core: remove vendored lazy_static on no-std (#2173)

Currently, `no_std` targets use a vendored version of `lazy_static` that
uses the `spin` crate's `Once` type, while the `std` target uses the
`once_cell` crate's `Lazy` type. This is unfortunate, as the
`lazy_static` macro has a different interface from the `Lazy` cell type.
This increases the amount of code that differs based on whether or not
`std` is enabled.

This branch removes the vendored `lazy_static` macro and replaces it
with a reimplementation of `once_cell::sync::Lazy` that uses
`spin::Once` rather than `once_cell::sync::OnceCell` as the inner "once
type". Now, all code can be written against a `Lazy` struct with the
same interface, regardless of whether or not `std` is enabled.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

tracing-core/src/callsite.rs

@@ -111,6 +111,7 @@ use crate::stdlib::{
 };
 use crate::{
     dispatcher::Dispatch,
+    lazy::Lazy,
     metadata::{LevelFilter, Metadata},
     subscriber::Interest,
 };
@@ -253,14 +254,7 @@ static CALLSITES: Callsites = Callsites {
 
 static DISPATCHERS: Dispatchers = Dispatchers::new();
 
-#[cfg(feature = "std")]
-static LOCKED_CALLSITES: once_cell::sync::Lazy<Mutex<Vec<&'static dyn Callsite>>> =
-    once_cell::sync::Lazy::new(Default::default);
-
-#[cfg(not(feature = "std"))]
-crate::lazy_static! {
-    static ref LOCKED_CALLSITES: Mutex<Vec<&'static dyn Callsite>> = Mutex::new(Vec::new());
-}
+static LOCKED_CALLSITES: Lazy<Mutex<Vec<&'static dyn Callsite>>> = Lazy::new(Default::default);
 
 struct Callsites {
     list_head: AtomicPtr<DefaultCallsite>,
@@ -514,8 +508,7 @@ mod private {
 
 #[cfg(feature = "std")]
 mod dispatchers {
-    use crate::dispatcher;
-    use once_cell::sync::Lazy;
+    use crate::{dispatcher, lazy::Lazy};
     use std::sync::{
         atomic::{AtomicBool, Ordering},
         RwLock, RwLockReadGuard, RwLockWriteGuard,

tracing-core/src/lazy.rs

@@ -0,0 +1,76 @@
+#[cfg(feature = "std")]
+pub(crate) use once_cell::sync::Lazy;
+
+#[cfg(not(feature = "std"))]
+pub(crate) use self::spin::Lazy;
+
+#[cfg(not(feature = "std"))]
+mod spin {
+    //! This is the `once_cell::sync::Lazy` type, but modified to use our
+    //! `spin::Once` type rather than `OnceCell`. This is used to replace
+    //! `once_cell::sync::Lazy` on `no-std` builds.
+    use crate::spin::Once;
+    use core::{cell::Cell, fmt, ops::Deref};
+
+    /// Re-implementation of `once_cell::sync::Lazy` on top of `spin::Once`
+    /// rather than `OnceCell`.
+    ///
+    /// This is used when the standard library is disabled.
+    pub(crate) struct Lazy<T, F = fn() -> T> {
+        cell: Once<T>,
+        init: Cell<Option<F>>,
+    }
+
+    impl<T: fmt::Debug, F> fmt::Debug for Lazy<T, F> {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.debug_struct("Lazy")
+                .field("cell", &self.cell)
+                .field("init", &"..")
+                .finish()
+        }
+    }
+
+    // We never create a `&F` from a `&Lazy<T, F>` so it is fine to not impl
+    // `Sync` for `F`. We do create a `&mut Option<F>` in `force`, but this is
+    // properly synchronized, so it only happens once so it also does not
+    // contribute to this impl.
+    unsafe impl<T, F: Send> Sync for Lazy<T, F> where Once<T>: Sync {}
+    // auto-derived `Send` impl is OK.
+
+    impl<T, F> Lazy<T, F> {
+        /// Creates a new lazy value with the given initializing function.
+        pub(crate) const fn new(init: F) -> Lazy<T, F> {
+            Lazy {
+                cell: Once::new(),
+                init: Cell::new(Some(init)),
+            }
+        }
+    }
+
+    impl<T, F: FnOnce() -> T> Lazy<T, F> {
+        /// Forces the evaluation of this lazy value and returns a reference to
+        /// the result.
+        ///
+        /// This is equivalent to the `Deref` impl, but is explicit.
+        pub(crate) fn force(this: &Lazy<T, F>) -> &T {
+            this.cell.call_once(|| match this.init.take() {
+                Some(f) => f(),
+                None => panic!("Lazy instance has previously been poisoned"),
+            })
+        }
+    }
+
+    impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {
+        type Target = T;
+        fn deref(&self) -> &T {
+            Lazy::force(self)
+        }
+    }
+
+    impl<T: Default> Default for Lazy<T> {
+        /// Creates a new lazy value using `Default` as the initializing function.
+        fn default() -> Lazy<T> {
+            Lazy::new(T::default)
+        }
+    }
+}

tracing-core/src/lazy_static/LICENSE

@@ -1,26 +0,0 @@
-
-Copyright (c) 2010 The Rust Project Developers
-
-Permission is hereby granted, free of charge, to any
-person obtaining a copy of this software and associated
-documentation files (the "Software"), to deal in the
-Software without restriction, including without
-limitation the rights to use, copy, modify, merge,
-publish, distribute, sublicense, and/or sell copies of
-the Software, and to permit persons to whom the Software
-is furnished to do so, subject to the following
-conditions:
-
-The above copyright notice and this permission notice
-shall be included in all copies or substantial portions
-of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
-ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
-TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
-PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
-SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
-CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
-OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
-IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
-DEALINGS IN THE SOFTWARE.

