compilation unit 'FSharp.Core' did not contain the namespace, module or type 'StringModule'

Description

I wrote a simple type provider that references String.length in the untyped quotation used to provide a constructor implementation. The type provider library builds, but a consuming project fails to build with the following error:

FSC : error FS0193: The module/namespace 'Microsoft.FSharp.Collections' from compilation unit 'FSharp.Core' did not contain the namespace, module or type 'StringModule' [/Users/ben/proj/oss/constrainedtypes/test/ConstrainedTypes.Test/ConstrainedTypes.Test.fsproj]

The type provider is implemented as follows:

namespace ConstrainedTypes
​
open System.IO
open System.Reflection
open FSharp.Quotations
open ProviderImplementation
open ProviderImplementation.ProvidedTypes
open FSharp.Quotations
open Microsoft.FSharp.Quotations
​
[<TypeProvider>]
type ConstrainedStringProvider (config : TypeProviderConfig) as this =
    inherit TypeProviderForNamespaces (config, addDefaultProbingLocation=true)
​
    let rootNs = "ConstrainedTypes"
    let thisAssembly = Assembly.GetExecutingAssembly()
    let boundedStringProvider = ProvidedTypeDefinition(thisAssembly, rootNs, "BoundedString", Some typeof<string>)
​
    do
        boundedStringProvider.DefineStaticParameters([ProvidedStaticParameter("Length", typeof<int>)], fun name args ->
            let length = args.[0] :?> int
            let provided = ProvidedTypeDefinition(thisAssembly, rootNs, name, Some typeof<string>)
​
            ProvidedConstructor(
                [ProvidedParameter("value", typeof<string>)],
                fun args ->
                    <@@
                        printfn "checking bound: %d" length
                        if (length < String.length %%(args.[0])) then
                            sprintf "provided value exceeded the bounds: '%s' > %d"
                                %%(args.[0]) length
                            |> invalidArg "value"
                    @@>
            )
            |> provided.AddMember
​
            provided
        )
​
        this.AddNamespace(rootNs, [boundedStringProvider])
​
[<TypeProviderAssembly>]
do ()

This implementation can be cloned here: https://github.com/aggieben/constrainedtypes

Repro steps

See implementation above. Clone the linked implementation and build the ConstrainedTypes.Test project to repro.

Expected behavior

I expected the use of the provided type BoundedString<10> to compile.

Actual behavior

The type provider fails at consumer compile time.

Known workarounds

None

Related information

• MacOS Catalina
• .NET Core 3.1.100

[sergey-tihon]

ops, sorry, my typo As error message says issue is in method accessability. You need to remove internal modifier from module declaration

Replace

module internal Utilities =

to

module Utilities =

[sergey-tihon]

Thank you, it definitely looks like a bug of mapping types from quotation to target runtime types.

It is a good practice to keep quotations as small as possible. You can move method implementation into runtime assembly and just call it from quotation.

[<AutoOpen>]
module internal Utilities =

    let x = 1

    let ctorBoundedString length str = 
        if (length < String.length str) then
            sprintf "provided value exceeds the bounds: '%s' > %d"
                str length
            |> invalidArg "value"

simple quotation that call implementation and pass parameters

            ProvidedConstructor(
                [ProvidedParameter("value", typeof<string>)],
                fun args -> <@@ ctorBoundedString length %%(args.[0]) @@>
            )
            |> boundedStringType.AddMember