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https://issues.apache.org/jira/browse/IMPALA-15220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18099003#comment-18099003
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Sreenath commented on IMPALA-15220:
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[~arawat] Please guide.
> [FE] Maintain an ANTLR4 SQL grammar to enable multi-language parser
> generation (Python, C++, Go, Rust)
> ------------------------------------------------------------------------------------------------------
>
> Key: IMPALA-15220
> URL: https://issues.apache.org/jira/browse/IMPALA-15220
> Project: IMPALA
> Issue Type: Improvement
> Components: Frontend
> Reporter: Shreya Chakraborty
> Priority: Minor
>
> *Problem Statement*
> Currently, Apache Impala's SQL parser is implemented in Java using JFlex /
> CUP inside the `fe` (frontend) module (`org.apache.impala.analysis.Parser`).
> While this works well for internal query planning inside the JVM coordinator,
> it creates significant friction for external tools, client drivers, and
> non-Java ecosystems:
> 1. *JVM Dependency:* Applications written in Python, Rust, Go, or C++ must
> either spin up a heavyweight JVM process or rely on complex IPC wrappers just
> to parse/validate Impala SQL statements.
> 2. *Ecosystem Fragmentation:* Third-party tools (CI/CD linters, query
> formatters, IDE extensions like VS Code, and semantic routing proxies) cannot
> easily re-use Impala's dialect parser natively.
> As seen in [Apache Superset
> (#32143)|https://github.com/apache/superset/issues/32143] and [SQLFluff
> (#6095)|https://github.com/sqlfluff/sqlfluff/issues/6095], downstream
> ecosystems are actively adopting multi-dialect parsers. Without an ANTLR
> grammar maintained in Impala as the source of truth, third-party tools either
> drop Impala support or rely on fragile fallback dialects.
> *Proposed Solution*
> Introduce an ANTLR4 grammar file (`ImpalaLexer.g4` and `ImpalaParser.g4`) for
> the Impala SQL dialect along with standard Visitor/Listener base classes.
> While ANTLR4 generates a Concrete Syntax Tree (CST) / Parse Tree
> out-of-the-box, its multi-target code generation allows developers in any
> supported backend (C++, Python, Go, Rust, Java) to implement generated
> Visitors or Listeners to walk the CST and construct their own domain-specific
> ASTs or IR representations.
> ANTLR4 generates standalone, high-performance parsers across multiple target
> languages, including C++, Java, Python, Go, Rust, and JavaScript.
> *Key Deliverables:*
> 1. *Grammar Specification (`.g4` files):* A formal ANTLR4 grammar matching
> Impala’s SQL dialect (reserved keywords, DDL, DML, SELECT expressions, and
> built-in functions).
> 2. *Build Integration:* Integrate ANTLR4 code generation into the build
> pipeline to keep the grammar in sync with dialect updates.
> 3. *Reference Parsers/AST:* Provide reference target implementations or
> artifacts for popular client languages (e.g., Python/Javascript).
> *Key Use Cases & Benefits*
> 1. *Multi-Language Client Backends:* Native client-side parsing and query
> validation in Python (e.g., `impala-python`), C++, Go, or Rust without
> requiring a Java runtime.
> 2. *Tooling & IDE Support:* Enables syntax highlighting, auto-completion, and
> static linting in editors (VS Code, JetBrains) and CI/CD SQL validation
> pipelines.
> 3. *Lightweight AST Transformations:* Allows tools to extract tables,
> columns, aliases, and predicates from queries before sending them to the
> cluster.
> *Reference Implementation*
> A prototype implementation demonstrating this pattern is being explored in
> Hue:
> 1. *Parse Tree Visitors:* Used specifically for extracting syntax structures
> to feed structured feedback loops into LLMs and run schema validation against
> metadata.
> 2. *Autocomplete Grammar Separation:* Note that while the core Impala parser
> requires a strict grammar, editor interactive tools may utilize a
> tailored/error-tolerant variant (`ImpalaAutocomplete.g4`) optimized for
> partial token streams.
> [PR in Hue|https://github.infra.cloudera.com/CDH/hue/pull/1096] -
> grammar/impala/Common.g4 (for the impala grammar files)
> Would love to get feedback from the maintainers on whether an ANTLR4 grammar
> could serve as an official repository component or a sub-module.
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