Workaround for accessing part sources while resolving a library.

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 a362771debb68339b52b03623ac369d82b827ddd..d900475ad09919c4d1e0f2152959f00b4ea1f5d9 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -653,6 +653,16 @@ class AnalysisDriver {
       AnalysisContext analysisContext = _createAnalysisContext(libraryContext);
       try {
         analysisContext.setContents(file.source, file.content);
+
+        // TODO(scheglov) Remove this.
+        // https://github.com/dart-lang/sdk/issues/28110
+        analysisContext.setContents(libraryFile.source, libraryFile.content);
+        for (FileState part in libraryFile.partedFiles) {
+          if (part.exists) {
+            analysisContext.setContents(part.source, part.content);
+          }
+        }
+
         CompilationUnit resolvedUnit = analysisContext.resolveCompilationUnit2(
             file.source, libraryFile.source);
         List<AnalysisError> errors = analysisContext.computeErrors(file.source);