Convert snippets tool to null safety (#78646)

dev/bots/analyze_sample_code.dart

@@ -355,7 +355,10 @@ class SampleChecker {
     } else {
       return Process.runSync(
         _dartExecutable,
-        <String>[path.canonicalize(_snippetsSnapshotPath!), ...args],
+        <String>[
+          path.canonicalize(_snippetsSnapshotPath!),
+          ...args,
+        ],
         workingDirectory: workingDirectory,
       );
     }

dev/snippets/lib/configuration.dart

@@ -27,7 +27,7 @@ String getEnumName(dynamic enumItem) {
 /// A class to compute the configuration of the snippets input and output
 /// locations based in the current location of the snippets main.dart.
 class Configuration {
-  Configuration({@required this.flutterRoot}) : assert(flutterRoot != null);
+  Configuration({required this.flutterRoot}) : assert(flutterRoot != null);
 
   final Directory flutterRoot;
 
@@ -37,20 +37,22 @@ class Configuration {
   Directory get configDirectory {
     _configPath ??= Directory(
         path.canonicalize(path.join(flutterRoot.absolute.path, 'dev', 'snippets', 'config')));
-    return _configPath;
+    return _configPath!;
   }
 
-  Directory _configPath;
+  // Nullable so that we can use it as a lazy cache.
+  Directory? _configPath;
 
   /// This is where the snippets themselves will be written, in order to be
   /// uploaded to the docs site.
   Directory get outputDirectory {
     _docsDirectory ??= Directory(
         path.canonicalize(path.join(flutterRoot.absolute.path, 'dev', 'docs', 'doc', 'snippets')));
-    return _docsDirectory;
+    return _docsDirectory!;
   }
 
-  Directory _docsDirectory;
+  // Nullable so that we can use it as a lazy cache.
+  Directory? _docsDirectory;
 
   /// This makes sure that the output directory exists.
   void createOutputDirectory() {

dev/snippets/lib/main.dart

@@ -22,13 +22,13 @@ const String _kTypeOption = 'type';
 const String _kShowDartPad = 'dartpad';
 
 String getChannelName() {
-  final RegExp gitBranchRegexp = RegExp(r'^## (.*)');
+  final RegExp gitBranchRegexp = RegExp(r'^## (?<branch>.*)');
   final ProcessResult gitResult = Process.runSync('git', <String>['status', '-b', '--porcelain']);
   if (gitResult.exitCode != 0)
     throw 'git status exit with non-zero exit code: ${gitResult.exitCode}';
-  final Match gitBranchMatch = gitBranchRegexp.firstMatch(
+  final RegExpMatch? gitBranchMatch = gitBranchRegexp.firstMatch(
       (gitResult.stdout as String).trim().split('\n').first);
-  return gitBranchMatch == null ? '<unknown>' : gitBranchMatch.group(1).split('...').first;
+  return gitBranchMatch == null ? '<unknown>' : gitBranchMatch.namedGroup('branch')!.split('...').first;
 }
 
 /// Generates snippet dartdoc output for a given input, and creates any sample
@@ -113,8 +113,7 @@ void main(List<String> argList) {
   }
 
   final SnippetType snippetType = SnippetType.values
-      .firstWhere((SnippetType type) => getEnumName(type) == args[_kTypeOption], orElse: () => null);
-  assert(snippetType != null, "Unable to find '${args[_kTypeOption]}' in SnippetType enum.");
+      .firstWhere((SnippetType type) => getEnumName(type) == args[_kTypeOption]);
 
   if (args[_kShowDartPad] == true && snippetType != SnippetType.sample) {
     errorExit('${args[_kTypeOption]} was selected, but the --dartpad flag is only valid '
@@ -132,7 +131,7 @@ void main(List<String> argList) {
     errorExit('The input file ${input.path} does not exist.');
   }
 
-  String template;
+  String? template;
   if (snippetType == SnippetType.sample) {
     final String templateArg = args[_kTemplateOption] as String;
     if (templateArg == null || templateArg.isEmpty) {
@@ -143,25 +142,24 @@ void main(List<String> argList) {
     template = templateArg.replaceAll(RegExp(r'.tmpl$'), '');
   }
 
-  String emptyToNull(String value) => value?.isEmpty ?? true ? null : value;
-  final String packageName = emptyToNull(args[_kPackageOption] as String);
-  final String libraryName = emptyToNull(args[_kLibraryOption] as String);
-  final String elementName = emptyToNull(args[_kElementOption] as String);
-  final String serial = emptyToNull(args[_kSerialOption] as String);
+  final String packageName = args[_kPackageOption] as String? ?? '';
+  final String libraryName = args[_kLibraryOption] as String? ?? '';
+  final String elementName = args[_kElementOption] as String? ?? '';
+  final String serial = args[_kSerialOption] as String? ?? '';
   final List<String> id = <String>[];
   if (args[_kOutputOption] != null) {
     id.add(path.basename(path.basenameWithoutExtension(args[_kOutputOption] as String)));
   } else {
-    if (packageName != null && packageName != 'flutter') {
+    if (packageName.isNotEmpty && packageName != 'flutter') {
       id.add(packageName);
     }
-    if (libraryName != null) {
+    if (libraryName.isNotEmpty) {
       id.add(libraryName);
     }
-    if (elementName != null) {
+    if (elementName.isNotEmpty) {
       id.add(elementName);
     }
-    if (serial != null) {
+    if (serial.isNotEmpty) {
       id.add(serial);
     }
     if (id.isEmpty) {
@@ -178,10 +176,10 @@ void main(List<String> argList) {
     showDartPad: args[_kShowDartPad] as bool,
     template: template,
     output: args[_kOutputOption] != null ? File(args[_kOutputOption] as String) : null,
-    metadata: <String, Object>{
+    metadata: <String, Object?>{
       'sourcePath': environment['SOURCE_PATH'],
       'sourceLine': environment['SOURCE_LINE'] != null
-          ? int.tryParse(environment['SOURCE_LINE'])
+          ? int.tryParse(environment['SOURCE_LINE']!)
           : null,
       'id': id.join('.'),
       'channel': getChannelName(),

dev/snippets/lib/snippets.dart

@@ -6,7 +6,6 @@ import 'dart:convert';
 import 'dart:io';
 
 import 'package:dart_style/dart_style.dart';
-import 'package:meta/meta.dart';
 import 'package:path/path.dart' as path;
 
 import 'configuration.dart';
@@ -19,7 +18,7 @@ void errorExit(String message) {
 // A Tuple containing the name and contents associated with a code block in a
 // snippet.
 class _ComponentTuple {
-  _ComponentTuple(this.name, this.contents, {String language}) : language = language ?? '';
+  _ComponentTuple(this.name, this.contents, {this.language = ''});
   final String name;
   final List<String> contents;
   final String language;
@@ -29,7 +28,7 @@ class _ComponentTuple {
 /// Generates the snippet HTML, as well as saving the output snippet main to
 /// the output directory.
 class SnippetGenerator {
-  SnippetGenerator({Configuration configuration})
+  SnippetGenerator({Configuration? configuration})
       : configuration = configuration ??
             // Flutter's root is four directories up from this script.
             Configuration(flutterRoot: Directory(Platform.environment['FLUTTER_ROOT']
@@ -52,7 +51,7 @@ class SnippetGenerator {
   File getOutputFile(String id) => File(path.join(configuration.outputDirectory.path, '$id.dart'));
 
