Prepare new test backend for Dart analysis

drift_dev/test/analysis/test_utils.dart

@@ -1,5 +1,13 @@
+import 'dart:io';
+import 'dart:isolate';
+
+import 'package:analyzer/dart/analysis/analysis_context.dart';
+import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
+import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/file_system/overlay_file_system.dart';
+import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:build/build.dart';
 import 'package:drift_dev/src/analysis/backend.dart';
 import 'package:drift_dev/src/analysis/driver/driver.dart';
@@ -7,18 +15,27 @@ import 'package:drift_dev/src/analysis/driver/error.dart';
 import 'package:drift_dev/src/analysis/driver/state.dart';
 import 'package:drift_dev/src/analyzer/options.dart';
 import 'package:logging/logging.dart';
+import 'package:package_config/package_config.dart';
+import 'package:path/path.dart' as p;
 import 'package:test/expect.dart';
 import 'package:test/scaffolding.dart';
 
+/// A [DriftBackend] implementation used for testing.
+///
+/// This backend has limited support for Dart analysis: [sourceContents] forming
+/// the package `a` are available for analysis. In addition, `drift` and
+/// `drift_dev` imports can be analyzed as well.
 class TestBackend extends DriftBackend {
-  final Map<String, String> sourceContents;
+  final Map<Uri, String> sourceContents;
 
   late final DriftAnalysisDriver driver;
 
+  AnalysisContext? _dartContext;
+
   TestBackend(Map<String, String> sourceContents, DriftOptions options)
       : sourceContents = {
           for (final entry in sourceContents.entries)
-            AssetId.parse(entry.key).uri.toString(): entry.value,
+            AssetId.parse(entry.key).uri: entry.value,
         } {
     driver = DriftAnalysisDriver(this, options);
   }
@@ -31,6 +48,50 @@ class TestBackend extends DriftBackend {
     return backend;
   }
 
+  Future<void> _setupDartAnalyzer() async {
+    final provider = OverlayResourceProvider(PhysicalResourceProvider.INSTANCE);
+
+    // Analyze example sources against the drift sources from the current
+    // drift_dev test runner.
+    final uri = await Isolate.packageConfig;
+    final hostConfig =
+        PackageConfig.parseBytes(await File.fromUri(uri!).readAsBytes(), uri);
+    final testConfig = PackageConfig([
+      ...hostConfig.packages,
+      Package('a', Uri.directory('/a/'), packageUriRoot: Uri.parse('lib/')),
+    ]);
+
+    // Write package config used to analyze dummy sources
+    final configBuffer = StringBuffer();
+    PackageConfig.writeString(testConfig, configBuffer);
+    provider.setOverlay('/a/.dart_tool/package_config.json',
+        content: configBuffer.toString(), modificationStamp: 1);
+
+    // Also put sources into the overlay:
+    sourceContents.forEach((key, value) {
+      if (key.scheme == 'package') {
+        final package = uri.pathSegments.first;
+        final path =
+            p.url.joinAll(['/$package/lib', ...uri.pathSegments.skip(1)]);
+
+        provider.setOverlay(path, content: value, modificationStamp: 1);
+      }
+    });
+
+    final collection = AnalysisContextCollection(
+      includedPaths: ['/a/'],
+      resourceProvider: provider,
+    );
+
+    _dartContext = collection.contexts.single;
+  }
+
+  Future<void> ensureHasDartAnalyzer() async {
+    if (_dartContext == null) {
+      await _setupDartAnalyzer();
+    }
+  }
+
   @override
   Logger get log => Logger.root;
 
@@ -46,9 +107,12 @@ class TestBackend extends DriftBackend {
   }
 
   @override
-  Future<LibraryElement> readDart(Uri uri) {
+  Future<LibraryElement> readDart(Uri uri) async {
-    // TODO: implement readDart
+    await ensureHasDartAnalyzer();
-    throw UnimplementedError();
+    final result =
+        await _dartContext!.currentSession.getLibraryByUri(uri.toString());
+
+    return (result as LibraryElementResult).element;
   }
 
   @override