[<Literal>] references fail in recursive modules

[cmeeren]

Values with [<Literal>] defined in recursive modules can not be used in contexts where a [<Literal>] is required.

The following examples compile fine:

module NonRecursive

let [<Literal>] x = ""
let [<Literal>] y = x

module NonRecursive

type MyAttribute(x: string) =
  inherit System.Attribute()

let [<Literal>] x = ""
let [<MyAttribute(x)>] y = ""

module rec Recursive

let [<Literal>] x = ""
let y = x  // literal not required, works fine even in recursive module

module NonRecursive

let [<Literal>] x = ""

module rec Recursive =

    let [<Literal>] y = x

The following examples do not compile:

module rec Recursive

let [<Literal>] x = ""
let [<Literal>] y = x
                 // ^ The value or constructor 'x' is not defined
                 // ^ This is not a valid constant expression or custom attribute value

module rec Recursive

type MyAttribute(x: string) =
  inherit System.Attribute()

let [<Literal>] x = ""
let [<MyAttribute(x)>] y = ""
               // ^ The value or constructor 'x' is not defined
               // ^ This is not a valid constant expression or custom attribute value

module rec Recursive =

    let [<Literal>] x = ""

module NonRecursive =

    let [<Literal>] y = x
                     // ^ The value or constructor 'x' is not defined
                     // ^ This is not a valid constant expression or custom attribute value

Known workarounds

Define literals outside recursive modules (may be infeasible in some cases).

Related information

May be related to #5227.

[TIHan]

The first two examples are a bug, but the last one is not correct to begin with and can be fixed by being qualified, Recursive.x, or opening the module:

module rec Recursive =

    let [<Literal>] x = ""

module NonRecursive =
    open Recursive

    let [<Literal>] y = x

or

module rec Recursive =

    let [<Literal>] x = ""

module NonRecursive =

    let [<Literal>] y = Recursive.x

These work fine.

[cmeeren]

Sorry about the last one, got blinded by testing all aspects of the problem and made a brain fart... :)

[dsyme]

See also

• the discussion about this in the nameof RFC discussion

• this duplicate Recursive namespaces not working properly with type providers static parameters #5227

It's the same underlying issue in each case - literals values are not established in a separate phase

[eiriktsarpalis]

I just bumped into this issue as well while trying to use xunit's MemberDataAttribute in conjuction with nameof in F#.