From 629ace010391f2e720f8f3b0133951514f003106 Mon Sep 17 00:00:00 2001
From: Wolfgang Walther <walther@technowledgy.de>
Date: Wed, 7 Feb 2024 21:52:38 +0100
Subject: [PATCH] ci: Replace actions cache for macos build job with smart
 cachix lookup

---
 .github/workflows/build.yaml | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index 3816dc6f5..3ba7b6d88 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -67,10 +67,19 @@ jobs:
         uses: ./.github/actions/setup-nix
         with:
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+      - name: Install gnu sed
+        run: brew install gnu-sed
 
       - name: Build everything
         run: |
-          nix-build
+          # The --dry-run will give us a list of derivations to download from cachix and
+          # derivations to build. We only take those that would have to be built and then build
+          # those explicitly. This has the advantage that pure verification will not include
+          # a download anymore, making it much faster. If something needs to be built, only
+          # the dependencies required to do so will be downloaded, but not everything.
+          nix-build --dry-run 2>&1 \
+            | gsed -e '1,/derivations will be built:$/d' -e '/paths will be fetched/Q' \
+            | xargs nix-build
 
 
   stack: