Scaffold api to support type converters in moor files

I still don't know how to parse expressions though :(

moor_generator/lib/src/analyzer/moor/inline_dart_resolver.dart

@@ -0,0 +1,45 @@
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/element/type.dart';
+import 'package:moor_generator/src/analyzer/session.dart';
+
+/// Resolves the type of Dart expressions given as a string. The
+/// [importStatements] are used to discover types.
+///
+/// The way this works is that we create a fake file for the analyzer. That file
+/// has the following content:
+/// ```
+/// import 'package:moor/moor.dart'; // always imported
+/// // all import statements
+///
+/// var expr = $expression;
+/// ```
+///
+/// We can then obtain the type of an expression by reading the inferred type
+/// of the top-level `expr` variable in that source.
+class InlineDartResolver {
+  final List<String> importStatements = [];
+  final MoorTask task;
+
+  InlineDartResolver(this.task);
+
+  Future<DartType> resolveDartTypeOf(String expression) async {
+    final template = _createDartTemplate(expression);
+    final unit = await task.backendTask.parseSource(template);
+
+    final declaration = unit.declarations.single as TopLevelVariableDeclaration;
+    return declaration.variables.variables.single.initializer.staticType;
+  }
+
+  String _createDartTemplate(String expression) {
+    final fakeDart = StringBuffer();
+
+    fakeDart.write("import 'package:moor/moor.dart';\n");
+    for (var import in importStatements) {
+      fakeDart.write("import '$import';\n");
+    }
+
+    fakeDart.write('var expr = $expression;\n');
+
+    return fakeDart.toString();
+  }
+}

moor_generator/lib/src/analyzer/moor/parser.dart

@@ -16,7 +16,10 @@ class MoorParser {
     final createdReaders = <CreateTableReader>[];
 
     for (var parsedStmt in results) {
-      if (parsedStmt.rootNode is CreateTableStatement) {
+      if (parsedStmt.rootNode is ImportStatement) {
+        final importStmt = (parsedStmt.rootNode) as ImportStatement;
+        task.inlineDartResolver.importStatements.add(importStmt.importedFile);
+      } else if (parsedStmt.rootNode is CreateTableStatement) {
         createdReaders.add(CreateTableReader(parsedStmt));
       } else {
         task.reportError(ErrorInMoorFile(

moor_generator/lib/src/analyzer/session.dart

@@ -6,6 +6,7 @@ import 'package:analyzer/dart/element/type.dart';
 import 'package:moor/moor.dart' show Table;
 import 'package:moor_generator/src/analyzer/dart/parser.dart';
 import 'package:moor_generator/src/analyzer/errors.dart';
+import 'package:moor_generator/src/analyzer/moor/inline_dart_resolver.dart';
 import 'package:moor_generator/src/analyzer/moor/parser.dart';
 import 'package:moor_generator/src/analyzer/results.dart';
 import 'package:moor_generator/src/analyzer/sql_queries/sql_parser.dart';
@@ -151,9 +152,12 @@ class DartTask extends FileTask<ParsedDartFile> {
 class MoorTask extends FileTask<ParsedMoorFile> {
   final String content;
   final TypeMapper mapper = TypeMapper();
+  /* late final */ InlineDartResolver inlineDartResolver;
 
   MoorTask(BackendTask task, MoorSession session, this.content)
-      : super(task, session);
+      : super(task, session) {
+    inlineDartResolver = InlineDartResolver(this);
+  }
 
   @override
   FutureOr<ParsedMoorFile> compute() {

moor_generator/lib/src/backends/backend.dart

@@ -1,3 +1,4 @@
+import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:logging/logging.dart';
 import 'package:moor_generator/src/analyzer/session.dart';
@@ -17,5 +18,6 @@ abstract class BackendTask {
   Logger get log;
 
   Future<LibraryElement> resolveDart(Uri uri);
+  Future<CompilationUnit> parseSource(String dart);
   Future<String> readMoor(Uri uri);
 }

moor_generator/lib/src/backends/build/build_backend.dart

@@ -1,3 +1,5 @@
+import 'package:analyzer/analyzer.dart';
+import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:build/build.dart' hide log;
 import 'package:build/build.dart' as build show log;
@@ -32,6 +34,11 @@ class BuildBackendTask extends BackendTask {
     return step.resolver.libraryFor(_resolve(uri));
   }
 
+  @override
+  Future<CompilationUnit> parseSource(String dart) async {
+    return null;
+  }
+
   @override
   Logger get log => build.log;
 }

moor_generator/test/utils/test_backend.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 
+import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:build/build.dart';
 import 'package:build_test/build_test.dart';
@@ -60,4 +61,9 @@ class _TestBackendTask extends BackendTask {
     await backend._ready;
     return await backend._resolver.libraryFor(AssetId.resolve(path.toString()));
   }
+
+  @override
+  Future<CompilationUnit> parseSource(String dart) {
+    return null;
+  }
 }