Fix summary handling of unresolved imports, exports, and parts.

pkg/analyzer/lib/src/dart/resolver/scope.dart

Index: pkg/analyzer/lib/src/dart/resolver/scope.dart
diff --git a/pkg/analyzer/lib/src/dart/resolver/scope.dart b/pkg/analyzer/lib/src/dart/resolver/scope.dart
index 05372697380fcfab4193a17a08c54e179d1336c3..ba5b275cbb1395f58ec9433ece3449d9870c7cfa 100644
--- a/pkg/analyzer/lib/src/dart/resolver/scope.dart
+++ b/pkg/analyzer/lib/src/dart/resolver/scope.dart
@@ -452,7 +452,8 @@ class LibraryImportScope extends Scope {
       int count = imports.length;
       for (int i = 0; i < count; i++) {
         ImportElement importElement = imports[i];
-        if (importElement.prefix?.name == prefix && !importElement.uriExists) {
+        if (importElement.prefix?.name == prefix &&
+            importElement.importedLibrary?.isSynthetic != false) {
           Iterable<NamespaceCombinator> showCombinators =
               getShowCombinators(importElement);
           if (showCombinators.isEmpty) {
@@ -471,7 +472,8 @@ class LibraryImportScope extends Scope {
       int count = imports.length;
       for (int i = 0; i < count; i++) {
         ImportElement importElement = imports[i];
-        if (importElement.prefix == null && !importElement.uriExists) {
+        if (importElement.prefix == null &&
+            importElement.importedLibrary?.isSynthetic != false) {
           for (ShowElementCombinator combinator
               in getShowCombinators(importElement)) {
             if (combinator.shownNames.contains(name)) {