push sheeet

pkgs/build-support/plugins.nix

@@ -0,0 +1,30 @@
+{ lib }:
+# helper functions for packaging programs with plugin systems
+{
+
+  /*
+    Takes a list of expected plugin names
+    and compares it to the found plugins given in the file,
+    one plugin per line.
+    If the lists differ, the build fails with a nice message.
+
+    This is helpful to ensure maintainers don’t miss
+    the addition or removal of a plugin.
+  */
+  diffPlugins = expectedPlugins: foundPluginsFilePath: ''
+    # sort both lists first
+    plugins_expected=$(mktemp)
+    (${lib.concatMapStrings (s: "echo \"${s}\";") expectedPlugins}) \
+      | sort -u > "$plugins_expected"
+    plugins_found=$(mktemp)
+    sort -u "${foundPluginsFilePath}" > "$plugins_found"
+
+    if ! mismatches="$(diff -y "$plugins_expected" "$plugins_found")"; then
+      echo "The the list of expected plugins (left side) doesn't match" \
+          "the list of plugins we found (right side):" >&2
+      echo "$mismatches" >&2
+      exit 1
+    fi
+  '';
+
+}