fix(isthmus)!: mirror negative and normalize zero decimal and floating-point RANGE offsets

[anasik]

• fix(isthmus)!: reject RANGE offsets that cannot be retyped to the ordering column #1206 mirrors a negative integral RANGE offset to the opposite bound with its magnitude, and normalizes a zero integral offset to CurrentRow, since the spec requires a non-negative RANGE distance. A decimal or floating-point offset skipped both checks entirely, so a negative one kept its sign and bound label, and a zero one stayed as Preceding/Following{0} instead of CurrentRow — the same spec-invalid offset_expr shapes the integral fix was meant to prevent.
• Extends both checks to Expression.DecimalLiteral, FP64Literal, and FP32Literal, reusing the same sign-check-and-flip logic as the integral case.
• Decimal negation is exact (BigDecimal), never needs widening, unlike integral where negating a type's minimum value can overflow.
• renamed negate to negateIntegral because it sounded too general.

Closes #1291

BREAKING CHANGE: a RANGE window's negative decimal or floating-point offset, previously converted with its sign and bound label unchanged, is now mirrored to the opposite bound with its positive magnitude, matching the existing integral behavior. A zero-valued decimal or floating-point offset, previously left as Preceding/Following{0}, now converts to CurrentRow. Both match the existing integral behavior.

Summary by CodeRabbit

• Bug Fixes

  • Corrected conversion of negative decimal and floating-point window offsets to the appropriate preceding or following bounds.
  • Preserved decimal precision, scale, and numeric types when converting window offsets.
  • Zero-valued decimal and floating-point offsets now correctly produce current-row bounds.
  • Positive floating-point preceding offsets continue to retain their expected behavior.

• Tests

  • Added coverage for zero, positive, and negative decimal, double, and real window offsets.

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• isthmus/src/main/java/io/substrait/isthmus/expression/WindowBoundConverter.java

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• isthmus/src/main/java/io/substrait/isthmus/expression/WindowBoundConverter.java

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📝 Walkthrough

Walkthrough

WindowBoundConverter now normalizes zero and negative decimal, floating-point, and integral offsets. It preserves literal types and decimal precision and scale. Regression tests cover the updated conversions.

Changes

Window offset normalization

Layer / File(s)	Summary
Literal offset normalization isthmus/src/main/java/io/substrait/isthmus/expression/WindowBoundConverter.java	Zero offsets become CURRENT ROW. Negative offsets reverse the bound direction and use positive magnitudes. Decimal and floating-point literals retain their types. Integral negation retains overflow protection.
Normalization regression coverage isthmus/src/test/java/io/substrait/isthmus/WindowBoundConverterTest.java	Tests cover zero decimal and floating-point offsets, negative decimal offsets with preserved precision and scale, and positive and negative DOUBLE and REAL offsets.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: nielspardon

Merge Risk: 🟡 Moderate · up to 5be41

Negative floating-point RANGE offsets may still be encoded with a type incompatible with the ordering expression, causing window-bound validation or execution failures. This compatibility concern should be resolved before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 6.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 15 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is a concise Conventional Commit title that clearly describes the main change: normalizing zero and mirroring negative decimal and floating-point RANGE offsets.
Description check	✅ Passed	The description explains the rationale, implementation scope, affected literal types, exact decimal negation, linked issue, and breaking behavior. It includes the required BREAKING CHANGE footer.
Linked Issues check	✅ Passed	The implementation satisfies issue #1291. WindowBoundConverter maps negative DECIMAL, FP32, FP64, and integral offsets to positive magnitudes and reverses PRECEDING or FOLLOWING. Decimal negatio…
Out of Scope Changes check	✅ Passed	The changes are limited to WindowBoundConverter and WindowBoundConverterTest. The production changes implement issue #1291. The added tests verify the required normalization and type behavior. No …

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[anasik]

@nielspardon looks like the CodeRabbit is breaking the PR Title Check

[nielspardon]

@nielspardon looks like the CodeRabbit is breaking the PR Title Check

it looks like the reason is that the PR title is too long with 115 characters vs max 100 characters per conventional commits

[anasik]

@nielspardon looks like the CodeRabbit is breaking the PR Title Check

it looks like the reason is that the PR title is too long with 115 characters vs max 100 characters per conventional commits

Fixed

[nielspardon]

Narrow the title from "non-integral" to "decimal and floating-point" — a negative or zero interval_day/interval_year offset still keeps its sign and its bound label (range between interval '-1' day preceding converts to Preceding{IntervalDayLiteral{days=-1}}, and interval '0' day preceding stays Preceding{...days=0}), and the title is what lands in CHANGELOG.md. fix(isthmus)!: mirror negative and normalize zero decimal and floating-point RANGE offsets is 90 chars, inside the limit.

Same word in reverse at line 22: the class Javadoc's "A negative integral offset is mirrored to the opposite bound with its magnitude" now covers decimal and FP too.

The retype half of #1291 is already tracked as #1230, so leaving it out here is right — just confirm you still want Closes #1291. The interval and ROWS gaps I'll file separately; the inline comments below are all non-blocking cleanups.

[nielspardon]

All six new tests pass Optional.empty() for orderingType, cover PRECEDING only, and use isRows=false, where the integral negative tests at lines 288/303 pass Optional.of(orderingType) and cover both directions. A decimal case with Optional.of(t(SqlTypeName.DECIMAL, 5, 2)) would pin down which behaviour is intended ahead of #1230 instead of leaving it unasserted, and a negative-FOLLOWING decimal case would cover the flip in the other direction.

A positive-FP case is the other gap: nothing fails today if isZero or negateIfNegative over-fires on an FP value, because precedingWithDecimalOffsetKeepsItsFraction only covers DECIMAL.

[nielspardon]

The notRetypedAgainstTheOrderingType test is the right shape — worth noting for #1230 that its assertion is the one that has to flip when the retype lands.

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Inline comments:
In
`@isthmus/src/main/java/io/substrait/isthmus/expression/WindowBoundConverter.java`:
- Around line 81-87: The floating RANGE offset normalization in
WindowBoundConverter must match the ordering type: after mirroring negative
offsets, widen FP32 literals to FP64 exactly, and narrow FP64 literals to FP32
only when round-tripping preserves the original value; otherwise throw a clear
UnsupportedOperationException. Update normalizeIntegralOffset and the
FP32Literal/FP64Literal handling while preserving CURRENT_ROW and both existing
mismatch cases.

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[nielspardon]

Last thing from my first pass: the class Javadoc at lines 21-23 still reads "A negative integral offset is mirrored to the opposite bound with its magnitude" — that now covers decimal and FP too. The @param orderingType note just below it stays accurate, and your new negativeDecimalPrecedingOffsetIsNotRetypedAgainstTheOrderingType test is what makes the distinction legible.

[anasik]

@nielspardon fixed

[nielspardon]

LGTM