   /// Gets the path to the template file requested.
-  File getTemplatePath(String templateName, {Directory templatesDir}) {
+  File? getTemplatePath(String templateName, {Directory? templatesDir}) {
     final Directory templateDir = templatesDir ?? configuration.templatesDirectory;
     final File templateFile = File(path.join(templateDir.path, '$templateName.tmpl'));
     return templateFile.existsSync() ? templateFile : null;
@@ -61,7 +60,7 @@ class SnippetGenerator {
   /// Injects the [injections] into the [template], and turning the
   /// "description" injection into a comment. Only used for
   /// [SnippetType.sample] snippets.
-  String interpolateTemplate(List<_ComponentTuple> injections, String template, Map<String, Object> metadata) {
+  String interpolateTemplate(List<_ComponentTuple> injections, String template, Map<String, Object?> metadata) {
     final RegExp moustacheRegExp = RegExp('{{([^}]+)}}');
     return template.replaceAllMapped(moustacheRegExp, (Match match) {
       if (match[1] == 'description') {
@@ -86,9 +85,12 @@ class SnippetGenerator {
         // mustache reference, since we want to allow the sections to be
         // "optional" in the input: users shouldn't be forced to add an empty
         // "```dart preamble" section if that section would be empty.
-        final _ComponentTuple result = injections
-            .firstWhere((_ComponentTuple tuple) => tuple.name == match[1], orElse: () => null);
-        return result?.mergedContent ?? (metadata[match[1]] ?? '').toString();
+        final int componentIndex = injections
+            .indexWhere((_ComponentTuple tuple) => tuple.name == match[1]);
+        if (componentIndex == -1) {
+          return (metadata[match[1]] ?? '').toString();
+        }
+        return injections[componentIndex].mergedContent;
       }
     }).trim();
   }
@@ -100,10 +102,15 @@ class SnippetGenerator {
   ///
   /// Takes into account the [type] and doesn't substitute in the id and the app
   /// if not a [SnippetType.sample] snippet.
-  String interpolateSkeleton(SnippetType type, List<_ComponentTuple> injections, String skeleton, Map<String, Object> metadata) {
+  String interpolateSkeleton(
+    SnippetType type,
+    List<_ComponentTuple> injections,
+    String skeleton,
+    Map<String, Object?> metadata,
+  ) {
     final List<String> result = <String>[];
     const HtmlEscape htmlEscape = HtmlEscape();
-    String language;
+    String language = 'dart';
     for (final _ComponentTuple injection in injections) {
       if (!injection.name.startsWith('code')) {
         continue;
@@ -133,11 +140,11 @@ class SnippetGenerator {
     final Map<String, String> substitutions = <String, String>{
       'description': description,
       'code': htmlEscape.convert(result.join('\n')),
-      'language': language ?? 'dart',
+      'language': language,
       'serial': '',
-      'id': metadata['id'] as String,
+      'id': metadata['id']! as String,
       'channel': channel,
-      'element': metadata['element'] as String ?? '',
+      'element': (metadata['element'] ?? '') as String,
       'app': '',
     };
     if (type == SnippetType.sample) {
@@ -146,7 +153,7 @@ class SnippetGenerator {
         ..['app'] = htmlEscape.convert(injections.firstWhere((_ComponentTuple tuple) => tuple.name == 'app').mergedContent);
     }
     return skeleton.replaceAllMapped(RegExp('{{(${substitutions.keys.join('|')})}}'), (Match match) {
-      return substitutions[match[1]];
+      return substitutions[match[1]] ?? '';
     });
   }
 
@@ -157,16 +164,16 @@ class SnippetGenerator {
     input = input.trim();
     final List<String> description = <String>[];
     final List<_ComponentTuple> components = <_ComponentTuple>[];
-    String language;
-    final RegExp codeStartEnd = RegExp(r'^\s*```([-\w]+|[-\w]+ ([-\w]+))?\s*$');
+    String? language;
+    final RegExp codeStartEnd = RegExp(r'^\s*```(?<language>[-\w]+|[-\w]+ (?<section>[-\w]+))?\s*$');
     for (final String line in input.split('\n')) {
-      final Match match = codeStartEnd.firstMatch(line);
+      final RegExpMatch? match = codeStartEnd.firstMatch(line);
       if (match != null) { // If we saw the start or end of a code block
         inCodeBlock = !inCodeBlock;
-        if (match[1] != null) {
-          language = match[1];
-          if (match[2] != null) {
-            components.add(_ComponentTuple('code-${match[2]}', <String>[], language: language));
+        if (match.namedGroup('language') != null) {
+          language = match[1]!;
+          if (match.namedGroup('section') != null) {
+            components.add(_ComponentTuple('code-${match.namedGroup('section')}', <String>[], language: language));
           } else {
             components.add(_ComponentTuple('code', <String>[], language: language));
           }
@@ -191,7 +198,7 @@ class SnippetGenerator {
   }
 
