Add semantic unit file comparison

Author: dannote

lib/systemd/unit_file.ex

@@ -74,6 +74,28 @@ defmodule Systemd.UnitFile do
           :ok | {:error, [Systemd.UnitFile.ValidationError.t()]}
   defdelegate validate(unit_file, type \\ nil), to: Validator
 
+  @doc """
+  Returns a normalized representation suitable for semantic-ish comparison.
+
+  This intentionally ignores trivia, directive ordering, and equivalent list
+  spellings for directives such as `Wants=` and `ReadWritePaths=`.
+  """
+  @spec normalize(t() | String.t()) :: map()
+  def normalize(text) when is_binary(text), do: text |> parse!() |> normalize()
+
+  def normalize(%__MODULE__{entries: entries}) do
+    entries
+    |> entries_with_sections()
+    |> Enum.reduce(%{}, &collect_normalized_entry/2)
+    |> Map.new(fn {section, directives} -> {section, drop_defaults(directives)} end)
+  end
+
+  @doc """
+  Compares two unit files after normalization.
+  """
+  @spec equivalent?(t() | String.t(), t() | String.t()) :: boolean()
+  def equivalent?(left, right), do: normalize(left) == normalize(right)
+
   @doc """
   Renders a unit file.
   """
@@ -150,6 +172,66 @@ defmodule Systemd.UnitFile do
   defp entry_to_iodata(%Directive{name: name, value: value}), do: [name, "=", value, "\n"]
   defp entry_to_iodata(%Raw{content: content}), do: [content, "\n"]
 
+  @list_directives MapSet.new([
+                     "after",
+                     "before",
+                     "bindsto",
+                     "conflicts",
+                     "documentation",
+                     "environmentfile",
+                     "readwritepaths",
+                     "requires",
+                     "requiredby",
+                     "wants",
+                     "wantedby"
+                   ])
+
+  defp collect_normalized_entry({section, %Directive{}}, acc) when is_nil(section), do: acc
+
+  defp collect_normalized_entry({section, %Directive{} = directive}, acc) do
+    section = normalize_name(section)
+    key = normalize_name(directive.name)
+    values = normalize_directive_values(key, directive.value)
+
+    update_in(acc, [Access.key(section, %{}), Access.key(key, [])], &(values ++ &1))
+  end
+
+  defp collect_normalized_entry(_entry, acc), do: acc
+
+  defp normalize_directive_values(key, value) do
+    value = normalize_value(value)
+
+    values =
+      if MapSet.member?(@list_directives, key) do
+        String.split(value, ~r/\s+/, trim: true)
+      else
+        [value]
+      end
+
+    Enum.sort(values)
+  end
+
+  defp drop_defaults(%{"type" => ["simple"]} = directives),
+    do: directives |> Map.delete("type") |> sort_values()
+
+  defp drop_defaults(directives), do: sort_values(directives)
+
+  defp sort_values(directives),
+    do: Map.new(directives, fn {key, values} -> {key, Enum.sort(values)} end)
+
+  defp normalize_name(name) do
+    name
+    |> String.trim()
+    |> String.replace("_", "")
+    |> String.downcase()
+  end
+
+  defp normalize_value(value) do
+    value
+    |> String.trim()
+    |> String.replace(~r/\s+/, " ")
+  end
+
   defp entries_with_sections(entries) do
     {_section, entries} =
       Enum.reduce(entries, {nil, []}, fn

test/systemd/unit_file_test.exs

@@ -45,6 +45,59 @@ defmodule Systemd.UnitFileTest do
            ]
   end
 
+  test "normalizes equivalent unit files" do
+    left = """
+    [Unit]
+    Description=Exograph public Elixir code search
+    After=network-online.target
+    Wants=network-online.target
+
+    [Service]
+    Type=simple
+    User=toys-exograph
+    Group=toys-exograph
+    WorkingDirectory=/opt/toys/src/exograph
+    EnvironmentFile=/etc/toys/exograph/env
+    ExecStart=/usr/local/bin/mix exograph.index.hex --mode latest --mirror https://hex.elixir.toys --prefix hex --backend duckdb --duckdb-shards 8 --duckdb-threads 2 --concurrency 8 --shard-dir /srv/toys/exograph/shards --manifest-path /srv/toys/exograph/hex-manifest.json --no-bm25 --web --port 4200
+    Restart=on-failure
+    RestartSec=10
+    NoNewPrivileges=true
+    PrivateTmp=true
+    ProtectSystem=full
+    ProtectHome=true
+    ReadWritePaths=/srv/toys/exograph /var/lib/toys/exograph /opt/toys/src/exograph
+
+    [Install]
+    WantedBy=multi-user.target
+    """
+
+    right = """
+    [Unit]
+    Wants=network-online.target
+    After=network-online.target
+    Description=Exograph public Elixir code search
+    [Service]
+    ReadWritePaths=/srv/toys/exograph
+    ReadWritePaths=/var/lib/toys/exograph
+    ReadWritePaths=/opt/toys/src/exograph
+    ProtectHome=true
+    ProtectSystem=full
+    PrivateTmp=true
+    NoNewPrivileges=true
+    RestartSec=10
+    Restart=on-failure
+    ExecStart=/usr/local/bin/mix exograph.index.hex --mode latest --mirror https://hex.elixir.toys --prefix hex --backend duckdb --duckdb-shards 8 --duckdb-threads 2 --concurrency 8 --shard-dir /srv/toys/exograph/shards --manifest-path /srv/toys/exograph/hex-manifest.json --no-bm25 --web --port 4200
+    EnvironmentFile=/etc/toys/exograph/env
+    WorkingDirectory=/opt/toys/src/exograph
+    Group=toys-exograph
+    User=toys-exograph
+    [Install]
+    WantedBy=multi-user.target
+    """
+
+    assert UnitFile.equivalent?(left, right)
+  end
+
   test "renders parsed unit files deterministically" do
     text = "[Unit]\nDescription=My app\n\n[Install]\nWantedBy=multi-user.target\n"