refactor: make c_str! simpler, add test

Signed-off-by: Thomas Mühlbacher <tmuehlbacher@posteo.net>

src/commands/mod.rs

@@ -27,13 +27,27 @@ enum Subcommands {
     Subvolume(subvolume::Cli),
 }
 
+// FIXME: Can be removed after bumping MSRV >= 1.77 in favor of `c""` literals
 #[macro_export]
 macro_rules! c_str {
     ($lit:expr) => {
-        unsafe {
-            std::ffi::CStr::from_ptr(concat!($lit, "\0").as_ptr() as *const std::os::raw::c_char)
-                .to_bytes_with_nul()
-                .as_ptr() as *const std::os::raw::c_char
-        }
+        ::std::ffi::CStr::from_bytes_with_nul(concat!($lit, "\0").as_bytes())
+            .unwrap()
+            .as_ptr()
     };
 }
+
+#[cfg(test)]
+mod tests {
+    use std::ffi::CStr;
+
+    #[test]
+    fn check_cstr_macro() {
+        let literal = c_str!("hello");
+
+        assert_eq!(
+            literal,
+            CStr::from_bytes_with_nul(b"hello\0").unwrap().as_ptr()
+        );
+    }
+}