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Disallow recursive structs with lifted type parameters #19031

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Merged
merged 4 commits into from
Nov 3, 2025
Merged

Disallow recursive structs with lifted type parameters #19031

merged 4 commits into from
Nov 3, 2025

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@brianrourkeboll
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@brianrourkeboll brianrourkeboll commented Oct 25, 2025 •
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Description

Fixes #18993.
Fixes #6069.

  • Emit "error FS0954: This type definition involves an immediate cyclic reference through a struct field or inheritance relation" for generic struct types that recursively reference themselves but (infinitely) lift their generic type parameter.

I don't know if "lifting" is the correct term for this; let me know if there is a more correct term or phrase that I should use to describe this in the comment and the tests. Maybe nested app ty/type application?

Checklist

  • Test cases added.
  • Release notes entry updated.

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github-actions bot commented Oct 25, 2025 •
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❗ Release notes required

✅ Found changes and release notes in following paths:

Change path Release notes path Description
src/Compiler docs/release-notes/.FSharp.Compiler.Service/11.0.0.md

brianrourkeboll
brianrourkeboll commented Oct 25, 2025
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@brianrourkeboll brianrourkeboll marked this pull request as ready for review October 25, 2025 17:23
@brianrourkeboll brianrourkeboll requested a review from a team as a code owner October 25, 2025 17:23
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edgarfgp commented Oct 27, 2025

I think this PR might also fix #6069 ?

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brianrourkeboll commented Oct 28, 2025

I think this PR might also fix #6069 ?

Hmm yes, probably. I will add a test/tests for mutually-recursive structs.

@github-project-automation github-project-automation bot moved this from New to In Progress in F# Compiler and Tooling Nov 3, 2025
@T-Gro T-Gro merged commit 9670f60 into dotnet:main Nov 3, 2025
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@brianrourkeboll brianrourkeboll deleted the recursive-generic-struct-types branch November 3, 2025 21:06
@dotnet-maestro dotnet-maestro bot mentioned this pull request Nov 4, 2025
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Compilation fails to terminate for polymorphic recursion on value types Infinite loop on expanding cycle for struct types

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