pikchr: add update script

pkgs/by-name/pi/pikchr/package.nix

@@ -48,6 +48,8 @@ stdenv.mkDerivation {
 
   doCheck = true;
 
+  passthru.updateScript = ./update.sh;
+
   meta = {
     description = "PIC-like markup language for diagrams in technical documentation";
     homepage = "https://pikchr.org";

pkgs/by-name/pi/pikchr/update.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p common-updater-scripts jq gawk
+
+set -euo pipefail
+
+nixpkgs="$(git rev-parse --show-toplevel)"
+cd "$(dirname "${BASH_SOURCE[0]}")"
+
+# Build and run nix-prefetch-fossil from the local nixpkgs
+prefetch_fossil="$(nix-build "$nixpkgs" -A nix-prefetch-scripts --no-out-link 2>/dev/null)/bin/nix-prefetch-fossil"
+
+echo "Fetching latest pikchr revision..." >&2
+
+# Run nix-prefetch-fossil and capture output
+output=$("$prefetch_fossil" https://pikchr.org/home trunk 2>&1)
+
+# Extract JSON from output (it's at the end after the blank line)
+json_output=$(echo "$output" | gawk '/^{/{p=1} p')
+
+# Extract revision, hash, and date
+full_rev=$(echo "$json_output" | jq -r '.rev')
+new_rev="${full_rev:0:16}"  # Use 16-char prefix for consistency
+new_hash=$(echo "$json_output" | jq -r '.hash')
+commit_date=$(echo "$json_output" | jq -r '.date')
+
+# Fallback to current date if extraction fails
+if [ -z "$commit_date" ] || [ "$commit_date" = "null" ]; then
+    commit_date=$(date +%Y-%m-%d)
+fi
+new_version="0-unstable-$commit_date"
+
+echo "Updating pikchr to $new_version (rev $new_rev)" >&2
+
+# Use update-source-version from the nixpkgs root
+(
+    cd "$nixpkgs"
+    update-source-version pikchr "$new_version" "$new_hash" \
+        --file="pkgs/by-name/pi/pikchr/package.nix" \
+        --rev="$new_rev"
+)