ci/website: simplify docs build

- Drop branch-specific composite action, target branches via flakeref
- Avoid flake-compat, using `nix build --impure` and `getEnv`

.github/actions/build-docs/action.yml

@@ -1,78 +0,0 @@
-name: Build Documentation
-description: >
-  Build Nixvim's documentation and upload an artifact.
-
-  Requires having nix installed and Nixvim checked out.
-
-inputs:
-  sub-path:
-    description: Move the docs to this sub-directory path.
-    default: ""
-  base-href:
-    description: The base href to use when building the docs.
-    default: /nixvim/
-  versions:
-    description: JSON array describing Nixvim versions to be linked in the docs.
-    default: "[]"
-  artifact-name:
-    description: Artifact name. Set to "" to prevent uploading.
-    default: docs
-  retention-days:
-    description: Days after which artifact will expire.
-    default: "1"
-
-outputs:
-  artifact-id:
-    description: The ID of the artifact that was uploaded.
-    value: ${{ steps.upload.outputs.artifact-id }}
-
-runs:
-  using: "composite"
-  steps:
-    - name: Create temp directory
-      id: out-dir
-      shell: bash
-      run: |
-        dir=$(mktemp -d)
-        {
-          echo "dir=$dir"
-          echo "out=$dir/out"
-        } >> "$GITHUB_OUTPUT"
-
-    - name: nix-build
-      shell: bash
-      env:
-        out: ${{ steps.out-dir.outputs.out }}
-        subPath: ${{ inputs.sub-path }}
-        baseHref: ${{ inputs.base-href }}
-        versions: ${{ inputs.versions }}
-      run: |
-        nix-build \
-            --out-link "$out/$subPath" \
-            --argstr baseHref "$baseHref" \
-            --argstr versionsJson "$versions" \
-            --expr '
-              {
-                baseHref,
-                versionsJson,
-                system ? builtins.currentSystem,
-              }:
-              let
-                # Import flake using flake-compat
-                flake = import ./.;
-                inherit (flake.outputs.packages.${system}) docs;
-              in
-              docs.override {
-                inherit baseHref;
-                availableVersions = builtins.fromJSON versionsJson;
-              }
-            '
-
-    - name: Upload artifact
-      id: upload
-      if: inputs.artifact-name
-      uses: actions/upload-pages-artifact@v5
-      with:
-        path: ${{ steps.out-dir.outputs.out }}
-        name: ${{ inputs.artifact-name }}
-        retention-days: ${{ inputs.retention-days }}

.github/workflows/website.yml

@@ -96,19 +96,23 @@ jobs:
           name: nix-community
           authToken: ${{ secrets.CACHIX_AUTH_TOKEN }}
 
-      - name: Checkout
-        uses: actions/checkout@v6
-        with:
-          ref: ${{ matrix.ref }}
-
-        # Uses the build-docs action from the checked-out nixvim branch
+      # Build the `docs` flake output from the corresponding branch
+      # Uses --impure to enable `getEnv`
       - name: Build docs
-        uses: ./.github/actions/build-docs
+        env:
+          ref: ${{ matrix.ref }}
+          outLink: build/${{ matrix.sub-path }}
+          NIXVIM_DOCS_BASE_HREF: ${{ matrix.base-href }}
+          NIXVIM_DOCS_AVAILABLE_VERSIONS: ${{ needs.prepare.outputs.versions }}
+        run: |
+          nix build "github:$GITHUB_REPOSITORY/$ref#docs" --impure --out-link "$outLink"
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v5
         with:
-          artifact-name: ${{ matrix.name }}-docs
-          sub-path: ${{ matrix.sub-path }}
-          base-href: ${{ matrix.base-href }}
-          versions: ${{ needs.prepare.outputs.versions }}
+          path: build
+          name: ${{ matrix.name }}-docs
+          retention-days: 1
 
   combine:
     name: Combine builds

docs/mdbook/default.nix

@@ -1,4 +1,5 @@
 # NOTE: to use defaults from the environment, you must build with --impure
+# This is used in CI to inject impure baseHref and availableVersions values
 {
   pkgs,
   callPackage,