[linter] Update missing_code_block_language_in_doc_comment to avoid l…

…inting indented code blocks.

After trying to add the lint to flutter (flutter/flutter#145354), I noticed that we lint on indented code blocks, which we should not be doing.

This CL uses the new code block type in https://dart-review.googlesource.com/c/sdk/+/358326 to make sure we only lint on fenced code blocks.

Change-Id: Ic13596dd3c95ce4ff64deeffe02da0fdb7a298e0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/359981
Reviewed-by: Samuel Rawlins <[email protected]>
Commit-Queue: Kallen Tu <[email protected]>

pkg/linter/lib/src/rules/missing_code_block_language_in_doc_comment.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/doc_comment.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 
 import '../analyzer.dart';
@@ -69,13 +70,14 @@ class _Visitor extends SimpleAstVisitor<void> {
   @override
   void visitComment(Comment node) {
     for (var codeBlock in node.codeBlocks) {
-      if (codeBlock.infoString == null) {
-        var openingCodeBlockFence = codeBlock.lines.first;
-        rule.reportLintForOffset(
-          openingCodeBlockFence.offset,
-          openingCodeBlockFence.length,
-        );
-      }
+      if (codeBlock.infoString != null) continue;
+      if (codeBlock.type != CodeBlockType.fenced) continue;
+
+      var openingCodeBlockFence = codeBlock.lines.first;
+      rule.reportLintForOffset(
+        openingCodeBlockFence.offset,
+        openingCodeBlockFence.length,
+      );
     }
   }
 }

pkg/linter/test/rules/missing_code_block_language_in_doc_comment_test.dart

@@ -22,6 +22,7 @@ class MissingCodeBlockLanguageInDocCommentTest extends LintRuleTest {
 /// ```dart
 /// test
 /// ```
+class A {}
 ''');
   }
 
@@ -43,6 +44,17 @@ class A {}
 ''');
   }
 
+  test_indentedCodeBlock() async {
+    await assertNoDiagnostics(r'''
+/// Example:
+///
+///     var printer = Printer();
+///     printer.printToStdout();
+///
+class A {}
+''');
+  }
+
   test_missingLanguage() async {
     await assertDiagnostics(r'''
 /// ```