build(nix): fix vendorHash + sandbox tests, automate hash upkeep

.github/workflows/nix-vendor-hash.yml

@@ -0,0 +1,54 @@
+name: Nix Vendor Hash
+
+# Keep flake.nix's buildGoModule vendorHash in sync after dependency-bearing
+# changes land on main. Only the go-modules fixed-output derivation is built
+# (no compile), so this is cheap. Pushes a fixup commit on drift.
+on:
+  push:
+    branches: [main]
+    paths:
+      - "go.mod"
+      - "go.sum"
+      - "go.work"
+      - "go.work.sum"
+      - "flake.nix"
+      - "flake.lock"
+      - "Makefile"
+      - "scripts/update-nix-vendor-hash.sh"
+      - ".github/workflows/nix-vendor-hash.yml"
+  workflow_dispatch:
+
+concurrency:
+  group: nix-vendor-hash-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: write
+
+jobs:
+  update:
+    name: update vendorHash
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@33c9ab3ef95cd57c164d9d6eb1f9a46338538d41 # main
+
+      - name: Update vendorHash
+        run: make nix-vendor-hash
+
+      - name: Commit updated vendorHash
+        run: |
+          set -euo pipefail
+          if git diff --quiet -- flake.nix; then
+            echo "vendorHash already current"
+            exit 0
+          fi
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git add flake.nix
+          git commit -m "chore(nix): update vendorHash"
+          git push origin "HEAD:${GITHUB_REF_NAME}"

Makefile

@@ -139,3 +139,8 @@ container-smoke: build
 clean:
 	rm -f strike $(COVER_PROFILE)
 	rm -rf web/dist web/node_modules
+
+# Recompute flake.nix vendorHash after go.mod/go.sum changes (CI also does this).
+.PHONY: nix-vendor-hash
+nix-vendor-hash:
+	./scripts/update-nix-vendor-hash.sh

flake.nix

@@ -18,12 +18,16 @@
 
           src = self;
           proxyVendor = true;
-          vendorHash = "sha256-ax5mSaryrwb+vSoqm6+Brl6RnA/2WZm+z+eEdxubhtQ=";
+          vendorHash = "sha256-kEJmV3MQt8k5KuXBjYoUy7+ZZrD3aTljpBziaRndJcU=";
 
           subPackages = [ "cmd/strike" ];
           preBuild = ''
             go generate ./internal/frontend/tui/app
           '';
+          # eval tests write under $HOME; the sandbox HOME (/homeless-shelter) is unwritable
+          preCheck = ''
+            export HOME="$(mktemp -d)"
+          '';
           ldflags = [
             "-s"
             "-w"

scripts/update-nix-vendor-hash.sh

@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+# Recompute flake.nix's buildGoModule vendorHash after go.mod/go.sum change.
+# Only realises the go-modules fixed-output derivation (.#default.goModules),
+# never compiles strike, so it's cheap. Prints the old -> new hash on change.
+set -euo pipefail
+
+repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+flake="${repo_root}/flake.nix"
+
+current_hash="$(
+  sed -nE 's/^[[:space:]]*vendorHash = "([^"]+)";[[:space:]]*$/\1/p' "${flake}" | head -n1
+)"
+
+if [[ -z "${current_hash}" ]]; then
+  echo "could not find quoted vendorHash in ${flake}" >&2
+  exit 1
+fi
+
+restore_current_hash() {
+  # NOTE: | delimiter because vendor hashes are base64 and may contain /,
+  # which would terminate an s/// substitution early.
+  perl -0pi -e "s|vendorHash = nixpkgs\\.lib\\.fakeHash;|vendorHash = \"${current_hash}\";|" "${flake}"
+}
+
+perl -0pi -e 's/vendorHash = "[^"]+";/vendorHash = nixpkgs.lib.fakeHash;/' "${flake}"
+trap restore_current_hash EXIT
+
+set +e
+build_output="$(cd "${repo_root}" && nix build .#default.goModules --no-link 2>&1)"
+build_status=$?
+set -e
+
+new_hash="$(
+  printf '%s\n' "${build_output}" |
+    sed -nE 's/^[[:space:]]*got:[[:space:]]*(sha256-[A-Za-z0-9+/=]+)[[:space:]]*$/\1/p' |
+    tail -n1
+)"
+
+if [[ -z "${new_hash}" ]]; then
+  printf '%s\n' "${build_output}" >&2
+  echo "nix did not report a replacement vendorHash" >&2
+  exit "${build_status}"
+fi
+
+trap - EXIT
+perl -0pi -e "s|vendorHash = nixpkgs\\.lib\\.fakeHash;|vendorHash = \"${new_hash}\";|" "${flake}"
+
+if [[ "${new_hash}" == "${current_hash}" ]]; then
+  echo "vendorHash already current: ${current_hash}"
+else
+  echo "updated vendorHash: ${current_hash} -> ${new_hash}"
+fi