Migrate package_meta, io_utils, and utils. (#2760)

* flatten

* Review comments

Author: jcollins-g

lib/src/dartdoc_options.dart

@@ -1388,12 +1388,12 @@ Future<List<DartdocOption>> createDartdocOptions(
         negatable: true),
     // This could be a ArgOnly, but trying to not provide too many ways
     // to set the flutter root.
-    DartdocOptionSyntheticOnly<String>(
-        'flutterRoot',
-        (DartdocSyntheticOption<String> option, Folder dir) => resourceProvider
-            .pathContext
-            .resolveTildePath(Platform.environment['FLUTTER_ROOT']),
-        resourceProvider,
+    DartdocOptionSyntheticOnly<String?>('flutterRoot',
+        (DartdocSyntheticOption<String?> option, Folder dir) {
+      var envFlutterRoot = Platform.environment['FLUTTER_ROOT'];
+      if (envFlutterRoot == null) return null;
+      return resourceProvider.pathContext.resolveTildePath(envFlutterRoot);
+    }, resourceProvider,
         optionIs: OptionKind.dir,
         help: 'Root of the Flutter SDK, specified from environment.',
         mustExist: true),

lib/src/io_utils.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 /// This is a helper library to make working with io easier.
 library dartdoc.io_utils;
 
@@ -37,16 +35,16 @@ extension PathExtensions on path.Context {
   /// Return a resolved path including the home directory in place of tilde
   /// references.
   String resolveTildePath(String originalPath) {
-    if (originalPath == null || !originalPath.startsWith('~/')) {
+    if (!originalPath.startsWith('~/')) {
       return originalPath;
     }
 
     String homeDir;
 
     if (io.Platform.isWindows) {
-      homeDir = absolute(io.Platform.environment['USERPROFILE']);
+      homeDir = absolute(io.Platform.environment['USERPROFILE'] ?? '\'');
     } else {
-      homeDir = absolute(io.Platform.environment['HOME']);
+      homeDir = absolute(io.Platform.environment['HOME'] ?? '/');
     }
 
     return join(homeDir, originalPath.substring(2));
@@ -67,8 +65,7 @@ extension ResourceProviderExtensions on ResourceProvider {
     if (this is PhysicalResourceProvider) {
       return io.Platform.resolvedExecutable;
     } else {
-      // TODO(srawlins): Return what is needed for tests.
-      return null;
+      throw UnimplementedError('resolvedExecutable not implemented');
     }
   }
 
@@ -77,8 +74,7 @@ extension ResourceProviderExtensions on ResourceProvider {
       var mode = io.File(file.path).statSync().mode;
       return (0x1 & ((mode >> 6) | (mode >> 3) | mode)) != 0;
     } else {
-      // TODO(srawlins)
-      return false;
+      throw UnimplementedError('isExecutable not implemented');
     }
   }
 
@@ -124,8 +120,11 @@ final RegExp newLinePartOfRegexp = RegExp('\npart of ');
 
 typedef TaskQueueClosure<T> = Future<T> Function();
 
+void _defaultOnComplete() {}
+
 class _TaskQueueItem<T> {
-  _TaskQueueItem(this._closure, this._completer, {this.onComplete});
+  _TaskQueueItem(this._closure, this._completer,
+      {this.onComplete = _defaultOnComplete});
 
   final TaskQueueClosure<T> _closure;
   final Completer<T> _completer;
@@ -137,7 +136,7 @@ class _TaskQueueItem<T> {
     } catch (e) {
       _completer.completeError(e);
     } finally {
-      onComplete?.call();
+      onComplete.call();
     }
   }
 }
@@ -150,7 +149,7 @@ class TaskQueue<T> {
   /// Creates a task queue with a maximum number of simultaneous jobs.
   /// The [maxJobs] parameter defaults to the number of CPU cores on the
   /// system.
-  TaskQueue({int maxJobs})
+  TaskQueue({int? maxJobs})
       : maxJobs = maxJobs ?? io.Platform.numberOfProcessors;
 
   /// The maximum number of jobs that this queue will run simultaneously.

lib/src/model/accessor.dart

@@ -76,6 +76,7 @@ class Accessor extends ModelElement implements EnclosedElement {
 
   @override
   String computeDocumentationComment() {
+    String docComment;
     if (isSynthetic) {
       // If we're a setter, only display something if we have something different than the getter.
       // TODO(jcollins-g): modify analyzer to do this itself?
@@ -85,12 +86,17 @@ class Accessor extends ModelElement implements EnclosedElement {
               definingCombo.hasGetter &&
               definingCombo.getter.documentationComment !=
                   definingCombo.documentationComment)) {
-        return stripComments(definingCombo.documentationComment);
+        docComment = definingCombo.documentationComment;
       } else {
-        return '';
+        docComment = '';
       }
+    } else {
+      docComment = super.computeDocumentationComment();
+    }
+    if (docComment != null) {
+      return stripComments(docComment);
     }
-    return stripComments(super.computeDocumentationComment());
+    return null;
   }
 
   @override