Add a grind script to sanity-check a release

.travis.yml

@@ -73,10 +73,15 @@ script: tool/travis/test.sh
 
 jobs:
   include:
-  # Deploy to GitHub.
-  - stage: deploy 1
+  # Sanity check before releasing anywhere.
+  - stage: sanity check
     if: &deploy-if
       (type IN (push, api)) AND (repo = sass/dart-sass) AND tag =~ ^\d+\.\d+\.\d+([+-].*)?$
+    script: pub run grinder sanity-check-before-release
+
+  # Deploy to GitHub.
+  - stage: deploy 1
+    if: *deploy-if
     env: &github-env
       - GITHUB_USER=sassbot
       # GITHUB_AUTH="..."

tool/grind.dart

@@ -13,6 +13,7 @@ export 'grind/chocolatey.dart';
 export 'grind/github.dart';
 export 'grind/homebrew.dart';
 export 'grind/npm.dart';
+export 'grind/sanity_check.dart';
 export 'grind/standalone.dart';
 export 'grind/synchronize.dart';
 

tool/grind/sanity_check.dart

@@ -0,0 +1,29 @@
+// Copyright 2019 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:io';
+
+import 'package:collection/collection.dart';
+import 'package:grinder/grinder.dart';
+import 'package:pub_semver/pub_semver.dart';
+
+import 'utils.dart';
+
+@Task('Verify that the package is in a good state to release.')
+sanityCheckBeforeRelease() {
+  var travisTag = environment("TRAVIS_TAG");
+  if (travisTag != version) {
+    fail("TRAVIS_TAG $travisTag is different than pubspec version $version.");
+  }
+
+  if (const ListEquality().equals(Version.parse(version).preRelease, ["dev"])) {
+    fail("$version is a dev release.");
+  }
+
+  var versionHeader =
+      RegExp("^## ${RegExp.escape(version)}\$", multiLine: true);
+  if (!File("CHANGELOG.md").readAsStringSync().contains(versionHeader)) {
+    fail("There's no CHANGELOG entry for $version.");
+  }
+}