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@abonie In other words, instead of what it is [right now](https://github.com/dotnet/fsharp/blob/97a2a75fae37f4357838d41f406ff01b5d732a29/src/Compiler/Symbols/Symbols.fs#L1786-L1791): ```fs member _.IsUnionCaseTester = checkIsResolved() match d with | P p -> p.IsUnionCaseTester | M m -> m.IsUnionCaseTester |...

@abonie Yes, that is correct, see above for an example F# code, and the AST for the generated union case tester member `get_IsCustom`.

@abonie Perhaps try inspecting the `IsCustom` symbol at this line `let b = a.IsCustom`.

@abonie Yes, while it is true that when using the symbol look up (`GetSymbolUseAtLocation`), you get the correct values, I would still argue that the correct behavior for `FSharpMemberOrFunctionOrValue.IsUnionCaseTester` is...

@MangelMaxime One would think that defensive struct copy would not be applicable to (nullable) reference types, but I'm not sure.

@MangelMaxime We could, technically, not make any changes to the Fable.AST, and just wrap nullable types in a Nullable as a marker, and then handle wrapped nullable types appropriately in...

This has been merged into and superseded by #4159.

@DunetsNM You are correct, this is a different issue than #3566. Also, we can leave #3822 closed and keep this one, as they're the same issue. #3566 was about the...

Some thoughts on JS/TS implementation: Since TypeScript doesn't support static methods in interfaces, we'll have to change the calling convention for those static calls and pass the class that implements...

@MangelMaxime For me `[]` on type is mostly useful for types that have `[]` members. But I can see extending this to cleanup more generated members. Perhaps a more concrete...