Upgrade to rustc 2026-01-04

.devcontainer/rust/devcontainer-feature.json

@@ -5,7 +5,7 @@
   "dependsOn": {
     "ghcr.io/devcontainers/features/rust:1": {
       // this should match the `rust-toolchain.toml`
-      "version": "nightly-2025-09-21",
+      "version": "nightly-2026-01-04",
       "profile": "minimal",
       "components": "rustfmt,clippy,rust-analyzer"
     }

Cargo.toml

@@ -484,4 +484,7 @@ webbrowser = "1.0.6"
 [patch.crates-io]
 bincode = { git = "https://github.com/bgw/bincode.git", branch = "bgw/patches" }
 virtue = { git = "https://github.com/bgw/virtue.git", branch = "bgw/fix-generic-default-parsing" }
+# We have to very frequently bump the swc major version of mdxjs-rs
 mdxjs = { git = "https://github.com/vercel-labs/mdxjs-rs-turbopack.git", branch = "turbopack" }
+# Doesn't compile on recent nightly versions because of https://github.com/Michael-F-Bryan/include_dir/pull/117
+include_dir = { git = "https://github.com/vercel-labs/include_dir", branch = "turbopack" }

rust-toolchain.toml

@@ -1,5 +1,5 @@
 # if you update this, also update `.devcontainer/rust/devcontainer-feature.json`
 [toolchain]
-channel = "nightly-2025-10-27"
+channel = "nightly-2026-01-04"
 components = ["rustfmt", "clippy", "rust-analyzer"]
 profile = "minimal"

turbopack/crates/turbo-tasks-fs/Cargo.toml

@@ -32,7 +32,7 @@ concurrent-queue = { workspace = true }
 dashmap = { workspace = true }
 dunce = { workspace = true }
 futures = { workspace = true }
-include_dir = { version = "0.7.2", features = ["nightly"] }
+include_dir = { version = "0.7.3", features = ["nightly"] }
 indexmap = { workspace = true }
 jsonc-parser = { version = "0.26.3", features = ["serde"] }
 mime = { workspace = true }

turbopack/crates/turbo-tasks-fs/src/lib.rs

@@ -8,6 +8,7 @@
 // stdlib into our source tree
 #![feature(normalize_lexically)]
 #![feature(trivial_bounds)]
+#![feature(downcast_unchecked)]
 // Junction points are used on Windows. We could use a third-party crate for this if the junction
 // API isn't eventually stabilized.
 #![cfg_attr(windows, feature(junction_point))]

turbopack/crates/turbo-tasks/src/effect.rs

@@ -298,7 +298,7 @@ impl ApplyEffectsContext {
                 .get_mut(&TypeId::of::<T>())
                 .map(|value| {
                     // Safety: the map is keyed by TypeId
-                    unsafe { value.downcast_mut_unchecked() }
+                    unsafe { value.downcast_unchecked_mut() }
                 })
                 .map(f)
         })
@@ -315,7 +315,7 @@ impl ApplyEffectsContext {
             });
             f(
                 // Safety: the map is keyed by TypeId
-                unsafe { value.downcast_mut_unchecked() },
+                unsafe { value.downcast_unchecked_mut() },
             )
         })
     }

turbopack/crates/turbo-tasks/src/lib.rs

@@ -37,7 +37,6 @@
 #![feature(downcast_unchecked)]
 #![feature(ptr_metadata)]
 #![feature(sync_unsafe_cell)]
-#![feature(vec_into_raw_parts)]
 #![feature(async_fn_traits)]
 
 pub mod backend;

turbopack/crates/turbo-tasks/src/scope.rs

@@ -209,13 +209,16 @@ impl<'scope, 'env: 'scope, R: Send + 'env> Scope<'scope, 'env, R> {
             *result_cell.lock() = Some(result);
         });
         let f: *mut (dyn FnOnce() + Send + 'scope) = Box::into_raw(f);
+
         // SAFETY: Scope ensures (e. g. in Drop) that spawned tasks is awaited before the
         // lifetime `'env` ends.
-        #[allow(
-            clippy::unnecessary_cast,
-            reason = "Clippy thinks this is unnecessary, but it actually changes the lifetime"
-        )]
-        let f = f as *mut (dyn FnOnce() + Send + 'static);
+        let f = unsafe {
+            std::mem::transmute::<
+                *mut (dyn FnOnce() + Send + 'scope),
+                *mut (dyn FnOnce() + Send + 'static),
+            >(f)
+        };
+
         // SAFETY: We just called `Box::into_raw`.
         let f = unsafe { Box::from_raw(f) };