Convert some lazy_static to OnceCell/OnceLock

These have clearer sync/unsync semantics and now ship with rust itself.
They don't paper over any possible cross-thread issues, and we can specifically
choose which we want for the purpose.

src/env/environment_impl.rs

@@ -24,15 +24,16 @@ use std::ops::{Deref, DerefMut};
 
 use std::sync::{atomic::AtomicU64, atomic::Ordering, Arc, Mutex, MutexGuard};
 
-// Universal variables instance.
-lazy_static! {
-    static ref UVARS: Mutex<EnvUniversal> = Mutex::new(EnvUniversal::new());
-}
-
 /// Getter for universal variables.
 /// This is typically initialized in env_init(), and is considered empty before then.
 pub fn uvars() -> MutexGuard<'static, EnvUniversal> {
-    UVARS.lock().unwrap()
+    use std::sync::OnceLock;
+    /// Universal variables instance.
+    static UVARS: OnceLock<Mutex<EnvUniversal>> = OnceLock::new();
+    UVARS
+        .get_or_init(|| Mutex::new(EnvUniversal::new()))
+        .lock()
+        .unwrap()
 }
 
 /// Whether we were launched with no_config; in this case setting a uvar instead sets a global.

src/env/var.rs

@@ -2,7 +2,6 @@ use crate::signal::Signal;
 use crate::wchar::{wstr, WString, L};
 use crate::wcstringutil::join_strings;
 use bitflags::bitflags;
-use lazy_static::lazy_static;
 use libc::c_int;
 use std::collections::HashMap;
 use std::path::PathBuf;
@@ -97,11 +96,6 @@ bitflags! {
     }
 }
 
-// A shared, empty list.
-lazy_static! {
-    static ref EMPTY_LIST: Arc<Box<[WString]>> = Arc::new(Box::new([]));
-}
-
 /// EnvVar is an immutable value-type data structure representing the value of an environment
 /// variable.
 #[derive(Clone, Debug, Eq, PartialEq)]
@@ -115,8 +109,13 @@ pub struct EnvVar {
 
 impl Default for EnvVar {
     fn default() -> Self {
+        use std::sync::OnceLock;
+        /// A shared read-only empty list.
+        static EMPTY_LIST: OnceLock<Arc<Box<[WString]>>> = OnceLock::new();
+        let empty_list = EMPTY_LIST.get_or_init(|| Arc::new(Box::new([])));
+
         EnvVar {
-            values: EMPTY_LIST.clone(),
+            values: Arc::clone(empty_list),
             flags: EnvVarFlags::empty(),
         }
     }