Revert removal of Arc from principal() and global()

This reverts commit c6d3bde0c6.
This reverts commit 4ce13f0adb.

src/bin/fish_indent.rs

@@ -990,7 +990,7 @@ fn throwing_main() -> i32 {
                 }
             }
             OutputType::Ansi => {
-                colored_output = colorize(&output_wtext, &colors, EnvStack::globals());
+                colored_output = colorize(&output_wtext, &colors, &**EnvStack::globals());
             }
             OutputType::Html => {
                 colored_output = html_colorize(&output_wtext, &colors);

src/complete.rs

@@ -2473,7 +2473,7 @@ pub fn complete_load(cmd: &wstr, parser: &Parser) -> bool {
     let path_to_load = completion_autoloader
         .lock()
         .expect("mutex poisoned")
-        .resolve_command(cmd, EnvStack::globals());
+        .resolve_command(cmd, &**EnvStack::globals());
     if let Some(path_to_load) = path_to_load {
         Autoload::perform_autoload(&path_to_load, parser);
         completion_autoloader

src/env/environment.rs

@@ -188,7 +188,7 @@ impl EnvStack {
 
     /// Return whether we are the principal stack.
     pub fn is_principal(&self) -> bool {
-        std::ptr::eq(self, Self::principal())
+        std::ptr::eq(self, &**Self::principal())
     }
 
     /// Helpers to get and set the proc statuses.
@@ -360,17 +360,17 @@ impl EnvStack {
 
     /// A variable stack that only represents globals.
     /// Do not push or pop from this.
-    pub fn globals() -> &'static EnvStack {
+    pub fn globals() -> &'static Arc<EnvStack> {
         use std::sync::OnceLock;
-        static GLOBALS: OnceLock<EnvStack> = OnceLock::new();
-        GLOBALS.get_or_init(|| EnvStack::new())
+        static GLOBALS: OnceLock<Arc<EnvStack>> = OnceLock::new();
+        &GLOBALS.get_or_init(|| Arc::new(EnvStack::new()))
     }
 
     /// Access the principal variable stack, associated with the principal parser.
-    pub fn principal() -> &'static EnvStack {
+    pub fn principal() -> &'static Arc<EnvStack> {
         use std::sync::OnceLock;
-        static PRINCIPAL_STACK: OnceLock<EnvStack> = OnceLock::new();
-        &PRINCIPAL_STACK.get_or_init(|| EnvStack::new())
+        static PRINCIPAL_STACK: OnceLock<Arc<EnvStack>> = OnceLock::new();
+        &PRINCIPAL_STACK.get_or_init(|| Arc::new(EnvStack::new()))
     }
 
     pub fn set_argv(&self, argv: Vec<WString>) {
@@ -554,7 +554,7 @@ fn setup_path() {
 pub static INHERITED_VARS: OnceCell<HashMap<WString, WString>> = OnceCell::new();
 
 pub fn env_init(paths: Option<&ConfigPaths>, do_uvars: bool, default_paths: bool) {
-    let vars = EnvStack::principal();
+    let vars = &**EnvStack::principal();
 
     let env_iter: Vec<_> = std::env::vars_os()
         .map(|(k, v)| (str2wcstring(k.as_bytes()), str2wcstring(v.as_bytes())))

src/function.rs

@@ -122,7 +122,7 @@ pub fn load(name: &wstr, parser: &Parser) -> bool {
         if funcset.allow_autoload(name) {
             if let Some(path) = funcset
                 .autoloader
-                .resolve_command(name, EnvStack::globals())
+                .resolve_command(name, &**EnvStack::globals())
             {
                 path_to_autoload = Some(path);
             }

src/operation_context.rs

@@ -65,7 +65,7 @@ impl<'a> OperationContext<'a> {
     // Return an operation context that contains only global variables, no parser, and never
     // cancels.
     pub fn globals() -> OperationContext<'static> {
-        OperationContext::background(EnvStack::globals(), EXPANSION_LIMIT_DEFAULT)
+        OperationContext::background(&**EnvStack::globals(), EXPANSION_LIMIT_DEFAULT)
     }
 
     /// Construct from a full set of properties.

src/parser.rs

@@ -402,13 +402,18 @@ impl Parser {
     pub fn principal_parser() -> &'static Parser {
         use std::cell::OnceCell;
         static PRINCIPAL: MainThread<OnceCell<ParserRef>> = MainThread::new(OnceCell::new());
-        &PRINCIPAL.get().get_or_init(|| {
-            // Safety: EnvStack::principal() returns a `static` variable guaranteed to always be
-            // alive. We just don't want to hard-code the lifetime in `Parser` so we wrap the
-            // `EnvStack` in an `Rc` before sending it along.
-            let env_rc = unsafe { Rc::from_raw(EnvStack::principal() as *const _) };
-            Parser::new(env_rc, true)
-        })
+        &PRINCIPAL
+            .get()
+            // The parser is !Send/!Sync and strictly single-threaded, but we can have
+            // multi-threaded access to its variables stack (why, though?) so EnvStack::principal()
+            // returns an Arc<EnvStack> instead of an Rc<EnvStack>. Since the Arc<EnvStack> is
+            // statically allocated and always valid (not even destroyed on exit), we can safely
+            // transform the Arc<T> into an Rc<T> and save Parser from needing atomic ref counting
+            // to manage its further references.
+            .get_or_init(|| {
+                let env_rc = unsafe { Rc::from_raw(&**EnvStack::principal() as *const _) };
+                Parser::new(env_rc, true)
+            })
     }
 
     /// Assert that this parser is allowed to execute on the current thread.