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Fix Python regex group counting inconsistency with C# (issue #28) #92

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Fix Python regex group counting inconsistency with C# (issue #28) #92

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@konard konard commented Sep 14, 2025 •
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Summary

  • Fixed inconsistency between C# and Python regex engines when counting inner groups
  • Replaced numbered groups with named groups for maintainable and consistent patterns
  • Updated both C# and Python implementations to use consistent named group syntax

Problem

Python regular expression engine counts inner groups differently than C#, causing inconsistent behavior between the two implementations. As shown in the original issue:

C#: "$1 $2$3{$4};$5"
Python: r"\1 \2\3{\5};\6"

The numbering of capture groups diverged between the two engines, making it difficult to maintain identical transformation logic.

Solution

  1. Updated C# regex pattern (line 286) from numbered groups to named groups:

    // Before
(new Regex(@"(struct|class) ([a-zA-Z0-9]+)(\s+){([\sa-zA-Z0-9;:_]+?)}([^;])"), "$1 $2$3{$4};$5", 0)

// After 
(new Regex(@"(?<type>struct|class) (?<name>[a-zA-Z0-9]+)(?<whitespace>\s+){(?<body>[\sa-zA-Z0-9;:_]+?)}(?<after>[^;])"), "${type} ${name}${whitespace}{${body}};${after}", 0)

  2. Updated Python regex patterns to match C# named groups:

    # Before
SubRule(r"(struct|class) ([a-zA-Z0-9]+)(\s+){([\sa-zA-Z0-9;:_]+?)}([^;])", r"\1 \2\3{\4};\5", max_repeat=0)

# After
SubRule(r"(?P<type>struct|class) (?P<name>[a-zA-Z0-9]+)(?P<whitespace>\s+){(?P<body>[\sa-zA-Z0-9;:_]+?)}(?P<after>[^;])", r"\g<type> \g<name>\g<whitespace>{\g<body>};\g<after>", max_repeat=0)

  3. Fixed all Python backreferences from \k<name> (C# syntax) to (?P=name) (Python syntax) throughout the entire codebase

Test Results

Benefits

  • Consistency: Both C# and Python implementations now use equivalent named group patterns
  • Maintainability: Named groups are self-documenting and easier to understand
  • Reliability: Eliminates group counting discrepancies between regex engines
  • Future-proof: Makes it easier to translate patterns between C# and Python

🤖 Generated with Claude Code

Resolves #28

@konard
Initial commit with task details for issue #28
6e14ad5 
Adding CLAUDE.md with task information for AI processing.
This file will be removed when the task is complete.

Issue: #28
@konard konard self-assigned this Sep 14, 2025
@konard @claude
Fix Python regex group counting inconsistency with C# (issue #28)
df5993a 
Replace numbered groups with named groups to ensure consistent behavior
between C# and Python regex engines when counting inner groups.

Changes:
- Updated C# regex pattern from numbered groups ($1, $2, etc.) to named groups (${type}, ${name}, etc.)
- Updated Python regex patterns to use named group syntax (?P<name>) and backreferences (?P=name)
- Fixed all Python \k<name> backreferences to use (?P=name) syntax
- Both versions now use consistent named group patterns for maintainability

This resolves the issue where Python regex counts inner groups differently
than C# regex, ensuring both transformers produce identical results.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>
@konard konard changed the title [WIP] Python regular expression counts inner groups differently Fix Python regex group counting inconsistency with C# (issue #28) Sep 14, 2025
@konard konard marked this pull request as ready for review September 14, 2025 01:19
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Python regular expression counts inner groups differently

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