how to get debug output for flutter using build_runner package?

Question

I'm trying to use the build_runner package to generate code in my project.

Nothing is getting generated with dart run build_runner build

How can I verify that my textBuilder is getting run? For example, is there a way that I can put some output statements into my textBuilder?

// lib/src/builder.dart
import 'package:build/build.dart';
import 'example.dart';

// how can I verify this code is getting run?

Builder textBuilder(BuilderOptions options) => TextBuilder();

or

// lib/src/example.dart
import 'dart:convert';
import 'package:build/build.dart';

class TextBuilder implements Builder {
  @override
  Map<String, List<String>> get buildExtensions => const {
        '^assets/{{}}.json': ['lib/generated/{{}}.dart'],
      };

  @override
  Future<void> build(BuildStep buildStep) async {

    // how can I verify this code is getting run?

    final inputId = buildStep.inputId;
    final outputId = AssetId(
      inputId.package,
      inputId.path
          .replaceFirst('assets/', 'lib/generated/')
          .replaceFirst('.json', '.dart'),
    );

    final messages = (json.decode(await buildStep.readAsString(inputId)) as Map)
        .cast<String, String>();

    final outputBuffer = StringBuffer('// Generated, do not edit\n');
    messages.forEach((key, value) {
      outputBuffer.writeln('const String $key = \'$value\';');
    });

    await buildStep.writeAsString(outputId, outputBuffer.toString());
  }
}

I've also tried setting the --verbose flag for build, but it doesn't get any extra output:

$ dart run build_runner build --verbose
[INFO] Entrypoint:Generating build script...
[INFO] Entrypoint:Generating build script completed, took 278ms
[INFO] BuildDefinition:Initializing inputs
[INFO] BuildDefinition:Reading cached asset graph...
[INFO] BuildDefinition:Reading cached asset graph completed, took 88ms
[INFO] BuildDefinition:Checking for updates since last build...
[INFO] BuildDefinition:Checking for updates since last build completed, took 937ms
[INFO] Build:Running build...
[INFO] Build:Running build completed, took 6ms
[INFO] Build:Caching finalized dependency graph...
[INFO] Build:Caching finalized dependency graph completed, took 61ms
[INFO] Build:Succeeded after 75ms with 0 outputs (0 actions)