Use once_cell instead of lazy_static

lazy_static has better ergonomics at the call/access sites (it returns a
reference to the type directly, whereas with once_cell we get a static Lazy<T>
that we must dereference instead) but the once_cell api is slated for
integration into the standard library [0] and has been the "preferred" way to
declare static global variables w/ deferred initialization. It's also less
opaque and easier to comprehend how it works, I guess?

(Both `once_cell` and `lazy_static` are already in our dependency tree, so this
should have no detrimental effect on build times. It actually negligibly
*improves* build times by not using macros, reducing the amount of expansion the
compiler has to do by a miniscule amount.)

[0]: https://github.com/rust-lang/rust/issues/74465

fish-rust/Cargo.lock

@@ -358,6 +358,7 @@ dependencies = [
  "miette",
  "nix",
  "num-traits",
+ "once_cell",
  "unixstring",
  "widestring",
  "widestring-suffix",

fish-rust/Cargo.toml

@@ -15,6 +15,7 @@ lazy_static = "1.4.0"
 libc = "0.2.137"
 nix = { version = "0.25.0", default-features = false, features = [] }
 num-traits = "0.2.15"
+once_cell = "1.17.0"
 unixstring = "0.2.7"
 widestring = "1.0.2"
 

fish-rust/src/lib.rs

@@ -4,9 +4,6 @@
 #![allow(clippy::needless_return)]
 #![allow(clippy::manual_is_ascii_check)]
 
-#[macro_use]
-extern crate lazy_static;
-
 mod fd_readable_set;
 mod fds;
 #[allow(rustdoc::broken_intra_doc_links)]

fish-rust/src/wchar_ffi.rs

@@ -9,6 +9,7 @@
 use crate::ffi;
 pub use cxx::CxxWString;
 pub use ffi::{wchar_t, wcharz_t};
+use once_cell::sync::Lazy;
 pub use widestring::U32CString as W0String;
 pub use widestring::{u32cstr, utf32str};
 pub use widestring::{Utf32Str as wstr, Utf32String as WString};
@@ -72,14 +73,12 @@ macro_rules! wcharz {
 pub(crate) use c_str;
 pub(crate) use wcharz;
 
-lazy_static! {
-    /// A shared, empty CxxWString.
-    static ref EMPTY_WSTRING: cxx::UniquePtr<cxx::CxxWString> = cxx::CxxWString::create(&[]);
-}
+static EMPTY_WSTRING: Lazy<cxx::UniquePtr<cxx::CxxWString>> =
+    Lazy::new(|| cxx::CxxWString::create(&[]));
 
 /// \return a reference to a shared empty wstring.
 pub fn empty_wstring() -> &'static cxx::CxxWString {
-    &EMPTY_WSTRING
+    &*EMPTY_WSTRING
 }
 
 /// Implement Debug for wcharz_t.