Don't further analyze part files (#2185)

drift_dev/lib/src/analysis/resolver/discover.dart

@@ -5,6 +5,7 @@ import 'package:analyzer/dart/element/visitor.dart';
 import 'package:source_gen/source_gen.dart';
 import 'package:sqlparser/sqlparser.dart' hide AnalysisError;
 
+import '../backend.dart';
 import '../driver/driver.dart';
 import '../driver/error.dart';
 import '../driver/state.dart';
@@ -60,6 +61,14 @@ class DiscoverStep {
         try {
           library = await _driver.backend.readDart(_file.ownUri);
         } catch (e) {
+          if (e is! NotALibraryException) {
+            // Backends are supposed to throw NotALibraryExceptions if the
+            // library is a part file. For other exceptions, we better report
+            // the error.
+            _driver.backend.log
+                .warning('Could not resolve Dart library ${_file.ownUri}', e);
+          }
+
           _file.discovery = NotADartLibrary();
           break;
         }

drift_dev/lib/src/backends/build/drift_builder.dart

@@ -185,7 +185,14 @@ class _DriftBuildRun {
 
   /// Checks if the input file contains elements drift should generate code for.
   Future<bool> _checkForElementsToBuild() async {
-    if (!mode.embeddedAnalyzer) {
+    if (mode.embeddedAnalyzer) {
+      // Run the discovery step, which we'll have to run either way, to check if
+      // there are any elements to generate code for.
+      final state = await driver.prepareFileForAnalysis(buildStep.inputId.uri,
+          needsDiscovery: true);
+
+      return state.discovery?.locallyDefinedElements.isNotEmpty == true;
+    } else {
       // An analysis step should have already run for this asset. If we can't
       // pick up results from that, there is no code for drift to generate.
       final fromCache =

drift_dev/test/backends/build/build_integration_test.dart

@@ -1,3 +1,4 @@
+import 'package:build/build.dart';
 import 'package:build_test/build_test.dart';
 import 'package:logging/logging.dart';
 import 'package:test/test.dart';
@@ -104,4 +105,70 @@ selectAll: SELECT * FROM foo;
       'a|lib/database.drift.dart': decodedMatches(contains('selectAll')),
     }, result.dartOutputs, result);
   });
+
+  test('can work with existing part files', () async {
+    final logger = Logger.detached('build');
+    expect(logger.onRecord, neverEmits(anything));
+
+    final result = await emulateDriftBuild(
+      inputs: {
+        'a|lib/main.dart': '''
+import 'package:drift/drift.dart';
+
+part 'table.dart';
+
+@DriftDatabase(tables: [Users])
+class MyDatabase {}
+''',
+        'a|lib/table.dart': '''
+part of 'main.dart';
+
+class Users extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  TextColumn get name => text()();
+}
+''',
+      },
+      logger: logger,
+    );
+
+    checkOutputs(
+      {'a|lib/main.drift.dart': decodedMatches(contains('class User'))},
+      result.dartOutputs,
+      result,
+    );
+  });
+
+  test('handles syntax error in source file', () async {
+    final logger = Logger.detached('build');
+    expect(
+      logger.onRecord,
+      emits(
+        isA<LogRecord>()
+            .having((e) => e.message, 'message',
+                contains('Could not resolve Dart library package:a/main.dart'))
+            .having(
+                (e) => e.error, 'error', isA<SyntaxErrorInAssetException>()),
+      ),
+    );
+
+    final result = await emulateDriftBuild(
+      inputs: {
+        'a|lib/main.dart': '''
+import 'package:drift/drift.dart';
+
+class Users extends Table {
+  IntColumn id => integer().autoIncrement()();
+  TextColumn name => text()();
+}
+
+@DriftDatabase(tables: [Users])
+class MyDatabase {}
+''',
+      },
+      logger: logger,
+    );
+
+    checkOutputs({}, result.dartOutputs, result);
+  });
 }