feat: opt in to caching mise rust toolchains

.github/workflows/test.yml

@@ -128,6 +128,32 @@ jobs:
       - run: which jq
       - run: jq --version
 
+  rust_cache_setup:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+      - name: Setup mise with Rust cache paths
+        uses: ./
+        with:
+          install: false
+          cache_save: false
+          cache_key: "rust-cache-setup-${{ github.run_id }}"
+          cache_rust: true
+      - name: Check Rust cache paths
+        run: |
+          if [ -n "${MISE_DATA_DIR:-}" ]; then
+            mise_data_dir="$MISE_DATA_DIR"
+          elif [ -n "${XDG_DATA_HOME:-}" ]; then
+            mise_data_dir="$XDG_DATA_HOME/mise"
+          else
+            mise_data_dir="$HOME/.local/share/mise"
+          fi
+
+          test "$MISE_RUSTUP_HOME" = "$mise_data_dir/rustup"
+          test "$MISE_CARGO_HOME" = "$mise_data_dir/cargo"
+          test -d "$MISE_RUSTUP_HOME"
+          test -d "$MISE_CARGO_HOME"
+
   fetch_from_github:
     runs-on: ubuntu-latest
     steps:
@@ -153,6 +179,7 @@ jobs:
       - specific_version
       - checksum_failure
       - custom_cache_key
+      - rust_cache_setup
       - fetch_from_github
     runs-on: ubuntu-latest
     timeout-minutes: 1

README.md

@@ -20,6 +20,7 @@ jobs:
           install: true # [default: true] run `mise install`
           install_args: "bun" # [default: ""] additional arguments to `mise install`
           cache: true # [default: true] cache mise using GitHub's cache
+          cache_rust: false # [default: false] also cache Rust toolchains installed by mise
           experimental: true # [default: false] enable experimental features
           log_level: debug # [default: info] log level
           # automatically write this .tool-versions file
@@ -72,6 +73,7 @@ Available template variables:
 - `{{file_hash}}` - Hash of all mise configuration files
 - `{{mise_env}}` - The MISE_ENV environment variable value
 - `{{install_args_hash}}` - SHA256 hash of the sorted tools from install args
+- `{{cache_rust}}` - Whether the Rust toolchain cache integration is enabled
 - `{{default}}` - The processed default cache key (useful for extending)
 
 Conditional logic is also supported using Handlebars syntax like `{{#if version}}...{{/if}}`.
@@ -94,6 +96,38 @@ You can also extend the default cache key:
 
 This gives you full control over cache invalidation based on the specific aspects that matter to your workflow.
 
+### Rust Toolchain Cache
+
+By default, mise-action only caches mise's data directory. Rust is different from most mise tools because mise delegates Rust installation to rustup, which stores toolchains in `RUSTUP_HOME` and cargo/rustup proxy binaries in `CARGO_HOME/bin`. That state may live outside the mise data directory, so a restored mise cache can otherwise make `mise install` think Rust is present while components such as `rustfmt` or `clippy` are missing.
+
+If mise is responsible for installing Rust in your workflow, opt in to Rust toolchain caching:
+
+```yaml
+- uses: jdx/mise-action@v4
+  with:
+    cache_rust: true
+```
+
+When enabled, the action exports `MISE_RUSTUP_HOME` and `MISE_CARGO_HOME` to directories under the mise data dir before cache restore and install. Those directories are then restored and saved with the normal mise cache. With the default `env: true`, mise may also export `RUSTUP_HOME` and `CARGO_HOME` for later workflow steps so plain `cargo`, `rustfmt`, and `clippy` commands use the same cached homes. The default cache key includes a `-rust` segment when this option is enabled so Rust-enabled caches do not reuse older mise-only caches. If you override `cache_key`, include `{{cache_rust}}` or otherwise invalidate that key when enabling this option.
+
+This cache is intended for the Rust toolchain state that mise needs to restore: rustup toolchains and metadata in `RUSTUP_HOME`, plus cargo/rustup proxy binaries and Cargo-installed tool metadata in `CARGO_HOME`. `CARGO_HOME` can also contain registry and git dependency caches, but the mise-action cache key is based on mise configuration, not `Cargo.lock`, and mise-action saves before later workflow build steps run. Do not use `cache_rust` as a replacement for a Cargo dependency or `target` cache.
+
+Use `cache_rust` with `Swatinem/rust-cache` when mise installs Rust and you want rust-cache to manage Cargo registry, git dependency, and `target` build artifact caching:
+
+```yaml
+- uses: jdx/mise-action@v4
+  with:
+    cache_rust: true
+
+- uses: Swatinem/rust-cache@v2
+  with:
+    # Let mise-action own rustup/cargo proxy binaries and Cargo tools installed by mise.
+    # Remove this line if you want rust-cache to cache Cargo binaries installed later in the job.
+    cache-bin: "false"
+```
+
+Put `Swatinem/rust-cache` after mise-action so it sees the Rust version and `CARGO_HOME` exported by mise. Leave `cache_rust` as `false` when Rust is installed by another action such as `rustup` or `actions-rust-lang/setup-rust-toolchain`, and you use mise only for non-Rust tools.
+
 ## GitHub API Rate Limits
 
 When installing tools hosted on GitHub (like `gh`, `node`, `bun`, etc.), mise needs to make API calls to GitHub's releases API. Without authentication, these calls are subject to GitHub's rate limit of 60 requests per hour, which can cause installation failures.

action.yml

@@ -50,8 +50,31 @@ inputs:
     description: |
       Override the complete cache key (ignores all other cache key options).
       Supports template variables: {{version}}, {{cache_key_prefix}}, {{platform}}, {{file_hash}}, 
-      {{mise_env}}, {{install_args_hash}}, {{default}}, {{env.VAR_NAME}} for environment variables, 
+      {{mise_env}}, {{install_args_hash}}, {{cache_rust}}, {{default}}, {{env.VAR_NAME}} for environment variables,
       and conditional logic like {{#if version}}...{{/if}}
+  cache_rust:
+    required: false
+    default: "false"
+    description: |
+      Opt in to caching Rust toolchains installed by mise's Rust backend.
+
+      When `true`, the action exports `MISE_RUSTUP_HOME` and `MISE_CARGO_HOME`
+      to directories under the mise data dir before restoring the mise cache.
+      This lets the existing mise cache save/restore rustup toolchains,
+      rustup metadata, and cargo/rustup proxy binaries that mise needs for
+      Rust components such as rustfmt and clippy.
+
+      With the default `env: true`, mise may also export `RUSTUP_HOME` and
+      `CARGO_HOME` for later workflow steps so plain `cargo`, `rustfmt`, and
+      `clippy` commands use the same cached homes.
+
+      This is a Rust toolchain/proxy cache, not a Cargo dependency or build
+      cache. Use it with Swatinem/rust-cache when mise installs Rust and
+      rust-cache should own Cargo registry, git dependency, and target caches.
+
+      Default `false` keeps existing workflows unchanged, especially jobs that
+      install Rust with rustup, setup-rust-toolchain, or another standard Rust
+      action and use mise only for other tools.
   experimental:
     required: false
     default: "false"