fix(cubesql): Support EXTRACT(EPOCH) over timestamp diff on Snowflake

[MazterQyou]

Check List

• Tests have been run in packages where changes have been made if available
• Linter has been run for changed code
• Tests for the changes have been added if not covered yet
• Docs have been added / updated if required

Description of Changes Made

This PR detects EXTRACT(EPOCH FROM (a - b)) over a timestamp subtraction in the wrapper and, when the dialect provides an expressions/extract_epoch_diff template, renders the operands separately as a seconds diff. This is needed because Snowflake accepts EPOCH on a timestamp but not on an interval. Snowflake maps it to DATEDIFF(SECOND, b, a); all other dialects fall back to the existing EXTRACT(EPOCH FROM (a - b)) output unchanged. Related test is included.

[claude]

Claude finished @MazterQyou's task in 50s —— View job

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Code Review

Verdict: LGTM — 0 high, 0 medium, 2 low (nits)

• Read PR diff
• Inspect surrounding wrapper logic
• Verify template-existence pattern matches existing usage
• Check edge cases (Cast peeling, non-diff EPOCH, SQL injection)

Summary

Clean, well-scoped change. The detection path is correctly gated: dialect must opt in via expressions/extract_epoch_diff, otherwise behavior is unchanged. The SQL-injection guard on date_part runs before the new branch (wrapper.rs:3139), so the new code only executes for the literal "epoch". args[1] is safe — guarded by args.len() >= 2. The contains_template opt-in pattern is consistent with the existing expressions/interval handling in transport/service.rs:802.

The timestamp_diff_operands helper recursively peels Cast wrappers, which correctly handles EXTRACT(EPOCH FROM CAST(a - b AS …)) and falls through cleanly for non-subtraction inputs (regular EXTRACT(EPOCH FROM ts_column) still uses the standard expressions/extract template). Good fallback hygiene.

Snowflake template DATEDIFF(SECOND, {{ right }}, {{ left }}) correctly inverts operand order to match left - right semantics.

The test covers both arms — generic dialect keeps EXTRACT(epoch …), Snowflake-style dialect emits DATEDIFF(SECOND, …).

Nits (low)

1. wrapper.rs:3066-3078 — timestamp_diff_operands only matches BinaryExpr with Operator::Minus. Semantically equivalent forms like Expr::Negative + addition, or DataFusion's date_sub/timestamp_sub scalar functions, won't be routed through the new path. Probably fine since the rewriter normalizes the typical incoming shape, but worth noting if Snowflake users report EXTRACT(EPOCH FROM <interval>) slipping through from other expression shapes.

2. wrapper.rs:3144-3151 — Minor: sql_generator.get_sql_templates() is called twice (once for contains_template, once for extract_epoch_diff_expr). Not hot-path, just slightly noisy. A local binding would tidy it up.
   • Branch: cubesql/snowflake-extract-epoch-diff

[codecov]

Codecov Report

❌ Patch coverage is 85.88235% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.10%. Comparing base (28c6938) to head (80cba97).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...t/cubesql/cubesql/src/compile/engine/df/wrapper.rs	74.35%	10 Missing ⚠️
...bejs-schema-compiler/src/adapter/SnowflakeQuery.ts	0.00%	1 Missing ⚠️
rust/cubesql/cubesql/src/compile/mod.rs	97.22%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11105      +/-   ##
==========================================
- Coverage   83.61%   79.10%   -4.51%     
==========================================
  Files         256      472     +216     
  Lines       78904    96264   +17360     
  Branches        0     3524    +3524     
==========================================
+ Hits        65975    76152   +10177     
- Misses      12929    19597    +6668     
- Partials        0      515     +515     

Flag	Coverage Δ
cube-backend	58.50% <0.00%> (?)
cubesql	83.61% <86.90%> (-0.01%)	⬇️

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