Summary

On Windows, C++ minja produces output with one fewer newline than Python Jinja2 for certain templates, specifically around blank lines.

Reproduction

The zai-org/GLM-4.6 template with tool_use context fails on Windows:

• Expected (Python Jinja2): # Tools\n\nYou may call... (blank line)
• Actual (C++ minja): # Tools\nYou may call... (no blank line)

The test passes on macOS and Linux.

Investigation

• Template from HuggingFace has pure LF line endings (0a 0a = \n\n)
• No CRLF (\r\n) in the source template
• The normalize_newlines() function correctly handles CRLF→LF conversion
• The issue appears to be Windows-specific behavior in either:
  • Template parsing
  • std::regex behavior
  • File I/O handling

Current Workaround

tests/test-supported-template.cpp uses collapse_blank_lines() on Windows to normalize consecutive newlines before comparison. This masks the real difference but allows CI to pass.

Next Steps

To properly debug this, we need to:

1. Add diagnostic output to the test to print exact bytes on Windows CI
2. Trace through the template parser to find where the newline is lost
3. Check if std::regex or file reading behaves differently on Windows

/cc @ochafik