DAS plugins: Add an SDK constraint to generated pubspec

Change-Id: I98765c019d5e41b347b11b874165e3de0e381002
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/404760
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: srawlins

pkg/analysis_server/lib/src/plugin2/generator.dart

@@ -61,6 +61,8 @@ Future<void> main(List<String> args, SendPort sendPort) async {
     buffer.write('''
 name: plugin_entrypoint
 version: 0.0.1
+environment:
+  sdk: ^3.6.0
 dependencies:
   analyzer: '$analyzerVersion'
   analyzer_plugin: '$analyzerPluginVersion'

pkg/analysis_server/test/src/plugin2/generator_test.dart

@@ -103,6 +103,17 @@ dependencies:
     );
   }
 
+  void test_pubspecContainsSdkConstraint() {
+    var pluginPackageGenerator = PluginPackageGenerator([]);
+    expect(
+      pluginPackageGenerator.generatePubspec(),
+      contains('''
+environment:
+  sdk: ^3.6.0
+'''),
+    );
+  }
+
   void test_pubspecContainsVersionedDependencies() {
     var pluginPackageGenerator = PluginPackageGenerator([
       PluginConfiguration(