feat(actions): setup-rust-toolchain-from-file

.github/actions/README.md

@@ -28,6 +28,9 @@ the action name to view its documentation:
 - **[setup-dioxus](setup-dioxus/README.md)** - Install Dioxus CLI
 - **[setup-ekg-cli](setup-ekg-cli/README.md)** - Build EKG CLI
   (project-specific)
+- **[setup-rust-toolchain-from-file](setup-rust-toolchain-from-file/README.md)** -
+  Read the channel from `rust-toolchain.toml` and install the toolchain,
+  optionally adding the Swatinem shared rust-cache
 
 ### Version Management Actions
 

.github/actions/setup-rust-toolchain-from-file/README.md

@@ -0,0 +1,102 @@
+# setup-rust-toolchain-from-file
+
+Read the Rust channel from `rust-toolchain.toml` and install that exact
+toolchain, optionally adding the
+[`Swatinem/rust-cache`](https://github.com/Swatinem/rust-cache) shared
+target cache. Collapses the boilerplate every Rust CI job otherwise
+repeats — sed-parse the channel out of `rust-toolchain.toml`, call
+`actions-rust-lang/setup-rust-toolchain`, then call `rust-cache` — into
+a single composite action.
+
+## Usage
+
+```yaml
+- name: Checkout code
+  uses: actions/checkout@v6
+
+- name: Set up Rust toolchain
+  uses: dataroadinc/github-actions/.github/actions/setup-rust-toolchain-from-file@main
+  with:
+    components: clippy,rustfmt
+    cache-shared-key: my-repo-ci
+```
+
+For lint-only or format-only jobs that do not build, skip the cache:
+
+```yaml
+- name: Set up Rust toolchain
+  uses: dataroadinc/github-actions/.github/actions/setup-rust-toolchain-from-file@main
+  with:
+    components: rustfmt
+    cache: "false"
+```
+
+## Inputs
+
+| Input | Default | Description |
+| ----- | ------- | ----------- |
+| `path` | `rust-toolchain.toml` | Path (relative to checkout root) of the rust-toolchain file to read. |
+| `components` | `""` | Comma-separated rustup components forwarded to `actions-rust-lang/setup-rust-toolchain`. |
+| `cache` | `"true"` | When `"true"`, invokes `Swatinem/rust-cache`. Set to `"false"` for jobs that do not compile. |
+| `cache-shared-key` | `""` | `shared-key` passed to `Swatinem/rust-cache`. Multiple jobs in the same workflow should share a value. |
+
+## Outputs
+
+| Output | Description |
+| ------ | ----------- |
+| `toolchain` | The toolchain channel resolved from the file (e.g. `nightly-2025-08-29`). |
+
+## What it does
+
+1. Resolves the channel from `rust-toolchain.toml` (one `channel = "..."` line under `[toolchain]`).
+2. Calls
+   [`actions-rust-lang/setup-rust-toolchain@v1`](https://github.com/actions-rust-lang/setup-rust-toolchain)
+   with that channel and the requested components.
+3. Optionally calls
+   [`Swatinem/rust-cache@v2`](https://github.com/Swatinem/rust-cache)
+   with the supplied shared key.
+
+## Why a composite action
+
+Without this action, every Rust job in a workflow repeats the same
+three blocks (≈30 lines each):
+
+```yaml
+- name: Resolve Rust toolchain
+  id: rust_toolchain
+  run: |
+    VERSION="$(sed -n 's/^channel = "\([^"]*\)"/\1/p' rust-toolchain.toml | head -n 1)"
+    if [ -z "$VERSION" ]; then
+      echo "Failed to resolve Rust toolchain channel" >&2
+      exit 1
+    fi
+    echo "version=$VERSION" >> "$GITHUB_OUTPUT"
+
+- name: Set up Rust toolchain
+  uses: actions-rust-lang/setup-rust-toolchain@v1
+  with:
+    toolchain: ${{ steps.rust_toolchain.outputs.version }}
+    components: clippy,rustfmt
+
+- name: Cache Rust artifacts
+  uses: Swatinem/rust-cache@v2
+  with:
+    shared-key: my-repo-ci
+```
+
+A workflow with 8 Rust jobs ends up carrying ≈240 lines of boilerplate
+that drift independently and have no single source of truth. This
+action makes that block one `uses:` line per job.
+
+## Failure modes
+
+- **Missing file**: `error file=<path>::rust-toolchain file not found`.
+- **No `channel` line**: `error file=<path>::no channel = "..." line found in <file>`.
+
+Both surface via `::error` annotations that GitHub renders inline on
+the PR diff.
+
+## Versioning
+
+Use `@main` while iterating. After this and sibling actions stabilise,
+the repository bumps to `v1.0.0` and consumers should pin to `@v1`.