tracing-core/src/lazy_static/core_lazy.rs

@@ -1,30 +0,0 @@
-// Copyright 2016 lazy-static.rs Developers
-//
-// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
-// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
-// http://opensource.org/licenses/MIT>, at your option. This file may not be
-// copied, modified, or distributed except according to those terms.
-
-use crate::spin::Once;
-
-pub(crate) struct Lazy<T: Sync>(Once<T>);
-
-impl<T: Sync> Lazy<T> {
-    pub(crate) const INIT: Self = Lazy(Once::INIT);
-
-    #[inline(always)]
-    pub(crate) fn get<F>(&'static self, builder: F) -> &T
-    where
-        F: FnOnce() -> T,
-    {
-        self.0.call_once(builder)
-    }
-}
-
-#[macro_export]
-#[doc(hidden)]
-macro_rules! __lazy_static_create {
-    ($NAME:ident, $T:ty) => {
-        static $NAME: $crate::lazy_static::lazy::Lazy<$T> = $crate::lazy_static::lazy::Lazy::INIT;
-    };
-}

tracing-core/src/lazy_static/mod.rs

@@ -1,89 +0,0 @@
-// Copyright 2016 lazy-static.rs Developers
-//
-// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
-// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
-// http://opensource.org/licenses/MIT>, at your option. This file may not be
-// copied, modified, or distributed except according to those terms.
-
-/*!
-A macro for declaring lazily evaluated statics.
-Using this macro, it is possible to have `static`s that require code to be
-executed at runtime in order to be initialized.
-This includes anything requiring heap allocations, like vectors or hash maps,
-as well as anything that requires function calls to be computed.
-*/
-
-#[path = "core_lazy.rs"]
-pub(crate) mod lazy;
-
-#[doc(hidden)]
-pub(crate) use core::ops::Deref as __Deref;
-
-#[macro_export]
-#[doc(hidden)]
-macro_rules! __lazy_static_internal {
-    // optional visibility restrictions are wrapped in `()` to allow for
-    // explicitly passing otherwise implicit information about private items
-    ($(#[$attr:meta])* ($($vis:tt)*) static ref $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
-        $crate::__lazy_static_internal!(@MAKE TY, $(#[$attr])*, ($($vis)*), $N);
-        $crate::__lazy_static_internal!(@TAIL, $N : $T = $e);
-        $crate::lazy_static!($($t)*);
-    };
-    (@TAIL, $N:ident : $T:ty = $e:expr) => {
-        impl $crate::lazy_static::__Deref for $N {
-            type Target = $T;
-            fn deref(&self) -> &$T {
-                #[inline(always)]
-                fn __static_ref_initialize() -> $T { $e }
-
-                #[inline(always)]
-                fn __stability() -> &'static $T {
-                    $crate::__lazy_static_create!(LAZY, $T);
-                    LAZY.get(__static_ref_initialize)
-                }
-                __stability()
-            }
-        }
-        impl $crate::lazy_static::LazyStatic for $N {
-            fn initialize(lazy: &Self) {
-                let _ = &**lazy;
-            }
-        }
-    };
-    // `vis` is wrapped in `()` to prevent parsing ambiguity
-    (@MAKE TY, $(#[$attr:meta])*, ($($vis:tt)*), $N:ident) => {
-        #[allow(missing_copy_implementations)]
-        #[allow(non_camel_case_types)]
-        #[allow(dead_code)]
-        $(#[$attr])*
-        $($vis)* struct $N {__private_field: ()}
-        #[doc(hidden)]
-        $($vis)* static $N: $N = $N {__private_field: ()};
-    };
-    () => ()
-}
-
-#[macro_export]
-#[doc(hidden)]
-macro_rules! lazy_static {
-    ($(#[$attr:meta])* static ref $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
-        // use `()` to explicitly forward the information about private items
-        $crate::__lazy_static_internal!($(#[$attr])* () static ref $N : $T = $e; $($t)*);
-    };
-    ($(#[$attr:meta])* pub static ref $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
-        $crate::__lazy_static_internal!($(#[$attr])* (pub) static ref $N : $T = $e; $($t)*);
-    };
-    ($(#[$attr:meta])* pub ($($vis:tt)+) static ref $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
-        $crate::__lazy_static_internal!($(#[$attr])* (pub ($($vis)+)) static ref $N : $T = $e; $($t)*);
-    };
-    () => ()
-}
-
-/// Support trait for enabling a few common operation on lazy static values.
-///
-/// This is implemented by each defined lazy static, and
-/// used by the free functions in this crate.
-pub(crate) trait LazyStatic {
-    #[doc(hidden)]
-    fn initialize(lazy: &Self);
-}

tracing-core/src/lib.rs

@@ -254,10 +254,7 @@ macro_rules! metadata {
     };
 }
 
-// Facade module: `no_std` uses spinlocks, `std` uses the mutexes in the standard library
-#[cfg(not(feature = "std"))]
-#[macro_use]
-mod lazy_static;
+pub(crate) mod lazy;
 
 // Trimmed-down vendored version of spin 0.5.2 (0387621)
 // Dependency of no_std lazy_static, not required in a std build

tracing-core/src/stdlib.rs

@@ -64,11 +64,11 @@ mod no_std {
         }
 
         impl<T> Mutex<T> {
-            pub(crate) fn new(data: T) -> Self {
-                Self {
-                    inner: crate::spin::Mutex::new(data),
-                }
-            }
+            // pub(crate) fn new(data: T) -> Self {
+            //     Self {
+            //         inner: crate::spin::Mutex::new(data),
+            //     }
+            // }
 
             pub(crate) fn lock(&self) -> Result<MutexGuard<'_, T>, ()> {
                 Ok(self.inner.lock())