Add script to automate Nix vendorHash updates (#235)

* Add script to automate Nix vendorHash updates

- Create update-nix-hash.sh to automate vendorHash calculation
- Update vendorHash (to be usedafter recent Go dependency changes)
- Script uses ed for OS agnostic in-place editing and extracts hash from nix output

Co-Authored-By: Claude <noreply@anthropic.com>

* Fix Test Nix Flake CI job

* Revert CI change - bd outputs help by default without 'help' arg

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Steve Yegge <stevey@sourcegraph.com>

default.nix

@@ -9,7 +9,7 @@ pkgs.buildGoModule {
   subPackages = [ "cmd/bd" ];
   doCheck = false;
   # Go module dependencies hash (computed via nix build)
-  vendorHash = "sha256-m/2e3OxM4Ci4KoyH+leEt09C/CpD9SRrwPd39/cZQ9E=";
+  vendorHash = "sha256-eUwVXAe9d/e3OWEav61W8lI0bf/IIQYUol8QUiQiBbo=";
 
   # Git is required for tests
   nativeBuildInputs = [ pkgs.git ];

scripts/update-nix-hash.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+set -e && cd "$(dirname "$0")/.."
+
+# Update the vendorHash in default.nix after Go dependency changes
+# Usage: ./scripts/update-nix-hash.sh
+
+echo "Getting correct vendorHash from nix..."
+
+# Set pkgs.lib.fakeHash to force nix to output the correct one
+printf ',s|vendorHash = ".*";|vendorHash = pkgs.lib.fakeHash;|\nw\n' | ed -s default.nix
+
+# Extract correct hash from nix build error
+CORRECT_HASH=$(nix build --no-link 2>&1 | grep "got:" | awk '{print $2}')
+
+if [ -z "$CORRECT_HASH" ]; then
+    echo "Error: Could not get hash from nix build"
+    git restore default.nix
+    exit 1
+fi
+
+# Update with correct hash
+printf ',s|vendorHash = pkgs\.lib\.fakeHash;|vendorHash = "%s";|\nw\n' "$CORRECT_HASH" | ed -s default.nix
+
+echo "✓ Updated vendorHash to: $CORRECT_HASH"