Report an error when a part-of refers to an unnamed library.

pkg/analyzer/lib/src/error/codes.dart

Index: pkg/analyzer/lib/src/error/codes.dart
diff --git a/pkg/analyzer/lib/src/error/codes.dart b/pkg/analyzer/lib/src/error/codes.dart
index 9a04fd2e9e8cffc3c647587e1e9c567c5863f9b8..92345331f86cc442be79a800b9edc509f0989821 100644
--- a/pkg/analyzer/lib/src/error/codes.dart
+++ b/pkg/analyzer/lib/src/error/codes.dart
@@ -4419,6 +4419,22 @@ class StaticWarningCode extends ErrorCode {
           "Try including a different part, or "
           "changing the name of the library in the part's part-of directive.");
 
+  /**
+   * Parts: It is a static warning if the referenced part declaration
+   * <i>p</i> names a library that does not have a library tag.
+   *
+   * Parameters:
+   * 0: the URI of the expected library
+   * 1: the non-matching actual library name from the "part of" declaration
+   */
+  static const StaticWarningCode PART_OF_UNNAMED_LIBRARY =
+      const StaticWarningCode(
+          'PART_OF_UNNAMED_LIBRARY',
+          "Library is unnamed. Expected a URI not a library name '{0}' in the "
+          "part-of directive.",
+          "Try changing the part-of directive to a URI, or try including a"
+          " different part.");
+
   /**
    * 7.6.2 Factories: It is a static warning if the function type of <i>k'</i>
    * is not a subtype of the type of <i>k</i>.