Incorrect Coverage Reporting for Extension Methods with Split Return Type and Name

[GiancarloCante]

The coverage tool incorrectly marks function names as uncovered when the extension method's name appears on a different line from its return type.

This results in inaccurate coverage reports despite the code being fully tested.

Example

The following patterns all show the issue:

extension.dart

class AbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyz {}

extension FunctionNameInOtherLineByLongReturnTypeExtension on String {
  AbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyz
  functionNameInOtherLineByLongReturnType() {
    return AbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyz();
  }
}

extension FunctionNameInOtherLineByCommentsExtension on String {
  bool
  //
  functionNameInOtherLineByComments() {
    return true;
  }
}

extension FunctionNameInOtherLineByLongNameExtension on String {
  bool
  functionNameInOtherLineByLongNameAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrs() {
    return true;
  }
}

extension_test.dart

import 'package:test_coverage_demo/extension.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  test('function Name In Other Line By Long Return Type', () {
    expect(''.functionNameInOtherLineByLongReturnType(), isA<Object>());
  });
  test('function Name In Other Line By Comments', () {
    expect(''.functionNameInOtherLineByComments(), isA<Object>());
  });

  test('function Name In Other Line By Long Name', () {
    expect(
      ''.functionNameInOtherLineByLongNameAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrs(),
      isA<Object>(),
    );
  });
}

flutter test --coverage && \
genhtml coverage/lcov.info -o coverage/html && \
open coverage/html/index.html

Line data    Source code
 1              : class AbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyz {}
 2              : 
 3              : extension FunctionNameInOtherLineByLongReturnTypeExtension on String {
 4            1 :   AbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyz
 5            0 :   functionNameInOtherLineByLongReturnType() {
 6            1 :     return AbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrstuvwxyz();
 7              :   }
 8              : }
 9              : 
10              : extension FunctionNameInOtherLineByCommentsExtension onString {
11            1 :   bool
12              :   //
13            0 :   functionNameInOtherLineByComments() {
14              :     return true;
15              :   }
16              : }
17              : 
18              : extension FunctionNameInOtherLineByLongNameExtension onString {
19            1 :   bool
20            0 :  functionNameInOtherLineByLongNameAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnpqrstuvwxyzAbcdefghijklmnopqrstuvwxyzAbcdefghijklmnopqrs() {
21              :     return true;
22              :   }
23              : }

Environment

• Dart version 3.7.0

[a-siva]

//cc @liamappelbe

[liamappelbe]

Can't repro this using the latest Dart/Flutter, or an older version. @GiancarloCante what version of package:coverage are you using? Is there anything else about your setup that could help me repro this?

[GiancarloCante]

Hi @liamappelbe, just confirming that I can reproduce the issue on my end.

Repro steps:

1. Created a fresh Flutter project using:

   flutter create test_coverage_demo

2. Copied the code examples exactly as described in this issue.

3. Ran the following command:

   flutter test --coverage && genhtml coverage/lcov.info -o coverage/html && open coverage/html/index.html

My environment:

Flutter 3.29.2 • Dart 3.7.2
macOS 15.3.2 (Apple Silicon)

[liamappelbe]

Ok, I'm able to repro it now. I had tried to repro this in Dart 3.6 and 3.8, but it seems it only repros in 3.7. In any case, it's fixed at head, so there's nothing to do here.