feat: enable sccache for cargo-pgrx builds in GitHub Actions

Speed up rust builds by enabling sccache caching for cargo-pgrx builds in
GitHub Actions. We mount a persistent disk at /var/cache/sccache and
configure sccache to use it.

Author: jfroche

.github/actions/nix-install-ephemeral/action.yml

@@ -5,6 +5,10 @@ inputs:
     description: 'Whether to push build outputs to the Nix binary cache'
     required: false
     default: 'false'
+  enable-sccache-sandbox-path:
+    description: 'Whether to expose /var/cache/sccache in the Nix sandbox'
+    required: false
+    default: 'false'
   aws-region:
     description: 'AWS region for the Nix binary cache S3 bucket'
     required: false
@@ -48,4 +52,5 @@ runs:
           substituters = https://cache.nixos.org https://nix-postgres-artifacts.s3.amazonaws.com
           trusted-public-keys = nix-postgres-artifacts:dGZlQOvKcNEjvT7QEAJbcV6b6uk7VF/hWMjhYleiaLI= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
           ${{ inputs.push-to-cache == 'true' && 'post-build-hook = /etc/nix/upload-to-cache.sh' || '' }}
+          ${{ inputs.enable-sccache-sandbox-path == 'true' && 'sandbox-paths = /var/cache/sccache?' || '' }}
           max-jobs = 4

.github/workflows/nix-build.yml

@@ -36,11 +36,21 @@ jobs:
       - name: Checkout Repo
         if: ${{ matrix.attr != '' }}
         uses: actions/checkout@v4
+      - name: Mount sccache disk
+        if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
+        uses: useblacksmith/stickydisk@v1
+        with:
+          key: ${{ github.repository }}-sccache-${{ runner.os }}-${{ runner.arch }}
+          path: /var/cache/sccache
+      - name: Allow sccache cache write access
+        if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
+        run: sudo chmod 1777 /var/cache/sccache
       - name: Install nix (ephemeral)
         if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
         uses: ./.github/actions/nix-install-ephemeral
         with:
           push-to-cache: 'true'
+          enable-sccache-sandbox-path: 'true'
         env:
           DEV_AWS_ROLE: ${{ secrets.DEV_AWS_ROLE }}
           NIX_SIGN_SECRET_KEY: ${{ secrets.NIX_SIGN_SECRET_KEY }}
@@ -67,11 +77,21 @@ jobs:
       - name: Checkout Repo
         if: ${{ matrix.attr != '' }}
         uses: actions/checkout@v4
+      - name: Mount sccache disk
+        if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
+        uses: useblacksmith/stickydisk@v1
+        with:
+          key: ${{ github.repository }}-sccache-${{ runner.os }}-${{ runner.arch }}
+          path: /var/cache/sccache
+      - name: Allow sccache cache write access
+        if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
+        run: sudo chmod 1777 /var/cache/sccache
       - name: Install nix (ephemeral)
         if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
         uses: ./.github/actions/nix-install-ephemeral
         with:
           push-to-cache: 'true'
+          enable-sccache-sandbox-path: 'true'
         env:
           DEV_AWS_ROLE: ${{ secrets.DEV_AWS_ROLE }}
           NIX_SIGN_SECRET_KEY: ${{ secrets.NIX_SIGN_SECRET_KEY }}
@@ -144,10 +164,20 @@ jobs:
       - name: Checkout Repo
         if: ${{ matrix.attr != '' }}
         uses: actions/checkout@v4
+      - name: Mount sccache disk
+        if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
+        uses: useblacksmith/stickydisk@v1
+        with:
+          key: ${{ github.repository }}-sccache-${{ runner.os }}-${{ runner.arch }}
+          path: /var/cache/sccache
+      - name: Allow sccache cache write access
+        if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
+        run: sudo chmod 1777 /var/cache/sccache
       - name: Install nix
         if: ${{ matrix.attr != '' }}
         uses: ./.github/actions/nix-install-ephemeral
         with:
+          enable-sccache-sandbox-path: 'true'
           push-to-cache: 'true'
         env:
           DEV_AWS_ROLE: ${{ secrets.DEV_AWS_ROLE }}
@@ -172,10 +202,20 @@ jobs:
       - name: Checkout Repo
         if: ${{ matrix.attr != '' }}
         uses: actions/checkout@v4
+      - name: Mount sccache disk
+        if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
+        uses: useblacksmith/stickydisk@v1
+        with:
+          key: ${{ github.repository }}-sccache-${{ runner.os }}-${{ runner.arch }}
+          path: /var/cache/sccache
+      - name: Allow sccache cache write access
+        if: ${{ matrix.attr != '' && matrix.runs_on.group != 'self-hosted-runners-nix' }}
+        run: sudo chmod 1777 /var/cache/sccache
       - name: Install nix
         if: ${{ matrix.attr != '' }}
         uses: ./.github/actions/nix-install-ephemeral
         with:
+          enable-sccache-sandbox-path: 'true'
           push-to-cache: 'true'
         env:
           DEV_AWS_ROLE: ${{ secrets.DEV_AWS_ROLE }}

nix/cargo-pgrx/buildPgrxExtension.nix

@@ -35,6 +35,7 @@
   darwin,
   writeShellScriptBin,
   defaultBindgenHook,
+  sccache,
 }:
 
 # The idea behind: Use it mostly like rustPlatform.buildRustPackage and so
@@ -56,7 +57,7 @@
   postgresql,
   # enable override to generate bindings using bindgenHook.
   # Some older versions of cargo-pgrx use a bindgenHook that is not compatible with the
-  # current clang version present in stdenv
+  # current clang version present in stdenv
   bindgenHook ? defaultBindgenHook,
   # cargo-pgrx calls rustfmt on generated bindings, this is not strictly necessary, so we avoid the
   # dependency here. Set to false and provide rustfmt in nativeBuildInputs, if you need it, e.g.
@@ -135,12 +136,22 @@ let
         postgresql
         pkg-config
         bindgenHook
+        sccache
       ]
       ++ lib.optionals useFakeRustfmt [ fakeRustfmt ];
 
     buildPhase = ''
       runHook preBuild
 
+      if [[ -d "/var/cache/sccache" && -w "/var/cache/sccache" ]]; then
+        echo "sccache: cache directory available, enabling"
+        export RUSTC_WRAPPER="${sccache}/bin/sccache"
+        export SCCACHE_DIR="/var/cache/sccache"
+        export SCCACHE_CACHE_SIZE="100G"
+      else
+        echo "sccache: cache directory not available, skipping"
+      fi
+
       echo "Executing cargo-pgrx buildPhase"
       ${preBuildAndTest}
       ${maybeEnterBuildAndTestSubdir}