Incorrect compiler error message for out-of-order members

[brianberns]

Repro steps

Compile the snippet below:

type MyType =
    { MyField : string }
    member this.Length = this.MyProperty.Length
    member this.MyProperty = this.MyField

Expected behavior

Either:

• Program compiles successfully, because order of members is irrelevant.
• Program fails to compile with a correct error message, because order of members is relevant.

The expected error message in the second case would be:

The type 'MyType' does not define the field, constructor or member 'MyProperty'

Actual behavior

Compiler error message on Length property:

Program.fs(3,26): error FS0072: Lookup on object of indeterminate type...

This is an incorrect error message, because specifying the type of this does not fix the problem:

member this.Length = (this : MyType).MyProperty.Length   // "Lookup on object of indeterminate type"

Note that Visual Studio suggests the following fix instead, which also does not work:

member (this: MyType).Length = this.MyProperty.Length   // "Unexpected symbol '.' in member definition"

Known workarounds

Swap the order of the two members.

Related information

Microsoft (R) F# Compiler version 12.8.401.0 for F# 8.0

[edgarfgp]

Adding type annotation seems to also work

type MyType =
    { MyField : string }
    member this.Length = this.MyProperty.Length
    member this.MyProperty: string = this.MyField
                          ^^^^^^^^

[brianberns]

Oh, that's interesting and not what I expected. I thought the problem was that this has an indeterminate type, but it's actually that MyProperty has an indeterminate type.

[vzarytovskii]

Might use some more precise ranges, yeah.

[edgarfgp]

Might use some more precise ranges, yeah.

This will be fixed when I finish #17556. Just need to fix some Editor tests(AutoCompletion etc..) that are really annoying if you do not have a windows machine