Roll rustc_private toolchain to nightly-2025-01-01

Port refactoring, analysis, PDG, and instrumentation to the Rust 1.85-era
compiler with representative Rust 2024 rewrite and runtime coverage.
Retain workspace edition 2021, published MSRV 1.70, and separate generated
2021/2024 compiler pins.

Replace private compiler layout ownership with public callbacks, preserve
AST/HIR identity and transformed macro fragments, adapt binder and MIR
handling, and retain instrumentation permissions and unwind behavior.
Use equivalent exposed-provenance casts for generated edition 2021 code.

Validate against an isolated baseline: 270 workspace tests (all 234 prior
passing identities retained), 29 refactor shell cases, 148 translator
successes with the same two expected failures, and json-c/Lua end-to-end
workflows. Keep the existing PDG Miri skip and documented baseline limits.

Author: thedataking

.github/workflows/ci-c2rust-postprocess.yml

@@ -49,8 +49,10 @@ jobs:
 
       - name: Install Rust toolchains
         run: |
-          rustup toolchain install nightly-2023-04-15 \
+          rustup toolchain install nightly-2025-01-01 \
             --profile minimal --component rustfmt,rustc-dev
+          rustup toolchain install nightly-2023-04-15 \
+            --profile minimal --component rustfmt
 
       - name: Provision Debian Packages
         run: |

.github/workflows/ci.yml

@@ -60,8 +60,10 @@ jobs:
       # Run after `rust-cache` so that this is cached.
       - name: Install Rust toolchains
         run: |
-          rustup toolchain install nightly-2023-04-15 \
+          rustup toolchain install nightly-2025-01-01 \
             --profile minimal --component rustfmt,rustc-dev
+          rustup toolchain install nightly-2023-04-15 \
+            --profile minimal --component rustfmt
           rustup toolchain install nightly-2026-03-03 \
             --profile minimal --component rustfmt
       

.github/workflows/internal-testsuite.yml

@@ -65,8 +65,10 @@ jobs:
 
     - name: Install Rust toolchains
       run: |
-        rustup toolchain install nightly-2023-04-15 \
+        rustup toolchain install nightly-2025-01-01 \
           --profile minimal --component rustfmt,rustc-dev
+        rustup toolchain install nightly-2023-04-15 \
+          --profile minimal --component rustfmt
 
     - name: Provision Debian Packages
       run: |

LICENSE

@@ -14,3 +14,4 @@ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 Portions of C2Rust are derived from packages written by third parties. The following third party packages are included, and carry their own copyright notices and license terms:
 
 * c2rust-ast-printer. Dual-licensed under Apache 2.0 and MIT, see c2rust-ast-printer/COPYRIGHT for details.
+* c2rust-refactor's copied Rust AST walkers. MIT-licensed, see c2rust-refactor/src/ast_manip/fold/COPYRIGHT for details.

README.md

@@ -8,7 +8,7 @@
 
 [Latest Version]: https://img.shields.io/crates/v/c2rust.svg
 [crates.io]: https://crates.io/crates/c2rust
-[rustc Version]: https://img.shields.io/badge/rustc-nightly--2023--04--15-lightgrey.svg "rustc nightly-2023-04-15"
+[rustc Version]: https://img.shields.io/badge/rustc-nightly--2025--01--01-lightgrey.svg "rustc nightly-2025-01-01"
 
 <!-- ANCHOR: intro -->
 
@@ -161,12 +161,16 @@ You should also set `LLVM_CONFIG_PATH` accordingly if required as described abov
 
 `c2rust` and `c2rust-transpile` are installed by default and can be built on `stable` `rustc`.
 The other tools, such as `c2rust-refactor`, use `rustc` internal APIs, however,
-and are thus pinned to a specific `rustc` `nightly` version: `nightly-2023-04-15`.
+and are thus pinned to a specific `rustc` `nightly` version: `nightly-2025-01-01`.
 These are also not published to `crates.io`.
+The workspace remains edition 2021. Generated code uses separate toolchains:
+`nightly-2023-04-15` for edition 2021 and `nightly-2026-03-03` for edition 2024,
+which retain the SIMD and C variadic APIs emitted for each edition.
+The standalone programs under `tools/` use their own stable toolchain.
 To install these, these can be installed with `cargo` with the pinned nightly.  For example,
 
 ```sh
-cargo +nightly-2023-04-15 install --locked --git https://github.com/immunant/c2rust.git c2rust-refactor
+cargo +nightly-2025-01-01 install --locked --git https://github.com/immunant/c2rust.git c2rust-refactor
 ```
 
 However, we recommend installing them from a full checkout,