.github/actions/setup-rust-toolchain-from-file/action.yml

@@ -0,0 +1,78 @@
+name: Setup Rust toolchain from file
+description: >-
+  Read the channel from rust-toolchain.toml and install that exact toolchain,
+  optionally adding the Swatinem shared rust-cache. Collapses the ~30 lines of
+  boilerplate each Rust CI job otherwise repeats (sed-parse the channel, call
+  setup-rust-toolchain, call rust-cache) into a single composite action.
+
+inputs:
+  path:
+    description: >-
+      Path (relative to the checkout root) of the rust-toolchain file to read.
+      Defaults to rust-toolchain.toml at the repository root.
+    required: false
+    default: rust-toolchain.toml
+  components:
+    description: >-
+      Comma-separated list of rustup components to install alongside the
+      toolchain. Forwarded verbatim to actions-rust-lang/setup-rust-toolchain.
+      Leave empty to install only the toolchain.
+    required: false
+    default: ""
+  cache:
+    description: >-
+      Whether to invoke Swatinem/rust-cache after toolchain setup.
+      `true` (default) enables the cache; `false` skips it for jobs that do not
+      build (for example, lint-only or formatting jobs).
+    required: false
+    default: "true"
+  cache-shared-key:
+    description: >-
+      Shared cache key passed to Swatinem/rust-cache as `shared-key`.
+      Multiple jobs in the same workflow should set the same value so they
+      share a target/ cache. Ignored when `cache` is `false`.
+    required: false
+    default: ""
+
+outputs:
+  toolchain:
+    description: >-
+      The toolchain channel resolved from the rust-toolchain file.
+      Example: `nightly-2025-08-29`.
+    value: ${{ steps.resolve.outputs.toolchain }}
+
+runs:
+  using: composite
+  steps:
+    - name: Resolve Rust toolchain channel
+      id: resolve
+      shell: bash
+      run: |
+        set -e
+        file='${{ inputs.path }}'
+        if [ ! -f "$file" ]; then
+          echo "::error file=$file::rust-toolchain file not found"
+          exit 1
+        fi
+        # `rust-toolchain.toml` always has exactly one `channel = "..."` line
+        # under `[toolchain]`. We tolerate but defensively ignore additional
+        # matches by taking only the first via `head -n 1`.
+        channel="$(sed -n 's/^channel = "\([^"]*\)"/\1/p' "$file" | head -n 1)"
+        if [ -z "$channel" ]; then
+          echo "::error file=$file::no `channel = \"...\"` line found in $file" >&2
+          exit 1
+        fi
+        echo "toolchain=$channel" >> "$GITHUB_OUTPUT"
+        echo "Resolved Rust toolchain channel: $channel"
+
+    - name: Set up Rust toolchain
+      uses: actions-rust-lang/setup-rust-toolchain@v1
+      with:
+        toolchain: ${{ steps.resolve.outputs.toolchain }}
+        components: ${{ inputs.components }}
+
+    - name: Cache Rust artifacts
+      if: ${{ inputs.cache == 'true' }}
+      uses: Swatinem/rust-cache@v2
+      with:
+        shared-key: ${{ inputs.cache-shared-key }}