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Fix dynamic resumable code path of taskSeq, and duplicated last item (#452) by majocha · Pull Request #506 · fsprojects/FSharp.Control.TaskSeq · GitHub
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Fix dynamic resumable code path of taskSeq, and duplicated last item (#452) #506

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Fix dynamic resumable code path of taskSeq, and duplicated last item (#452) #506

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94a38f7
Fix dynamic resumable code path of taskSeq, and duplicated last item …
majocha Nov 9, 2026
77af9d6
Use a single code path for Bind and Yield in static and dynamic code
majocha Nov 9, 2026
b795aaa
Await MoveNextAsync's ValueTask directly in static WhileAsync
majocha Nov 9, 2026
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5 changes: 5 additions & 0 deletions release-notes.txt
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Release notes:

Unreleased
- fixes the dynamic resumable code path of `taskSeq` (used in FSI and whenever the F# compiler does not compile the CE to a static state machine, e.g. Debug builds with .NET SDK 10.0.4xx): a `let!`/`do!` on an awaitable that does not complete synchronously dropped the rest of the computation (truncating the sequence, swallowing exceptions, or hanging in loops); `for .. in` over an `IAsyncEnumerable` discarded the awaited `MoveNextAsync` result and called it again; and `DisposeAsync` did not run pending `finally`/`use` compensations. This is the cause of the Debug-only truncation in #473, #505
- fixes the dynamic resumable code path of `for .. in` over a `taskSeq` inside `task { .. }`, which crashed with a `NullReferenceException` when `MoveNextAsync` did not complete synchronously, #505
- fixes `taskSeq { for x in source do .. }`, and functions built on it like `TaskSeq.map`, reporting the last item twice when the source's `DisposeAsync` completes asynchronously, #452
- perf: `for .. in` over an `IAsyncEnumerable` inside `taskSeq`, and therefore most `TaskSeq` functions, awaits a pending `MoveNextAsync` through its `ValueTask` awaiter instead of `AsTask()`, saving a `Task` allocation per suspension
- test: add TaskSeq.Dynamic.Forced.Tests.CE.fs, which forces the dynamic resumable code path (the existing `taskSeqDynamic` tests are compiled statically and never exercised it)
- fix: `TaskSeq-replicateUntilNoneAsync re-runs the computation from its initial state on each fresh enumeration` test hung CI by declaring its loop counter `n` inside the computation function, so it reset to 0 on every call and the terminating `None` branch was never reached; `n` is now shared across calls as intended
- test: add SideEffects module to TaskSeq.ReplicateInfinite.Tests.fs and TaskSeq.ThreadState.Tests.fs, verifying computation/generator/folder call counts and re-enumeration semantics
- test: add direct unit test coverage for the `ValueTask` helper module (`fromResult`, `ofSource`, `ofTask`, `ignore`, `True`/`False`, plus their deprecated aliases), closing a gap where these functions had no dedicated tests despite the `Task`/`Async` equivalents being covered
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1 change: 1 addition & 0 deletions src/FSharp.Control.TaskSeq.Test/FSharp.Control.TaskSeq.Test.fsproj
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<Compile Include="TaskSeq.ThreadState.Tests.fs" />
<Compile Include="TaskSeq.Tests.CE.fs" />
<Compile Include="TaskSeq.Dynamic.Tests.CE.fs" />
<Compile Include="TaskSeq.Dynamic.Forced.Tests.CE.fs" />
<Compile Include="TaskSeq.StateTransitionBug.Tests.CE.fs" />
<Compile Include="TaskSeq.StateTransitionBug-delayed.Tests.CE.fs" />
<Compile Include="TaskSeq.Realworld.fs" />
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