Succinct description

When collectible = true is passed as an argument to FsiEvaluationSession.Create, the FSI-ASSEMBLY is never unloaded, contrary to expectations.

Repro steps

The problem can be reproduced by following these steps:

1. Run the provided collectionTest function in the Collectible code generation section of the FCS API documentation: https://fsharp.github.io/fsharp-compiler-docs/fcs/interactive.html#Collectible-code-generation
2. Observe that the FSI-ASSEMBLY is never unloaded.

Expected behavior

When collectible = true is set, the FSI-ASSEMBLY should be unloaded when it's no longer needed.

Actual behavior

The FSI-ASSEMBLY is never unloaded, even when collectible = true.

Known workarounds

There are currently no known workarounds for this issue.

Potential solution

A potential fix might involve modifying the defineDynamicAssemblyAndLog function in ilreflect.fs to ensure that the assembly is created within a CollectibleAssemblyLoadContext. Here's the current implementation of the function:

let defineDynamicAssemblyAndLog (asmName, flags, asmDir: string) =
    let asmB = AssemblyBuilder.DefineDynamicAssembly(asmName, flags)

    if logRefEmitCalls then
        printfn "open System"
        printfn "open System.Reflection"
        printfn "open System.Reflection.Emit"

        printfn
            "let assemblyBuilder%d = System.AppDomain.CurrentDomain.DefineDynamicAssembly(AssemblyName(Name=\"%s\"), enum %d, %A)"
            (abs <| hash asmB)
            asmName.Name
            (LanguagePrimitives.EnumToValue flags)
            asmDir

    asmB

Related information

Operating system: Windows 10 Pro 21H2 (19044.3086)
.NET Runtime kind: .NET 7.0.306
Editing Tools: Visual Studio Code