Took me a minute to even reproduce it cleanly.
Start by reproducing the issue with a minimal test case to confirm the behavior, then systematically trace the parser's logic to identify where quotation marks are being discarded. Propose a fix that correctly handles quoted fields, including edge cases like escaped quotes and embedded delimiters, and validate with comprehensive tests.
Pro tip: Demonstrate awareness of CSV parsing complexities (e.g., RFC 4180) and mention that silent data corruption is worse than a crash—so adding validation or logging for malformed input is crucial. Also, consider whether to fix the parser in-house or adopt a battle-tested library, weighing trade-offs.
Create a minimal CSV input that triggers the issue, such as a field with quotes, and run the parser to confirm the quotation marks are dropped. Isolate the parsing logic to narrow down where the loss occurs.
Step through the parser code or add debug logging to see how tokens are processed. Check if the parser treats quotes as special characters and strips them without preserving them in the output.
Modify the parser to retain quotation marks when they are part of the field content, ensuring proper handling of escaped quotes (e.g., "") and quoted fields containing delimiters. Consider using a state machine or regex-based approach.
Apply the fix and write unit tests covering normal cases, quoted fields, escaped quotes, and malformed input. Run the tests to verify the output now includes quotation marks correctly.
Test with real-world CSV files and edge cases. Add monitoring or assertions to detect silent data corruption in the future, and document the fix.
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