[Bartok9]

Summary

• WrenDialect dropped every UNBOUNDED PRECEDING .. CURRENT ROW frame before unparse, including an explicit ROWS frame.
• Engines that omit the frame default to RANGE, which includes peer rows and changes the result (issue [Bug] wren-core silently drops explicit ROWS window frame during transform_sql #2745).
• Keep the frame through unparse, then strip only the implicit RANGE form so existing planned SQL stays the same.

Test

mdl::test::test_window_function_frame asserts an explicit ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW survives planning. It fails without the dialect change.

Fixes #2745

Summary by CodeRabbit

• Bug Fixes
  • Explicit ROWS and GROUPS window frames with unbounded preceding and current row bounds are now retained in generated SQL.
  • Explicit RANGE frames with bounds other than unbounded preceding to current row are also preserved.
  • Generated SQL omits the default RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW frame when it is not explicitly requested.

[coderabbitai]

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• core/wren-core/core/src/mdl/dialect/wren_dialect.rs
• core/wren-core/core/src/mdl/mod.rs

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• core/wren-core/core/src/mdl/dialect/wren_dialect.rs

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Walkthrough

The dialect delegates window-frame support checks to the inner dialect. SQL transformation removes a RANGE frame only when it has unbounded preceding and current-row bounds. Other frames remain in the AST.

Changes

Window Frame Preservation

Layer / File(s)	Summary
Window frame handling and regression test core/wren-core/core/src/mdl/dialect/wren_dialect.rs, core/wren-core/core/src/mdl/mod.rs	The dialect delegates frame support checks to the inner dialect. SQL transformation removes only the matching default RANGE frame. Explicit ROWS and GROUPS frames, and other RANGE bounds, remain unchanged. A regression assertion checks that an explicit ROWS frame remains in transformed SQL.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: goldmedal

Merge Risk: ⚪ Minimal · up to 57d64

Explicit ROWS frames remain in planned SQL, with no identified issue blocking merge.

Pre-merge checks: 3 · 2

Failed checks: 2 warnings

Check name	Status	Explanation	Resolution
Description check		The description includes a useful summary and test reference, but it omits the required failure reproduction with actual error output and the required duplicate check. It also uses Test instead of the…	Add the observed reproduction and actual error output for issue #2745. Add the How is it tested? section with the CI execution details. Add the Duplicate check section and list the open PRs reviewed, or state that none were found.
Docstring Coverage		Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly identifies the primary behavior change: preserving explicit ROWS window frames in planned SQL.
Linked Issues check		Issue #2745 requires preservation of explicit ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW frames. WrenDialect now delegates frame support. mdl removes only the implicit RANGE frame with t…
Out of Scope Changes check		The changes modify window-frame handling, remove only the targeted implicit RANGE form, and update the related regression test. These changes directly support issue #2745. No unrelated product behav…

Full details: Description check

Explanation

The description includes a useful summary and test reference, but it omits the required failure reproduction with actual error output and the required duplicate check. It also uses Test instead of the template heading How is it tested?.

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_{A rabbit checks each window frame,
The ROWS clause stays just the same.
RANGE defaults are cleared with care,
GROUPS frames keep their bounds to bear.
Hop, hop—the query keeps its shape.}

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Actionable comments posted: 1

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Inline comments:
Review comments at @core/wren-core/core/src/mdl/mod.rs:
- Around line 640-646: Update the frame-removal logic in
transform_sql_with_ctx_with_access_control so it removes implicit frames only
from SQL frame nodes, not matching text inside string literals or quoted
identifiers. Prefer removing frames from the SQL AST before string conversion;
otherwise, tokenize the SQL and skip literals and quoted identifiers while
searching.

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• core/wren-core/core/src/mdl/dialect/wren_dialect.rs
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[Bartok9]

Pushed a follow-up that skips string literals and quoted identifiers when stripping the implicit RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW frame. A selected literal with that text is left intact; unquoted implicit frames are still removed so existing planned SQL stays the same.

Docstring-coverage and description-template warnings are noted; the change is covered by test_window_function_frame.

[goldmedal]

Thanks for tracking this down — keeping an explicit ROWS frame is the right behaviour, since dropping it lets the target engine fall back to RANGE and silently change results when the ORDER BY key has ties. I'm requesting one change to how the default frame is removed.

Please strip the default RANGE frame on the AST instead of scanning the rendered SQL string.

At the point where preserve_explicit_rows_frame runs, transform_sql_with_ctx_with_access_control still holds the unparsed ast::Statement; the block right above already mutates it with visit_relations_mut. Every window function's WindowFrame { units, start_bound, end_bound } is available there as structured data, with units telling Range and Rows apart. Serialising first and then pattern-matching the text throws that structure away and rebuilds it with a hand-written lexer. Today's unparser output satisfies the lexer's assumptions about quote characters, escape forms, keyword case and whitespace. But nothing states or enforces them: another identifier quote style or a Display change would break the scan silently. The quote-skipping branch also has no test coverage.

A visitor removes all of that:

fn strip_default_range_frame(statement: &mut ast::Statement) {
    let _ = ast::visit_expressions_mut(statement, |expr| {
        if let ast::Expr::Function(ast::Function {
            over: Some(ast::WindowType::WindowSpec(spec)),
            ..
        }) = expr
        {
            if matches!(
                &spec.window_frame,
                Some(ast::WindowFrame {
                    units: ast::WindowFrameUnits::Range,
                    start_bound: ast::WindowFrameBound::Preceding(None),
                    end_bound: Some(ast::WindowFrameBound::CurrentRow),
                })
            ) {
                spec.window_frame = None;
            }
        }
        std::ops::ControlFlow::<()>::Continue(())
    });
}

Call it as strip_default_range_frame(&mut sql); right after the visit_relations_mut block, then sql.to_string() as before; preserve_explicit_rows_frame can be deleted. I tried this locally on this branch. The existing window-frame snapshots, your new ROWS assertion and the rest of the wren-core lib suite pass (with RUST_MIN_STACK=8388608, as in CI).

I also checked that DataFusion's strict-ordering frame doesn't leak out now that the dialect no longer drops UNBOUNDED PRECEDING .. CURRENT ROW. DataFusion picks ROWS for that frame (WindowFrame::new(Some(true))) when the order key is functionally unique. row_number()/rank() ordered by a primary key or a GROUP BY key still unparse without a frame on Postgres, MSSQL and BigQuery, so no issue there.

Non-blocking:

• Please use assert_snapshot! for the new case, like the rest of test_window_function_frame, so the full planned SQL is pinned rather than a substring.
• Consider adding row_number() OVER (ORDER BY <primary key>) on a model with a primaryKey, asserting no frame is emitted. That pins the strict-ordering behaviour above, which this change now relies on.
• cargo fmt reformats a few of the new lines: the window_func_support_window_frame delegation, the extra blank line before the new doc comment, and the long transform_sql_with_ctx(...) call in the test. CI doesn't run fmt, so please run it locally.

[Bartok9]

Pushed the AST strip you asked for. strip_default_range_frame walks the planned statement and clears only RANGE + UNBOUNDED PRECEDING + CURRENT ROW on WindowSpec, then to_string() as before. The string scan is gone, so quote style and keyword spacing no longer matter.

test_window_function_frame now pins the explicit ROWS case with assert_snapshot! (the planned SQL casts the sum to BIGINT and keeps the ROWS frame). cargo fmt is applied. I did not add the primary-key row_number() case in this push — happy to follow up if you still want that pinned.

[goldmedal]

Thanks @Bartok9 👍