Fix for searching top-level declarations in parts.

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index 5f8be4c71509ffb422986a4f0364fea5d3a7bf6f..a362771debb68339b52b03623ac369d82b827ddd 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -1573,6 +1573,9 @@ class _TopLevelNameDeclarationsTask {
       if (!file.isPart) {
         bool isExported = false;
         TopLevelDeclaration declaration = file.topLevelDeclarations[name];
+        for (FileState part in file.partedFiles) {
+          declaration ??= part.topLevelDeclarations[name];
+        }
         if (declaration == null) {
           declaration = file.exportedTopLevelDeclarations[name];
           isExported = true;