Deduplicate loader classes into a single parameterized Loader (#22)

DeprecatedReferencesLoader and PackageTodoLoader were ~95% identical,
differing only in the YAML filename they loaded. Replace both with a
single Loader class that accepts the filename as a constructor argument.

https://claude.ai/code/session_015Ta3iW5HnXWCEcu9SHtjQ6

Co-authored-by: Claude <noreply@anthropic.com>

Author: samuelgiles

lib/graphwerk.rb

@@ -8,8 +8,7 @@
 require 'graphwerk/version'
 require 'graphwerk/constants'
 require 'graphwerk/layout'
-require 'graphwerk/deprecated_references_loader'
-require 'graphwerk/package_todo_loader'
+require 'graphwerk/loader'
 require 'graphwerk/presenters/package'
 require 'graphwerk/builders/graph'
 require 'graphwerk/railtie' if defined?(Rails)

lib/graphwerk/deprecated_references_loader.rb

@@ -0,0 +1,30 @@
+# typed: strict
+# frozen_string_literal: true
+
+module Graphwerk
+  class Loader
+    extend T::Sig
+
+    sig { params(package: Packwerk::Package, root_path: Pathname, filename: String).void }
+    def initialize(package, root_path, filename)
+      @package = package
+      @root_path = root_path
+      @filename = filename
+    end
+
+    sig { returns(T::Array[String]) }
+    def load
+      return [] if !file.exist?
+
+      (YAML.safe_load_file(file) || {}).keys
+    end
+
+    private
+
+    sig { returns(Pathname) }
+    def file
+      @file = T.let(@file, T.nilable(Pathname))
+      @file ||= @root_path.join(@package.name, @filename)
+    end
+  end
+end

lib/graphwerk/loader.rb

@@ -24,14 +24,14 @@ def dependencies
 
       sig { returns(T::Array[String]) }
       def deprecated_references
-        DeprecatedReferencesLoader.new(@package, @root_path).load.map do |reference|
+        Loader.new(@package, @root_path, 'deprecated_references.yml').load.map do |reference|
           Name.new(reference).node_name
         end
       end
 
       sig { returns(T::Array[String]) }
       def package_todos
-        PackageTodoLoader.new(@package, @root_path).load.map do |todo|
+        Loader.new(@package, @root_path, 'package_todo.yml').load.map do |todo|
           Name.new(todo).node_name
         end
       end

lib/graphwerk/package_todo_loader.rb

@@ -50,23 +50,22 @@ module Builders
         subject(:diagram) { builder.build.to_s }
 
         let(:deprecated_references_loader_for_images) do
-          instance_double(DeprecatedReferencesLoader, load: ['.'])
+          instance_double(Loader, load: ['.'])
         end
 
         let(:package_todo_loader_for_frontend) do
-          instance_double(PackageTodoLoader, load: ['components/storage_providers/s3'])
+          instance_double(Loader, load: ['components/storage_providers/s3'])
         end
 
         before do
-          allow(DeprecatedReferencesLoader).to receive(:new).and_call_original
-          allow(DeprecatedReferencesLoader)
+          allow(Loader).to receive(:new).and_call_original
+          allow(Loader)
             .to receive(:new)
-            .with(images_package, an_instance_of(Pathname))
+            .with(images_package, an_instance_of(Pathname), 'deprecated_references.yml')
             .and_return(deprecated_references_loader_for_images)
-          allow(PackageTodoLoader).to receive(:new).and_call_original
-          allow(PackageTodoLoader)
+          allow(Loader)
             .to receive(:new)
-            .with(frontend_package, an_instance_of(Pathname))
+            .with(frontend_package, an_instance_of(Pathname), 'package_todo.yml')
             .and_return(package_todo_loader_for_frontend)
         end
 
@@ -130,7 +129,7 @@ module Builders
 
         context 'when a deprecated reference points to a package not in the graph' do
           let(:deprecated_references_loader_for_images) do
-            instance_double(DeprecatedReferencesLoader, load: ['.', 'components/unknown'])
+            instance_double(Loader, load: ['.', 'components/unknown'])
           end
 
           specify do
@@ -148,7 +147,7 @@ module Builders
 
         context 'when a package todo points to a package not in the graph' do
           let(:package_todo_loader_for_frontend) do
-            instance_double(PackageTodoLoader, load: ['components/storage_providers/s3', 'components/nonexistent'])
+            instance_double(Loader, load: ['components/storage_providers/s3', 'components/nonexistent'])
           end
 
           specify do

lib/graphwerk/presenters/package.rb

@@ -0,0 +1,80 @@
+# typed: false
+# frozen_string_literal: true
+
+module Graphwerk
+  describe Loader do
+    let(:service) { described_class.new(package, root_path, filename) }
+
+    let(:package) do
+      Packwerk::Package.new(
+        name: 'components/admin',
+        config: { 'dependencies' => ['components/security', 'components/orders'] }
+      )
+    end
+    let(:root_path) { Pathname.new('.') }
+
+    shared_examples 'a YAML loader' do
+      describe '#load' do
+        subject { service.load }
+
+        let(:file) { instance_double(Pathname) }
+
+        before do
+          expect(root_path)
+            .to receive(:join)
+            .with('components/admin', filename)
+            .and_return(file)
+          expect(file)
+            .to receive(:exist?)
+            .and_return(file_is_present)
+        end
+
+        context 'when no file is present' do
+          let(:file_is_present) { false }
+
+          it { is_expected.to be_empty }
+        end
+
+        context 'when a file is present' do
+          let(:file_is_present) { true }
+
+          before do
+            expect(YAML)
+              .to receive(:safe_load_file)
+              .with(file)
+              .and_return(
+                '.' => {
+                  "::Order" => {
+                    "violations" => ["dependency"],
+                    "files" => ["components/admin/interfaces/gateway.rb"]
+                  }
+                }
+              )
+          end
+
+          it { is_expected.to contain_exactly('.') }
+        end
+      end
+
+      describe '#load with a real YAML fixture file' do
+        let(:root_path) { Pathname.new(File.expand_path('../../support/fixtures', __dir__)) }
+
+        it 'parses the file with safe_load_file and returns the keys' do
+          expect(service.load).to contain_exactly('.', 'components/shipping')
+        end
+      end
+    end
+
+    context 'with deprecated_references.yml' do
+      let(:filename) { 'deprecated_references.yml' }
+
+      it_behaves_like 'a YAML loader'
+    end
+
+    context 'with package_todo.yml' do
+      let(:filename) { 'package_todo.yml' }
+
+      it_behaves_like 'a YAML loader'
+    end
+  end
+end