Warn about unparsed customConstraints

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

@@ -418,15 +418,12 @@ class DartTableResolver extends LocalElementResolver<DiscoveredDartTable> {
 
     if (expression is ListLiteral) {
       for (final entry in expression.elements) {
-        if (entry is StringLiteral) {
-          final value = entry.stringValue;
-          if (value != null) {
-            foundConstraints.add(value);
-            foundConstraintSources.add(entry);
-          }
+        if (entry case StringLiteral(:final stringValue?)) {
+          foundConstraints.add(stringValue);
+          foundConstraintSources.add(entry);
         } else {
-          reportError(DriftAnalysisError.inDartAst(
-              element, entry, 'This must be a string literal.'));
+          reportError(DriftAnalysisError.inDartAst(element, entry,
+              'Drift can only verify custom constraints set as constant string literals.'));
         }
       }
     } else {

drift_dev/test/analysis/resolver/dart/table_test.dart

@@ -491,4 +491,36 @@ class Preferences extends Table {
     expect(file.allErrors,
         [isDriftError(contains('is only meaningful for `STRICT` tables'))]);
   });
+
+  test('warns about non-constant custom constraints', () async {
+    final backend = await TestBackend.inTest({
+      'a|lib/main.dart': r'''
+import 'package:drift/drift.dart';
+
+@DataClassName('MyTable')
+class MyTables extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  TextColumn get name => text().nullable()();
+}
+
+@DataClassName('MyOtherThing')
+class MyOtherThings extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  IntColumn get otherId => integer()();
+  IntColumn get blahId => integer()();
+  TextColumn get name => text().nullable()();
+
+  @override
+  List<String> get customConstraints => ["UNIQUE(${otherId.name}, ${blahId.name})"];
+}
+
+''',
+    });
+
+    final file = await backend.analyze('package:a/main.dart');
+    expect(file.allErrors, [
+      isDriftError(contains(
+          'can only verify custom constraints set as constant string literals.'))
+    ]);
+  });
 }