Make some improvements to release notes script

pubspec.yaml

@@ -4,5 +4,6 @@ environment:
   sdk: '>=3.0.0 <4.0.0'
 
 dependencies:
+  collection:
   http:
   path:

tool/generate_release_notes.dart

@@ -1,22 +1,45 @@
 import 'dart:convert';
 import 'dart:io';
 
+import 'package:collection/collection.dart';
 import 'package:http/http.dart' as http;
-import 'package:path/path.dart';
+import 'package:path/path.dart' as path;
 
 main() async {
-  Directory.current = dirname(Platform.script.toFilePath());
+  Directory.current = path.dirname(Platform.script.toFilePath());
 
   final List<dynamic> milestones = (await fetchJson(
       'milestones?state=open&sort=completeness&direction=desc'));
 
   final milestone =
       milestones.firstWhere((m) => (m['title'] as String).startsWith('v'));
-  final name = milestone['title'];
+  final name = milestone['title'] as String;
   final int key = milestone['number'];
 
-  print('# $name');
-  print('');
+  final versionSegments = name.replaceAll('v', '').split('.');
+  final majorMinorVersion = versionSegments.take(2).join('.');
+  final outputRelativeFilePath =
+      path.join('..', '_releases', 'v$majorMinorVersion.md');
+  final outputFilePath = path.normalize(path.absolute(outputRelativeFilePath));
+  final outputFile = File(outputFilePath);
+  print('Writing release notes to ${outputFile}');
+
+  final output = StringBuffer();
+
+  output.writeln('---');
+  output.writeln('title: v$majorMinorVersion');
+  output.writeln('sort_order: '
+      'v${versionSegments[0].padLeft(4, '0')}'
+      '_${versionSegments[1].padLeft(4, '0')}');
+  output.writeln('excerpt: "..."');
+  output.writeln('---');
+  output.writeln('');
+
+  final now = DateTime.now();
+  final year = now.year;
+  final month = now.month;
+  output.writeln('# $name _$year-$month-??_');
+  output.writeln('');
 
   final Map<String, Map<int, dynamic>> issuesByLabel = {};
   final List<dynamic> issues =
@@ -26,9 +49,7 @@ main() async {
   }
   for (final issue in issues) {
     final labels = issue['labels'] as List<dynamic>;
-    final primaryLabel = labels
-        .map((l) => l['name'] as String)
-        .firstWhere((l) => l.startsWith('in '), orElse: () => 'in other');
+    final primaryLabel = _getPrimaryLabel(labels);
 
     // Non-functional changes don't go in release notes.
     if (labels.any((l) => l['name'] == 'is non-functional')) {
@@ -39,21 +60,85 @@ main() async {
     issuesByLabel[primaryLabel]![issue['number'] as int] = issue;
   }
 
-  issuesByLabel.forEach((label, issues) {
-    var category = label.substring(3, 4).toUpperCase() + label.substring(4);
-    if (category == 'Other') {
-      category = 'Misc';
+  final labels =
+      _sortLabels(issuesByLabel.keys.toList(), forPrimarySelection: false);
+  for (final label in labels) {
+    final issues = issuesByLabel[label]!;
+    String category;
+    String? text;
+    if (label.startsWith('relies on sdk')) {
+      category = 'Features/Fixes Enabled with Future SDKs';
+      text =
+          'The following items depend on changes to the Dart/Flutter SDKs that have not yet been released to stable channels. '
+          'They may be able to test in the current beta/master channels and will show up in future SDK releases.';
+    } else {
+      category = _getLabelTitle(label);
+    }
+    output.writeln('## $category');
+    output.writeln('');
+    if (text != null) {
+      output.writeln(text);
+      output.writeln('');
     }
-    print('## $category');
-    print('');
     issues.forEach((issueNumber, issue) {
       final title = issue['title'] as String;
       final isPr = issue['pull_request'] != null;
-      print(
+      output.writeln(
           '- ${isPr ? 'PR ' : ''}[#$issueNumber](https://github.com/Dart-Code/Dart-Code/issues/$issueNumber): ${title.endsWith(".") ? title : '$title.'}');
     });
-    print('');
-  });
+    output.writeln('');
+  }
+
+  outputFile.writeAsStringSync(output.toString());
+  print('Done!');
+}
+
+String _getPrimaryLabel(List<Object?> labels) {
+  final labelNames = labels
+      .cast<Map<String, Object?>>()
+      .map((l) => l['name'] as String)
+      .where((l) => l.startsWith('in ') || l.startsWith('relies on sdk'))
+      .toList();
+
+  return _sortLabels(labelNames, forPrimarySelection: true).firstOrNull ??
+      'in other';
+}
+
+String _getLabelTitle(String label) {
+  if (label == 'in devtools sidebar') {
+    return 'Flutter Sidebar';
+  } else if (label == 'in devtools') {
+    return 'DevTools';
+  } else if (label == 'in other') {
+    return 'Misc';
+  } else if (label.startsWith('in ')) {
+    return label.substring(3, 4).toUpperCase() + label.substring(4);
+  } else {
+    throw 'Unhandled label: "$label"';
+  }
+}
+
+List<String> _sortLabels(List<String> labels,
+    {required bool forPrimarySelection}) {
+  // Use this label first for primary selection, but sort it at the end for
+  // display.
+  final reliesOnSdkRank = forPrimarySelection ? -1000 : 10;
+  const priorities = {
+    'in flutter': -10,
+    'in editor': -9,
+    'in testing': -8,
+    'in debugger': -7,
+    'in commands': -6,
+    'in views': -5,
+    'in cli': 1,
+  };
+  final labelRanks = {
+    for (final label in labels)
+      label: priorities[label] ??
+          (label.startsWith('relies on sdk') ? reliesOnSdkRank : 0),
+  };
+
+  return labels.sortedBy<num>((label) => labelRanks[label] ?? 0);
 }
 
 Future<dynamic> fetchJson(String uri) async {