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Fix FS1110 in task { let! } when generic IL extension is in scope#19938

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Fix FS1110 in task { let! } when generic IL extension is in scope#19938
T-Gro wants to merge 3 commits into
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fix/issue-19936

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@T-Gro T-Gro commented Jun 12, 2026

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Fixes #19936

task { let! x = ... } (and other CEs) raised an internal compiler
error FS1110 when a generic IL extension method whose this-parameter
is a method-level type variable was in scope (e.g. open ReactiveUI).
Regression from #19536.

Copilot and others added 3 commits June 12, 2026 14:51
…n scope (#19936)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
…9936)

- Move IsExtensionMethCompatibleWithTy above ExtensionMethInfosOfTypeInScope.
- Pass FormalMethodInst (not []) to GetObjArgTypes so IL method-typar this-args
  import successfully. Wrap in narrow try/with that rethrows
  OperationCanceledException for cancellable IDE paths.
- Confine the AtMostOneResult short-circuit so dangling unindexed extensions
  only mask hierarchy-indexed candidates when at least one is compatible with
  the target type. AllResults branch preserved byte-identically.

Regression from PR #19536 (issue #19349 fix).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
…19936)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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❗ Release notes required

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✅ Found changes and release notes in following paths:

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Change path Release notes path Description
src/Compiler docs/release-notes/.FSharp.Compiler.Service/11.0.100.md No current pull request URL (#19938) found, please consider adding it

@github-actions github-actions Bot added the AI-Tooling-Check-Bypassed Tooling check: non-fork PR, not diff-analyzed label Jun 12, 2026
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FS1110 internal compiler error: task { let! } + open ReactiveUI on .NET SDK 10.0.301

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