Fable: Records with single field of type unit generate broken constructor

Created on 6 Sep 2018 · 3Comments · Source: fable-compiler/Fable

Description

When creating a record of a single element of type unit, the generated class constructor is invalid and produces a ReferenceError at run-time.

Repro code

Fable REPL samples...

type Test = {
    Abc: unit
}

printfn "%A" <| { Abc = () }

produces:

import { setType } from "fable-core/Symbol";
import _Symbol from "fable-core/Symbol";
import { compareRecords, equalsRecords, Unit } from "fable-core/Util";
import { printf, toConsole } from "fable-core/String";
export class Test {
  constructor() {
    this.Abc = abc;
  }

  [_Symbol.reflection]() {
    return {
      type: "Test.Test",
      interfaces: ["FSharpRecord", "System.IEquatable", "System.IComparable"],
      properties: {
        Abc: Unit
      }
    };
  }

  Equals(other) {
    return equalsRecords(this, other);
  }

  CompareTo(other) {
    return compareRecords(this, other) | 0;
  }

}
setType("Test.Test", Test);
toConsole(printf("%A"))(new Test());

Notice that the constructor is missing the abc argument that it uses to initialize the field.

type Test = {
    Abc: unit
    Xyz: int
}

printfn "%A" <| { Abc = (); Xyz = 123 }

produces:

import { setType } from "fable-core/Symbol";
import _Symbol from "fable-core/Symbol";
import { compareRecords, equalsRecords, Unit } from "fable-core/Util";
import { printf, toConsole } from "fable-core/String";
export class Test {
  constructor(abc, xyz) {
    this.Abc = abc;
    this.Xyz = xyz | 0;
  }

  [_Symbol.reflection]() {
    return {
      type: "Test.Test",
      interfaces: ["FSharpRecord", "System.IEquatable", "System.IComparable"],
      properties: {
        Abc: Unit,
        Xyz: "number"
      }
    };
  }

  Equals(other) {
    return equalsRecords(this, other);
  }

  CompareTo(other) {
    return compareRecords(this, other) | 0;
  }

}
setType("Test.Test", Test);
toConsole(printf("%A"))(new Test(null, 123));

So when another field is added to the record, the constructor is properly formed.