Interface imported in generated javascript when DU has an interface type constraint

[sasmithjr]

Description

When an interface is defined in one file and the interface is used as a generic interface type constraint for a discriminated union in another file, the generated JavaScript file containing the DU attempts to import the interface even though no code is generated for the interface.

This bug is not present in 4.1.2; it was introduced in 4.1.3 and it is still present in 4.2.2.

Repro code

https://github.com/sasmithjr/fable-interface-union for a repo that demonstrates the error.

The interface is defined here https://github.com/sasmithjr/fable-interface-union/blob/7eedf8c90b4d7c45319f32a6e3bfc0c2d35d2e38/Source.fs

The DU with the interface type constraint is defined here https://github.com/sasmithjr/fable-interface-union/blob/7eedf8c90b4d7c45319f32a6e3bfc0c2d35d2e38/Program.fs#L16C1-L17C22

The generated Program.fs.js will contain import { IErrorInterface } from "./Source.fs.js"; even though no Source.fs.js is created, and if a Source.fs.js was created (e.g. the file contains functions), there wouldn't be an IErrorInterface in it to import anyways.

In Program.fs, you can uncomment the types defined above ErrorUnion and then comment out ErrorUnion, and you'll be able see that the other types do not generate code which attempts to import the interface.

Expected and actual results

The generated JavaScript does not import the interface.

Related information

• Operation system: macOS 14.0
• .NET SDK: 7.0.401 and 8.0.100-rc.2.23502.2
• Fable compiler: 4.1.3 and 4.2.2