_void) -> c::DWORD {
+            // Next, reserve some stack space for if we otherwise run out of stack.
+            stack_overflow::reserve_stack();
+            // Finally, let's run some code.
+            Box::from_raw(main as *mut Box<dyn FnOnce()>)();
             0
         }
     }
@@ -59,15 +57,19 @@ extern "system" fn thread_start(main: *mut c_void) -> c::DWORD {
     pub fn set_name(name: &CStr) {
         if let Ok(utf8) = name.to_str() {
             if let Ok(utf16) = to_u16s(utf8) {
-                Self::set_name_wide(&utf16)
+                unsafe {
+                    // SAFETY: the vec returned by `to_u16s` ends with a zero value
+                    Self::set_name_wide(&utf16)
+                }
             };
         };
     }
 
-    pub fn set_name_wide(name: &[u16]) {
-        unsafe {
-            c::SetThreadDescription(c::GetCurrentThread(), name.as_ptr());
-        };
+    /// # Safety
+    ///
+    /// `name` must end with a zero value
+    pub unsafe fn set_name_wide(name: &[u16]) {
+        c::SetThreadDescription(c::GetCurrentThread(), name.as_ptr());
     }
 
     pub fn join(self) {