Null exception in comment_writer

[fishythefish]

Hit a bug in the formatter when formatting pkg/compiler/test/closure/data/captured_variable.dart.
Please report at github.com/dart-lang/dart_style/issues.
Null check operator used on a null value
#0      CommentWriter._commentsBefore (package:dart_style/src/front_end/comment_writer.dart:81:47)
#1      CommentWriter.takeCommentsBefore (package:dart_style/src/front_end/comment_writer.dart:62:12)
#2      SequenceBuilder.addCommentsBefore (package:dart_style/src/front_end/sequence_builder.dart:125:38)
#3      SequenceBuilder.visit (package:dart_style/src/front_end/sequence_builder.dart:103:5)
#4      PieceFactory.writeBody (package:dart_style/src/front_end/piece_factory.dart:152:16)
#5      PieceFactory.writeBlock (package:dart_style/src/front_end/piece_factory.dart:172:5)
#6      AstNodeVisitor.visitBlock (package:dart_style/src/front_end/ast_node_visitor.dart:225:5)
#7      BlockImpl.accept (package:analyzer/src/dart/ast/ast.dart:2006:50)
#8      AstNodeVisitor.visitNode (package:dart_style/src/front_end/ast_node_visitor.dart:1969:10)
#9      PieceWriter.visit (package:dart_style/src/front_end/piece_writer.dart:145:14)
#10     AstNodeVisitor.visitBlockFunctionBody (package:dart_style/src/front_end/ast_node_visitor.dart:232:12)
#11     BlockFunctionBodyImpl.accept (package:analyzer/src/dart/ast/ast.dart:1958:50)
#12     AstNodeVisitor.visitNode (package:dart_style/src/front_end/ast_node_visitor.dart:1969:10)
#13     PieceWriter.visit (package:dart_style/src/front_end/piece_writer.dart:145:14)
#14     PieceFactory.writeFunction.<anonymous closure>.<anonymous closure> (package:dart_style/src/front_end/piece_factory.dart:597:16)
#15     PieceFactory.writeFunctionAndReturnType (package:dart_style/src/front_end/piece_factory.dart:615:20)
#16     PieceFactory.writeFunction.<anonymous closure> (package:dart_style/src/front_end/piece_factory.dart:584:7)
#17     PieceWriter.withMetadata (package:dart_style/src/front_end/piece_writer.dart:265:20)
#18     PieceFactory.writeFunction (package:dart_style/src/front_end/piece_factory.dart:583:12)
#19     AstNodeVisitor.visitFunctionDeclaration (package:dart_style/src/front_end/ast_node_visitor.dart:798:5)
#20     FunctionDeclarationImpl.accept (package:analyzer/src/dart/ast/ast.dart:8357:50)
#21     AstNodeVisitor.visitNode (package:dart_style/src/front_end/ast_node_visitor.dart:1969:10)
#22     PieceFactory.nodePiece.<anonymous closure> (package:dart_style/src/front_end/piece_factory.dart:1485:7)
#23     PieceWriter.build (package:dart_style/src/front_end/piece_writer.dart:189:18)
#24     PieceFactory.nodePiece (package:dart_style/src/front_end/piece_factory.dart:1484:25)
#25     SequenceBuilder.visit (package:dart_style/src/front_end/sequence_builder.dart:104:18)
#26     AstNodeVisitor.run (package:dart_style/src/front_end/ast_node_visitor.dart:112:18)
#27     DartFormatter.formatSource (package:dart_style/src/dart_formatter.dart:219:24)
#28     _processFile (package:dart_style/src/io.dart:175:28)
<asynchronous suspension>
#29     _processDirectory (package:dart_style/src/io.dart:134:10)
<asynchronous suspension>
#30     formatPaths (package:dart_style/src/io.dart:95:12)
<asynchronous suspension>
#31     FormatCommand.run (package:dart_style/src/cli/format_command.dart:267:7)
<asynchronous suspension>
#32     CommandRunner.runCommand (package:args/command_runner.dart:212:13)
<asynchronous suspension>
#33     DartdevRunner.runCommand (package:dartdev/dartdev.dart:240:18)
<asynchronous suspension>
#34     runDartdev (package:dartdev/dartdev.dart:47:16)
<asynchronous suspension>
#35     main (file:///b/f/w/pkg/dartdev/bin/dartdev.dart:13:5)
<asynchronous suspension>

[fishythefish]

I suspect that this comes from having a snippet like this:

@override
// ignore: overridden_fields
final FunctionEntity _member;

(Note that this is how VSCode quick fix will add the ignore comment.)

If I change it to

@override
final FunctionEntity _member; // ignore: overridden_fields

then the formatter works fine.

[munificent]

Thanks, I'll take a look.

[munificent]

There may have been two issues in that file. With the latest dart_style, I didn't get a crash on the // ignore comment after a metadata annotation. If that's what was crashing for you, it was probably already fixed by #1612 (which I haven't rolled into the SDK yet).

But I did get another crash in that same file with the same stack trace. That one was caused by:

  var /**/ local = parameter;

Because Dart used to use Javadoc style doc comments ages ago, it seems the parser treats /**/ as a doc comment. Also, analyzer has a somewhat confusing thing where it treats doc comments part of the AST when the formatter really wants to handle them separately. Even more confusing, it treats that /**/ as a doc comment for the entire variable declaration statement even though it's embedded in the middle of it.

Either way, the formatter handles this (incredibly rare) case better now.