   String _loadFileAsUtf8(File file) {
-    return file.readAsStringSync(encoding: Encoding.getByName('utf-8'));
+    return file.readAsStringSync(encoding: utf8);
   }
 
   String _addLineNumbers(String app) {
@@ -228,13 +235,12 @@ class SnippetGenerator {
     File input,
     SnippetType type, {
     bool showDartPad = false,
-    String template,
-    File output,
-    @required Map<String, Object> metadata,
+    String? template,
+    File? output,
+    required Map<String, Object?> metadata,
   }) {
     assert(template != null || type != SnippetType.sample);
-    assert(metadata != null && metadata['id'] != null);
-    assert(input != null);
+    assert(metadata['id'] != null);
     assert(!showDartPad || type == SnippetType.sample, 'Only application samples work with dartpad.');
     final List<_ComponentTuple> snippetData = parseInput(_loadFileAsUtf8(input));
     switch (type) {
@@ -244,10 +250,9 @@ class SnippetGenerator {
           stderr.writeln('Unable to find the templates directory.');
           exit(1);
         }
-        final File templateFile = getTemplatePath(template, templatesDir: templatesDir);
+        final File? templateFile = getTemplatePath(template!, templatesDir: templatesDir);
         if (templateFile == null) {
-          stderr.writeln(
-              'The template $template was not found in the templates directory ${templatesDir.path}');
+          stderr.writeln('The template $template was not found in the templates directory ${templatesDir.path}');
           exit(1);
         }
         final String templateContents = _loadFileAsUtf8(templateFile);
@@ -261,20 +266,19 @@ class SnippetGenerator {
         }
 
         snippetData.add(_ComponentTuple('app', app.split('\n')));
-        final File outputFile = output ?? getOutputFile(metadata['id'] as String);
+        final File outputFile = output ?? getOutputFile(metadata['id']! as String);
         stderr.writeln('Writing to ${outputFile.absolute.path}');
         outputFile.writeAsStringSync(app);
 
         final File metadataFile = File(path.join(path.dirname(outputFile.path),
             '${path.basenameWithoutExtension(outputFile.path)}.json'));
         stderr.writeln('Writing metadata to ${metadataFile.absolute.path}');
-        final _ComponentTuple description = snippetData.firstWhere(
-          (_ComponentTuple data) => data.name == 'description',
-          orElse: () => null,
-        );
+        final int descriptionIndex = snippetData.indexWhere(
+                (_ComponentTuple data) => data.name == 'description');
+        final String descriptionString = descriptionIndex == -1 ? '' : snippetData[descriptionIndex].mergedContent;
         metadata.addAll(<String, Object>{
           'file': path.basename(outputFile.path),
-          'description': description?.mergedContent,
+          'description': descriptionString,
         });
         metadataFile.writeAsStringSync(jsonEncoder.convert(metadata));
         break;

dev/snippets/pubspec.yaml

@@ -5,7 +5,7 @@ description: A code snippet dartdoc extension for Flutter API docs.
 homepage: https://github.com/flutter/flutter
 
 environment:
-  sdk: ">=2.2.2 <3.0.0"
+  sdk: ">=2.12.1 <3.0.0"
 
 dartdoc:
   # Exclude this package from the hosted API docs (Ironically...).

dev/snippets/test/configuration_test.dart

@@ -9,7 +9,7 @@ import 'package:test/test.dart' hide TypeMatcher, isInstanceOf;
 
 void main() {
   group('Configuration', () {
-    Configuration config;
+    late Configuration config;
 
     setUp(() {
       config = Configuration(flutterRoot: Directory('/flutter sdk'));

dev/snippets/test/snippets_test.dart

@@ -12,10 +12,10 @@ import 'package:test/test.dart' hide TypeMatcher, isInstanceOf;
 
 void main() {
   group('Generator', () {
-    Configuration configuration;
-    SnippetGenerator generator;
-    Directory tmpDir;
-    File template;
+    late Configuration configuration;
+    late SnippetGenerator generator;
+    late Directory tmpDir;
+    late File template;
 
     setUp(() {
       tmpDir = Directory.systemTemp.createTempSync('flutter_snippets_test.');