Fix stacked borrows violation in get2_unchecked_mut

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Install Rust
         run: rustup update stable
       - name: Install cargo-hack
@@ -34,7 +34,7 @@ jobs:
           - 1.31.0
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Install Rust
         run: rustup update ${{ matrix.rust }} && rustup default ${{ matrix.rust }}
       - run: cargo build
@@ -47,32 +47,43 @@ jobs:
           - 1.36.0
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Install Rust
         run: rustup update ${{ matrix.rust }} && rustup default ${{ matrix.rust }}
       - run: rustup target add thumbv7m-none-eabi
       - run: cargo build --no-default-features --target thumbv7m-none-eabi
 
+  miri:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Rust
+        run: rustup toolchain install nightly --component miri && rustup default nightly
+      - run: cargo miri test --workspace --all-features
+        env:
+          MIRIFLAGS: -Zmiri-check-number-validity -Zmiri-symbolic-alignment-check -Zmiri-tag-raw-pointers -Zmiri-disable-isolation
+          RUSTFLAGS: ${{ env.RUSTFLAGS }} -Z randomize-layout
+
   clippy:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Install Rust
         run: rustup update stable
       - run: cargo clippy --all-features
 
   fmt:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Install Rust
         run: rustup update stable
       - run: cargo fmt --all -- --check
 
   docs:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Install Rust
         run: rustup update nightly && rustup default nightly
       - run: cargo doc --no-deps --all-features

.github/workflows/release.yml

@@ -14,7 +14,7 @@ jobs:
     if: github.repository_owner == 'tokio-rs'
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Install Rust
         run: rustup update stable
       - run: cargo package

src/lib.rs

@@ -830,8 +830,10 @@ impl<T> Slab<T> {
     /// assert_eq!(slab[key2], 1);
     /// ```
     pub unsafe fn get2_unchecked_mut(&mut self, key1: usize, key2: usize) -> (&mut T, &mut T) {
-        let ptr1 = self.entries.get_unchecked_mut(key1) as *mut Entry<T>;
-        let ptr2 = self.entries.get_unchecked_mut(key2) as *mut Entry<T>;
+        debug_assert_ne!(key1, key2);
+        let ptr = self.entries.as_mut_ptr();
+        let ptr1 = ptr.add(key1);
+        let ptr2 = ptr.add(key2);
         match (&mut *ptr1, &mut *ptr2) {
             (&mut Entry::Occupied(ref mut val1), &mut Entry::Occupied(ref mut val2)) => {
                 (val1, val2)