Fix OOM in SQL Parser ErrorHandler due to infinite loop in ATN traversal

[JackieTien97]

Description

Fixes an OOM issue caused by infinite recursion in ErrorHandler.isReachable when parsing certain invalid SQL queries (e.g., offset X limitY with syntax errors). The isReachable method was traversing the ANTLR ATN without tracking visited states, leading to infinite loops in the presence of epsilon transition cycles.

Changes

• Modified ErrorHandler.java: Added a visited set to the isReachable BFS traversal to prevent processing the same state multiple times.
• Added SqlParserErrorHandlerTest.java: A new unit test that reproduces the issue and verifies that the parser now correctly throws a ParsingException instead of hanging.

Verification

• Added unit test SqlParserErrorHandlerTest passes.
• Verified manually that select * from t1 offset 40 limit1 no longer causes OOM.

[Copilot]

Pull request overview

This PR fixes an Out-of-Memory (OOM) issue in the SQL parser's error handling caused by infinite recursion when traversing ANTLR's ATN (Augmented Transition Network) for error reporting. The bug occurred when parsing certain malformed SQL queries with syntax errors in LIMIT/OFFSET clauses.

Changes:

• Added visited state tracking in ErrorHandler.isReachable() to prevent infinite loops in epsilon transition cycles
• Added unit test to verify the parser correctly throws ParsingException instead of hanging
• Updated .gitignore to exclude ANTLR-generated files

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/sql/parser/ErrorHandler.java	Fixed infinite loop in isReachable BFS traversal by adding visited set to track processed states; reformatted long comments
iotdb-core/datanode/src/test/java/org/apache/iotdb/db/queryengine/plan/relational/sql/ast/SqlParserErrorHandlerTest.java	Added unit test to verify parser throws exception instead of hanging on malformed LIMIT/OFFSET syntax
.gitignore	Added entry to ignore ANTLR-generated files in relational-grammar module

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 39.35%. Comparing base (337ac47) to head (1118527).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #17023      +/-   ##
============================================
+ Coverage     39.22%   39.35%   +0.12%     
  Complexity      212      212              
============================================
  Files          5075     5075              
  Lines        340393   340397       +4     
  Branches      43443    43444       +1     
============================================
+ Hits         133536   133974     +438     
+ Misses       206857   206423     -434     

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[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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