Upgrade to sqlglot 30.9.0 to support external dialect plugins #5840

Summary

While working on a DB2 adapter for SQLMesh, I encountered a compatibility issue with sqlglot 30.9.0.

The DB2 implementation relies on an external DB2 dialect plugin, which currently requires sqlglot==30.9.0. However, SQLMesh is currently pinned to sqlglot~=30.8.0. Upgrading to sqlglot 30.9.0 exposes an API incompatibility in SQLMesh's parser overrides.

Observed Error

TypeError: _parse_join() got an unexpected keyword argument 'alias_tokens'

Root Cause

The signature of Parser._parse_join() changed between sqlglot 30.8.0 and 30.9.0.

sqlglot 30.8.0

def _parse_join(
    self,
    skip_join_token: bool = False,
    parse_bracket: bool = False,
)

sqlglot 30.9.0

def _parse_join(
    self,
    skip_join_token: bool = False,
    parse_bracket: bool = False,
    alias_tokens: t.Collection[TokenType] | None = None,
)

SQLMesh overrides this method in dialect.py, but the override does not currently accept the new alias_tokens parameter.

As a result, when sqlglot 30.9.0 internally invokes:

_parse_join(alias_tokens=...)

SQLMesh raises the exception shown above.

Impact

• Prevents SQLMesh from working with sqlglot 30.9.0
• Blocks integration with external dialect plugins that depend on newer sqlglot versions
• Affects DB2 adapter development, where the DB2 dialect plugin currently requires sqlglot 30.9.0

Possible Resolution

Either:

1. Upgrade SQLMesh to support sqlglot 30.9.0, or
2. Make the _parse_join() override forward-compatible with newer sqlglot parser signatures.

Additional Context

I discovered this issue while implementing a DB2 adapter, but the underlying problem appears to be a general compatibility issue with newer sqlglot releases rather than something specific to DB2.

Proposed Contribution

I believe I have a fix for this issue and would be happy to contribute it as a PR if maintaining compatibility with sqlglot 30.9.0 is something the project would like to support.