Refactor handling of generateDocs:false (#4095)

Not sure if anyone is using this option really. But I think the handling
can be simplified.

But it seems that having multiple Generator classes just for deciding
whether to write files or not is excessive, and likely to get out of
sync (does the EmptyGenerator really still do whatever GeneratorFrontend
does, just without writing files?)

Author: sigurdm

bin/dartdoc.dart

@@ -20,8 +20,5 @@ void main(List<String> arguments) {
   final packageConfigProvider = PhysicalPackageConfigProvider();
   final packageBuilder =
       PubPackageBuilder(config, pubPackageMetaProvider, packageConfigProvider);
-  final dartdoc = config.generateDocs
-      ? Dartdoc.fromContext(config, packageBuilder)
-      : Dartdoc.withEmptyGenerator(config, packageBuilder);
-  dartdoc.executeGuarded();
+  Dartdoc.fromContext(config, packageBuilder).executeGuarded();
 }

lib/src/dartdoc.dart

@@ -9,7 +9,6 @@ import 'dart:io' show Platform, exitCode, stderr;
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:dartdoc/src/dartdoc_options.dart';
 import 'package:dartdoc/src/failure.dart';
-import 'package:dartdoc/src/generator/empty_generator.dart';
 import 'package:dartdoc/src/generator/generator.dart';
 import 'package:dartdoc/src/generator/html_generator.dart';
 import 'package:dartdoc/src/logging.dart';
@@ -27,10 +26,28 @@ const String programName = 'dartdoc';
 // Update when pubspec version changes by running `pub run build_runner build`
 const String dartdocVersion = packageVersion;
 
+/// Used for the generateDocs:false option.
+///
+/// Writes nothing.
+class NoFileWriter implements FileWriter {
+  @override
+  void write(String filePath, String content, {Warnable? element}) {
+    // Do nothing
+  }
+
+  @override
+  void writeBytes(String filePath, List<int> content,
+      {bool allowOverwrite = false}) {
+    // Do nothing
+  }
+
+  @override
+  Set<String> get writtenFiles => {};
+}
+
 class DartdocFileWriter implements FileWriter {
   final String _outputDir;
-  @override
-  final ResourceProvider resourceProvider;
+  final ResourceProvider _resourceProvider;
   final Map<String, Warnable?> _fileElementMap = {};
   @override
   final Set<String> writtenFiles = {};
@@ -43,7 +60,7 @@ class DartdocFileWriter implements FileWriter {
 
   DartdocFileWriter(
     this._outputDir,
-    this.resourceProvider, {
+    this._resourceProvider, {
     int maxFileCount = 0,
     int maxTotalSize = 0,
   })  : _maxFileCount = maxFileCount,
@@ -115,8 +132,8 @@ class DartdocFileWriter implements FileWriter {
   /// Returns the file at [outFile] relative to [_outputDir], creating the
   /// parent directory if necessary.
   File _getFile(String outFile) {
-    var file = resourceProvider
-        .getFile(resourceProvider.pathContext.join(_outputDir, outFile));
+    var file = _resourceProvider
+        .getFile(_resourceProvider.pathContext.join(_outputDir, outFile));
     var parent = file.parent;
     if (!parent.exists) {
       parent.create();
@@ -144,19 +161,6 @@ class Dartdoc {
   @visibleForTesting
   set generator(Generator newGenerator) => _generator = newGenerator;
 
-  /// Factory method that builds Dartdoc with an empty generator.
-  factory Dartdoc.withEmptyGenerator(
-    DartdocOptionContext config,
-    PackageBuilder packageBuilder,
-  ) {
-    return Dartdoc._(
-      config,
-      config.resourceProvider.getFolder('UNUSED'),
-      initEmptyGenerator(),
-      packageBuilder,
-    );
-  }
-
   /// Builds Dartdoc with a generator determined by [context].
   factory Dartdoc.fromContext(
     DartdocGeneratorOptionContext context,
@@ -165,12 +169,14 @@ class Dartdoc {
     var resourceProvider = context.resourceProvider;
     var outputPath = resourceProvider.pathContext.absolute(context.output);
     var outputDir = resourceProvider.getFolder(outputPath)..create();
-    var writer = DartdocFileWriter(
-      outputPath,
-      resourceProvider,
-      maxFileCount: context.maxFileCount,
-      maxTotalSize: context.maxTotalSize,
-    );
+    var writer = context.generateDocs
+        ? DartdocFileWriter(
+            outputPath,
+            resourceProvider,
+            maxFileCount: context.maxFileCount,
+            maxTotalSize: context.maxTotalSize,
+          )
+        : NoFileWriter();
     return Dartdoc._(
       context,
       outputDir,

lib/src/dartdoc_options.dart

@@ -1278,6 +1278,9 @@ class DartdocGeneratorOptionContext extends DartdocOptionContext {
   bool get useBaseHref => optionSet['useBaseHref'].valueAt(context);
 
   String? get resourcesDir => optionSet['resourcesDir'].valueAt(context);
+
+  /// Whether to generate docs or perform a dry run.
+  bool get generateDocs => optionSet['generateDocs'].valueAt(context);
 }
 
 class DartdocProgramOptionContext extends DartdocGeneratorOptionContext
@@ -1288,9 +1291,6 @@ class DartdocProgramOptionContext extends DartdocGeneratorOptionContext
   DartdocProgramOptionContext.fromDefaultContextLocation(
       super.optionSet, super.resourceProvider)
       : super.fromDefaultContextLocation();
-
-  /// Whether to generate docs or perform a dry run.
-  bool get generateDocs => optionSet['generateDocs'].valueAt(context);
 }
 
 List<DartdocOption<bool>> createDartdocProgramOptions(