Undefined or unsolved type variable

[NinoFloris]

Running on 5.0 preview 8, probably fixed by #9633

type DuCaseName<'T> =
    static member ToCaseName<'t, 'u>(value: 't) =
        failwith "just here to provide delayed resolution"
    static member ToCaseName(value: 'T) =
        match FSharp.Reflection.FSharpValue.GetUnionFields(value, typeof<'T>) with
        | case, _ -> case.Name

    static member inline Invoke(value: 'a) =
        let inline call (other: ^M, value: ^I) = ((^M or ^I) : (static member ToCaseName: ^I -> string) value)
        call (Unchecked.defaultof<DuCaseName<'T>>, value)

error FS0073: internal error: Undefined or unsolved type variable: '_?2272016

https://sharplab.io/#v2:EYLgxg9gTgpgtADwGwBYA0AbEAzAzgHwBcBPABxgAIARAVwGEBDXGAOQYFsYAeAcgBUAfBQC8AWABQFKRVyEGhAJZgKndsBhQKfCI2ZtOvQmgo8aAgBQA3BhhowQJwgEoRE6e4rYGCjAHcFhAAWFABEAFY0shSBGpSEEBSkUBCWCgAmlBkYDMQwaRSwuBC2ihAAdiFu0rLySiowahpaOkysHDBWNnYO/C5ikh5S7PJgwQBiAMqBDFCkAHQASjDYGDBgpWVzk9OzAGpdMHMA4jCEAKplCuVjCjAYabidtjDGJOQQ2LyCLv5BVYP4ChgVrGAD6FDgQmBzDm+hgEn+MjkimUqnUmgUZQwmMoAEkypYIABrDrWZ49Bh9RHuVaECiY7FlSjAjAYCjmCBBDQOAB6AFljGTuhQebi+uzzPyKNARWKKA5zDUUfVGpptLo2pxebiIUJZFBMQBzFxCmBOanSFls8wXUZrElpOYZLw0DDxT60DVwr4CASCg5OIA

    static member ToCaseName<'t, 'u>(value: 't) =
        failwith "just here to provide delayed resolution"

The phantom 'u seems to be the culprit in this instance.

[dsyme]

Could you try with feature/ext?

[github-actions]

🤖 This is an automated response from Repo Assist.

This bug appears to have been fixed in the current compiler. The repro code now compiles and runs correctly — DuCaseName(Foo).Invoke A returns "A" as expected.

The issue itself noted "probably fixed by #9633". Looking at the related issue #9416 (a similar FS0073: internal error: Undefined or unsolved type variable case), that was closed as completed in January 2024. The SRTP improvements that went into the compiler (likely from the RFC FS-1043 work) appear to have resolved this class of bugs.

Maintainers may want to close this issue.

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