Fix: Remove Extra Curly Braces from Data Table Variables in Scenario Outlines

[tide-khushal]

🐛 Problem

When using BDD scenario outlines with data tables containing variables from the Examples table, the generated Dart code incorrectly wrapped variable values in extra curly braces {}, causing invalid Dart syntax as reported in #110.

Before (Broken):

const bdd.DataTable([
  ['counter', 'color'],
  [
    {'5'},    // ❌ not an intuitive syntax - extra curly braces
    {'blue'}  // ❌ not an intuitive syntax - extra curly braces
  ]
])

After (Fixed):

const bdd.DataTable([
  ['counter', 'color'],
  [
    '5',      // ✅ Improved syntax
    'blue'    // ✅ Improved syntax
  ]
])

🔧 Root Cause & Solution

Issue Analysis

The bug was in lib/src/scenario_generator.dart in the _replacePlaceholders() function at line 131:

replaced = replaced.replaceAll('<$e>', '{${example[e]}}');

This function indiscriminately wrapped all placeholder substitutions in curly braces, including data table variables where they shouldn't be wrapped.

Core Fix

• Refactored: _replacePlaceholders() → _replacePlaceholdersInLine()
• Added: Logic to detect data table steps (LineType.dataTableStep)
• Conditional replacement:
  • Data table variables: Substitute directly without curly braces
  • Regular step variables: Maintain existing curly brace wrapping behavior

// New implementation
BddLine _replacePlaceholdersInLine(BddLine line, Map<String, String> example) {
  var replaced = line.value;
  final isDataTable = line.type == LineType.dataTableStep;
  for (final e in example.keys) {
    final replaceWith = isDataTable ? '${example[e]}' : '{${example[e]}}';
    replaced = replaced.replaceAll('<$e>', replaceWith);
  }
  return BddLine.fromValue(line.type, replaced);
}

🧪 Testing & Validation

Comprehensive Test Coverage

• Added: 'Scenario Outline with data table variables' test in test/data_tables_test.dart
• Validates: Exact scenario from issue Data Table Variables Incorrectly Wrapped in Curly Braces in Generated Dart Code #110
• Ensures: No regression for existing functionality

Real-World Example

• Enhanced: Example app with working scenario outline + data table
• Demonstrates: The fix in action with a complete working example
• Includes: Proper step implementation for data table validation

📋 Files Changed

File	Change Type	Description
lib/src/scenario_generator.dart	🔧 Fix	Core logic fix for data table variable substitution
test/data_tables_test.dart	✅ Test	Regression test covering issue #110
example/*	📝 Example	Working demonstration of the fix

✅ Verification

• Issue Data Table Variables Incorrectly Wrapped in Curly Braces in Generated Dart Code #110 scenario works: Variables in data tables no longer have extra braces
• Backward compatible: Regular step parameters still work correctly
• All tests pass: No regression in existing functionality
• Example validates: Real-world usage demonstrates the fix

🎯 Impact

Resolves: Issue #110 - Data table variables incorrectly wrapped in curly braces
Enables: Proper BDD testing with scenario outlines using data tables
Maintains: Full backward compatibility with existing features

This fix ensures that generated Dart code is syntactically correct and tests can execute properly when using scenario outlines with data table variables.

[olexale]

Hey, thanks for the PR! 🙌 That’s definitely a bug, so I really appreciate you fixing it. Could you please revert the changes to the example app, though?

I feel that data tables should be used with caution: they don’t allow compile-time type validation and can break at runtime if someone accidentally changes a type. On top of that, I find them harder to read. Even in your artificial example, something like:

Then I see <counter> counter value on <color> background color

would be much clearer.

Since I’d prefer not to promote this functionality, I think it’s best to exclude it from the example.