fix: fix unclosed literal error for consecutive backslashes

[rayudu3745]

Issue: SpannerStatementParser
failed to correctly parse SQL string literals containing consecutive backslashes (e.g., SELECT '\'). When two backslashes were placed together, the parser would incorrectly assume the character immediately following them (like a closing quote) was being escaped. This caused the parser to skip the closing quote and eventually throw an INVALID_ARGUMENT: SQL statement contains an unclosed literal exception on valid SQL.

Fix: Updated SpannerStatementParser.java
to toggle the boolean escape state (lastCharWasEscapeChar = !lastCharWasEscapeChar;) when encountering a backslash. This ensures consecutive backslashes correctly cancel each other out in pairs, perfectly preserving the string literal boundaries.

[gemini-code-assist]

Summary of Changes

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This pull request resolves a critical parsing bug in the SpannerStatementParser that caused valid SQL statements containing consecutive backslashes within string literals to fail with an "unclosed literal" exception. The fix involves a precise adjustment to the escape character handling logic, ensuring that the parser correctly interprets backslash sequences and maintains accurate string literal boundaries. This enhancement improves the robustness of the SQL parser and prevents erroneous parsing failures.

Highlights

• Fix for SQL string literal parsing: The SpannerStatementParser was incorrectly handling consecutive backslashes in SQL string literals, leading to INVALID_ARGUMENT: SQL statement contains an unclosed literal errors for valid SQL like SELECT '\\'. This issue has been resolved.
• Updated escape character logic: The logic for tracking escape characters (lastCharWasEscapeChar) in the parser was modified to toggle its state (!lastCharWasEscapeChar) when a backslash is encountered. This ensures that pairs of backslashes correctly cancel each other out, preserving string literal boundaries.
• Enhanced test coverage: New unit tests were added to SpannerStatementParserTest to specifically validate the correct parsing of SQL statements containing single and double escaped backslashes, and to confirm that expected SpannerExceptions are thrown for truly unclosed literals.

Changelog

• google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/SpannerStatementParser.java
  • Updated the logic for handling backslash characters within string literals to correctly manage the escape state.
• google-cloud-spanner/src/test/java/com/google/cloud/spanner/connection/SpannerStatementParserTest.java
  • Added new imports for ErrorCode.INVALID_ARGUMENT, SpannerException, and fail assertion.
  • Introduced a new test method testRemoveCommentsAndTrim to verify the parser's behavior with various valid and invalid SQL statements containing backslashes.

Activity

• No specific activity has been recorded for this pull request yet.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a parsing issue with consecutive backslashes in SQL string literals by toggling the escape state. The changes in SpannerStatementParser.java are logical and the new tests in SpannerStatementParserTest.java effectively validate the fix for removeCommentsAndTrim. I've added a couple of suggestions for further improvement.