Bug fix: Fix issue where statements where not downcasted to IDataValue for case when

[Ulimo]

No description provided.

[Copilot]

Pull Request Overview

This PR fixes an issue with CASE expressions not correctly downcasting to IDataValue. The changes include adding an acceptance test to cover the edge case and updating the expression visitor to enforce proper conversion of both the else and then branches to IDataValue.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/FlowtideDotNet.AcceptanceTests/SelectTests.cs	Adds an acceptance test to validate downcasting in CASE expressions
src/FlowtideDotNet.Core/Compute/Columnar/ColumnarExpressionVisitor.cs	Updates conversion logic to ensure both else and then expressions are cast to IDataValue

Comments suppressed due to low confidence (2)

src/FlowtideDotNet.Core/Compute/Columnar/ColumnarExpressionVisitor.cs:213

• Verify that forcing a conversion on elseStatement using Expression.Convert correctly handles all value types (including the explicit use of new NullValue()) and preserves the intended evaluation semantics.

if (elseStatement.Type != typeof(IDataValue))

src/FlowtideDotNet.Core/Compute/Columnar/ColumnarExpressionVisitor.cs:235

• Ensure that converting thenStatement to IDataValue via Expression.Convert does not inadvertently change its behavior; consider adding a clarifying code comment to maintain clarity on why the conversion is required.

if (thenStatement.Type != typeof(IDataValue))

[github-actions]

Benchmark

Benchmark suite	Current: ede4514	Previous: 22d4209	Ratio
FlowtideDotNet.Benchmarks.Stream.StreamBenchmark.InnerJoin	416802780 ns (± 12561423.928290226)	458826533.3333333 ns (± 10640413.19005047)	0.91
FlowtideDotNet.Benchmarks.Stream.StreamBenchmark.LeftJoin	479855355.5555556 ns (± 23170147.270254407)	564994640 ns (± 28550338.329818636)	0.85
FlowtideDotNet.Benchmarks.Stream.StreamBenchmark.ProjectionAndNormalization	165795080 ns (± 17950867.73710706)	169842820 ns (± 7144067.768715523)	0.98
FlowtideDotNet.Benchmarks.Stream.StreamBenchmark.SumAggregation	171794990 ns (± 13623705.568946114)	171581250 ns (± 12415362.812660772)	1.00
FlowtideDotNet.Benchmarks.Stream.StreamBenchmark.ListAggWithMapAggregation	1805940440 ns (± 95011696.74410793)	1982296640 ns (± 123349811.75190067)	0.91
FlowtideDotNet.Benchmarks.Stream.StreamBenchmark.WindowSum	367513480 ns (± 15220572.565230403)
FlowtideDotNet.Benchmarks.Stream.StreamBenchmark.ListAggWithStructAggregation	1415626060 ns (± 78487765.79391848)

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