Remove old <nodoc> syntax (dart-lang#3261)

Co-authored-by: Janice Collins <jcollins@google.com>

Author: parlough

lib/src/model/documentation_comment.dart

@@ -829,10 +829,6 @@ mixin DocumentationComment on Documentable, Warnable, Locatable, SourceCode {
         }
       }
     }
-    if (!hasNodoc && docComment.contains('<nodoc>')) {
-      // TODO(srawlins): Stop supporting this old format.
-      hasNodoc = true;
-    }
     _hasNodoc = hasNodoc;
     _hasInjectHtml = hasInjectHtml;
     _hasTemplate = hasTemplate;

test/src/utils.dart

@@ -30,7 +30,7 @@ import 'package:test/test.dart';
 
 /// The number of public libraries in testing/test_package, minus 2 for
 /// the excluded libraries listed in the initializers for _testPackageGraphMemo
-/// and minus 1 for the <nodoc> tag in the 'excluded' library.
+/// and minus 1 for the @nodoc tag in the 'excluded' library.
 const int kTestPackagePublicLibraries = 27;
 
 final _resourceProvider = pubPackageMetaProvider.resourceProvider;

testing/test_package/lib/example.dart

@@ -26,7 +26,8 @@ const String COLOR_ORANGE = 'orange';
 
 const String COMPLEX_COLOR = 'red' + '-' + 'green' + '-' + 'blue';
 
-/// top level var <nodoc>
+/// top level var
+/// @nodoc
 const DO_NOT_DOCUMENT = 'not documented';
 
 /// This is the same name as a top-level const from the fake lib.
@@ -139,7 +140,7 @@ class Apple {
   /// The read-write field `m`.
   int m = 0;
 
-  /// <nodoc> no docs
+  /// @nodoc no docs
   int? notDocumented;
 
   ///Constructor
@@ -180,7 +181,7 @@ class Apple {
   void methodWithTypedefParam(processMessage p) {}
 
   /**
-   * <nodoc> method not documented
+   * @nodoc method not documented
    */
   void notAPublicMethod() {}
 
@@ -481,15 +482,8 @@ class ShapeType extends _RetainedEnum {
 /// that has some operators
 class SpecializedDuration extends Duration {}
 
-/**
- * class <nodoc>
- */
-class unDocumented {
-  String? s;
-}
-
 /// @nodoc
-class unDocumented2 {
+class unDocumented {
   String? s;
 }
 

testing/test_package/lib/excluded.dart

@@ -1,6 +1,7 @@
 /// This library is excluded from the documentation
 /// even though it is located in the lib folder by
-/// using the <nodoc> tag
+/// using the nodoc tag.
+/// @nodoc
 
 library excluded;