Migrate the wasmtime-slab crate to no_std (#8483)

Nothing major here other than renaming crate imports and such.

Author: alexcrichton

.github/workflows/main.yml

@@ -372,6 +372,9 @@ jobs:
     - run: cargo check -p wasmtime-asm-macros
       env:
         CARGO_BUILD_TARGET: x86_64-unknown-none
+    - run: cargo check -p wasmtime-slab
+      env:
+        CARGO_BUILD_TARGET: x86_64-unknown-none
 
     # Check that wasmtime-runtime compiles with panic=abort since there's some
     # #[cfg] for specifically panic=abort there.

crates/slab/src/lib.rs

@@ -120,18 +120,23 @@
 //! }
 //! ```
 
+#![no_std]
 #![forbid(unsafe_code)]
 #![deny(missing_docs, missing_debug_implementations)]
 
-use std::num::NonZeroU32;
+extern crate alloc;
+
+use alloc::vec::Vec;
+use core::fmt;
+use core::num::NonZeroU32;
 
 /// An identifier for an allocated value inside a `slab`.
 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 #[repr(transparent)]
 pub struct Id(EntryIndex);
 
-impl std::fmt::Debug for Id {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl fmt::Debug for Id {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_tuple("Id").field(&self.0.index()).finish()
     }
 }
@@ -167,11 +172,11 @@ pub struct Slab<T> {
     len: u32,
 }
 
-impl<T> std::fmt::Debug for Slab<T>
+impl<T> fmt::Debug for Slab<T>
 where
-    T: std::fmt::Debug,
+    T: fmt::Debug,
 {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_map().entries(self.iter()).finish()
     }
 }
@@ -218,7 +223,7 @@ impl<T> Default for Slab<T> {
     }
 }
 
-impl<T> std::ops::Index<Id> for Slab<T> {
+impl<T> core::ops::Index<Id> for Slab<T> {
     type Output = T;
 
     #[inline]
@@ -228,7 +233,7 @@ impl<T> std::ops::Index<Id> for Slab<T> {
     }
 }
 
-impl<T> std::ops::IndexMut<Id> for Slab<T> {
+impl<T> core::ops::IndexMut<Id> for Slab<T> {
     #[inline]
     fn index_mut(&mut self, id: Id) -> &mut Self::Output {
         self.get_mut(id)
@@ -282,7 +287,7 @@ impl<T> Slab<T> {
         // we add some amount of minimum additional capacity, since doubling
         // zero capacity isn't useful.
         const MIN_CAPACITY: usize = 16;
-        let additional = std::cmp::max(self.entries.capacity(), MIN_CAPACITY);
+        let additional = core::cmp::max(self.entries.capacity(), MIN_CAPACITY);
         self.reserve(additional);
     }
 
@@ -419,7 +424,7 @@ impl<T> Slab<T> {
     /// deallocate an arbitrary value.
     #[inline]
     pub fn dealloc(&mut self, id: Id) -> T {
-        let entry = std::mem::replace(
+        let entry = core::mem::replace(
             self.entries
                 .get_mut(id.0.index())
                 .expect("id from a different slab"),
@@ -428,7 +433,7 @@ impl<T> Slab<T> {
         match entry {
             Entry::Free { .. } => panic!("attempt to deallocate an entry that is already vacant"),
             Entry::Occupied(value) => {
-                let next_free = std::mem::replace(&mut self.free, Some(id.0));
+                let next_free = core::mem::replace(&mut self.free, Some(id.0));
                 self.entries[id.0.index()] = Entry::Free { next_free };
                 self.len -= 1;
                 value