Open vladmw5 opened 1 month ago
Here is the link to the discussion of the same issue on the TS github server:
https://discord.com/channels/508357248330760243/1239320604713287830
According to discriminateContextualTypeByObjectMembers
the function expression used for the loader
isn't possibly a discriminant value. So it's not discriminated based on that. When it comes to the optional property in the contextual type... the type is discriminated based on that only when your node doesn't have that property - but you have the loader
property.
I'd be curious if we could use never
/ undefined
as possible discriminants here. Would be interested to experiment
🔎 Search Terms
discriminated union, discriminated union with an optional discriminator, type inference in objects
🕗 Version & Regression Information
I have a simple piece of code (see the playground/below)
The runtime flow is very simple: whatever gets returned by the loader func gets passed as
data
to thehandle
'scrumbBuilder
method. If the loader is absent thendata
will also be absentBut when it comes to typing those behaviors then 2 issues arise:
1) At first, the discriminated union is not being resolved properly: in the second case it should be a string but TS cannot infer it and defaults to
any
2) At second, we still have to explicitly annotate or assert thedata
type, however from theloader
definition it is possible to infer its return type. Is there a syntax way to say 'the type of data is the whatever awaited type the loader function returns?. I have tried to achieve that behaviour using generics and the
satisifies` keyword but failed to⏯ Playground Link
https://www.typescriptlang.org/play/?#code/C4TwDgpgBACghsAFgZQgcwLYQHbCgXigHsAjAKwgGNgBtAXQG4BYAKFdEigAk5sATADYQAPABUAIgjgA+AlADerKMqiUATgFcMJAEIaAlgL4Q1ALigAKPlPMSpASgKz4SVJhy1GrAL6t24aAAZIjhjNTFJYBk5Czg1NABnc3koMDi4DCSoACUqIjU+YQTgNX1sNAAaKGLS8tlvR3xnNSIMfQSROyjpZjYWDmhsog1gCB5+IXCuuDleEFl8JRUAHwUllRVEXkEIc3Gd4WwIADcTHvWNqAEQsIB+cyPTtV6N3xYN1cV3y+Utid3uNshBEpOdvj9rqETOZglCppEZBdvL1WJQiNhilAWiMxkCTAB1fRIYbAWFhORfDZ-HbJC4bdRaXQGIzQyzWKKNWT0KoAeh57Jm7VU+TUVGAAhAUDKADMTKK+FA4AkoI8TEifNUEO1pfoIMqhjj9pM-Cw0Ri8NjRkaTBSLpCwuYlSBsJRLHFEpy1uDLqLgBo1NhFfEEgA6NJqDKhjQdNQAST4LxU3gqF2pQlp3vpmm0ekMDrZDicUHoUD5AqlyuwRDwMrlEAVSuqJTKaHVLG8muA2t1+pJuP+4RqLekQA
💻 Code
🙁 Actual behavior
data
is not inferred as string🙂 Expected behavior
1) data should be inferred as a string
2) there is no need to explicitly annotate or assert the
data
type , and it must be inferred from the loader return typeAdditional information about the issue
No response